Chapter 7
Nonopioid analgesia alternatives and locoregional blocks

Vaidehi Paranjape and Stephen Cital

Opioids form an integral part of an anesthesia regime to provide perioperative analgesia, sedation, and anesthetic‐sparing effects in small animals. However, their significant side‐effects and restricted availability due to the ongoing abuse crisis in humans warrant their limited use. Hence, opioid alternative techniques are increasingly being used to enhance the anesthetic and postanesthetic experience in animals. These include nonopioid analgesic infusions, oral gabapentanoids, psychotropic drugs, cannabinoids, antiinflammatories, nonpharmacologic pain modalities and robust use of local‐regional anesthetic techniques, which are briefly reviewed in this chapter.

I. Nonopioid analgesic constant‐rate infusions

Ketamine (N‐methyl‐D‐aspartate receptor antagonist), dexmedetomidine (alpha‐2 adrenoreceptor agonist), and lidocaine (sodium channel blocker) are routinely used as constant‐rate infusions (CRIs) to provide analgesia in the perioperative period. With basic understanding of the major pain pathways, these drugs are used as either primary analgesics or adjunctive analgesics to provide multimodal analgesia.

A. Ketamine

The NMDA receptor is a ligand‐gated, voltage‐dependent ion channel, widely distributed in the CNS and primary sensory neurons. It serves as a binding site for glutamate, which is released with noxious peripheral stimuli.

1.Clinical uses

It serves as a noncompetitive antagonist at the NMDA receptor and is used at subanesthetic doses of 0.12–1.2 mg/kg/h as an adjunctive to other analgesics. These doses are less likely to produce dissociative and cardiostimulatory effects. Activation of NMDA receptor leads to the development of cancer, chronic, neuropathic and wind‐up pain, central sensitization and hyperalgesia [1]. It may be more effective for somatic pain than visceral pain [2]. Additionally, it exhibits opioid‐sparing effects and counteracts opioid‐induced hyperalgesia. Authors recommend its cautious use in cats with progressive renal disease and hypertrophic cardiomyopathy.

B. Dexmedetomidine

1. Pharmacology

Alpha‐2 adrenoceptors are a class of G protein‐coupled receptors that serve as a primary site for norepinephrine and epinephrine. They are found peripherally and at spinal and supraspinal sites within the CNS. They induce antinociception by:

stimulation of spinal alpha‐2 receptors and direct inhibition of spinal cord neurons
presynaptic inhibition of neurotransmitter release from the primary afferents in the dorsal horn
neuronal hyperpolarization and inhibition of substance P release via postsynaptic actions
inhibitory neuronal action at higher supraspinal structures [3].

2.Clinical uses

Dexmedetomidine is the most selective drug for alpha‐2 adrenoreceptors, with a binding affinity for alpha‐2:alpha‐1 receptors reported as 1620:1. It is a pure S‐enantiomer of the racemic medetomidine and is twice as potent as medetomidine. Micro‐bolus doses of 0.0005–0.002 mg/kg can be given intraoperatively as needed, or 0.0005–0.002 mg/kg/h administered as a CRI for sedation, anxiolytic effect, anesthetic adjunct, inhalant‐sparing effect, supplemental somatic and visceral analgesia, and muscle relaxation [4]. Cardiorespiratory monitoring is essential when it is used postoperatively. If excessive sedation or significant cardiovascular effects are extended into the recovery period, reversal with atipamezole IM is considered. Side‐effects requiring possible intervention include bradycardia, atrioventricular blocks, respiratory depression, nausea, vomiting, and ileus. This drug should be avoided in patients with moderate‐severe cardiac disease, cardiac arrhythmias, preexisting hypertension, and hypovolemia.

C. Lidocaine

1. Pharmacology

The systemic analgesic action is thought to be due to lidocaine’s interaction with Na+, Ca2+, and K+ channels and the NMDA receptor [5].

2.Clinical uses

It is the only local anesthetic that is administered intravenously to provide analgesia and inhalant‐sparing effects. It possesses antiinflammatory effects and free radical scavenging properties that contribute to management of inflammatory pain. In dogs, IV loading dose of 1–2 mg/kg followed by infusion rates of 3–6 mg/kg/h are commonly used for intraoperative analgesia. Lower infusion rates of 0.6–1.5 mg/kg/h are used postoperatively. In cats, studies show that the doses required to achieve inhalant‐sparing effects can cause greater cardiovascular depression compared to an equipotent dose of isoflurane alone [6].

II. Oral gabapentinoids

Gabapentin was traditionally used as an anticonvulsant, but its benefits include anxiolysis, analgesia, antiallodynia, and antihyperalgesia. Pregabalin is structurally similar to gabapentin but has higher oral bioavailability and a longer half‐life. However, at the time of writing, it is expensive. This makes gabapentin a more popular gabapentanoid for use during chronic pain; the authors encourage the reader to evaluate the prices from your distributors.

1.Pharmacology

Gabapentin is a structural analogue of gamma‐aminobutyric acid (GABA) but does not interact with GABA receptors to produce analgesia. It binds to the α2δ subunit on the voltage‐dependent calcium channels located in neurons of the peripheral and CNS. This reduces calcium influx into neurons and inhibits release of excitatory neurotransmitters like glutamate, substance P and norepinephrine that are actively involved in pain pathways.

2.Clinical uses

Dogs: The therapeutic dose of gabapentin is 10–20 mg/kg PO 2–3 times daily. Sedation is a common side‐effect. When included in the analgesic regime, it successfully controls pain associated with Chiari malformation and syringomyelia [7], neuropathies, mastectomy [8], and intervertebral disc surgery [9]. When 20 mg/kg PO is given 2 h prior to anesthetic induction, isoflurane requirement is reduced by 20 ± 14% with no effect on hemodynamic variables or vital parameters [10].
Cats: Pharmacokinetic data suggest a dosing regimen of 5–10 mg/kg PO every 8–12 h for chronic musculoskeletal pain [11], hyperesthesia syndrome [12], and osteoarthritis [13]. It is often recommended orally to decrease the stress associated with transportation and veterinary examinations [14]. Sedation, ataxia, hypersalivation, and vomiting are reported side‐effects, which tend to resolve 8 h after oral administration. Interestingly, IV gabapentin does not have a detectable effect on isoflurane requirement in cats [15].

III. Psychotropic drugs

Neuropathic pain is a result of a lesion or disease affecting the somatosensory system and is generally chronic and challenging to treat. With prolonged use, psychotropic drugs possibly relieve neuropathic pain by (1) recruitment of noradrenergic descending pathways, (2) peripheral recruitment of noradrenaline from sympathetic fibers sprouting into dorsal root ganglia, and (3) action via adrenergic receptors. Tricyclic antidepressants (TCAs, e.g., amitriptyline), selective serotonin reuptake inhibitors (SSRIs, e.g., fluoxetine), NMDA antagonists (e.g. amantadine), and atypical antidepressants (e.g., trazodone) are often used as adjunctive therapy for managing chronic pain states [16–18].

Amitriptyline: Predominantly inhibits serotonin reuptake, whereas its metabolite nortriptyline specifically inhibits norepinephrine reuptake. Analgesic action is attributed to the blockade of voltage‐gated sodium channels and NMDA receptors, as well as inhibition of norepinephrine reuptake. Antagonistic effects are also seen on alpha‐1, cholinergic, and histamine receptors.
Fluoxetine: Exclusively inhibits serotonin reuptake with eventual downregulation of postsynaptic serotonergic receptors.
Amantadine: Antagonizes NMDA receptors in the CNS which helps prevent central sensitization, wind‐up, allodynia, and opioid tolerance.
Trazodone: Inhibits both serotonin transporter and serotonin type 2 receptors. It inhibits serotonin reuptake and blocks the histamine and alpha‐1‐adrenergic receptors [19].

1.Clinical uses

Psychotropic drugs are useful in clinical scenarios manifesting neuropathic pain such as Chiari‐like malformation/syringomyelia, radiculopathy caused by chronic cervical or lumbosacral disc disease, diabetic or other polyneuropathies, spinal cord injury caused by intervertebral disc extrusion, chronic osteoarthritis, and musculoskeletal pain. Drug interactions can occur when different serotonin‐enhancing agents are administered together (e.g., fluoxetine with tramadol or fluoxetine with selegiline) leading to “serotonin syndrome” (see Chapter 5, p. 154) [20]. It is vital that these interactions are well known to the prescribing clinician and owners. Other common adverse effects of psychotropic drugs include lethargy, sedation, vomiting, diarrhea, panting, hyperactivity, ataxia, increased anxiety, increased appetite, shaking, restlessness, and/or agitation. Arrhythmias, tachycardia, and orthostatic hypotension can be seen with high doses of TCAs.

2.Dosage

Amitriptyline: 2–4 mg/kg PO q12h (dogs); 0.5–1 mg/kg PO q24h (cats).
Fluoxetine: 1–2 mg/kg PO q24h (dogs); 0.5–1 mg/kg PO q24h (cats).
Amantadine: 3–5 mg/kg PO q24 in dogs and cats.
Trazodone: 5–7 mg/kg PO q24 (dogs); 50–100 mg total dose PO q24 (cats).

IV. Cannabinoids

1. Endocannabinoid system (ECS) and pain

The ECS is the largest G‐protein‐coupled receptor system with neuromodulatory functions. It is now known as one of the key endogenous systems regulating pain sensation, with modulatory actions at all stages of pain‐processing pathways. Its effects are mediated by the interaction of cannabinoid receptors (CB1, CB2), endogenous ligands, and synthesizing and hydrolyzing enzymes [21,22]. CB1 receptors are mainly present in the brain and spinal cord and are responsible for centrally mediated analgesia as well as adverse central effects. They inhibit acetylcholine, L‐glutamate, GABA, norepinephrine, dopamine, and serotonin. CB2 receptors are found in the hematopoietic and immune cells, including microglial cells. These are possibly involved in immune regulation and antiinflammatory effects [23].

Phytocannabinoids are molecules produced by the Cannabis sativa plant which can act on the ECS receptors. Hemp and marijuana are both varieties of the Cannabis genus. Hemp is a variety of cannabis that produces large amounts of cannabidiolic acid compared to the amount of tetrahydrocannabinolic acid produced. The inverse is true for marijuana. After harvesting and drying of the plant material, particularly the flowering tops of female plants, the acidic forms of these two prominent phytocannabinoids become decarboxylated into their mainstream personalities – cannabidiol (CBD) and tetrahydrocannabinol (THC). Tetrahydrocannabinol is a major intoxicating compound, associated with unpleasant clinical presentation in animals that consume this molecule. Animals may experience increased anxiety with mild‐moderate doses of THC. Tolerance can be built up to THC as it is the only phytocannabinoid to sit in the orthosteric binding site on the CB1 receptor. The stronger affinity of THC compared to endogenous ligands when dosed chronically can downregulate endocannabinoid production which may have adverse physiologic consequences. Also, because of the risk and particular sensitivity of THC in companion animals, it may be best to avoid THC‐dominant products and utilize products derived from hemp.

In addition, newer research has shown that THC alone is not a good analgesic for chronic [24] pain states. On the other hand, CBD may possess analgesic effects, best described in chronic or neuropathic pain states. Both of these phytochemical compounds, among the hundreds of other phytocannabinoids, have predominantly allosteric binding to ECS receptors and affinity/dimerizing effects on several receptors systems related to pain signaling which include the transient receptor potential vanilloid (TRPV), NMDA, glycine, G‐protein‐coupled (GPR55), GABA, and serotonin (5‐HT) receptors [25].

2.Clinical uses

Well‐controlled studies in companion animals on the efficacy of these compounds are increasing. Three pharmacokinetic studies in dogs found that doses of 2 mg/kg create adequate serum concentrations, related to therapeutic benefits extrapolated from other lab animals and human subjects. Three long‐term studies (12, 39, and 56 weeks) have been performed in dogs with doses from 2 mg/kg up to 100 mg/kg. Mild‐moderate elevations of liver enzymes were noted in the higher dose long‐term studies [26,27]. In cats, only two studies have been published, elucidating that a 2 mg/kg dose may need to be given more than twice a day to maintain suspected therapeutic serum concentrations [28,29].

Efficacy of hemp CBD products has also been evaluated for management of osteoarthritic pain in dogs [30–32]. These studies had successful outcomes, particularly for pets on traditional pharmaceuticals such as NSAIDs and gabapentin. Owners were also able to eliminate the traditional pharmaceuticals out of the analgesia regime. Acute pain studies are still under way in companion animals; currently, only anecdote abounds [33].

Dosing of CBD‐dominant products will depend on the other phytocannabinoids and terpenes present. Terpenes are aromatic molecules also produced by the Cannabis plant that have their own set of therapeutic potentials. Doses from the two canine studies found oral doses of a full/complete spectrum cannabinoid product of 2 mg/kg twice a day to be safe and effective. The authors would suggest a dosing range of 0.5–2 mg/kg, or higher, depending on clinical response.

Clinicians prescribing cannabinoid products must be fully aware of the primary source (hemp vs marijuana), the concentration and the phytocannabinoid/terpene profile of the product verified by a certificate of analysis (COA). There are a few different types of phytocannabinoid products on the market being sold as animal supplements [34]. Clinicians may notice increased lethargy in patients that are on concurrent oral narcotics or gabapentanoids. Doses of the cannabinoid product or pharmaceutical are adjusted to minimize this effect. Other notable drug interactions occur with benzodiazepines, where patients may seem uncoordinated or ataxic.

V. Antiinflammatories

Long‐term pharmacological management of pain in small animals includes use of nonsteroidal antiinflammatory drugs (NSAIDs) or corticosteroids. Nonsteroidal drugs possess antipyretic, antiinflammatory, and analgesic effects. Significant analgesic and antiinflammatory clinical effects are due to the inhibition of the COX enzyme isoforms and central pain transmission. They are widely used to control mild‐moderate pain during the perioperative period as well as for chronic pain states. On the other hand, corticosteroids inhibit the production of arachidonic acid, which can stop the inflammation and stop the production of prostaglandins, similar to NSAIDs. They do not have a direct effect on nociception and are not primary analgesics. However, they are beneficial in controlling pain mediated via inflammatory processes as seen in musculoskeletal and joint disorders. More information on this class of drugs is available in the drug formulary (Section II).

VI. Nonpharmacological pain therapy

Acupuncture and physical rehabilitation are fundamental in the multimodal management of pain, especially of a chronic nature. These aid in balancing analgesic regimes, strengthening human–pet relationships, and increasing the quality of patient care and comfort.

A. Acupuncture

Acupuncture involves placement of percutaneous needles in specific anatomic locations on the body, like nerve bifurcations or neurovascular structures in tissues, in order to stimulate an endogenous response facilitating analgesia, healing, and immunomodulation. It also improves blood flow, inhibits inflammation, reduces muscle tension, resets proprioceptive mechanisms and posture, and affects autonomic nervous system. Stimulation of A‐β, A‐δ and C nociceptive fibers prevents pain transmission via local spinal inhibition of nociception, spinal release of endogenous opioids, and activation of inhibitory interneurons and descending inhibitory pain pathways. The bioactive acupuncture points lie along “meridians” that serve as an energetic distribution network following specific peripheral nerve pathways targeted for preventing nociception. Stimulation of acupuncture points in animals is manifested by a response to needle placement followed by sudden relaxation.

Acupuncture is a complex intervention requiring additional training. Clinical scenarios for its use include spinal cord injury/disease [35], wounds, chronic pain, osteoarthritis [36], visceral pain, and myofascial trigger point pain [37].

B. Physical rehabilitation

Physical rehabilitation involves objective assessment, diagnosis, and treatment of musculoskeletal and neurologic impairments during acute, subacute, and chronic pain states. The assessment utilizes careful evaluation of posture, gait, function, strength, muscle extensibility, passive range of motion, and joints to create a problem list and develop an assessment from which targeted treatment modalities are developed. These modalities provide pain relief, promote soft tissue healing, improve muscle extensibility, and facilitate muscle strengthening. Some of the commonly used physical therapy modalities are described below.

1.Superficial thermotherapy

Application of heat to tissues increases nerve conduction velocity and blood flow, facilitating healing, muscle relaxation, and resolution of local ischemia. Heat activates cutaneous thermal receptors that inhibit pain transmission. Heat can be applied with hot packs or warm baths for 15–20 min at a time. It is avoided in acute stages of tissue injury.

2.Cryotherapy

Cooling results in vasoconstriction and a reduction in tissue metabolism and oxygen requirement, sensory and motor nerve conduction velocity, edema, and muscle spasm [37]. It is used in the acute inflammatory state. Ice packs should not be placed directly over the skin and their application should not exceed 10 min at a time. Portable machines, based on active compression and cold exchange loop technology, facilitate icing of limbs with tailored protocols, and may be quite useful to practices which extensively treat orthopedic pain [39,40].

3.Laser

Low‐level laser therapy is light energy used to stimulate healing, provide pain relief, and facilitate the reorganization of injured tissues. The range of therapeutic window for this therapy is 600–1000 nm. It aims at imparting analgesia within the target tissue, and causes cartilage stimulation, fibroblast production, enhancement of immune cells to combat pathogens, acceleration of collagen synthesis, and increasing vascularity of the healing tissue [41]. It is used to reduce inflammation and treat musculoskeletal, neuropathic, and osteoarthritic pain [42–45]. Studies are conflicting regarding the benefits of this therapy.

4.Transcutaneous electrical nerve stimulation (TENS)

Electrotherapy targets sensory and motor nerve fibers, causing nerve cell excitation and changes in cell membrane permeability. This enables skeletal muscle and smooth muscle contraction, enhancing muscle‐pumping action and improving joint mobility and circulatory and lymphatic drainage [46]. TENS decreases pain and inflammation by providing a low‐level electrical current which disrupts the normal pain perception pathways. The pulse rate and width are adjusted to deliver the desired effect [47].

5.Extracorporeal shockwave therapy

This is production of high‐pressure sound waves emitted at high velocity by a generator that converts electrical energy into mechanical energy. The acoustic waves are delivered either in a focused manner, with greater penetration into the deeper tissues, or in a radial manner, affecting a wider area. Its benefits include angiogenesis, increase in collagen synthesis, increase in bone remodeling, and decrease in inflammatory mediators. It is incorporated in analgesic protocols for various musculoskeletal and joint disorders [48–50].

6.Massage, therapeutic exercises

These therapeutic novelties increase connective tissue extensibility, vascular supply, and lymphatic drainage, and improve joint range of motion. Active and passive exercises are recommended for treatment of chronic pain associated with osteoarthritis. Reduced activity and deconditioning cause decreased muscle mass and strength, loss of endurance, increased joint stiffness, and loss of cardiovascular fitness. Reduction of pain and disability is achieved through improvement of muscle strength, stability of joints, and range of motion (ROM). Passive ROM exercises are used to enhance analgesia in inflamed joints and assist tissue stretching. Active ROM exercises are required to prevent muscle atrophy, increase strength and endurance, and enhance circulation [51].

7.Glucosamine‐chondroitin, hyaluronic acid (HA) and platelet‐rich plasma (PRP)

Glucosamine hydrochloride and chondroitin sulfate are commonly recommended natural health products for treating osteoarthritis in small animals. Glucosamine regulates the synthesis of collagen in cartilage and possesses mild antiinflammatory effects. Chondroitin sulfate inhibits destructive enzymes in joint fluid and cartilage [52]. Other novel therapies include PRP and HA, which are gaining momentum for their beneficial effects in canine osteoarthritis, as evidenced both clinically and histologically [53,54]. Both therapies are accessible and cost‐effective for veterinary practitioners using commercially available products and kits [55].

8.Other nonpharmacologic techniques

Other nonpharmacologic techniques used in adjunctive management of acute and chronic pain include pulsating electromagnetic fields (PEMF), therapeutic ultrasound, neuromuscular electrical stimulation (NMES), myofascial release and trigger point therapy, nutraceuticals, and palliative radiotherapy.

VII. Local‐regional anesthetic techniques

A. Local anesthetics (LAs)

1. Pharmacology

Local anesthetics consist of a lipophilic benzene ring (confers liposolubility) and a hydrophilic amine group (confers hydrosolubility). These two structures are linked together with an ester or amide linkage. Drugs with ester linkage include cocaine, procaine, tetracaine, and benzocaine that undergo hydrolysis by pseudocholinesterase in the blood and require minimal liver metabolism. Drugs with amide linkage include lidocaine, mepivacaine, bupivacaine, and ropivacaine which undergo extensive oxidative metabolism in the liver via cytochrome P450. Hepatic blood flow and hepatic function determine the clearance of these drugs. Hence, they are used cautiously in patients with liver disease. More information regarding the most commonly used LAs is provided in Table 7.1.

Table 7.1 Commonly used local anesthetics and their toxic doses.

Source: Adapted from [56].

Drug name	Onset of action	Duration of action	Comments
Lidocaine	1–3 min	1–2 h	Dose 4–6 mg/kg (dogs); 2–4 mg/kg (cats) Toxic IV dose for CNS toxicity: 20–mg/kg (dogs); 12–mg/kg (cats) Toxic IV dose for cardiovascular collapse: 80–mg/kg (dogs); 47 mg/kg (cats) Authors suggest do not exceed 6 mg/kg in dogs and 3 mg/kg in cats by any route
Mepivacaine	3–5 min	2–3 h	Dose 4–6 mg/kg (dogs); 2–3 mg/kg (cats) Toxic IV dose for CNS toxicity: 29–mg/kg (dogs) Toxic IV dose for cardiovascular collapse: 80–mg/kg (dogs); unknown in cats Authors suggest do not exceed 6 mg/kg in dogs and 3 mg/kg in cats
Ropivacaine	5–10 min	5–8 h	Dose 1–3 mg/kg (dogs); 1–2 mg/kg (cats) Toxic IV dose for CNS toxicity: 4.8 mg/kg (dogs); unknown in cats Toxic IV dose for cardiovascular collapse: 42 mg/kg (dogs); unknown in cats Authors suggest do not exceed 3 mg/kg in dogs and 2 mg/kg in cats
Bupivacaine	2–20 min	4–8 h	Dose 1–2 mg/kg (dogs); 1 mg/kg (cats) Toxic IV dose for CNS toxicity: 4–8 mg/kg (dogs); 4 mg/kg (cats) Toxic IV dose for cardiovascular collapse: 20 mg/kg (dogs); 18 mg/kg (cats) Authors suggest do not exceed 3 mg/kg in dogs and 2 mg/kg in cats

Note: It is important to bear in mind the sliding scale of toxicity of these agents. In humans, the first known side‐effect of accumulating local anesthetic is tinnitus, or ringing in the ears. As this would be difficult to identify in companion animal species, veterinarians often see nausea and vomiting, which can progress to seizures (CNS toxicity) and then cardiovascular collapse. Suggested doses are given with the intent to reduce all complications, although this may vary by patient.

CNS, central nervous system; IV, intravenous.

2.Analgesic action

Local anesthetics bind to sodium channels present in the peripheral neurons during their inactive state. This prevents subsequent channel activation and inhibition of sodium permeability that occurs with membrane depolarization. As the threshold level for the action potential is not attained, suppression of nerve signal transmission occurs between neurons.

3.Clinical considerations

Local anesthetics with larger molecular weights, greater lipid solubility, and higher protein binding (e.g., bupivacaine) have a longer duration of action. The onset of action is related to the lipid solubility of the drug. The rate at which a LA diffuses into a nerve is determined by its concentration. The higher the concentration, the more rapid the onset of the block. Because of the lack of evidence showing a consistent advantage of mixing LAs, the authors prefer to simply select a single agent based on its desired and predictable characteristics [57].

4.Adjuncts used with LAs

Epinephrine may be used with LAs to cause vasoconstriction and therefore prolong the duration of action of LAs and intensity of the blockade. It also reduces the systemic absorption of LAs and decreases the probability of systemic toxicity. However, caution is advised if LA with epinephrine is used on extremities, as ischemia of the tissue may result. Preservative‐free buprenorphine (0.004 mg/kg) with bupivacaine injected into the epidural space provided up to 24 h analgesia in dogs undergoing stifle arthroplasty [56]. It is also used for perineural injections in order to extend the analgesic duration of LAs.

Alpha‐2 agonists like dexmedetomidine when added to LAs enhance analgesia via hyperpolarization of C fibers during neuraxial anesthesia and peripheral nerve blocks. These drugs can produce analgesia through supraspinal and spinal mechanisms (via adrenergic receptors) and have inhibitory effects on conduction of nerve impulses. A dose of 0.1 μg/kg added to LA in femoral nerve blocks effectively prolongs analgesia for 24 h [56]. The same dose is also used for perineural injections.

Ketamine produces localized hypoalgesia due to its LA‐like effects, which may be through its ability to inhibit neuronal sodium channels. Apart from causing NMDA blockade‐mediated analgesia in the CNS and spinal cord receptors, ketamine also interacts with opioid and monoaminergic receptors. Thoracic epidural administration of lidocaine with ketamine provides longer duration of analgesia of the thorax and forelimbs bilaterally in dogs [58].

5.Local anesthetic toxicity

Administration of an incorrect dose and inadvertent IV administration are likely the most common causes of systemic toxicity. Cats are most susceptible to developing methemoglobinemia after topical exposure to products containing benzocaine, which should be avoided in these species [59]. Toxicity of local anesthetics is additive by nature and may be due to multiple routes of exposure (topical and regional), mixtures of local anesthetics, or recurrent dosing. Post IV overdose, initial clinical signs include salivation, vomiting, and hypothermia. There is an immediate progression to pronounced CNS signs like nystagmus, muscle twitching, convulsions, tremors/seizures, and generalized CNS depression. These are then followed by cardiovascular effects like hypotension, bradycardia, and arrhythmias. Muscle tremors and seizures are managed with benzodiazepines (0.2–0.4 mg/kg IV) or propofol (2–4 mg/kg IV).

Hypotension is treated with IV crystalloids and a vasopressor (phenylephrine 0.1–3 μg/kg/min). 20% lipid emulsion is recommended at 4 mL/kg initial bolus over 2 min followed by an infusion 0.25 mL/kg/min for 20–30 min. This extracts the LA from the aqueous plasma into a “lipid sink,” making it unavailable to the tissues [60].

Other supportive therapy includes airway management, treating arrhythmias, and cardiopulmonary resuscitation if cardiac arrest ensues.

B. Equipment used for local‐regional anesthesia

1. Needles

Small‐gauge needles (25–27 G) minimize the risk of nerve injury and are generally used for infiltration anesthesia and superficial blocks (e.g., dental blocks). Large‐gauge needles of a longer length (19–22 G, 1.5–3.5 inch) are used for deeper blocks (e.g., brachial plexus, epidural). Spinal needles with removable stylets are sharp, specially designed for penetrating the dura mater. Tuohy needles are blunt‐ended, curved at the distal tip, and used for epidural injections or placement of indwelling epidural catheters. Insulated nerve block needles, which are also blunt‐ended, are coated with a thin layer of nonconducting material over the entire length of the needle except for a small area at the distal tip. When the needle is connected to a peripheral nerve stimulator, low‐intensity currents (0.2–0.5 mA) can stimulate motor fibers, allowing successful identification of the target nerves.

2.Peripheral nerve stimulator (PNS)

This device generates a square‐wave electrical current to locate target nerves, when used with an insulated needle (Figure 7.1). At sufficiently low currents (0.4–1 mA), if the stimulating needle elicits contractions of the muscle group of the target nerve, it indicates that the needle‐to‐nerve proximity is ideal for an injection of LA to cause a sensory block. If current is still conducted at 0.4 mA or less, it is likely that the needle is intraneuronal; it is advised to back the needle out prior to injection to avoid perineural injections, which may damage the nerve.

3.Ultrasound machine

Ultrasound allows for real‐time visualization of the stimulating needle, as well as identification of peripheral nerves and other anatomic structures such as vessels, muscles, and fasciae. Ultrasound guidance and electrolocation are often used together while performing nerve blocks, to increase the accuracy of nerve location and efficacy of the blockade. High‐frequency linear transducers (10–15 MHz) are suitable for performing most peripheral nerve blocks, and imaging superficial nerves that are less than 5 cm in depth. It is crucial that the anesthetist has: (1) a thorough understanding of the operative functions and basic principles of the ultrasound machine; (2) knowledge of anatomy and landmarks surrounding the target nerves; and (3) training to identify the echogenicity of the peripheral nerves, muscles, bones, fasciae, and blood vessels.

Photo depicts a peripheral nerve stimulator in use for the placement of a sacrococcygeal epidural injection. — **Figure 7.1** A peripheral nerve stimulator in use for the placement of a sacrococcygeal epidural injection.

C. Local‐regional anesthesia

Injection of LA around a particular nerve or nerve roots produces loss of sensation (sensory block) with or without paralysis (motor block) in that region, depending on the drug and its concentration. Different techniques for delivering LAs include topical anesthesia, infiltration anesthesia, neuraxial anesthesia, and peripheral nerve blocks. Some of the most common techniques are briefly reviewed below but fully described in the digital addendum. Additional resources for regional anesthesia strategies in small animals are listed at the end of this chapter.

1.Topical anesthesia

Topical lidocaine spray (2%, 4% or 10% solution) is available for laryngeal desensitization before tracheal intubation. A eutectic mixture of local anesthetics (EMLA) cream or patches (2.5% lidocaine and 2.5% prilocaine) prevent pain associated with peripheral catheter placement [61,62], superficial skin closure and blood sampling [63]. The cream is applied to the skin and covered with a dressing to enable absorption of the LAs. Time to achieve local effect is 45–60 min and it lasts up to 2 h after the dressing is removed. Transdermal self‐adhesive lidocaine patches (Lidoderm^®, 5%, Teikoku Pharma) are used for surgical, incisional or trauma wounds. The manufacturer recommends placing the patch about 1 cm from the incision edge, covering the entire length of the incision to produce prolonged dynamic pain control and reduce requirement of systemic opioids postoperatively. However, some investigators found no adverse effects when the patch was placed directly over the incision [64]. This patch is cut to the desired length and shape. Plasma peak lidocaine concentrations are reached in 12–60 h in dogs and cats, with duration of analgesic effect lasting for 3–5 days [65,66]. Lidoderm and EMLA cream provide dermal anesthesia and minimal systemic absorption of the LA occurs via these methods.

2.Infiltration anesthesia

Incisional, intraperitoneal, and tissue infiltration of LAs is used for a variety of surgeries, wound care, multimodal analgesia, and in sterilization programs carried out in countries with limited drug availability [67]. Splash blocks are performed prior to closure of an incisional site to provide local analgesia [68] (Table 7.2). Wound infiltration using a multifenestrated catheter inserted into the surgical wound at the end of the procedure is a novel method of permitting repeated or continuous infusion of LAs for a prolonged period of time for postoperative analgesia [69] (Figure 7.2). The nerve endings in the tissues or in the area of infiltration are desensitized, thus preventing nociception. Infiltration technique should be avoided in infected tissues/wounds, as pH changes render LAs ineffective, and for masses where malignant cells may be spread beyond margins by the needle used. Care must be taken not to exceed the toxic dose for LAs (see Table 7.1).

Table 7.2 Infiltrative or splash blocks.

Materials: 20–22 G needle, appropriately sized labeled syringe with local anesthetic solution, aseptic preparation, disposable or sterile gloves
Drugs: 0.5–0.75% bupivacaine 1–2 mg/kg for dogs and 1 mg/kg for cats; 2% lidocaine 3 mg/kg in dogs and 2 mg/kg in cats. Dilution can be achieved by 0.9% normal saline
Infiltrative technique: An infiltrative block involves distribution of local anesthetic into tissue, usually subcutaneous, around a mass or area of incision. Area is clipped and aseptically prepped prior to block
Splash technique: Splash block involves the “splashing” of local anesthetic over an incision after closure of the muscle layer, but prior to closure of the skin. The solution is given sterilely to the surgeon for administration or splashed sterilely into incision

Photo depicts a soaker catheter placed by the surgical team for wound infiltration. — **Figure 7.2** A soaker catheter placed by the surgical team for wound infiltration.

A liposome‐encapsulated injectable suspension of bupivacaine (Nocita^®, Elanco) is the newest FDA‐approved formulation for providing postoperative analgesia using a single injection technique at the time of incision closure for stifle surgery in dogs [70,71], and for regional analgesia following onychectomy in cats. It is also used for tissue infiltration during wound/incision closure (off‐label) and nerve blocks not at incisional sites (off‐label except for blockade of the radius/ulnar/musculocutaneous nerves). It consists of a unique liposomal delivery technology that encapsulates the bupivacaine with liposomal chambers. Post administration, these chambers break down, gradually releasing the bupivacaine over an extended period (72 h). Injection at closure prevents liposome disruption during surgical tissue manipulation. Slow bupivacaine release results in lower systemic exposure and decreased incidence of adverse effects. It is essential to use a 22 G or larger bore needle for the injection as smaller‐bore needles can disrupt the liposomes [72]. This liposomal bupivacaine may not be as effective when used for a splash block.

Dosage for liposome‐encapsulated injectable suspension of bupivacaine is as follow.

Dogs: 5.3 mg/kg (0.4 mL/kg) total dose for local infiltration injection. The label indication allows for an equivalent amount of saline added to the drug to cover a larger surface area.
Cats: 5.3 mg/kg per forelimb (0.4 mL/kg per forelimb) prior to onychectomy; total dose 10.6 mg/kg.

3. Neuraxial anesthesia

Epidural anesthesia is the administration of LA (or other drugs, e.g., opioids) into the epidural space (outside the dura) (Figure 7.3). If the drug is injected in the subarachnoid space, it is called spinal/intrathecal anesthesia. Epidural blocks are typically performed in anesthetized or heavily sedated patients, to relieve acute and chronic pain associated with a variety of surgeries and medical conditions. Analgesia occurs due to the bathing of the spinal nerve roots with the LAs. The extent of spinal nerve blockade following an epidural injection depends on the site of injection and the volume injected. Greater volumes cause cranial spread of the injected solution, increasing the area of desensitization. Also, higher concentrations of LAs are associated with more profound and prolonged blockade.

Schematic illustration of demonstrating landmarks for epidural placement. — **Figure 7.3** Diagram demonstrating landmarks for epidural placement.

*Source:*Courtesy of Teton NewMedia.

a. Lumbosacral (LS) epidural anesthesia (Table 7.3)

Table 7.3 Lumbosacral (LS) epidural placement (Figures 7.4–7.7).

Materials: Aseptic skin preparation supplies, sterile gloves, spinal needle/Tuohy needle of appropriate diameter and length, drugs in appropriately labeled syringes, +/– glass syringe, +/– nerve stimulator and appropriate insulated needle, +/– sterile 0.9% normal saline
Drugs: Preservative‐free (PF) morphine 0.1 mg/kg +/– bupivacaine PF 0.5–1.0 mg/kg or lidocaine PF 0.5 mg/kg not to exceed calculated total volumecssStyle=” cssStyle=”color:#0563C1″ a
Technique:
Once patient is heavily sedated or anesthetized, place animal in lateral or sternal recumbency and pull hindlimbs ventral (forward). Clip a 10 × 10 cm square area over the LS space; aseptically prepare site. Open gloves and sterilely place necessary materials on glove cover paper; glove carefully, avoiding contaminating materials. Palpate the iliac wings with thumb and middle finger. Use index finger to palpate the LS junction (usually just caudal to a line drawn between the two iliac wings). In the canine, on midline, insert the needle perpendicular to the skin, approximately halfway between the spinous process of L7 and the sacrum (S1). In the feline, the junction is slightly more caudal. Remove stylet from the spinal needle, once through the skin, and place a few drops of sterile 0.9% normal saline in the needle hub. On further advancement of the needle, feel for two “pops” (resistance which dissipates abruptly). The first minor pop is passage through muscle fascia. The next, more prominent pop signifies passing through the ligamentum flavum. If bone is encountered while advancing the needle, withdraw the needle to just below the surface of the skin, reassess location, and redirect the needle if no blood is present in the needle hub. At this point, the saline is pulled into the epidural space (“sucked”) from the hub of the needle. Positive “hanging drop” test signifies aspiration of fluid in the hub of the needle as the epidural space is entered. The other confirmatory tests are loss of resistance (LOR) and nerve stimulation. LOR: Place 1–2 mL of air in a glass syringe or loss of resistance syringe and secure to the spinal needle. Test for loss of resistance by injecting air to see if the plunger of the syringe advances smoothly. If there is no resistance, the needle is in the epidural space. Nerve stimulation: When using a nerve stimulator, a nerve stimulation test (0.7 mA, 1 Hz, 0.1 ms) will elicit muscle contraction of the pelvic limbs and tail. However, it does not differentiate if the needle tip is in the epidural or subarachnoid space. If cerebrospinal fluid (CSF) is present in the needle hub, reduce the dose of drugs by 50%. CSF is more likely to be encountered in cats because the spinal cord ends (L7–S1) more caudally than in dogs. If blood is present in the needle hub, remove needle completely. Another fresh attempt can be made or adopt an alternative analgesic technique. A 1 mL air bubble placed in the drug syringe helps to confirm that the needle remained in the epidural space (during injection of drugs, the air bubble will not collapse). Some anesthesiologists recommend aspirating prior to drug injection for blood or CSF. Inject drugs slowly over 90–120 seconds; injections should be smooth (no resistance). The authors advocate putting the affected limb down to encourage epidural spread to that region, especially if local anesthetics were used.

^a Total volume calculation options: 1 mL/10 kg for perianal, 1 mL/7 kg for hindlimb procedures, 1 mL/5 kg for thoracic/abdominal procedure. Avoid total volumes over 6 mL. Sterile 0.9% normal saline is used to add volume if desired.

Photo depicts L7–S1 epidural placement in a canine patient in lateral recumbency. — **Figure 7.4** L7–S1 epidural placement in a canine patient in lateral recumbency.

Photo depicts canine patient in sternal positioning during an epidural technique. — **Figure 7.5** Canine patient in sternal positioning during an epidural technique.

Photo depicts threading of an epidural catheter in the L7–S1 space of a canine patient. — **Figure 7.6** Threading of an epidural catheter in the L7–S1 space of a canine patient.

Photo depicts L7–S1. Left: Epidural catheter placed and secured in a canine patient. Right: Final fixation of the epidural catheter with an adhesive plaster. — **Figure 7.7** L7–S1. *Left*: Epidural catheter placed and secured in a canine patient. *Right*: Final fixation of the epidural catheter with an adhesive plaster.

Area and nerves blocked: Pelvic plexus nerves, pelvic limbs, perineum, and tail. If total injectate volume is 0.2–0.3 mL/kg, desensitization can extend up to T13.
Landmarks: Dorsal midline between L7 and S1.
Indications: To provide analgesia for procedures involving the perineal/urogenital region, middle and caudal abdomen, pelvic limbs, and tail.
Complications: (1) Excess injectate volume can cause cranial migration, leading to blockade of the diaphragm, impairing ventilation; (2) urinary retention if preservative‐free morphine is used; (3) spinal injection can cause hypotension, cardiovascular collapse, and apnea; (4) LA toxicity can occur with high doses; (5) spinal cord and nerve root damage; (6) intravascular injection in the internal venous plexus.
Contraindications: Skin infection over lumbosacral region, abnormal pelvic anatomy, patients with bleeding disorders, uncorrected hypovolemia or hypotension, neoplasia at the site of injection, sepsis.
Practical points: (1) Epidural catheters are an option in larger dogs and maintained for several days to allow continuous or intermittent delivery of analgesic drugs; (2) in cats, there is a risk of spinal cord damage with traumatic injection as their spinal cord ends at L7, as opposed to the canine patient whose spinal cord ends at L5–6; (3) epidural anesthesia may provide long duration (12–24 h) of analgesia, and reduce inhalant requirements; (4) preservative‐free drugs are recommended; (4) postoperative expression of urinary bladder must be performed (more so if morphine is used), and the patient is observed to ensure normal urination for 24 h post epidural.

b. Sacrococcygeal (SC) or intercoccygeal (IC) epidural anesthesia (Table 7.4)

Table 7.4 Sacrococcygeal (SC) or intercoccygeal (IC) epidural anesthesia placement.

Materials: Aseptic skin preparation supplies, sterile gloves, spinal needle or hypodermic needle of appropriate diameter and length, drugs in appropriately labeled syringes, +/− nerve stimulator and appropriate insulated needle, +/− sterile 0.9% normal saline
Drugs: Preservative‐free (PF) morphine 0.1 mg/kg +/− 0.5% bupivacaine PF 0.5 mg/kg or 2% lidocaine PF 0.5 mg/kg not to exceed calculated total volumecssStyle=” cssStyle=”color:#0563C1″ a
Technique:
Once patient is heavily sedated/anesthetized, place animal in sternal recumbency. Clip a 10 × 10 cm square area over the SC or IC space; aseptically prepare site. Open gloves and sterilely place necessary materials on glove cover paper; glove carefully, avoiding contaminating materials. Palpate the most mobile joint caudal to the sacrum with the nondominant index finger (sacrococcygeal or 1st intercoccygeal space). It is identified by up‐and‐down movement (“pumping”) of the tail. An attendant mobilizes the tail to avoid breaking sterility. The dominant hand is used to insert a hypodermic or spinal needle at a 30–45° angle through the skin on the dorsal midline. Remove stylet from the spinal needle, once through the skin. If the needle hits the vertebral bone, it is repositioned by making slight changes in the angle of entry until it pierces through the ligamentum flavum, generating a palpable “pop”. Confirmation of accurate needle tip placement: (1) palpable “pop” may be encountered as the needle penetrates the ligamentum flavum (sharpness of hypodermic needles can cause lack of “pop” response in spite of being in the correct location); (2) loss of resistance while injecting; (3) relaxation of the rectum and tail muscles; (4) nerve stimulation test (0.7 mA, 0.1 ms, 1 Hz) will elicit muscle contraction of the middle and distal third of the tail (SC approach). If blood is present in the needle hub, remove needle completely. Another fresh attempt can be made or adopt an alternative analgesic technique. A 1 mL air bubble placed in the drug syringe helps to confirm that the needle remained in the epidural space (during injection of drugs, the air bubble will not collapse). Inject drugs slowly over 90–120 seconds; injections should be smooth (no resistance). If tail/anus relaxation does not occur within 5 min (within 8–10 min with bupivacaine), the injection may have been made subcutaneously.

^a Total volume calculation options: 1. To block pelvic limb motor function, use total volume of 0.2 mL/kg; 2. for tail and perineal surgeries use total volume of 0.1 mL/kg. Avoid total volumes over 6 mL. Sterile 0.9% NaCl is used to add volume if desired.

Area and nerves blocked: Pudendal, pelvic, and caudal nerves supplying soft tissue structures of the sacrum, perineum, and tail region.
Landmarks: SC space or IC articulation between first and second coccygeal vertebrae.
Indications: To provide analgesia for tail amputation, anal sacculectomy, perineal urethrostomy, perineal mass removal, deobstipation, assisted vaginal delivery of puppies or kittens, correction of urinary obstruction.
Complications: (1) Excess injectate volume can cause cranial migration, leading to motor nerve blockade of the pelvic region; (2) urinary retention if morphine is used (see Practical points); and (3) LA toxicity can occur with high doses.
Contraindications: Patients with bleeding disorders, uncorrected hypovolemia and hypotension, infections, and neoplasia at the site of injection and sepsis.
Practical points: (1) Chances of spinal cord damage or intrathecal injection with SC and IC approach are eliminated; (2) in scenarios where these approaches cannot be performed, lumbosacral injection is considered; (3) preservative‐free drugs are recommended; (4) expression of urinary bladder must be performed (more so if morphine is used), and the patient is observed to ensure normal urination for 24 h post epidural.

D. Peripheral nerve blocks

1. Head

a. Infraorbital nerve block

Area and nerves blocked: Infraorbital nerves supplying the caudal, medial, and rostral superior alveolar nerves, multiple nerve branches innervating the upper lip, buccal and nasal areas (Figures 7.8. and 7.9).
Landmarks: Infraorbital foramen and zygomatic arch.
Indications: Analgesia for maxillary canine, molar, and premolar extractions, surgeries on hard and soft tissues of ipsilateral maxilla, nose, and upper lip, rhinotomy, rhinoscopy, and palatal surgery.
Complications: (1) Nerve, vessel, or soft tissue injury from the needle; (2) injury to the ocular globe (especially in cats due to a short infraorbital canal).
Contraindications: Infection, inflammation, or neoplasia at the site of injection.
Practical points: (1) Required drug volumes are low due to small size of foramen; (2) foramen size in dogs is 1–2‐cm long (shorter in brachycephalic breeds) and 4 mm long in cats, which warrants use of short needles or a 24 G catheter (Table 7.5).

Photo depicts infraorbital nerve block in canine skeleton. — **Figure 7.8** Infraorbital nerve block in canine skeleton.

*Source*: Courtesy of Anderson da Cunha.

Photo depicts infraorbital nerve block in the feline skeleton. — **Figure 7.9** Infraorbital nerve block in the feline skeleton.

*Source*:Courtesy of Anderson da Cunha.

Table 7.5 Infraorbital nerve block.

Materials: Disposable or sterile gloves, hypodermic needles (23–25 G) or 24 G catheter, drug solution labeled in 1 mL syringe
Drugs: 0.5% bupivacaine or 2% mepivacaine or 2% lidocaine 1–1.5 mg/kg. Generally, the dose per site is dependent on the patient size and weight and is 0.1–1 mL/site (dog) and 0.1–0.3 mL/site (cat)
Technique:
Place the heavily sedated or anesthetized patient in lateral or sternal recumbency. Palpate the infraorbital foramen (on the buccal side of the maxilla, usually above the 3rd premolar in dogs and 2nd premolar in cats). Place the index finger over the foramen to guide needle and insert a 23–25 G needle or 24 G catheter (sliding catheter into the foramen into the canal) into the opening of the foramen. Inserting a needle deeper into foramen increases the chance of injecting into the nerve. A shorter needle engages into the foramen. Aspirate; if no blood is present, inject local anesthetic solution over 30 seconds around opening of and slightly within the foramen. Little to no resistance to injection is felt when the needle is correctly placed.

b. Maxillary nerve block

Area and nerves blocked: All maxillary teeth and associated soft structures, skin of the nose, cheek, upper lip and possibly ipsilateral hard and soft palate.
Indications: Analgesia for performing procedures on any tooth or soft and hard tissues of the ipsilateral maxilla.
Landmarks: Maxillary tuberosity, maxillary molar teeth, zygomatic arch, pterygopalatine fossa (Figures 7.10 and 7.11).
Complications: Nerve, vessel or soft tissue injury from the needle; puncture or laceration of the maxillary artery.
Contraindications: Infection, inflammation, or neoplasia at the site of injection.
Practical points: Required drug volumes are low due to small size of foramen. This warrants short needles (Table 7.6).

Photo depicts maxillary nerve block via internal approach in the skeleton of a dog. — **Figure 7.10** Maxillary nerve block via internal approach in the skeleton of a dog.

*Source*: Courtesy of Anderson da Cunha.

Photo depicts maxillary nerve block via internal approach in the skeleton of a cat. — **Figure 7.11** Maxillary nerve block via internal approach in the skeleton of a cat.

*Source*: Courtesy of Anderson da Cunha

Table 7.6 Maxillary nerve block.

Materials: Disposable or sterile gloves, hypodermic needles (23–25 G), drug solution labeled in 1 mL syringe
Drugs: 0.5% bupivacaine or 2% mepivacaine or 2% lidocaine up to 1–1.5 mg/kg. Generally, the dose per site is dependent on the patient size and weight and is 0.1–1 mL/site (dog) and 0.1–0.3 mL/site (cat).
Technique (inside mouth approach):
Place the heavily sedated or anesthetized patient in lateral or dorsal recumbency. Open the mouth wide and retract lips at the lateral commissure. Laterally from the caudal nasal spine of the palatine lies the pterygopalatine fossa and pterygoid process (the maxillary nerve passes through the pterygoid fossa). Insert a 23–25 G needle into the area near the pterygoid fossa, dorsally immediately caudal to the maxillary second and third molars, in a perpendicular angle to the maxilla. Aspirate to rule out blood, and then inject the drug solution over 30 seconds. Little to no resistance to injection is felt when the needle is correctly placed.
Technique (from outside mouth):
A 23–25 G needle is inserted perpendicular to the skin just ventral to the zygomatic arch and 0.5 cm caudal to the lateral canthus of the eye. Direct the needle perpendicular to the arch. Insert the needle to the level of the pterygopalatine fossa and maxillary nerve. Aspirate to rule out blood, and then inject the drug solution over 30 seconds. Little to no resistance to injection is felt when the needle is correctly placed.

c. Caudal inferior alveolar (mandibular) nerve block

Area and nerves blocked: Mandibular tooth, rostral lower lip, rostral intermandibular region, lower dental arch and soft tissue and periosteum of the lingual side of the mandible (Figures 7.12–7.14).
Indications: Extraction of mandibular tooth, procedures involving lower lip and intermandibular region.
Landmarks: Mandibular foramen, angular process of mandible, last molar tooth.
Complications: Nerve, vessel or soft tissue injury from the needle
Contraindications: Infection, inflammation, or neoplasia at the site of injection.
Practical points: Required drug volumes are low due to small size of foramen. This warrants short needles (Table 7.7).

Photo depicts approaches for a caudal inferior alveolar (mandibular) nerve block in a canine skull. — **Figure 7.12** Approaches for a caudal inferior alveolar (mandibular) nerve block in a canine skull.

*Source*: Courtesy of Anderson da Cunha.

Photo depicts caudal inferior alveolar (mandibular) nerve block in a feline skull. — **Figure 7.13** Caudal inferior alveolar (mandibular) nerve block in a feline skull.

*Source*: Courtesy of Anderson da Cunha.

Photo depicts caudal inferior alveolar (mandibular) nerve block in canine patient. — **Figure 7.14** Caudal inferior alveolar (mandibular) nerve block in canine patient.

*Source*:Courtesy of Anderson da Cunha.

Table 7.7 Caudal inferior alveolar (mandibular) nerve block.

Materials: Disposable or sterile gloves, hypodermic needles (23–25 G), drug solution labeled in 1 mLsyringe.
Drugs: 0.5% bupivacaine or 2% mepivacaine or 2% lidocaine up to 1–1.5 mg/kg. Generally, the dose per site is dependent on the patient size and weight and is 0.1–1 mL/site (dog) and 0.1–0.3 mL/site (cat).
Technique:
Place the heavily sedated or anesthetized patient in a lateral or dorsal recumbency. Palpate the mandibular foramen on the caudal, medial (lingual) surface of the ramus (curve of the mandible) behind the last molar. The foramen is palpable both internally on the lingual side of the ramus, or externally. Use index finger of the opposite hand to guide the 23–25 G needle and a 1 mL syringe of local anesthetic near the foramen, between the mucosa and bone. If the approach is through the skin, the skin is first aseptically prepared. Aspirate syringe. If no blood is present, inject local anesthetic around the mandibular foramen. Little to no resistance to injection is felt when the needle is correctly placed.

d. Mental nerve block

Area and nerves blocked: Middle mental nerve, rostral alveolar branch of inferior alveolar nerve, lower incisors and canine tooth, rostral intermandibular region and lower lip (Figures 7.15 and 7.16).
Indications: Analgesia for mandibular canine, molar and premolar extractions, rostral intermandibular region, and lower lip mass removal.
Landmarks: Middle mental foramen, mandibular canine tooth.
Complications: Nerve, vessel or soft tissue injury from the needle.
Contraindications: Infection, inflammation, or neoplasia at the site of injection.
Practical points: Required drug volumes are low due to small size of foramen. This warrants short needles (Table 7.8).

Photo depicts mental nerve block in canine skull. — **Figure 7.15** Mental nerve block in canine skull.

*Source*: Courtesy of Anderson da Cunha.

Photo depicts mental nerve block in a feline skull. — **Figure 7.16** Mental nerve block in a feline skull.

*Source*: Courtesy of Anderson da Cunha.

Table 7.8 Mental nerve block.

Materials: Disposable or sterile gloves, hypodermic needles (23–25 G), drug solution labeled in 1 mL syringe.
Drugs: 0.5% bupivacaine or 2% mepivacaine or 2% lidocaine up to 1–1.5 mg/kg. Generally, the dose per site is dependent on the patient size and weight and is 0.1–1 mL/site (dog) and 0.1–0.3 mL/site (cat).
Technique:
Place the heavily sedated or anesthetized patient in a lateral or sternal recumbency. The mandibular labial frenulum is retracted ventrally. Palpate the middle mental foramen on the buccal side of the mandible, ventral to the rostral aspect of second premolar. In cats, it is at the apex of mandibular canine. Insert 23–25 G needle in front of the mental foramen. Aspirate to rule out blood, and then inject the drug solution over 30 seconds. The needle can be introduced a couple of millimeters into the foramen or, in very small patients, the local anesthetic can be infiltrated on the area just outside the foramen. Little to no resistance to injection is felt when the needle is correctly placed.

e. Retrobulbar nerve block

Area and nerves blocked: Oculomotor, trochlear, trigeminal, and abducens nerves, ciliary ganglion, conjunctiva, cornea, and uvea [73].
Indications: Analgesia for enucleation, evisceration with intrascleral prosthesis and necessity for central rotation of the globe.
Landmarks: Lateral canthus, middle of lower eyelid and bony rim of the lower orbit (Figure 7.17).
Complications: (1) Globe penetration; (2) nerve or vessel injury; (3) inadvertent injection of local anesthetic in the perineural optic nerve sheath; (4) retrobulbar hemorrhage and proptosis of the eye (seen with higher volumes in brachycephalic breeds); (5) intrathecal injection.
Contraindications: Infection, inflammation, or neoplasia at the site of injection.
Practical points: There are several approaches with different complications depending on the experience of the individual performing the block (Table 7.9).

Photo depicts retrobulbar nerve block. — **Figure 7.17** Retrobulbar nerve block.

*Source*: Courtesy of Filipe Espinheira Gomes.

Table 7.9 Retrobulbar nerve block: inferior temporal palpebral technique.

Materials: 22 G spinal needle (length is dependent on size of patient but is typically 3–5 cm), drug solution labeled in a 3 mL syringe, aseptic preparation, sterile gloves
Drugs: 2% lidocaine or 0.5% bupivacaine up to 1 mg/kg; maximum volume of injection is 1–3 mL in dogs and 0.3–0.5 mL in cats. Dilution is achieved with sterile 0.9% normal saline
Technique:
Once animal is adequately anesthetized, aseptically prepare the injection site for the procedure.Bend the needle tip to approximately 20° angle to conform to the orbit. Insert the needle at the 7 o’clock position, below the eyelid. When placing the needle, preferentially allow the needle to traverse along the bony orbit to avoid puncturing the globe and/or blood vessels. The needle is directed along the floor of the orbit and then redirected dorsally and towards the nose to reach the apex of the orbit. A slight popping sensation may be detected on piercing of the orbital fascia. The needle is then redirected slightly dorsally and nasally toward the orbital apex.The globe will rotate caudally until the conjunctival sac is breached, then the globe will rotate back to a standard position.If any resistance is felt, immediately stop and withdraw the needle slightly. Aspirate for blood, fluid, or resistance. If none is present, inject a test dosage (0.5 mL or less) of local anesthetic. If there is no resistance, and patient remains stable, continue with the rest of the injection over 30 seconds.

f. Auriculotemporal nerve block and greater auricular nerve block

Area and nerves blocked: Auriculotemporal nerve, great auricular nerve, external acoustic meatus, base of the auricle or pinna [74] (Figures 7.18 and 7.19).
Indications: Analgesia for procedures of the external acoustic meatus, tympanic bulla, and pinna, acute and chronic auricular pain management.
Landmarks: Zygomatic arch, auriculotemporal joint, auricular cartilage, and the wing of atlas [75].
Complications: (1) Nerve or vessel injury; (2) parotid gland laceration; (3) lingual nerve blockade leading to desensitization of the tongue and subsequent self‐mutilation lesions.
Contraindications: Infection, inflammation, or neoplasia at the site of injection.
Practical points: (1) In brachycephalic breeds, the location of the auriculotemporal nerve may be more ventral, towards the temporomandibular joint. (2) Due to the close proximity between auriculotemporal nerve, facial nerve and auriculopalpebral nerve, desensitization of motor branches of the facial nerve can occur. Hence, evaluation of palpebral reflex and use of eye lubricants are necessary to protect the corneal surface during the duration of the nerve blockade (Table 7.10).

Photo depicts auriculotemporal nerve block. — **Figure 7.18** Auriculotemporal nerve block.

Photo depicts greater auricular nerve block. — **Figure 7.19** Greater auricular nerve block.

Table 7.10 Auriculotemporal nerve block and greater auricular nerve block.

Materials: 22–25 G hypodermic needle, 1 or 3 mL syringe, sterile gloves, aseptic preparation
Drugs: 0.5% bupivacaine or 2% lidocaine up to 1 mg/kg; maximum volume limited to 0.5–3 mL /site (dogs) and 0.2–0.5 mL (cats). Dilution can be achieved by sterile 0.9% normal saline.
Technique:
Place the heavily sedated or anesthetized patient in lateral recumbency with the affected side up. Clip and aseptically prepare the skin of the parotid region and the lateral area of the neck. For auriculotemporal nerve block, the needle is inserted in the skin between the rostral aspect of the ear canal and the dorsal aspect of the most caudal part of the zygomatic arch. Once the needle is advanced half of the distance between the skin and the bone, the solution is deposited at that site. For the greater auricular nerve block, the needle is inserted in the skin ventral to the wing of the atlas and caudal to the ear canal. The needle is advanced into the subcutaneous tissue, and the solution is deposited at the site caudal to the vertical ear canal. Aspirate to ensure there is no air or blood. Continue to inject as the needle is withdrawn out of the skin during the greater auricular nerve block. This will maximize the success of the blockade of both the greater auricular nerve and the auricular branches of the facial nerve. If blood or air is aspirated, withdraw, reposition the needle, and then aspirate again.

2. Thorax and cranial abdomen

a. Intercostal nerve block

Area and nerves blocked: Intercostal nerve caudal to the associated rib, lateral chest wall and associated bony and soft tissue structures distal to the injection.
Indications: Analgesia for lateral thoracotomies, thoracic wounds, thoracic wall tumor removal, placement and removal of thoracic drain, rib fractures, thoracic wall injury.
Landmarks: Intercostal space, ribs (dependent on the affected/surgical site) (Figures 7.20 and 7.21).
Complications: (1) Accidental puncture of the thoracic cavity may result in pneumothorax; (2) accidental injection into nerve, artery, or vein.
Contraindications: Active infection over the site of injection, coagulopathy.
Practical points: (1) Intercostal nerve blocks provide a reliable unilateral dermatomal band of analgesia for the vertebral level at which they are performed; (2) care is taken to perform this block under sterile technique to avoid infection; (2) history of coagulopathy or anticoagulation is taken into consideration to reduce the risk of bleeding; (3) systemic absorption with this block may be significant, hence always stay below the local anesthetic toxic dose range (Table 7.11).

Photo depicts intercostal nerve block in canine patient. — **Figure 7.20** Intercostal nerve block in canine patient.

Table 7.11 Intercostal nerve block.

Materials: 22–25 G hypodermic needle, 3 mL syringe, sterile gloves, aseptic preparation
Drugs: 0.5% bupivacaine or 2% lidocaine up to 2 mg/kg; maximum volume limited to 0.5–2 mL /site (dogs) and 0.5–1 mL (cats). Dilution can be achieved by sterile 0.9% normal saline.
Technique:
Place the heavily sedated or anesthetized patient in lateral recumbency with the affected side up. Clip and aseptically prepare two cranial spaces, target space, and two caudal rib spaces for the block. Palpate between the intervertebral foramen and the caudal border of each of the five rib spaces (two spaces cranial to the location of interest, the location of interest, and two spaces caudal to the location of interest). Place needle through the skin, just below the intervertebral foramen, caudal to rib. For appropriate depth, the needle must penetrate just below the intercostal muscles. Direct the needle dorsally and medially, and “walk” the needle off the caudal border of each rib. This will help reduce the likelihood of causing pneumothorax. Aspirate to ensure there is no air or blood. Inject at this point and continue to inject as the needle is withdrawn out of the muscle layers and skin. If blood or air is aspirated, withdraw and reposition the needle, and then aspirate again.

b. Transversus abdominis plane block

Area and nerves blocked: Sensory blockade of abdominal wall and the parietal peritoneum. The transverse abdominal plane contains ventral branches of the last 3–4 intercoastal nerves and the first 2–3 lumbar vertebrae [76,77]. If the block is performed bilaterally, complete desensitization of the abdominal ventral midline is achieved.
Indications: Analgesia for abdominal surgeries [78,79], mastectomy [80], pancreatitis, and abdominal wall wound repairs.
Landmarks: Abdominal ventral midline, interfacial plane formed by the transversus abdominis muscle and the internal oblique abdominal muscle
Complications: (1) Intraperitoneal injection; (2) abdominal organ/vessel puncture.
Contraindications: Soft tissue infection of the abdominal wall and skin.
Practical points: Addition of dexmedetomidine to the local anesthetic solution can aid in prolonging duration of the blockade and analgesia [81] (Table 7.12).

Table 7.12 Transversus abdominis plane block.

Materials: Clippers, aseptic skin preparation solutions, disposable or sterile gloves, 20–22 G 2.5 m (cats, dogs <5 kg) and 5–6 cm (dogs) hypodermic or spinal needles, +/– extension set, drug solution in appropriately labeled syringe, ultrasound guidance using high‐frequency linear transducer (7.5–15 MHz)
Drugs: 0.5% bupivacaine (preferred due to longer duration of action) 1 mg/kg or 2% lidocaine up to 2 mg/kg; maximum volume limited to 1 mL/kg/injection site. Dilution can be achieved by sterile 0.9% normal saline
Technique:
Clip hair at the level of lateral and ventral abdominal wall and aseptically prepare the skin for the block. This block can be approached with the anesthetized patient in either lateral or dorsal recumbency. Place a high‐frequency (7.5–15 MHz) linear array transducer connected to an ultrasound system in a longitudinal orientation (with the marker cranially) in the area between the posterior margin of the last rib and the anterior margin of the iliac crest at the level of the axilla (3–4 cm from the abdominal midline). Clear imaging of the three abdominal muscle layers (external abdominal oblique, internal abdominal oblique, transversus abdominis) is obtained (Figures 7.22 and 7.23). Attach the needle (+/– extension set) to the labeled syringe with drug solution. Insert the needle tip cranial to the transducer. An “in‐plane” technique is used to obtain continuous real‐time visualization of the needle, advancing through the external and internal oblique abdominal muscles until the fascial plane overlying the transversus abdominis muscle is reached. Aspirate to ensure there is no blood. A small test dose (0.5 mL) can be injected into the observed space to confirm the correct positioning of the needle in the transversus abdominis plane. Once space is confirmed, inject the remaining volume of the drug solution. Two approaches that can be made for this block are: (1) paracostal approach: caudal to the caudal border of the last rib and dorsal to the midaxillary line; 2) umbilical approach: cranial to the iliac crest at the level of the umbilicus and dorsal to the midaxillary line. Some anesthesiologists will use both sites to provide more extensive coverage.

Photo depicts local anesthetic solution injected in the transverse abdominis plane using an ultrasound system with linear array transducer. — **Figure 7.22** Local anesthetic solution injected in the transverse abdominis plane using an ultrasound system with linear array transducer. D, dorsal; V, ventral; EO, external oblique abdominal muscles; IO, internal oblique abdominal muscle; P, peritoneum; TA, transversus abdominis muscle.

Photo depicts spinal needle (attached to the syringe with the local anesthetic solution) insertion cranial to the linear array transducer (13-6^MHz) for placement of the transverse abdominis plane block. — **Figure 7.23** Spinal needle (attached to the syringe with the local anesthetic solution) insertion cranial to the linear array transducer (13‐6 MHz) for placement of the transverse abdominis plane block.

3. Thoracic and pelvic limb

a. Brachial plexus block

Area and nerves blocked: Soft tissues from the mid to distal humerus, extending to the tip of the digits supplied by the musculocutaneous, supra‐ and subscapular, axillary, radial, median, and ulnar nerves. Consistent desensitization of the elbow does not occur.
Indications: Analgesia for procedures involving mid to distal humerus, extending to the tip of digits (e.g., amputation, fracture repair, wound explore, arthroscopy).
Landmarks: Scapulohumeral joint, acromion process, greater tubercle, trachea, jugular vein, first rib.
Complications: (1) Nerve trauma or hematoma compressing the nerve can cause neurologic deficits; (2) puncture of the thoracic cavity; (3) perforation of brachial artery; (4) ventricular fibrillation was reported after a stimulating needle was unintentionally introduced into the thorax [82]; (5) possible blockade of phrenic nerve.
Contraindications: (1) Skin infection in area of injection; (2) blocking of both front limbs (as patient may lose motor function and therefore ability to ambulate).
Practical points: The technique may be difficult to perform in obese patients. Addition of dexmedetomidine to the local anesthetic solution can enhance the duration of sensory and motor block, as well as duration of analgesia [83] (Table 7.13).

Table 7.13 Brachial plexus block (Figures 7.24–7.27).

Materials: 20 22 G 2.5–5 cm spinal needle (patient size dependent), aseptic preparation, sterile gloves, labeled syringe containing drug solution, +/– nerve stimulator with appropriately sized insulated needle
Drugs: 2% lidocaine or 0.5% bupivacaine up to 2 mg/kg; maximum volume limited to 0.2–0.3 mL/kg. Dilution can be achieved by sterile 0.9% normal saline
Technique:
The anesthetized patient lies in lateral recumbency with the limb to be blocked uppermost. Locate the point of the shoulder (scapulohumeral joint). Clip a 5 ×5 cm area with the point of the shoulder in the center; prepare aseptically. Insert the spinal needle at the point of the shoulder, through the skin. The needle is placed lateral to the chest wall/medial to the scapula, and parallels the transverse processes of the cervical vertebrae, directed towards the scapula to avoid entering the thorax. The needle tip is slowly advanced caudal to the second rib. With the blind technique, once the needle is inserted, attach the drug syringe, then aspirate and if no blood or air is present, approximately one‐third of the drug volume is injected. The needle is withdrawn 1–2 cm, aspirate and another third of the drug volume is administered. This continues until all drug is administered. With the nerve stimulator and insulated locator needle technique, once needle tip is near the musculocutaneous nerve, contractions of the biceps brachii muscle will cause flexion and supination of the elbow. Extension of the elbow indicates radial nerve response. Pronation of the extremity and flexed carpus indicates median/ulnar nerve response. Initially, locate a strong twitch with current amperage of 1.0 mA. Then follow with a reduced current amperage of 0.5 mA; decision to inject the drug solution is made when correct muscular response is still observed at <0.5 mA. Aspirate to ensure there is no blood. Inject the drug solution over 30–60 seconds. No resistance should be noted during injection. To ensure effectiveness, some anesthesiologists advocate depositing local anesthetic as the needle is slowly removed.

Schematic illustration of demonstrating brachial plexus block with a nerve locator and insulated needle. — **Figure 7.24** Diagram demonstrating brachial plexus block with a nerve locator and insulated needle.

*Source*:Courtesy of Teton NewMedia.

Photo depicts brachial plexus block in canine patient using a peripheral nerve stimulator. — **Figure 7.25** Brachial plexus block in canine patient using a peripheral nerve stimulator. Source: Courtesy of Patricia Queiroz‐Williams.

Photo depicts brachial plexus block in feline patient using a nerve stimulator. — **Figure 7.26** Brachial plexus block in feline patient using a nerve stimulator.

Photo depicts brachial plexus block in canine patient using the blind technique. — **Figure 7.27** Brachial plexus block in canine patient using the blind technique.

b. Metacarpal/metatarsal ring block

Area and nerves blocked: (1) Forelimb: superficial branches of the radial nerve, dorsal and palmar branches of the ulnar nerve, palmar median nerve at the level of the carpus; (2) hindlimb: superficial and deep peroneal nerve, tibial nerve, and/or lateral and plantar nerves (Figure 7.28).
Indications: Analgesia for digit amputations, interdigital tumor removal and digit wounds.
Landmarks: (1) Forelimb: proximal region to the carpus; (2) hindlimb: dorsal and plantar surfaces, at the level of the tarsometatarsal joint.
Complications: Injection into a nerve, artery, or vein.
Contraindications: (1) Skin infection in area of injection; (2) inflammation in the area of injection.
Practical points: (1) Do not use epinephrine because of the potential for ischemia in extremities; (2) stay below local anesthetic toxic dose range; (3) individual digits may also be blocked by injecting the local anesthetic solution subcutaneously in a circumferential ring pattern proximal to the affected digit (Table 7.14).

Schematic illustration of radial, ulnar, and medial nerve block. — **Figure 7.28** Diagram for radial, ulnar, and medial nerve block.

*Source*:Courtesy of Teton NewMedia.

Table 7.14 Metacarpal/metatarsal ring block.

Materials: 22–25 G hypodermic needle, 1–3 mL syringe, local anesthetic solution, aseptic skin preparation, disposable, or sterile gloves

Drugs: 0.5% bupivacaine 1–2 mg/kg for dogs and 1 mg/kg for cats; 2% lidocaine up to 3 mg/kg in dogs and 2 mg/kg in cats. Divide this between limbs if procedure involves multiple limbs. Maximum total volume is limited to 0.1–0.3 mL/kg. This total volume is divided equally per site, depending on the total number of sites of injection. Dilution can be achieved by sterile 0.9% normal saline.

Technique:

Place the heavily sedated or anesthetized patient in lateral or dorsal recumbency.
The affected limb is aseptically prepared for block. (Remember to avoid alcohol for preparation if laser declaw method is used.)
For forelimb: insert the 22–25 G hypodermic needle attached to the labeled syringe with drug solution subcutaneously in three sites: (1) lateral and proximal to the accessory carpal pad, (2) medial to the accessory carpal pad, and (3) at the dorsal‐medial aspect of the proximal carpus. Always aspirate to check for no blood before injecting at each site. There should be no resistance while injecting.
For hindlimb: insert the 22–25 G hypodermic needle attached to the labeled syringe with drug solution subcutaneously on the dorsal and plantar surfaces, at the level of the tarsometatarsal joint. Then, a simple circumferential ring block is performed at this location. Always aspirate to check for no blood before injecting at each site. There should be no resistance while injecting.

c. Femoral (FNB) and sciatic nerve block (SNB)

Area and nerves blocked: (1) FNB: mid‐diaphysis to distal end of the femur, femorotibial joint, femorotibial intraarticular structures, skin of dorsomedial tarsus and first digit; (2) SNB: stifle, tibia, tarsus, metatarsus, and digits (except 1st digit and proximal aspect of 2nd digit).
Indications: Analgesia for stifle surgery, procedures involving mid‐diaphysis to distal end of the femur, tarsus, metatarsus, and digits of pelvic limb (e.g., fracture repair, wound explore, arthroscopy).
Landmarks: The femoral nerve arises from L4–L6 vertebrae, and the sciatic nerve arises from L6–S2 vertebrae. In general, the femoral nerve provides innervation to the medial aspect of the hindlimb distally to just below the stifle. The sciatic nerve, along with its branches, provides innervation to the remainder of the hindlimb. For FNB, palpate the femoral artery and femoral triangle (cranial sartorius muscle, caudal pectineus muscle, proximal iliopsoas). For SNB, palpate the greater trochanter of femur, ischiatic tuberosity, and semitendinosus muscle [84].
Complications: Injection into a nerve, artery, or vein.
Contraindications: (1) Skin infection in the area of injection; (2) inflammation in the area of injection.
Practical points: (1) Accuracy of this nerve block is significantly increased with ultrasound guidance and/or peripheral nerve stimulation; (2) addition of dexmedetomidine to the local anesthetic solution can aid in prolonging duration of the blockade and analgesia [85,86] (Table 7.15).

Table 7.15 Femoral (FNB) and sciatic nerve block (SNB) (Figures 7.29–7.31).

Materials: 20–22 G insulated needle (length depends on size of patient), peripheral nerve stimulator, labeled syringe with drug solution, aseptic skin preparation, sterile gloves

Drugs: Up to 2 mg/kg of 0.5% bupivacaine (preferred due to longer duration of action) or 2% lidocaine. Total injection volume is 0.1 mL /kg for each FNB and SNB [84,87].

Technique:

Aseptically prepare the site once the patient is heavily sedated or anesthetized. The initial setting of the nerve stimulator is set at 0.5–1.0 mA, 2 Hz, 0.10 ms.
FNB: The patient is placed in lateral recumbency, with the limb for blockade uppermost. The limb is abducted 90° and extended caudally with access to the medial side of the thigh. Palpate for the femoral artery in the femoral triangle. Cranial to the femoral artery, and caudal to the rectus femoris, lies the femoral nerve. A 20–22 G insulated needle is introduced through the quadriceps femoris targeting the location of the femoral nerve. Nerve stimulator‐elicited muscle contraction includes contraction of the quadriceps muscle or extension of the stifle. This response is persistent even at a lower amperage of 0.4 mA. Aspirate to rule out blood and then deposit the local anesthetic solution. There should be no resistance during injection.
SNB: The patient is placed in lateral recumbency, with the limb for blockade uppermost. Palpate the ischiatic tuberosity and insert the 20–22 G insulated needle perpendicular to the skin through the semitendinosus muscle. Nerve stimulator‐elicited muscular response includes either dorsiflexion or plantar extension of the foot. This response is persistent even at a lower amperage of 0.4–mA. Aspirate to rule out blood and then deposit the local anesthetic solution. There should be no resistance during injection.

Photo depicts palpation of landmarks for a sciatic nerve block with the assistance of a nerve locator and insulated needle. — **Figure 7.29** Palpation of landmarks for a sciatic nerve block with the assistance of a nerve locator and insulated needle.

Photo depicts placement of the stimulating needle using an ultrasound system and a linear array transducer (13-6^MHz) while performing a sciatic nerve block. — **Figure 7.30** Placement of the stimulating needle using an ultrasound system and a linear array transducer (13‐6 MHz) while performing a sciatic nerve block.

Photo depicts placement of the stimulating needle using a peripheral nerve stimulator, an ultrasound system and a linear array transducer (13-6^MHz) while performing a femoral nerve block. — **Figure 7.31** Placement of the stimulating needle using a peripheral nerve stimulator, an ultrasound system and a linear array transducer (13‐6 MHz) while performing a femoral nerve block.

VIII. Conclusion

To summarize, in both acute and chronic pain settings, opioids are a mainstay in providing analgesia. However, they are associated with possible detrimental effects, as well as being subject to shortages caused by things like natural disasters or pandemics. Nonopioid analgesia alternatives include an assortment of pharmacologic and nonpharmacologic interventions. Also, development of novel regional anesthesia techniques for small animals has grown tremendously in recent times. Veterinary clinicians and technicians should be aware of these potential options and consider them when developing a multimodal approach to pain management.

Tags: Small Animal Anesthesia Techniques

May 13, 2023 | Posted by admin in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off

Veterian Key

Fastest Veterinary Medicine Insight Engine

Nonopioid analgesia alternatives and locoregional blocks

I. Nonopioid analgesic constant‐rate infusions

A. Ketamine

1.Clinical uses

B. Dexmedetomidine

1. Pharmacology

2.Clinical uses

C. Lidocaine

1. Pharmacology

2.Clinical uses

II. Oral gabapentinoids

1.Pharmacology

2.Clinical uses

III. Psychotropic drugs

1.Clinical uses

2.Dosage

IV. Cannabinoids

1. Endocannabinoid system (ECS) and pain

2.Clinical uses

V. Antiinflammatories

VI. Nonpharmacological pain therapy

A. Acupuncture

B. Physical rehabilitation

1.Superficial thermotherapy

2.Cryotherapy

3.Laser

4.Transcutaneous electrical nerve stimulation (TENS)

5.Extracorporeal shockwave therapy

6.Massage, therapeutic exercises

7.Glucosamine‐chondroitin, hyaluronic acid (HA) and platelet‐rich plasma (PRP)

8.Other nonpharmacologic techniques

VII. Local‐regional anesthetic techniques

A. Local anesthetics (LAs)

1. Pharmacology

2.Analgesic action

3.Clinical considerations

4.Adjuncts used with LAs

5.Local anesthetic toxicity

B. Equipment used for local‐regional anesthesia

1. Needles

2.Peripheral nerve stimulator (PNS)

3.Ultrasound machine

C. Local‐regional anesthesia

1.Topical anesthesia

2.Infiltration anesthesia

3. Neuraxial anesthesia

a. Lumbosacral (LS) epidural anesthesia (Table 7.3)

b. Sacrococcygeal (SC) or intercoccygeal (IC) epidural anesthesia (Table 7.4)

D. Peripheral nerve blocks

1. Head

a. Infraorbital nerve block

b. Maxillary nerve block

c. Caudal inferior alveolar (mandibular) nerve block

d. Mental nerve block

e. Retrobulbar nerve block

f. Auriculotemporal nerve block and greater auricular nerve block

2. Thorax and cranial abdomen

a. Intercostal nerve block

b. Transversus abdominis plane block

3. Thoracic and pelvic limb

a. Brachial plexus block

b. Metacarpal/metatarsal ring block

c. Femoral (FNB) and sciatic nerve block (SNB)

VIII. Conclusion

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