Anesthesia and Pain Management in Dental and Oral Procedures

Chapter 11 Anesthesia and Pain Management in Dental and Oral Procedures



Meghan Richey


There is a vast amount of information about anesthesia that is beyond the scope of this book in terms of the nuances, idiosyncrasies, and precautions, that should be investigated more thoroughly by the reader. This chapter is intended to serve as a user-friendly guide to some convenient anesthesia protocols, routes of administration, and management suggestions before, during, and after operative dentistry on the small animal patient.



GENERAL ANESTHESIA



General Comments



• General anesthesia is a necessary part of most dental procedures to provide immobility required for safe and total access to the oral cavity.

• Dental patients are usually categorized, according to the American Society of Anesthesiologists (ASA) classification, as class I or II (normal patient or patient with mild systemic disease; see below). An exception to this may be the geriatric patient or the patient that is immunologically or metabolically compromised.

• Safe anesthesia protocols are available, even for young puppies and kittens, so they can be placed under general anesthesia for various dental procedures such as interceptive orthodontic extractions.

• General anesthesia is often a major concern of the client, particularly when multiple sessions are required.

• A significant portion of the cost of any dental procedure is generated by anesthesia, supportive measures during anesthesia, and preoperative laboratory evaluations.

• Monitoring the physiologic changes that occur during anesthesia, such as hypothermia, hypotension, and cardiorespiratory depression with appropriate intervention, will help to ensure a safer anesthesia session.

• With proper attention to their physiologic needs, healthy geriatric patients or patients with mild systemic diseases can be anesthetized safely. These patients can be treated for their dental disease and will benefit from improved oral health.

• Anesthesia records should include administration time, route, and duration of anesthetic drugs; dosages used; fluids administered; catheter type, size, and location; endotracheal tube size; monitoring parameters; and vaporizer settings and oxygen and nitrous oxide flow rates. The anesthesia record should continue until the patient can maintain sternal recumbency unassisted.

• Charting heart rate, respiratory rate, and any other parameters monitored is a necessity. Any anesthesia complication or excessive delay in recovery should be noted so that future anesthesia protocols can be adjusted (Table 11-1).

• To reduce the incidence of aspiration during anesthesia, food should be withheld for 12 hours prior to induction of anesthesia, except to prevent hypoglycemia in young patients and diabetics. Water should be available to the patient until the morning of the procedure.


Table 11-1 EXAMPLE OF A SIMPLE ANESTHETIC RECORD

image


Chart: American Society of Anesthesiologists (ASA) Classifications1



ASA I: a normal patient with no organic disease.

ASA II: a patient with mild systemic disease.

ASA III: a patient with severe systemic disease limiting activity but not incapacitating.

ASA IV: a patient with incapacitating disease that is a constant threat to life.

ASA V: a moribund patient not expected to live 24 hours with or without surgery.


• Age is not a factor in assigning risk. While many healthy older patients may have early organ dysfunction, it poses no greater risk than to a young patient with equivalent organ dysfunction. Patient evaluation prior to anesthesia includes (1) signalment (species, breed, age, and sex), (2) a complete physical examination, (3) the chief complaint, and (4) the medical history.


Preprocedure Workup



• The decision to perform preanesthetic laboratory workups, and the degree of comprehensiveness of such workups, will vary based on several factors including the laboratory capability of the practice, the age of the patient, the physical examination findings, the anxiety level of the client over the procedure, and even the timing of the procedure. Remember that normal laboratory values do not ensure a safe, successful anesthetic episode but rather are screening for problems in one of three categories: (1) immediate life-threatening problems, (2) problems necessitating changes in the anesthesia protocol, and (3) problems that are more longstanding that will require follow-up subsequent, and unrelated, to the anesthesia. Most problems identified will fall in category 3 and less often in category 2. Rarely will a life-threatening problem be identified solely by laboratory values.

• A basic preanesthesia profile should include packed blood cell volume (PCV), total blood protein or solids value, and urine specific gravity. Other tests may be added based on the patient evaluation. It is often recommended that young healthy patients have a PCV; total protein, blood glucose, and blood urea nitrogen levels; and a urine specific gravity performed. Older patients or those with significant findings in their initial physical examination should have a complete blood count and chemistry profile performed as a minimal database. Additionally, tests for thyroid function, feline leukemia, and feline immunodeficiency virus (for cats), complete urinalysis, electrocardiogram, ultrasonographic examinations, and thoracic radiography should be scheduled, depending on the patient’s condition and the client’s permission.

• Other considerations for determining the anesthesia protocol include weight, temperament, procedure to be performed, length of anticipated procedure, concurrent diseases (e.g., epilepsy, heart disease, kidney disease, liver disease, endocrine disease, gastrointestinal disease, or bleeding disorders), medications administered previously or concurrently, previous anesthesia experiences, and dietary history.2


Preanesthetic Medications



Comments



• Preanesthetic medications are used to reduce the anxiety level of the patient, provide preemptive analgesia, reduce the amount of induction and maintenance drugs and, on occasion, to reduce the volume of secretions.

• These drugs usually are given intramuscularly 10 to 30 minutes prior to the induction of general anesthesia.

• In select instances they can be administered intravenously immediately before the induction agent. This route should not be used for routine administration of premedication due to the possibility of rapid changes in cardiorespiratory function. Dosages should be reduced by at least 50% when these drugs are administered intravenously.

• Intravenous administration in compromised patients may cause a more profound effect than desired; it is preferable to administer these drugs intramuscularly.

• Dosages provided here are for young, healthy patients; older or debilitated patients will require reduced dosages.


Anticholinergic Agents



Comments



• To maintain heart rate and hence cardiac output in patients receiving vagotonic drugs, such as α2-agonists and opioid agonists, patients who may be subject to strong vagal reflexes, or those patients whose cardiac output is heart rate dependent, such as very young patients, patients with significant cardiac disease (i.e., hypertrophic cardiomyopathy), procedures in the oropharynx, or inadvertent application of ocular or carotid pressure.

• To help reduce the volume of salivary secretions.

• Two commonly used drugs are atropine and glycopyrrolate.

• The use of these drugs has declined with the introduction of others that either maintain heart rate or have minimal effects on heart rate. The blanket use of these drugs often results in tachycardia and a reduction of cardiac output. As such, these drugs should be used only if indicated.


Atropine



• Dosage: cat or dog, 0.01 to 0.04 mg/kg IM or SC.3,4


Advantages


• Short onset time.

• Can be given intraoperatively to increase heart rate if a significant sinus bradycardia or second-degree atrioventricular (AV) block develops.

• Indicated in emergency or crisis situations.


Disadvantages


• Duration of 30 to 90 minutes.

• Can cause sinus tachycardia or even transient second-degree AV block.


Glycopyrrolate



• Dosage: cat or dog, 0.01 to 0.02 mg/kg IM or SC.3,4


Advantages


• Less effect on heart rate than atropine.

• Lasts longer than atropine (2 to 3 hours).


Disadvantages


• May take 30 to 45 minutes to reach peak effect following IM administration.

• More expensive than atropine.

• Indicated as a prophylactic anticholinergic agent rather than as an emergency drug.


Tranquilizers and Sedatives



Comments



• Reduce nervousness, reduce the amount of induction agent required to allow intubation, smooth the transition to and from general anesthesia, and reduce the amount of anesthetic drug required to maintain anesthesia.

• Classified as major tranquilizers (phenothiazine derivatives such as acepromazine), minor tranquilizers (benzodiazepines such as diazepam [Valium]), and sedative-hypnotics (α2-adrenoreceptor agonists such as xylazine).


Phenothiazine Derivatives



Comments


• The α-adrenoreceptor blockers, +/− antihistaminergic, +/− antidopaminergic, depending on chemical structure changes.

• Major tranquilizer, produces calming effect, although patient is still rousable and responsive.

• Most commonly used drug in this class is acepromazine. Others include chlorpromazine, prochlorpromazine, and trimeprazine, to name a few.


Acepromazine


• Dosage: cat or dog, 0.01 to 0.1 mg/kg IM, SC, or IV.

• In the dog, as the dosage is increased there is a concomitant increase in magnitude of adverse or undesirable effects. If increased sedation is desired, it is recommended that opioids be administered with the acepromazine to prevent excessive vasodilation, hypotension, and hypothermia associated with increased dosages of acepromazine.

• Dogs with quiet, calm temperaments and older dogs will require only the low end of the dosage range in order to achieve adequate sedation.

• In the cat, one often fails to see any outward clinical signs of sedation. However, significant cardiovascular and central nervous system (CNS) depression is present, just as in the dog, despite the lack of obvious signs.


Advantages


• Produces a calming effect on most patients.

• Inexpensive.

• Can be protective against cardiac arrhythmias related to catecholamine release.


Disadvantages


• Caution must be exercised when used in compromised patients due to vasodilation with resultant hypotension and a relative hypovolemia.

• Peripheral vasodilation potentiates hypotension and hypothermia.

• Requires biotransformation in the liver; can have a prolonged effect in some patients, especially when used at higher dosages.

• No analgesic effect.

• Antidopaminergic effect can result in lasting behavioral changes when used at higher dosages.


Benzodiazepines



Comments


• Minimal cardiorespiratory depression.

• Muscle relaxation.

• Amnesiac.

• GABA-nergic (gamma aminobutyric acid [GABA] is an inhibitory CNS neurotransmitter).

• Disinhibition occurs in approximately 25% of veterinary patients, with resultant transient excitation following intravenous administration. Most common in young adult, normal, healthy patients.

• Most commonly used drug in veterinary medicine is diazepam. Midazolam (Versed) and zolazepam (found in Telazol) are other benzodiazepines used in veterinary medicine. Unlike diazepam, these and other benzodiazepines are water soluble.


Diazepam


• Dosage: cat or dog, 0.1 to 0.5 mg/kg IV or IM.3,4

• Note: midazolam is a water-soluble benzodiazepine that is very similar to diazepam and, as such, may be substituted for diazepam if necessary.


Advantages


• Minimal central nervous system or cardiovascular depression.

• Produces muscle relaxation.

• Antiseizure activity.

• When combined with a dissociative agent (i.e., ketamine or tiletamine), can be used as a combination induction agent or to provide short-term anesthesia.

• When used with an opioid medication, provides good sedation and tranquilization in older or quieter patients.

• Can be reversed by flumazenil if necessary.


Disadvantages


• When administered intramuscularly it can provide unpredictable absorption due to its poor solubility in water.

• Rapid intravenous injection can lead to hypotension and bradycardia due to the propylene glycol vehicle.

• Minimal to no outward signs of sedation in normal, healthy, young adult dogs and cats.


Alpha2 Adrenoreceptor Agonists



Comments


• Drugs in this group are sedative-hypnotics and will result in a quiet to minimally responsive patient. As the dosage is increased, a state resembling hypnosis can be achieved such that the patient is essentially unresponsive to external stimuli. However, anesthesia is not achieved, even at high dosages.

• Significant cardiorespiratory depression can occur with the drugs in this class. Manipulation of chemical structure has reduced this effect in many of the newer drugs. Bradycardia and peripheral vasoconstriction are the most common undesirable effects.

• Alpha2 receptor activation prevents release of norepinephrine from the presynaptic nerve terminal, with a resultant lack of stimulation of postsynaptic neurons.

• To date, all α2 agonists also have α1 activity, although the relative α2-to-α1 activity varies significantly among the drugs in this class.

• Because of the profound cardiac depression, it is recommended these drugs be administered intramuscularly whenever possible.

• Specific antagonists are available for each drug. Due to differences in α2-to- α1 activity by both the agonists and the antagonists, one should be sure the antagonist is appropriate for the agonist.


Xylazine


• Dosage: dog, 0.5 to 1 mg/kg IM; cat, 0.25 to 0.5 mg/kg IM.


Advantages


• Provides profound sedation alone or in combination with opioids.

• Used in conjunction with ketamine to provide chemical restraint resembling anesthesia and may be suitable for minor procedures.

• Provides excellent analgesia.

• Provides good muscle relaxation.

• Specific antagonist is available (yohimbine).


Disadvantages


• Emesis.

• Profoundly vagotonic, resulting in bradycardia that can be prevented with the use of an anticholinergic agent. Bradycardia is due to a direct cholinergic effect as well as activation of the baroceptor response.

• Gastrointestinal stasis and ileus are common due to its cholinergic effect.

• Profound vasoconstriction occurs due to α1 activation, resulting in an increase in the systemic vascular resistance.

• The ratio of α2-to-α1 activity is 160:1, indicating a significant α1 effect in addition to the desired α2 effect.

• Use of α2-antagonists other than yohimbine may not reverse cardiovascular or gastrointestinal effects.

• Several studies have demonstrated a significant hypoxemia without hypercapnia.

• Not recommended for use in debilitated or older patients.


Medetomidine


• Dosage: dog, 1 to 40 μg/kg IM; cat, 5 to 40 μg/kg IM.


Advantages


• Higher α2-to-α1 activity reduces many of adverse effects.

• Longer duration of effect than xylazine.

• Bradycardia is a physiologic response due to the baroceptor response to vasoconstriction (α1) as opposed to a cholinergic effect.

• Sedative effects are dose responsive.

• Few to no effects at receptors other than α-adrenoceptors.

• Profound analgesia and muscle relaxation.

• When used in combination with opioids or dissociatives, there is a significant dosage reduction in medetomidine.

• Significant minimum alveolar concentration (MAC)-sparing effect and induction dosage requirements when used as a premedicant.

• Specific antagonist is available (atipamezole).


Disadvantages


• The α1 effect is long lasting.

• Emesis may occur.

• Sudden arousal, especially when working around the patient’s head, can occur, with the potential for bites to occur.

• Peripheral vasoconstriction results in peripheral cyanosis, especially when higher dosages are administered.


Opioids



Comments


• Opioids used as a preanesthetic medication provide analgesia as well as sedation (synergistic when used in combination with a sedative-tranquilizer).

• Administering opioids as preanesthetic medication can reduce dramatically the amount of anesthetic agent required to maintain anesthesia.

• Morphine, oxymorphone, and hydromorphone (opioid agonists) produce greater pain relief, but also greater sedation.

• Meperidine (Demerol) is significantly less potent than morphine, oxymorphone, or hydromorphone and has a short duration of action (2 to 3 hr). It is the only opioid that causes vagolytic and negative inotropic effects at clinically used dosages.5 As such, it should be used cautiously in debilitated patients, as well as in those with hypothyroidism or hyperthyroidism, severe renal insufficiency, and adrenocortical insufficiency. It also causes significant histamine release and therefore should not be administered intravenously.

• Fentanyl is a very short-acting opioid agonist that causes significant bradycardia and respiratory depression when administered intravenously or intramuscularly.

• Buprenorphine is a partial opioid agonist (mu). It provides adequate analgesia for most moderately painful procedures. The duration of action is dose dependent and can range from 2 to 10 hours, depending on amount used. Onset of effect ranges from 30 minutes following intravenous administration to 1 hour following intramuscular administration. Buprenorphine causes minimal sedation or other adverse effects associated with opioids, even when used at high dosages. Due to the lack of sedation and longer onset time, its use as a premedicant is limited.

• Butorphanol, a mixed agonist-antagonist, is an adequate analgesic for short-term (1 to 2 hours) relief of mild pain. It is quite useful for its sedative effects.


Dosages


• Morphine: dog, 0.5 to 1.0 mg/kg IM, IV, or SC q 4 to 6 hr3,4; cat, 0.1 to 0.5 mg/kg IM or SC q 4 to 6 hr.

• Note: when administered intravenously, morphine must be given slowly to prevent histamine release.

• Oxymorphone: dog, 0.05 to 0.2 mg/kg IM, IV, or SC q 4 to 6 hr; cat, 0.05 to 0.1 mg/kg IM, IV, or SC q 4 to 6 hr.

• Hydromorphone: dog, 0.1 to 0.2 mg/kg IM, IV, or SC q 2 to 3 hr.

• Meperidine: cat or dog, 2 to 5 mg/kg IM or SC4 q 2 to 3 hr. Do not administer intravenously due to significant histamine release.

• Fentanyl: 5 to 10 μg/kg IM or IV q 15 to 60 min or 0.3 to 0.7 μg/kg/min as a continuous-rate infusion.

• Butorphanol: cat or dog, 0.1 to 0.2 mg/kg IM, IV, or SC3,4 q 1 to 2 hr.

• Buprenorphine: cat or dog, 5 to 40 μg/kg IM or IV q 2 to 10 hr. Duration is dose dependent. Example: 5 μg/kg = 2 to 3 hr, 40 μg/kg = 10 to 12 hr.


Advantages


• Provide analgesia.

• Provide sedation (except buprenorphine).

• Can be given with sedative-tranquilizer for additional sedation.

• Reduce other anesthetic requirements.

• Do not depress myocardial contractility.

• Can be reversed with an opioid antagonist such as naloxone.


Disadvantages


• May cause sinus bradycardia when used at higher dosages (applies to opioid agonists only).

• May cause respiratory depression when used at higher dosages.

• May cause panting and flatulence.

• Can create startle response with loud or sharp noises.


Neuroleptanalgesia



Comments



• Combines a tranquilizer or sedative (i.e., neuroleptic) with an opioid (i.e., analgesia) as a preanesthetic medication.

• Two examples of combinations and dosages follow. However, there are many other combinations.


Dog


• Acepromazine 0.02 to 0.05 mg/kg SC or IM.

• Morphine 0.5 mg/kg SC or IM.


Cat or dog


• Acepromazine 0.02 to 0.05 mg/kg SC or IM.

• Butorphanol 0.1 to 0.2 mg/kg SC or IM.


Advantages



• Provides analgesia.

• Provides sedation.

• Reduces amount of induction agent required.

• Good for aggressive or anxious patients.

• Provides sedation for quiet inductions.

• Opioid effect can be reversed; the effects of some tranquilizers and sedatives can be reversed.


Disadvantages



• Attention must be paid to the dosages of each drug used. Synergism results in reduced dosage requirements, especially of the sedative-tranquilizer.

• Onset times of the two drugs may not coincide.

• Reversal of the opioid may result in renarcotization later due to longer duration of the opioid than that of the antagonist.

• Combining acepromazine with morphine may not inhibit the emetic effect of the morphine.

• Combining two vagotonic drugs (e.g., an opioid agonist and an α2-agonist) can result in profound or significant bradycardia.


Induction Drugs



Comments



• Induction drugs are used to induce unconsciousness in a smooth, struggle-free manner.

• These drugs generally are administered intravenously to effect to allow intubation.

• Adverse effects of these drugs are dosage dependent; therefore, techniques which minimize the induction dosage requirement are desirable.

• Because these drugs have induced anesthesia, intubation of the trachea is necessary to protect the airway from debris and to provide ventilatory support.


Barbiturates



Thiopental sodium


• Dosage: dogs and cats, 5 to 15 mg/kg IV, to effect.

• Available commercially in 1 g bottles to dilute to a final desired concentration. For example, to make a 5% solution, 20 ml of diluent is added to 1 g of sterile powder.

• A 2.0% or 2.5% solution is recommended for use in smaller or older dogs.4

• A 1.25% solution is recommended for use in cats, toy dogs, or unstable patients.4


Advantages


• Inexpensive.

• Rapid, smooth induction.

• Good relaxation for intubation.

• Short acting.

• Recovery from anesthesia is due to redistribution of the drug from the brain to other tissues.


Disadvantages


• Requires redistribution from the brain to fat and muscle for termination of effect. Repeated doses can result in prolonged recoveries due to saturation of muscle and fat.

• Requires hepatic transformation for final elimination from the body.

• Can cause severe tissue necrosis if injected perivascularly (in greater than 2% solutions).

• Can cause hypotension, arrhythmias, and apnea if given too rapidly.

• Rate of onset affected by patient’s cardiac output and acid-base status.


Dissociative Agents



Ketamine


• Dosage: cat, 5 to 30 mg/kg IM or IV.4

• Dog: not recommended to be used alone due to high incidence of seizures.

• Often given intravenously with diazepam as an induction agent (5 mg/kg ketamine and 0.25 mg/kg diazepam) in dogs and cats.


Advantages


• Relatively inexpensive.

• Minimal effect on cardiac output and blood pressure in the normal patient.

• Causes immobility due to dissociation from the environment.

• No tissue reaction if accidentally given extravenously.

• Useful in combination with another agent for short periods of chemical restraint.


Disadvantages


• Causes increased salivation. Low doses of anticholinergic agents can be given before use.

• Causes central nervous system excitement in dogs, with a strong possibility of seizures.

• Renally excreted in cats (unchanged), hepatic biotransformation in dogs and in cats if renal excretion is not possible.

• Poor analgesic when used at induction dosages.

• Muscle rigidity often excessive, requires use of sedative-tranquilizer to provide muscle relaxation.

• Despite common misconceptions, pharyngeal and ocular reflexes, while present, are not protective.

• Is painful if given extravenously, especially in cats.


Propofol


Comments


• A safe, short-acting anesthetic agent that is milky white, for intravenous injection.8,9,11

• Dosage: cat or dog, 1 to 4 mg/kg IV with sedation; 4 to 8 mg/kg without sedation. Given to effect.3,4,13


Advantages


• Short duration of anesthesia.

• Can be given as repeated injections or continuous infusion due to minimal accumulation of the drug in the dog.

• Rapid recovery (approximately 15 to 30 minutes until patient is standing unaided) without residual effect.


Disadvantages


• Causes profound and significant respiratory depression when given rapidly. Preoxygenation is strongly recommended.

• Does not contain preservatives; not suitable for storage beyond 6 hours after opening vial; strict aseptic procedure must be followed to prevent inadvertent contamination of vial after opened.

Related posts:

  1. Regional and Local Anesthesia
  2. General Health Safety and Ergonomics in the Veterinary Dental Workplace
  3. Dental Prophylaxis and Periodontal Disease Stages
  4. Periodontal Therapy and Surgery

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Sep 22, 2016 | Posted by in SMALL ANIMAL | Comments Off on Anesthesia and Pain Management in Dental and Oral Procedures

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