1. Characteristics

• Ferrets are often treated like cats in regard to drug dosing and intubation.
  
• If not descented, ferrets may spray scent glands when stressed or threatened.
  
• Ferrets have thick skin, requiring confidence when administering a SC injection.
  
• Ferrets produce copious respiratory secretions, making inclusion of an anticholinergic a suitable choice for anesthesia when not contraindicated.

2. Anesthetic considerations

• Handling and restraint: If required, squeeze cages might be helpful in restraining the unfriendly ferret. They have very sharp teeth and inflict severe bites. For the tame ferret, scruffing the nape of the neck and supporting the lower half of the body with the other hand works well for restraint (Figure 6.1).

  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  

  Species	Adult weights (kg)	HR a(bpm)	RR a(breaths/min)	Temperature (°F)	Fasting recommendation
  Ferret	0.7–3.0	200–275	30–35	100–104	6–8 h (unless the patient has a suspected insulinoma)
  Hedgehog	0.3–1.2	200–280	25–50	95–99	Not recommended
  Pot‐bellied pig	40–90	70–120	25–35	101–104	12–24 h
  Rabbits	1–6	130–325	30–60	99–103	2–4 h for food only
  Rats	0.25–0.5	250–450	70–130	99–100	Not recommended
  Mice	0.02–0.04	350–800	60–200	98–100.5	Not recommended
  Hamster	0.085–0.15	250–500	40–140	101–103	Not recommended
  Gerbil	0.05–0.10	250–500	90–150	99–102	Not recommended
  Guinea pig	0.7–1.2	230–380	50–100	101–103	2–4 h
  Chinchilla	0.4–0.6	200–350	45–80	102–103	Not recommended

  
  

  ^a Respiratory rates and heart rates may be lower during anesthesia.

  
  

  bpm, beats per minute; RR, respiratory rate.

  
  
• Premedication: Agents that sedate and provide preemptive analgesia help to facilitate catheter placement and reduce induction and maintenance drug requirements; a variety of agents are suitable in the healthy ferret (Table 6.2). The hindlimb muscles are common locations for IM injections; sadly, for these little creatures, the patient is often sore on the limb afterwards and may limp where the injection was given, espe cially if large volumes are given. IV access includes the cephalic, jugular, and saphenous veins (Figure 6.2). It is helpful to nick the skin prior to attempting catheterization. Alfaxalone (5 mg/kg) has proven useful, in combination with butorphanol (0.2 mg/kg), with mild transient cardiorespiratory derangements [2].
  
• Induction: If IV access is not achieved under premedication, mask or box inductions with isoflurane or sevoflurane is the most common approach. If IV access is available, IV induction agents are administered (see Table 6.2).
  
• Intubation: Intubation is achieved with small endotracheal (ET) tubes similar to intubating a cat. The patient is placed in sternal recumbency with the head and neck hyperextended by an assistant. Some individuals suggest extending the head toward the person intubating while keeping the body straight. Lidocaine is used on the arytenoids to minimize laryngeal spasms. The tongue is pulled gently out of the mouth and a laryngeal scope is used for visualization. Small ET tubes ranging from 2.0 to 3.5 mm internal diameter (ID) (cuffed or noncuffed) are commonly used. Placement of the ET tube is verified by auscultation of lungs bilaterally for respiratory noises on inspiration or with the use of a capnograph.
  
• Maintenance: All the modern inhalants are commonly used. Total intravenous anesthesia (TIVA) is also used if IV access is available.
  
• Monitoring during anesthesia (see Figure 6.2): An ECG and Doppler are recommended. Blood pressure (BP) is obtained with a cuff and sphygmomanometer. Pulse oximetry is obtained by placing a probe over a foot. Anesthetic depth is monitored similarly to the average small animal patient. Jaw tone, eye position, and palpebral reflex are indicators of depth. Additionally, changes in respiratory rate (RR) and BP may indicate changes in anesthetic depth.
  
• Recovery: Keep the patient warm in recovery and continue to monitor vital signs. Because ferrets have such a variety of endocrinologic disease requiring anesthesia and surgery, tailor each recovery to the specific patient. Additional analgesia is administered.

3. Common complications

• Intraoperative hypothermia: Forced air warming units, circulating hot water blankets, and/or companion animal warming units are helpful to maintain body temperature.
  
• Hypoglycemia: Hypoglycemia occurs due to high metabolic rates; 2.5% dextrose is added to the anesthetic maintenance fluids to correct this. The ferret with an insulinoma is a particular challenge in this regard, as it is a balance between providing enough dextrose without triggering release of an insulin surge.

1. Characteristics

• Some species of hedgehog (European) hibernate when conditions are extreme (unlikely in the household pet).
  
• Nocturnal (i.e., normally inactive during the day and active in the evening).
  
• Spines cover the dorsal aspect of body.

2. Anesthetic considerations

• Handling and restraint: Handling and restraint are difficult, especially if the patient rolls into a ball. Some will unroll if rump spines are stroked. Leather gloves are recommended. While these animals rarely bite, they are reclusive by nature and often resent handling, regardless of the degree of socialization.
  
• Premedication: Often patients are masked or boxed down without the use of injectable premedications. However, SC injections are given with the assistance of forceps to grasp a fold of skin between the spines over the flank of the patient. IM injections are given in the thigh. Soreness results if large volumes are administered IM (Table 6.3).
  
• IV access: Catheters are placed in the jugular or saphenous vein. Intraosseous (IO) catheters are placed in the proximal femur.
  
• Induction: Attempts at intubation are made using a 1–1.5 mm ID ET tube; however, care is taken to avoid trauma to the larynx which causes swelling, bleeding, and airway obstruction. Supraglottic airway devices designed for rabbits have shown promise in reducing trauma to the airway while providing quick access and adequate ventilation as well as delivery of inhalant anesthetics to produce maintenance anesthesia (see Table 6.3).
  
• Maintenance: Mask induction and maintenance with an inhalant anesthetic is common clinical practice.
  
• Monitoring: A Doppler is vital for monitoring the heart rate (HR) in these animals. Pulse oximetry is useful if the probe is placed on a foot in the unrolled hedgehog. ECG provides information on HR, but most monitors are only capable of displaying up to 250 bpm. RR is monitored by watching chest excursions.
  
• Recovery: Recover hedgehogs in a quiet, nonstimulating environment. Keep the patient warm in recovery and continue to monitor vital signs. Additional analgesia is administered as warranted.

3. Common complications

Complications are typically a result of the hedgehog’s high metabolic rate and the anesthetist’s underestimation of the patient’s requirements.

• Hypoglycemia: Do not fast and administer 2.5% dextrose in fluids for extended procedures.
  
• Hypothermia: Hypothermia due to small body size, use of nonrebreathing (NRB) circuits, and decreased metabolism is common. Esophageal temperature probes for continuous monitoring and forced air warming units are helpful.

1. Characteristics

• PBPs have small tracheas compared to body weight; additionally, there is a sigmoid curvature to the airway and a ventral diverticulum anteroventral to the arytenoid fold preventing a straightforward intubation.
  
• PBPs have a high fat to muscle ratio (anatomically present as a thick layer of subcutaneous fat), making the effect of drug injections less predictable and intra‐fat (rather than IM) injection more likely.
  
• Pigs are cannibalistic.
  
• Twelve‐ to 24‐hour fasting of adult pigs is recommended.
  
• Difficulty accessing veins means most anesthetic plans are developed with minimal biochemical and hematologic information.

2. Anesthesia considerations

• Handling and restraint: Pigs are difficult to restrain due to their shape and size. Often chemical restraint is used to avoid stress. Large pigs are controlled with a board or cage door front “squeezed” against a wall while an IM injection is given, or snared just behind the canine teeth. Small pigs are manually restrained (Figure 6.3).
  
• Premedication: Behind the ear is the most common site for IM injections. In young PBPs, there is less fat in this area so the effectiveness of the drugs is more predictable. The epaxial muscles are avoided because of the large layer of back fat and the tradition of avoiding this muscle group in pigs for market. Injection in the semimembranosus and semitendinosus muscles with a 3.5 inch stylet from a catheter is a possible alternative. Intranasal midazolam 0.5 mg/kg may quiet the pig to a degree and facilitate limited handling. In general, pigs are less susceptible to the sedative effects of opioids, phenothiazines, and alpha‐2 agonists. Butyrophenones, such as azaperone (2.5 mg/kg IM), are often used for sedation in noncompanion pigs and are potentially useful in the PBP. Alfaxalone has proved useful in commercial swine, with or without the use of an alpha‐2 agonist, and may be useful in the PBP [3,4] (Table 6.4).
  
• IV access: Veins are difficult to access. The easiest vessels for catheterization include the medial and lateral auricular veins (Figure 6.4) and lateral saphenous veins, which are typically catheterized following induction. Cephalic veins are occasionally attempted, but venipuncture in this area is performed blindly, as these vessels are difficult to palpate and visualize.
  
• Induction: If IV access is obtained following premedication, injectable agents are given to facilitate intubation. Otherwise, mask induction with isoflurane or sevoflurane is most common until the patient is intubated (see Table 6.4).
  
• Intubation: Intubation in pigs is a challenge for a number of reasons. The mouth does not open widely, and the larynx is at an angle to the trachea. Pigs have a pharyngeal diverticulum, as well as a tracheal bronchus; inaccurate placement of the tube in either of these areas results in trauma, swelling, or bleeding. Stylets or ET tubes inadvertently placed in the tracheal bronchus cause pneumomediastinum and inadequate ventilation. Cuffed ET tubes of various sizes (smaller than for an equivalent‐sized canine patient) are used; for an average 60 kg PBP, an 8–9 mm ID ET tube is used. Place the patient in sternal recumbency. Gauze or dog leashes facilitate visualization, when placed behind the canine teeth and used to open the mouth. A long blade laryngoscope is helpful in visualizing the larynx by placing the blade at the base of the tongue and pressing down to displace the epiglottis. Lidocaine is placed on the arytenoids to minimize laryngeal spasms, which readily occur. Introduce a long, thin stylet (crafted from small French urinary catheters connected together with tape or glue, approximately three times the length of the ET tube) into the trachea to assist intubation. If no resistance is encountered, an ET tube is passed over the stylet and gently rotated 180° once it passes beyond the larynx. Laryngeal mask airways are used with success in pigs and may reduce the potential for airway trauma. Auscultation and capnography confirm appropriate placement. If resistance is encountered, rotating the stylet gently while advancing it forward may help; however, significant resistance warrants backing out of the trachea and trying again. Intubation attempts are minimized to prevent trauma.
  
• Maintenance: Inhalant anesthetics are most commonly used following intubation. IM injectable drugs, in combination with local blocks, facilitate adequate sedation and immobilization for minor procedures like castration, hoof trim, or tusk filing.
  
• Monitoring anesthetic depth: Palpebral reflex and jaw tone will give an indication of the depth of anesthesia. PBPs have small eyes, making ocular signs of anesthetic depth difficult to obtain. Vital parameters may also indicate changes in depth. An ECG and Doppler are recommended for monitoring the HR and rhythm. Pigs have little excess skin, so using sticky pads to monitor ECG is preferable to ECG clips. The Doppler crystal, BP cuff, and a sphygmomanometer give an indication of trends. The Doppler is often placed distal to the accessory claw, with the cuff below the carpus on the forelimb, or on the hindlimb above the hock. Invasive blood pressure (IBP) is obtained from placing a catheter in the artery of the ear or dorsal pedal artery. It is also useful to monitor RR and EtCO₂. Pulse oximetry is obtained by placing a pulse oximeter probe on the tongue. Temperature is continuously monitored during anesthesia and into recovery.
  
• Recovery: Pigs are recovered without herd mates and only returned to the herd once completely recovered. They are placed in sternal recumbency for recovery, if possible. Pigs may obstruct post extubation due to laryngeal swelling. It is important to ensure they are capable of swallowing and adequate independent ventilation is present prior to extubation. Nonsteroidal antiinflammatory drugs (NSAIDs) are used, if not otherwise contraindicated, to minimize any airway swelling. Pigs experience postanesthetic sleep; although they appear conscious enough to extubate, once extubated, they sleep quite heavily, which contributes to the possibility of postextubation obstruction. Temperature is monitored during and following recovery. Additional analgesic drugs are administered as warranted.

3. Common complications

• Airway obstruction at extubation is possible. The anesthetist must be ready with additional induction agent (IV catheter remains in place until the patient is fully recovered) and a size smaller ET tube to intubate the patient if an obstruction occurs.
  
• Hypoventilation, if not from excessive anesthetic depth, is often addressed with mechanical ventilation (MV).
  
• Hypothermia (especially in in small pigs) occurs intraoperatively and postoperatively. Use of circulating warm water blankets and forced air warming units reduces the degree of hypothermia.
  
• Dysphoric or rough recoveries are possible, especially in stimulating environments and with inadequate analgesia and sedation.

1. Characteristics

• Birds have a highly efficient respiratory system compared to mammals. Birds have higher V_T, lower RR, and larger minute ventilation. Inspiration and expiration are both active phases in the bird; that is, respiratory movements are accomplished by cervical, thoracic, and abdominal muscle contractions (there is no diaphragm to contribute to the active phase). Two complete respiratory cycles exchange inhaled gases via cross‐current gas exchange.
  
• The trachea is longer and has an increased diameter compared to mammals, resulting in more dead space. Unlike mammals, the tracheal rings are complete. For this reason, the anesthetist utilizes uncuffed ET tubes. It is wise to review the specific species with regard to variations in respiratory anatomy; for example, some penguins have a double trachea and emus have a tracheal diverticulum.
  
• The epiglottis is absent.
  
• Birds have high metabolic rates which require higher substrate levels (blood glucose [BG] is greater than 200 mg/dL) and higher fluid rates (10–30 mL/kg/h).
  
• Cardiovascular differences include larger stroke volume (SV), increased cardiac output (CO), and higher mean arterial pressure (MAP). HR varies considerably depending on the size of the patient.
  
• Circulation influences the effect of various drugs. Birds possess a renal portal system. This network of vessels around the kidney, which selectively channels blood through or past it, results in a potential first‐pass effect of drugs administered in the caudal half of the body, altering the drug’s intended effect. When a drug is given in the lower half of the body, it is metabolized by the renal portal system before reaching the central nervous system, the target site for effect.
  
• Fasting is highly variable depending on the size of the bird; in general, fasting is usually less than 3 hours, but may not be performed at all for very small birds.

1. Characteristics

• The heart has three chambers (two atria, one ventricle). This allows for mixing of oxygenated and deoxygenated blood with changes in vascular resistance under anesthesia. This “shunting” significantly worsens perfusion of vital tissues.
  
• Reptiles are ectothermic; therefore, body temperature influences drug metabolism and clearance, as well as physiologic parameters.
  
• Prior to anesthetizing a reptile, the reader is advised to review the individual species variations in regard to respiratory anatomy and physiology, as this is beyond the scope of this chapter. For example, many reptiles do not possess a diaphragm. Instead, abdominal, pectoral, and pelvic muscles control ventilation. However, crocodilians have a nonmuscular tissue which functions as a rudimentary diaphragm. Most snakes possess a single elongated right lung, although boas possess the left lung lobe in addition to the right. Most reptiles have simplified sacs with folds allowing for respiratory gas exchange, but there is a whole spectrum of complexity. The trachea in a turtle is short and bifurcates early compared with most reptiles. Some reptiles, such as turtles, possess complete tracheal rings.
  
• A renal portal system is present in reptiles as it is in birds. This network of vessels around the kidney, which selectively channels blood through or past it, results in a potential first‐pass effect of drugs administered in the caudal half of the body, altering the drug’s intended effects.
  
• Although fasting is often not required, timing of last large meal (especially for snakes) is important to know. A recent large meal affects the patient’s ability to adequately ventilate.

2. Anesthesia considerations

• Restraint and handling: This varies greatly by species restrained. All reptiles are capable of biting; many have claws and tails that are used in defense. Leather gloves are useful in preventing trauma to the handler for large reptile species. Nonpoisonous snakes are grasped at the base of the head with one hand while the other hand supports the body. Lizards are similarly handled, although the body is often tucked under the arm of the handler or restrained in the other hand (Figure 6.12). Turtles and tortoises are held at the shell; the length of the neck determines how far caudal on the carapace the animal is restrained. Some species of turtles have extremely long necks and can deliver a powerful bite to an unsuspecting restrainer.
  
• Preanesthetic assessment: In nonpoisonous and tame species, perform a PE prior to anesthesia to obtain a baseline HR, RR, body temperature, and accurate body weight. Physical parameters such as HR are greatly influenced by body temperature, environmental stress, and presence of noxious stimuli. Due to the large variation in reptilian species, normal physical parameters are based on species‐specific reference material and the patient’s examination.
  
• Premedication: Benefits of a premedication in animals include reduced dosages of induction drugs, analgesia, and sedation. However, clearance is prolonged in reptiles compared to mammals. Therefore, reversible drugs are chosen when possible. Some reptiles have mu opioid receptors, making mu opioids such as morphine an effective analgesic option, although respiratory depression may result [35,36]. Other opioids may be effective at providing analgesia but differences between species are notable [37,38]. Other alternative analgesic drugs, including alpha‐2 agonists such as dexmedetomidine and medetomidine, may provide analgesia in some retiles [39–41]. Any injectable premedication is administered in the cranial portion of the animal if possible [42]; more effective sedation with injectable drugs such as alfaxalone was evident when the drug was administered cranially [43]. However, safety of the handler is prioritized over concern regarding the renal portal system. There is also evidence that intracelomic administration of alfaxalone is a viable route in snakes [44,45]. Indeed, with its favorable routes of administration, alfaxalone is a versatile drug for use in many reptile species [46,47].
  
• Induction: When premedication is insufficient, reptiles can be induced with inhalants via mask or chamber (Figure 6.13). Inhalants are administered to the patient until it is relaxed and intubation is accomplished (Table 6.10). Turtles and tortoises may be induced with IV induction agents by IV access or injection through the subcarapacial sinus under their shells (Figure 6.14). Intubation of snakes and lizards is straightforward, as the position of the glottis is rostral (Figure 6.15). Noncuffed ET tubes, Cole tubes, or 16–19 G catheters are used for smaller reptiles. Typically, the best method of securing the ET tube is taping it to the patient’s lower jaw. In turtles (Figure 6.16), the glottis is located at the base of the tongue. They have short tracheas so care is taken to ensure ET tubes are not advanced too far, causing an endobronchial intubation. In reptiles, IV access is infrequently achieved. In turtles and tortoises, catheterized vessels include the jugular or coccygeal veins; alternatively, IO catheters are commonly placed (Figure 6.17).
  
• Maintenance: General anesthesia is maintained primarily with inhalant anesthetics. Alfaxalone has potential for a surgical plane of anesthesia in some lizard species [48]. Because these animals are ectothermic, external heat support is necessary throughout the anesthetic period to keep them in their optimal thermoregulatory range.
  
• Monitoring vitals: A Doppler is useful for monitoring HR (Figure 6.18); a pencil probe is ideal for the anesthetist to obtain HR via the ocular artery by placing this probe (well lubed) onto the eye. An esophageal stethoscope is also useful for obtaining HR. RR is visually observed. Assisted ventilation of 1–4 breaths per minute is recommended due to the long periods of apnea; MV is indicated for most reptiles. Capnography is not an adequate representation of ventilation due to intrapulmonary shunting (i.e., EtCO₂ is increased compared to true PaCO₂), but does provide some evidence for the presence of CO₂. Pulse oximetry is not accurate in reptiles due to their alternative form of hemoglobin and difficulty placing the probe.
  
• Monitoring anesthetic depth: Muscle tone will decrease in the reptile as it becomes anesthetized. In the snake, relaxation occurs initially at the head, then through the torso, and proceeds caudally, lastly affecting the tail; recovery occurs in the opposite order. In snakes, the tongue retraction reflex will only subside in a deep plane of anesthesia. Palpebral reflexes may give an indication of anesthetic depth. Corneal reflexes are also lost in a deep plane. Toe or tail pinch is absent during the surgical plane of anesthesia. Jaw tone is also monitored in species where this is safe to assess.
  
• Recovery: Snakes typically take longer than lizards to recover; turtles, especially those that are capable of holding their breath, take an extraordinarily long time to recover. There is evidence that administration of epinephrine may expedite recovery from inhalant in sea turtles [49]. Maintaining optimal body temperature is critical to recovery. All reptiles are placed on room air to recover due to the downregulation of a reptile’s respiratory system secondary to increased FiO₂. Continuing assisted ventilation is often necessary on room air (Figure 6.19). Extubation occurs once the patient is capable of spontaneous ventilation and pharyngeal reflexes have returned. Additional analgesia is administered as warranted.

3. Common complications

• Hypothermia: Hypothermia is reduced by using circulating hot water blankets and forced air warming units.
  
• Hypoventilation: Hypoventilation secondary to apnea and respiratory depression is common in most reptiles, requiring assisted ventilation.