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Preanesthetic Agents

Atropine (0.01-0.02mg/kg) may be administered subcutaneously or intramuscularly as a preanesthetic agent approximately 30 minutes before anesthesia. Atropine prevents the drop in heart rate and excessive salivation that may be caused by agents such as inhalant anesthetics and ketamine. Glycopyrrolate (Robinal®) (0.02-0.04 mg/kg) subcutaneously or intramuscularly is an effective alternative to atropine when given 15 minutes prior to surgery. Glycopyrrolate has a longer duration of action than atropine.

Diazepam (Valium®) and midazolam (Versed®) are sedatives with no analgesic activity and minimal effects upon the cardiac system. These agents are useful for minimizing anxiety, excitement, and improving restraint. These agents provide good muscle relaxation and are very useful in combination with an opioid analgesic such as butorphanol (Stadol®, Torbugesic®). Midazolam is water soluble and may provide better absorption than diazepam when administered intramuscularly. Both of these agents can be reversed with flumazenil (Romazicon®) if needed during a prolonged recovery.

Ketamine (Ketoset®) a dissociative agent, provides good immobilization, yet increases secretions and provides poor muscle relaxation. Ketamine has a wide margin of safety and is used to facilitate gas anesthesia induction. Ketamine can be used alone or can be combined with a sedative such as valium or midazolam to minimize the muscle rigidity and movement which may occur if used alone.

Xylazine (Rompum®) is an alpha-2 agonist, which possesses analgesic, sedative, and muscle relaxant properties. It is most commonly used in combination with ketamine to produce light to moderate surgical anesthesia or to facilitate gas anesthesia induction. Xylazine has a short duration of action and produces negative effects upon the cardiovascular system such as lowering of heart rate and decreasing cardiac output. If gas inhalant anesthesia will be used, a safer preanesthetic combination for facilitating induction would be midazolam and butorphanol.

Inhalant Anesthetics

Isoflurane has become the anesthetic agent of choice for both short and lengthy procedures due to its rapid and reliable recovery. Other inhalant anesthetics such as halothane are also preferred over injectable anesthetic agents. Isoflurane can be delivered via a face mask or an anesthetic induction chamber to induce birds. Once induction has occurred maintenance anesthesia can be performed using a face mask or via an uncuffed endotracheal tube secured to the beak. Since birds have complete tracheal rings, an uncuffed endotracheal tube should be used to avoid tracheal damage. One must be careful to avoid placing the endotracheal tube too far into the trachea, thus intubating a main stem bronchus instead. Tubes must be watched for excessive mucous accumulation, blockage, or kinking. Always have a replacement endotracheal tube immediately available. Flow through anesthesia chambers and facemasks require a gas anesthesia machine with an oxygen source and a precision vaporizer. Due to the small respiratory volume in birds, a nonrebreathing system should be used. Anesthesia chambers and facemasks are commercially available. Furthermore, since air exchange is very efficient in birds, rapid changes in the depth of anesthesia can occur when using gas inhalants. When using inhalant anesthesia, a fume hood or an anesthetic system equipped with a gas scavenging system should be used to minimize occupational exposure to exiting gases.
 

Table 1. Injectable pre-anesthetics and sedatives (Abou-Madi, N., 2001).

Drug	Dosage and Route	Duration of Anesthesia	Comments
Sedatives
Diazepam (Valium®)	0.2-0.5 mg/kg IM 0.05-0.15 mg/kg IV	10-30 minutes	Sedation / no analgesia
Midazolam (Versed®)	0.05-0.15 mg/kg IV 0.1-0.5 mg/kg IM	10-30 minutes	Sedation / no analgesia
Butorphanol (Stadol®, Torbugesic®) + midazolam	1 mg/kg IM but. + 0.1-0.5 mg/kg IM mid.	10-30 minutes	Sedation / analgesia
Dissociatives
Ketamine (Ketoset®)	20-40mg/kg IM	20-30 minutes	Immobilization / mild analgesia
Ketamine + xylazine (Rompun®)	10-30mg/kg IM ket. + 2-6 mg/kg IM xyl.	20-30 minutes	Light to medium surgical anesthesia
Ketamine + diazepam (Valium®)	20-40 mg/kg IM ket. + 1-1.5 mg/kg IM dia.	20-30 minutes	Sedation / immobilization Medium surgical anesthesia
Ketamine + midazolam (Versed®)	20-40 mg/kg IM ket. + 4 mg/kg IM mid.	20-30 minutes	Sedation / immobilization Medium surgical anesthesia

Intramuscular (IM), Intravenous (IV)

Table 2. Inhalant anesthetics used in birds (Muir, W., 1995).

Drug	Dosage	Comments
Isoflurane (Forane®, Aerane®)	3-4% for induction 0.5-2% for maintenance	Maintenance requires use of a calibrated vaporizer Recommended
Halothane	2.5-3.5% for induction 1-2% for maintenance	Maintenance requires use of a calibrated vaporizer

Monitoring

Reflexes and responses to stimulation should be monitored to maintain a light to medium depth of anesthesia (Table 3). Breathing should be observed for rate and depth of respirations. Birds do not tolerate decreases in respiration and may need assisted or manual ventilation if pausing between breaths is greater than ten seconds. Manually ventilate the bird 10-15 breaths per minute, being careful not to over-inflate the lungs. Decreasing the vaporizer setting to produce a lighter depth of anesthesia will improve respiratory function. The cardiovascular system can be monitored by evaluating mucous membrane color (should be pink not blue) and by listening for a heartbeat.

Table 3. Monitoring levels of anesthesia (Abou-Madi, N., 2001).

Parameter	Light	Medium	Deep
Voluntary blinking	Slow or absent	Slow or absent	Absent
Muscle relaxation	Moderate-good (unless ketamine used)	Good (unless ketamine used)	Absent
Breathing pattern	Rapid and deep	Slow, deep, regular	Slow, shallow
Palpebral reflex	Present or slow	Slow, intermittent	Absent
Pedal reflex	Present or slow	Slow, intermittent	Absent
Corneal	Present or slow	Slow, intermittent	Absent
Stimulation	No response	No response	No response

Recovery

Provide warmth and subcutaneous fluids (up to 30ml/kg in divided sites) if intraoperative fluids were not administered. Wrap the bird in a towel to control wings and recover in a dark and quiet area. If a bird shows signs of excitation, hand-hold the wrapped bird until it fully recovers. Analgesics can be administered immediately postoperatively to produce a smooth recovery.

Analgesics

Signs of pain in birds may include agitation, restlessness, vocalization, and decreased interest in surroundings, inappetence, and weight loss, lack of grooming or overgrooming of a painful site. Since it can be difficult to accurately assess pain in birds, it is recommended to treat for pain if any potentially painful procedure has occurred. Analgesics are best given preoperatively to smooth induction and recovery. Distress may intensify pain in birds. Therefore, the bird should be kept in a quiet, warm, and nonstressful environment at all times. Analgesics for treatment of pain in birds include opioids, nonsteroidal anti-inflammatory drugs, and local anesthetics (Table 4).

Table 4. Analgesic agents for treatment of pain in birds (Paul-Murphy, J and Ludders, JW., 2001).

Opioids	Dose
Butorphanol	1-3 mg/kg SQ/IM q4-6h
Nonsteroidal Anti-Inflammatory Agents
Ibuprofen	5-10 mg PO 2-3x/day
Ketoprofen	2 mg/kg SQ/IM 1-3x/day
Carprofen	2-4 mg/kg PO 2-3x/day
Piroxicam	0.5 mg/kg PO 2x/day
Local Anesthetics
Lidocaine Normal Saline	1-4 mg/kg irrigated into surgical site. May dilute 1:10 with 0.9%

Oral (PO), Subcutaneously (SQ), Intramuscular (IM)

Supportive Therapy:

Flumazenil	For prolonged sedation from diazepam or midazolam. 0.05 mg/kg; Administer ½ calculated dose IV, the other ½ dose SQ or IM.
Dextrose 50%	For low blood glucose levels. 1 ml/kg IV; Dilute in fluid, do not give IM or SQ.
Dexamethasone	For treatment of shock or anesthetic complications. 2-4mg/kg IV or IM.

Subcutaneously (SQ), Intramuscular (IM), Intravenous (IV)

References

Abou-Madi N (2001) Avian Anesthesia. Vet Clinics of North America: Exotic Animal Practice 4, 147-167.

Flecknell P (1992) Laboratory Animal Anesthesia, 2nd Edition. Academic Press, London, pp 217-220.

Muir WW, Hubbell JA (1995) Handbook of Veterinary Anesthesia, 2nd Edition. Mosby, St. Louis, pp 341-353.

Paul-Murphy J, Ludders JW (2001) Avian Analgesia. Vet Clinics of North America: Exotic Animal Practice 4, 35-45.