Raptor Anesthesia

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Anesthesia for Raptor and Swans with General Principles Applicable to Other Species of BirdsPatrick T. Redig DVM, PhD Associate Professor Director, The Raptor Center Note: The links (underlined words) in the text will open a new browser window with the appropriate picture. Use the buttons on the "Task Bar" (Windows 95/98) to switch between the pictures and the text. For your convenience, there are navigation buttons on each picture page, if you wish to simply view the pictures.) The majority of articles and chapters written about avian anesthesia dutifully recite the litany of various injectable and inhalant agents that are available. For my part, with the exception of isoflurane, nearly all of these can now be archived as relics of the past -- something to be referred to for amazement and amusement, but not regarded as serious candidates for avian anesthesia. I refer here to all combinations of barbiturates, (e.g. Equithesin -- a mixture of pentobarbital, magnesium sulfate and chloral hydrate), methoxyflurane, halothane and nitrous oxide -- the latter useful only for the surgeon prior to beginning a long procedure. Since occasions may arise where isoflurane is not available, appended to this article are tables of empirically derived and extensively tested dosages for the use of combinations ofketamine and xylazine (fig 14) specifically in raptors. With the 50% reduction in the price of isoflurane (figure 3), the last and oft repeated impediment to its routine use has been eliminated. True, the acquisition of the requisite precision vaporizer (figure 4), oxygen source and flow regulators represent sizable one-time investments, but the safety and utility make the investment more than worthwhile one -- and not just for in-

clinic use. I've dedicated one unit for field use. Mounted on a 2" aluminum plate affixed to a frame pack, this unit has been taken to remote canyons in Idaho for field anesthesia of wild prairie falcons and to the rainforest of Panama to anesthetize a Harpy eagle for repair of a fracture of the radius and ulna. Across a wide range of avian species, this agent elicits a remarkable uniformity of response. Subtle nuances and differences do exist however, and it is the purpose of this seminar to describe some of these as they have been observed in raptors over the last 10 years in over 6000 birds and probably more than 20,000 anesthetic episodes. The physical properties of isoflurane and the unique anatomy of the avian respiratory system (figure 17) and its highly efficient gas exchange mechanisms have been thoroughly described in recent literature (Sinns, in Ritchie and Harrison, Heard in Altman, Fitzgerald and Blais in Raptor Biomedicine). Briefly, the low aqueous solubility of the methyl ethyl hydrocarbon known as isoflurane results in rapid equilibration between air capillaries and blood with very little solubilization in the aqueous phase. It is eliminated almost entirely through the respiratory system, with only about 15% being metabolized and excreted by the liver. The efficiency of the avian respiratory system allows very rapid gas exchange. Consequently, all aspects of anesthesia administration, from induction to recovery and including changes in depth of anesthesia are very rapid and easily controlled. Thus, isoflurane can be administered to sick and debilitated birds with a greater margin of safety than any agent that is more soluble in blood (e.g. halothane) or requires post-administration metabolism for elimination (methoxyflurane and injectable agents). The general considerations for equipment requirements, administration, vaporizer settings, recovery, monitoring, and pre-anesthetic considerations have been well described for avian species (Heard, 1996). What is lacking at this point is species specific or at least group specific descriptions in the administration of and the response to isoflurane. This paper will address these topics for raptors with additional comments on trumpeter swans as these are the species with which I have a large and direct experience. These remarks pertain to both wild raptors as well as tame and trained falconry birds, both imprints and otherwise. In general, these points pertain well to psittacines and most other birds as well. Preanesthetic considerations: Physiologic condition, medications Isoflurane can be safely given to birds in a wide range of conditions. Debilitated and anemic birds and those with moderate to severe dyspnea, patients traditionally regarded as high risks, can be induced with safety. The latter often achieve a degree of relief from the stress of their condition. Since restraint for examination and sample collection is stressful to most birds,

severely compromised patients can be managed more effectively under anesthesia (Harrison, 1986). In my opinion, the advantages of relief from stress of handling under such situations outweigh the potential risk of anesthesia. For elective procedures, food should be withheld anywhere from 6 - 12 hours beforehand. For larger raptors and other birds, fasts of this duration and even longer, up to 24 - 48 hours, pose no risk. For species whose weights are generally less than 120 grams (kestrels, saw-whet owls), no more than an overnight fast is recommended. For small psittacines (cockatiels, budgies, lovebirds), a fast of 3 to 4 hours with water available is recommended. To avoid complications that might arise from a pellet in the stomach (raptors), only meat devoid of feathers or fur (e.g. skinned mice or "clean meat") is fed the night before. If anesthesia is required in a raptor with food in its stomach or crop, or the status is uncertain (e.g. a new admission), precautions against regurgitation and aspiration are necessary. These include intubation (if possible), blocking the pharynx with a wad of 2 x 2 gauze sponges, inclining the body, and holding the patient in a vertical position during recovery. Great care must be undertaken in attempting anesthesia in a bird that has a distended abdomen. The causes may be the recent consumption of a very large meal or the retention of a very large pellet, intestinal blockage with stomach distension, ascites or other serious problems. All severely reduce respiratory volume and have caused anesthetic problems (Fitzgerald and Blais, 1993). Dehydration should be corrected or partially alleviated at the time of administration of anesthesia or before if possible. If no other medical conditions require immediate treatment, withholding further handling and anesthesia until subcutaneous or intravenous fluids have been given is advisable. Post-induction stabilization is recommended by some authors (Lawton, 1996, Heard, 1996) either as dextrose in lactated ringers solution to correct frank dehydration and hypoglycemia (Fitzgerald and Blais, 1993) or as a blood transfusion to correct anemia (Heard, 1996). Blood for a baseline CBC should be collected prior to any such treatments. There is general agreement among various authors that there is little indication for preanesthetic agents (Fitzgerald and Blais, Heard, 1996: Lawton, 1996). Atropine is indicated where bradycardia exists either preoperatively or intraoperatively (see below -- monitoring). Recommended dosage is 0.2 mg/kg given intramuscularly or other parenteral route. Sublingual and intratracheal routes can also be used. Administration Anesthesia is induced in all raptors by mask (figure 1,figure 2 and figure 13). Intubation of an awake patient (Heard, 1996) is extremely stressful and is not

recommended (Sedgwick, 1980). Any undue struggle during induction may result in release of endogenous catecholamines and result in cardiac arrhythmias (Hartsfield and McGrath, 1986 -- from Fitzgerald and Blais). The patient may be restrained in the arms of an assistant or in dorsal recumbency on a padded table.Falconer's birds, perched on the gloved fist and hooded, may be induced in situby gently placing a wide-mouthed mask over the top of the hood and covering the head of the bird to the level of their carpal joints. Once ataxic, the patient may be laid on a table. The mask and hood are removed and a suitably smaller mask is attached for further induction. For most birds an oxygen flow rate of 750 ml/min to 1 L/min is selected. A minimum flow rate of 600 ml/min is required for proper functioning of an open system (Fitzgerald and Blais, 1993). The gas concentration to be used for induction is controversial. Some authors recommend beginning induction at a vaporizer setting not exceeding 3% (Heard, 1996; Fitzgerald and Blais) and increasing it at 0.5% increments every 30 seconds. Others recommend rapid induction at 5% (Lawton, 1996; Sinn, 1994). My preference, borne out by experience, is to utilize the 5% rapid induction method. The main advantage is that the bird quickly passes through the excitatory stage of anesthesia with little or no struggle. The protocol used at The Raptor Center is as follows: Phase I: 5% for 1 - 1.5 minutes. Watch for increased spontaneous blink rate in the nictitans which slows and by the end of this period is manifested as a slow drawing of the nictitans across the cornea. Phase II: 3.5% to 4% for next two minutes. During this time muscle relaxation will be felt in the legs and neck and there will be partial to complete closure of the palpebrae. Check heart with a stethoscope at this time, listening in particular for evidence of arrhythmia. Breathing will be strong, rapid and of varying depth. Phase III: 2.5% - 3% or less for maintenance. Some individual birds may still be light at this point. Maintenance at this level for seven to ten minutes is required before painful procedures such as manipulation of painful joints or intubation can be attempted without awakening and struggle. Golden eagles and gyrfalcons require maintenance at 3.5% to 4%, while great horned owls and snowy owls will be maintained at 1.0% to 1.5%. Psittacines are typically maintained at 2.5 - 3%. While induction occurs smoothly in nearly all raptor patients, peregrine

falcons exhibit a most disconcerting gasping movement of the mouth in phase 2 of induction. Once past this, they assume an even and more normal appearing pattern of breathing, albeit usually at a rapid rate of 60- 80 breaths per minute. Long-term maintenance is best achieved with the bird in ventral recumbency, especially for larger birds. Since respiration is active in both inspiration and expiration in birds, positioning has been shown to have a significant affect on respiratory function (King and Payne, 1964).

Intubation While some authors flatly state that intubation is required for any anesthetic episodes exceeding ten minutes (Sinn, 1994), experience has otherwise indicated considerable flexibility in this matter. Where anesthesia is being used for non-invasive and non-painful procedures (feather imping, physical examination, radiology), patients can be maintained on mask delivery with spontaneous breathing for times exceeding 30 minutes or more. Most raptors in intermediate and early maintenance phases of anesthesia resist having a tube placed in their trachea. Bald eagles are unique in that tube placement invariably causes apnea regardless of the plane of anesthesia. Swabbing theglottis and the end of the tracheal tube with a local anesthetic such as lidocaine a few minutes prior to attempting intubation alleviates this problem. Cuffed tubes are not used. The tube should be inserted deeply into the trachea (figure 7) to eliminate excess dead space and be loose fitting. Intubation is practical in all but the smallest raptors (saw-whet owls); it is done routinely in sharp-shinned hawks, kestrels and larger size raptors as well as psittacines from the size of amazons on up and smaller if preferred. Tube sizes below 2 mm have a tendency to clog with secretions thereby limiting the lower end of sizes that can be used.

Intubation is advantageous because it provides a means of administering intermittent partial pressure ventilation and efficient scavenging of waste gases. Spontaneous respiration rates of anesthetized raptors are typically around twelve to fifteen per minute in eagles, large falcons and large hawks, while smaller birds respire at twenty to thirty per minute. While spontaneous rates

are generally maintained in these ranges, depth of breathing can become quite shallow resulting in reduced tidal volumes and altered blood gases. Our protocol for long anesthesia episodes involves manually ventilating spontaneous breathing birds two to three 3 cycles every minute (intermittent positive pressure ventilation or IPPV). This is accomplished by closing the scavenging valve (figure 5, figure 7) on the rebreathing bag (see below), allowing the bag to fill partially and then manually squeezing the bag contents into the patient. Sufficient pressure is applied to cause the breast or tailhead to rise to levels slightly greater than those observed during normal breathing. A loose fitting endotracheal tube prevents overinflation. For ventilating smaller birds, it is useful to replace the conventional black rubber rebreathing bag with a small toy balloon. Data gathered from patients under this mode are indicative of the adequacy of this procedure to maintain normal blood gases (figure 6). Some patients, especially great horned and snowy owls, have one or two bouts of apnea within the first hour of anesthesia which is overcome by first turning gas off and purging the system with pure oxygen, then ventilating them until spontaneous breathing returns, then finetuning the gas administration level. At the point spontaneous breathing is restored, some birds, especially owls, will be regaining reflexes and may start to struggle and once gas flow is re-established, they will again become apneic. One simply begins continuous ventilation for the duration of the procedure, maintaining the vaporizer setting at whatever level is necessary to provide suitable muscle relaxation. Monitoring Effective monitoring consists of minute by minute assessment of the patient's overall condition. Once sufficiently anesthetized to a level where noxious stimuli (feather pulling, toe pinch) no longer elicit a response, the overall condition of the patient should be one in which there is complete muscle relaxation throughout the limbs and neck. Breathing should be steady and of medium depth, heart rate should be at or above the allometrically determined level for that bird (Pokras and Sedgwick, 1993), and tactile stimulation of the cornea should elicit a slow extension of the nictitating membrane across the cornea. Most birds will have slow pupillary responses and a moderate degree of mydriasis. Again, great horned owls and snowy owls usually have near complete pupillary dilation. An alert, well-trained assistant is the best monitoring device a clinician can have. Such an individual will monitor respirations by watching the rhythmic rise and fall of the tailhead region of the ventrally recumbent bird or the abdominal panel between the legs of the dorsally recumbent bird. Taping a small filoplume feather adjacent to the nostril of the face-masked bird is an easy way to monitor respiration. Technicians also can observe condensation in the tracheal tube and the movement of the lightweight small volume rebreathing bag of the intubated patient. They can monitor cardiac function

by direct listening with a stethoscope placed to one side of the vertebral column or the keel, depending on patient position; pulse can be assessed digitally in the axillary region. Periodically, they can assess corneal response, capillary refill time and muscle relaxation, while administering IPPV. Monitoring can be enhanced with a modest investment in equipment. A most valuable piece of equipment is an esophageal stethoscope and amplifier (Bickford) (figure 11). While use of such equipment is by and large restricted to birds that have been intubated, it ought to be possible to bore a hole in the side of a face mask and place a snug fitting grommet through which the tube of an esophageal stethoscope may be passed. Placement of the esophageal stethoscope in the bird, just below the level of the thoracic inlet, is critical to its function. Only slight positional changes of the bird during surgery can cause them to no longer detect heart rate, a fact which does lead to frustration among attendants. However, their use should not be discouraged as a result. An EKG machine (figure 10) provides the next level in monitoring sophistication. A machine capable of no more than basic leads, especially lead II, with freeze function is adequate; a paper strip chart is an almost essential feature also. There is a large amount of used equipment available from human hospitals that can often be had for the asking. Heart rates in most raptors range between 200 and 400 bpm, too high to count accurately via audible signals and often beyond the range of digital readouts on many EKG machines. Therefore, the strip chart recorder is the most accurate means of assessing heart rate and provides the added benefit of detecting partial heart blocks and arrhythmias. Manual monitoring, while usually very adequate in and of itself, is certainly augmented and enhanced by the basic devices of esophageal stethoscope and EKG. Various authors describe other additional means such as apnea monitors, dopplers, pulse oximetry (figure 12) and capnography. While useful in fine tuning the monitoring process and providing additional margins of safety, such equipment is by no means essential for routine application of isoflurane anesthesia in raptors. Pulse oximeters are particularly problemmatic in birds as that presently available devices are difficult to keep positioned so that a reliable signal is continuously received. Scavenging To date, isoflurane, unlike halothane, has not been reported to possess toxic effects (Altman, 1992). However, the National Institute for Occupational Safety and Health (NIOSH) has recommended that occupational exposure to gas anesthetic agents in general should not exceed 2 ppm averaged over an eight hour period. Preventing exposure of operating personnel to waste gases can be largely eliminated by scavenging waste gases with a vacuum system and adopting procedures that minimize uncontrolled release of vapors. We

use an adaptor in our open system through which a negative pressure can be applied just above the mask. A hose connects this adaptor to a needle-valve controlled vacuum reduction block which in turn is attached to a vacuum regulator that is plugged into a wall mounted vacuum source. A negative pressure of 20 mm Hg is provided at the regulator and further reduced by the needle valve, so that only a very slight negative pressure is applied at the mask. Measurements and calibration with an infrared spectrophotometer have shown a more than ten-fold reduction in concentration of isoflurane in the breathing zone of the surgeons with this method with no detectable effect on the amount fed to the mask. The scavenging system is not used during induction, however. Gas concentrations were reduced from a range of 40 - 57 ppm to 0.1 - 0.4 ppm. Other measures include using Vetrap in place of a conventional rubber dam to form a seal around the mask and the bird's neck, and filling the vaporizer under a fume hood. For a minimal investment in equipment and time to alter procedures, exposure of hospital personnel to isoflurane vapors has been virtually eliminated.

Recovery As a surgical procedure is completed, recovery should be expedited by reducing vaporizor concentrations incrementally. Ideally, the patient would be breathing oxygen as the procedure is finished and starting to regain consciousness as the instruments and materials are cleared by the table. Whether this is so or not, the patient is best managed during recovery if it is held in a near vertical position in the arms of an assistant. The intubation tube can be removed as soon as head movements occur. The mouth should be inspected for accumulations of mucous and swabbed clean. While the majority of recoveries are uneventful, some birds will regurgitate stomach contents, thrash mildly and occasionally have bouts of apnea. Restraint (figure 19) allows all of these to be managed efficiently. Regurgitation is the most dangerous event as aspiration can easily follow. This response should be countered immediately by thrusting the head and the body of the bird downward and cleaning of the mouth of gauze sponges. Apnea should be managed by stimulating the glottis or the abdomen to induce breathing; in rare cases intubation and ventilation may be required. Recovery should be complete in the majority of patients within five to ten minutes of cessation of anesthesia.

Problems:

Apnea probably occurs in 10% of anesthetic episodes at some point. It occurs without fanfare or warning -- the patient may have a couple of irregularly spaced breaths, then just ceases to breath entirely. The time span between respiratory arrest and cardiac arrest is on the order of several minutes, so the only concern is to re-establish breathing. Without delay or uncertainty, remove the mask and proceed to intubate. Often times the stimulation of the glottis with the end of the tube will initiate breathing. If not, proceed to intubate, then ventilate by whatever practical means. Ideally, an ambou bag (figure 9) would be available, but failing that, one should not hesitate to ventilate via your own mouth placed on the tube connector. If the bird is already intubated and attached to a breathing apparatus, detach the latter (to use the rebreathing bag at this point would offload more anesthetic-laiden gas into the patient) and proceed as described. Whether by bag or by mouth, sufficient air should be forced into the bird to cause the abdomen to distend as it would in normal deep breathing -- watch for rise of tail head or abdomen depending on position of the bird. Repeat at a rate of about 10/minute. The first few excursions will produce expulsion of copious amounts of isoflurane. Once a rhythm is established, listen to the heart with a stethoscope and check corneal and palpebral reflexes. Spontaneous breathing should restart in 1 - 2 minutes -- but do not hesitate to continue ventilating for as long as it takes. If the heart is steady, there is no need to abandon whatever procedure is underway as long as ventilation can be maintained by artificial means. Emergencies: Major Emergency: Cardiac arrest is the only anesthetic emergency with isoflurane. In my experience, this event occurs unpredictably and without any warning, and fortunately only rarely. In ten years and many thousands of episodes, we have had five such deaths (2 peregrine falcons, 2 goshawks, 1 sharp-shinned hawk). Attempts to resuscuitate have been uniformally unsuccessful in my experience and this is consistent with reported experience of others (Sinn, 1993, Heidenreich, 1997). Severe arrythmias have been encountered in several others resulting in abortive procedures (1 osprey, 2 bald eagles, 1 great horned owl, most notably coracoid fracture repair)

Minor Emergency Ideally, every anesthetic episode would not be undertaken without a full complement of equipment to manage problems that arise. Inevitably, a bout of apnea will occur sometime and an appropriate tracheal tube is nowhere in sight. In such a circumstance, seize any appropriately sized tubular structure handy -- an old piece of catheter, a syringe barrel or any of a variety of items that are likely to be close by and will allow intubation and ventilation to be undertaken. In a worst case scenario where nothing is obviously available,

fold your fingers in a loose fist around the birds beak and blow forcefully through the opening in the top of your fist; sufficient air will be forced into the patient to effectively ventilate it. As a last point regarding anesthetic emergencies, I recommend writing up the protocol to be used in your clinic stating in stepwise fashion to procedure to be undertaken. Post this prominently, make sure everyone understands the contents and periodically conduct an emergency drill in order to guarantee the necessary proficiency when it is needed.

Species accounts Eagles: Over a range of diverse eagle species, including bald eagles, golden eagles, tawny eagles, harpy eagles, Philippine eagles, Philippine hawk eagles, gray-headed fishing eagles, only the bald eagle stands out as being an exceptional anesthetic candidate. While many thousands of episodes have been undertaken without loss, this species is the most likely to become apneic and exhibit cardiac arrythmias (Aguilar and Redig). Further, balds are almost totally intolerant of intubation, apnea being the immediate result. This response is reduced to a large extent by anesthetizing the glottis and trachea with lidocaine, however, if anesthetic problems are persistent thorughout an episode, it is oft time best to remove the tube and simply use a mask. Golden eagles handle isoflurane anesthesia remarkably well, but are notable in that decidedly higher vaporizer settings, usually around 4% are required for maintenance. Great Horned Owls and Snowy Owls: In both of these, a narrow margin between nearly conscious and struggling and deep plane of anesthesia exists. Surgical plane usually results in low ventilation to apneic conditions. They are extremely unlikely to develop cardiac arrest, but in a majority of cases assisted ventilation will have to be provided during surgical planes of anesthesia. A low dose of torbugesic (0.1 cc/kg) will smooth out this process. Other owls are very easily and dependably anesthetized with isoflurane. Falcons: Peregrines: generally straightforward, however, they are one

species in which occasional cardiac arrests have occurred (table x). They induce well at 5%, but in lighter planes of anesthesia the exhibit involuntary gasping-like movements of the mouth. Once fully induced, such movements cease and no further problems are typically encountered. Maintenance is between 2.5 and 3%. Two deaths have been encountered, both in the recovery phase, one following repair of a femoral fracture and the other after a protracted episode of feather imping (replacement of broken feathers). It is possible that orthostatic shock from abrupt positional changes occuring during recovery handling may have played a role in the event. Gyrfalcons: Gyrfalcons are among the easiest of all raptors to reliably and safely anesthetize. Apnea is rare, perhaps nonexistent. Vaporizer settings run a little higher than with other raptors, usually between 3.5 and 4%. Prairie falcons, merlins, saker falcons and kestrels pose no unusual anesthetic risks or peculiarities. Buteos: As a group, anesthesia is handled with no unusual responses, save for the red-shouldered hawk. This species has a narrow range between deep anesthesia and long-lasting apnea. We've experienced only a few of these birds owing to their rarity, but the experience in once case stands out and perhaps tends to color the perception. In any case, one red-shouldered hawk became apneic immediately upon induction and required assisted ventilation for the duration of a a 2.5 hr refracturing and repair of an humeral fracture. Recovery was quick and uneventful. An increased propensity toward apnea has been seen in other red-shoulders also. Red-tails, rough-legs, broad-wings, and ferruginous, as well as Harris Hawks are easily and safely anesthetized. Accipiters: The Coopers Hawk is not typically a notable anesthetic risk, but problems have been encountered in both the sharp-shinned hawk and goshawk. Both of these should be induced at lower vaporizer settings; 3.5 to 4% is recommended. All preanesthetic considerations should be given extra attention and ventilation needs to be carefully monitored and assisted if necessary. Deaths have been attributable to cardiac arrests. Inasmuch as these occured unpredictably and without warning, prevention was not possible and efforts to resuscitate were never successful. At this point, we must simply note that there is a higher risk of complication in this group of raptors. Trumpeter Swans: It is with no little amazement that one finds these longnecked birds with the additional sternal coiling of the trachea to be excellent anesthesia candidates. From a physiological point of view, one would expect anatomical dead space to be a source of significant problem -- yet that turns out to be not the case. We find that mask induction at 5% is well tolerated

and maintenance with mask or endotracheal tube is effective (figure 15). Apnea occurs on rare occasions and is managed as described for raptors. Cardiac arrest has not been noted. Conclusion Isoflurane is the anesthetic of choice for raptors and the myriad traumatic and medical problems that commonly befall them. The agent provides rapid induction, rapid recovery, good muscle relaxation and has a wide margin of safety in all but a few species. Even in goshawks and sharp-shinned hawks, it works better than any other agent or combination that has been devised. The occasional bout of apnea is readily managed by ventilation. Deaths, if they occur, are by cardiac arrest. It is an extremely rare event if all other aspect of anesthetic management are given proper consideration. Literature Cited: 1. Altman, RB. 1992. Method for reducing exposure to anesethetic waste gases. J. Am. Assoc. Av. Vets 692): 99 - 101 2. Heard, D.J. 1996. Anesthesia and analgesia pp. 807-827 In Altman, R.B. et al. Avian medicine and surgery. W. B. Saunders, Philadelphia. 4. King, AS, DC Payne,. Q1964. Normal breathing and the effects of posture inG. Domesticus. J. Physiol. 174: 340-347. 9. Samour, JH. Et al. 1984. Comparative studies of the use of some injectable anaesthetic agents in birds. Veterinary Record. 115:6-11. 10. Sinn, L.C. 1994. Anesthesiology pp. 1066 - 1080 In Ritchie, BW, GJ Harrison and LR Harrison (eds): Avian Medicine: Principles and Applications. Wingers Publishing, Inc. Lake Worth, FL. 10. Fitzgerald and Blais. Inhalation anesthesia in birds of prey. Raptor Biomedicine. 1993. Pp. 128 - 135. 11. Harrison GJ and LR Harrison (eds): Clinical Avian Medicine and Surgery, Philadelphia, Saunders, 1986, p.550. 12. Lawton, MPC: Anaesthesia in Beynon PH, Forbes NA, Harcourt-Brown (eds): Manual of Raptors, Pigeons, and Waterfowl. British Small Animal Association Ltd. 1966, pp.79-88. 13. Aguilar RF, VE Smith, P Ogburn, et al: Arrhythmias associated with isoflurane anesthesia in bald eagles. J.Zool. and Wildl Med 26:508-516,

1995. 14. Cornick-Seahorn, J. (Guest Editor) Seminars in Avian and Exotic Pet Medicine: Anesthesia and Analgesia. Vol 7, no.1. 1998.