ith the refractory attitudes of manybirds toward even mild restraint, seda-tives and local anesthetics are of littleuse in most avian species. General anes-

thesia, however, with appropriate agents, can enableclinicians to safely and rapidly perform fluid admini-stration, emergency procedures, blood collection andradiography, or to perform prolonged invasive surgi-cal procedures in avian patients.

Historically, avian anesthesia has been a problemfraught with continuous debate. Many clinicianshave had their preferred drug “cocktails,” and therewere many conflicting views with regard to dosageranges and choice of anesthetic regime. Anesthesiamachines have been altered in an attempt to meetthe specialized needs of avian patients, and numer-ous modified endotracheal tubes, non-rebreathingbags and delivery systems have been implemented.Sophisticated monitoring systems and equipmentdesigned for or found to be suitable for avian patientsare now commercially available.

As in other animal species, general anesthesia inbirds can be accomplished with either injectable orinhalant anesthetic agents. The goal of anesthetizinga patient is to select the safest drug that allows theminimum amount of physiologic changes. (Thereader is referred to Section Seven for use of anes-thetics in non-psittacine species.) Injectable anes-thetics are far inferior to gas anesthetics for use inavian patients, and for private avian practice, isoflu-rane is the only recommended anesthetic. This isparticularly true given that the vast majority of pa-tients are anything but healthy and are less tolerantof the physiologic compromises induced by most in-jectable and other inhalant anesthetics.

The basic principles of risk assessment and patientsupport used for mammalian anesthesia are alsoapplicable to the avian patient. Ability to assess thecondition of avian patients has improved, as has theability to provide physiologic support during the an-esthetic episode.

WC H A P T E R

39ANESTHESIOLOGY

Leslie C. Sinn

Anesthetic Agentsand Equipment

The ideal avian anesthetic agent is one that createsminimal stress in administration, has a high thera-peutic index, provides for rapid induction and recov-ery, induces minimal physiologic changes, providesadequate restraint for the desired procedure and canbe safely used in critical cases. Contraindications foranesthetizing an avian patient should include severeobesity, fatty liver, liver or kidney failure, dehydra-tion, shock, anemia, dyspnea and fluid in the crop.Unfortunately, patients presented with many ofthese problems are those that require anesthesia forproper resolution of the case. The choice of anestheticagent must be based on the patient’s status and theworking conditions that the clinician faces (eg, fieldvs. hospital anesthesia). In all situations, the anes-thetic of choice is isoflurane.a,b There are some indi-cations for the use of injectables in the field, andrecent work with reversal agents may make the useof injectables more appealing to some avian practitio-

ners. However, an isoflurane anesthetic unit de-signed for field use will fit into a small tool box (10"x 12" x 20"); the only other necessary equipment is anoxygen source (Figure 39.1).

When compared to injectable anesthetics, inhalationagents have numerous advantages. They can betitrated to effect, have a more consistent therapeuticindex and provide for rapid induction and smooth,rapid recoveries. Additionally, the anesthetic episodecan be maintained for variable durations as dictatedby the procedure and, particularly with isoflurane,effects can be instantly reversed.

Physiologic Effects of Inhalant Anesthesia

In administering avian inhalant anesthetics, thereare several important differences between the mam-malian and avian respiratory system that should beaddressed. The paramount difference is that theavian lung does not have alveoli. Instead, the aircapillaries function as the anatomic location of gasexchange.28 Avian species also lack a diaphragm, andinspiration is totally dependent on the correlativemovement of the coracoids, ribs and sternum. Thetotal lung capacity of avian species is much less thanthat of an equivalent-sized mammal; however, due tothe air sac system, the total respiratory volume issubstantially greater. There is also a high gas ex-change surface-to-volume ratio that accounts formore efficient gas exchange. This efficiency accountsfor the rapid equilibration of inspired componentswith arterial blood and for the rapid induction, rapidchanges in depth of anesthesia and speed of recoverywhen inhalant anesthetics are used in birds. Recov-ery from isoflurane is primarily a function of theexcretion of the gas by the lungs. Full recovery withagents such as methoxyflurane that are highly meta-bolized depends on the biotransformation of theagent by the liver. Birds are very sensitive to CO2

concentrations, and if the blood is depleted of CO2,the patient will become acutely apneic. The mini-mum level of CO2 in the blood that is necessary tostimulate respiration in birds has been suggested tobe 25 torrs.6

Because of the anatomy and structure of the avianrespiratory system, even healthy birds may not beproperly oxygenated when anesthetized and placedin dorsal recumbency.6 It may be impossible for somespecies that have a large pectoral muscle mass (eg,Galliformes and Anseriformes) to adequately venti-late. Because of their unique respiratory anatomy,intubation and the use of gentle intermittent positive

FIG 39.1 An isoflurane anesthesia circuit for use in birds that willfit into a small tool box is commercially available. a) The compo-nents of the system are shown separated and b) connected to forma functional circuit (courtesy of Exotic Animal Medical Products).

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pressure ventilation (IPPV) (20 to 40 per minute at15 mm H2O) is strongly recommended in anesthe-tized patients.28

IsofluraneIsoflurane is rapidly replacing halothane andmethoxyflurane as the gas anesthetic of choice forsmall animal patients. This surge in popularity isbased on isoflurane’s rapid induction time, rapid andsmooth recoveries, rapid change in anesthetic level,high margin of safety for both the patient and hospi-tal staff, reduced arrhythmogenic properties, re-duced cardiovascular depression and reduced respi-ratory depression. The drug can also be safely usedto obtain diagnostic information from high-risk andcritically ill birds. Recovery from even long surgicalprocedures requires only minutes.

Isoflurane can have a dose-related depressant effecton the respiratory and cardiovascular system. Fortu-nately, there is a substantial interval between respi-ratory and cardiac arrest.1,9,11,27 The hypotensive ef-fects of isoflurane have been shown to be severe incranes. The effect was dose-dependent and was po-tentiated by spontaneous respiration when com-pared to assisted ventilation (IPPV).19 Isoflurane isonly 0.3% metabolized compared to 15% for ha-lothane and 50% for methoxyflurane; thus, isoflu-rane does not produce the hepatic damage induced byhalothane and methoxyflurane. However, it has beenevaluated in the field for only 12 years, and precau-tions should still be used with this anesthetic gas.The low metabolism rate also means that when thegas is expired by the lungs, few residues or toxicmetabolites remain to further hinder the patient’srecovery. Isoflurane has a blood solubility of 1.4 com-pared to 13 for methoxyflurane and 2.4 for ha-lothane. Because the solubility is so low, the agent isnot dissolved in the blood, and the speed of inductionand recovery are extremely rapid. Minimum alveolarconcentration (MAC) has been found to be approxi-mately 1.3 (cranes and ducks).18,19 This would indi-cate that higher settings for isoflurane deliverymight predispose the patient to apnea, cardiac ar-rhythmias and cardiac arrest.

MethoxyfluraneMethoxyflurane is 50% metabolized, has a high de-gree of organ toxicity and produces prolonged effectson physiologic parameters. This gas is highly solublein blood, which accounts for its relatively long peri-ods of induction and recovery (may take hours). Thissolubility prevents the rapid change in anestheticdepth, which makes the anesthetized bird easier to

maintain. However, the quantity of gas dissolved inthe blood also prolongs the time required to lighten abird in critical situations. Methoxyflurane is knownto induce major hepatic and renal dysfunction inchronically exposed hospital personnel, and scaveng-ing systems should be used to remove waste gas fromthe hospital setting. Because of methoxyflurane’s lowvolatility, techniques have been described for admin-istering the gas in open anesthetic systems. This isan extremely dangerous method of providing anes-thesia in birds, and if an adequate oxygen supply isnot assured, it will result in rapid death of the pa-tient.

HalothaneHalothane is a relatively nonirritating gas that re-quires a precision vaporizer for proper delivery. Theblood:gas coefficient for mammals is 2.3, which,when combined with the rapid arterial gas exchangethat occurs in the avian respiratory system, accountsfor a rapid induction and recovery. Induction is usu-ally achieved within two to five minutes at a two tothree percent level; recovery time depends on thelength of the procedure but generally varies from 5 to20 minutes. Halothane will induce a rapid decreasein the heart rate that returns to normal shortly afterceasing anesthetic administration. Maintenance isusually achieved between 1 to 1.5%, which decreasesas the length of the procedure increases, and de-creases with the degree of induced hypothermia. Ha-lothane is only 15% metabolized. Disadvantages ofhalothane in the avian patient are that 1) apnea andcardiac arrest often occur at the same time, and 2)the gas does sensitize the heart to catecholamines,which may induce arrhythmias, particularly withlonger surgical procedures. The agent can cause liverdisease in chronically exposed hospital personnel,and scavenging systems should be used to removewaste gas from the hospital setting. Recoveries withhalothane are more prolonged than with isoflurane.

CL INICAL APPL ICAT IONSIsoflurane is an ideal anesthetic in birds because of its:

High therapeutic index

Rapid induction and recovery

Minimal physiologic changes

Adequate restraint for many procedures

Safety in critical patients

Reduced toxicity

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OxygenThe oxygen flow should be high enough to ensurethat a precision vaporizer is accurate in its deliveryof the anesthetic gas. For most precision vaporizers,the minimum flow rate is 500 ml/min. Some vaporiz-ers function adequately at low settings but the manu-facturer’s recommendations should always be fol-lowed. If a semi-open system is used, the oxygen flowshould be three times the respiratory minute volume,which for a 450 g bird is about 275 ml/min. As ageneral guideline, this ratio can be used to determinethe respiratory minute volume of any avian species.For most psittacine birds, the oxygen flow rate dur-ing induction is 1 l/min and maintenance is 0.5 to 1l/min depending on the size of the patient.

Nitrous OxideNitrous oxide (N2O) has successfully been used inbirds in combination with isoflurane anesthesia. N2Ois not potent enough to induce anesthesia on its own;however, it does allow for the reduction in the per-centage of isoflurane necessary for anesthetic main-tenance. Because cardiovascular and respiratory de-pression caused by isoflurane are dose-dependent,N2O is an important addition to the anesthetic re-gime. N2O does have the characteristic of diffusinginto closed gas spaces faster than nitrogen (room air)can diffuse out. This means that N2O is contraindi-cated in situations where dead gas spaces are pre-sent. Because the avian respiratory system includingthe air sacs freely intercommunicate, the use of N2Ois not contraindicated. Some species differences doexist. For instance, diving birds have naturally occur-ring subcutaneous air pockets, and the use of N2O inthese birds may lead to subcutaneous emphysema.3

Pre-anesthetics

The routine use of atropine as a pre-anesthetic hasbeen avoided in avian patients because it thickensrespiratory secretions, slows gastrointestinal motil-ity and increases the heart rate. The thickening ofrespiratory secretions could contribute to a life-threatening occlusion in patients intubated withsmall-diameter endotracheal tubes. Additional ele-vation of the heart rate is not desirable in patientsthat already have a rapid rate. Glycopyrrolate doesnot have as marked effect on the heart, but it toocauses thickening of respiratory secretions. Conse-quently, these drugs are used only as specific therapyfor bradycardia. Further studies on the use of thesedrugs in birds are needed.

Injectable Anesthetics

Injectable anesthetics in birds have the same disad-vantages that are recognized in mammalian species.There is a tremendous variability in therapeutic dos-ages and physiologic effects, both at the species andindividual patient levels. Likewise, many injectableanesthetics do not provide an adequate plane of an-esthesia without reaching tissue levels that threatenthe life of the patient. There is minimal ability totitrate injectable agents to effect, so levels of anes-thesia may be insufficient to perform a procedure ormay be so deep that the patient is in danger. Withmost commonly used injectable agents, the anesthet-ic level cannot be rapidly decreased, and the recoveryis prolonged because the drug must be totally re-moved by metabolic pathways. Increased recoverytimes create excessive stress, increase the period ofhypothermia and prolong the deviation from a physi-ologically normal state. With any anesthetic episode,a major goal should be to minimize the time betweeninduction and recovery, and injectable anesthetics donot effectively meet this criteria. Unfortunately,when using parenteral anesthetics, the period of re-covery may be far longer than the duration of usefulanesthesia.

The most commonly reported injectable anestheticsused in birds are combinations of ketamine and xy-lazine and, less frequently, ketamine and diazepam.Etorphine, methoxymol, propafol, midazolam, tileta-mine/zolezapam and barbiturates have all been usedin birds.4,7,12,15 Initial data are promising for some ofthese drugs, but in many cases actual clinical trialsare not available. In general, phenobarbital, metho-hexital, thiobarbiturates and barbital should not beused in companion birds. They have a low margin ofsafety, produce prolonged violent recoveries, must begiven IV to prevent perivascular damage and at bestprovide radically variable levels of anesthesia.

Ketamine, a cyclohexamine, produces a catalepticstate that inhibits movement, but does not provideadequate analgesia for major surgical procedures.This drug has a highly variable effect in differentavian species. It is metabolized by the kidneys and istherefore contraindicated in patients with renal in-sufficiency. Dose ranges for various species are re-ported from 5 to 75 mg/kg. The drug is most com-monly administered IM, and the first signs ofincoordination occur within three to five minutes.The typical duration of anesthesia is 10 to 30 min-utes, and recovery may take from 30 minutes toseveral hours, which is completely dose-dependent.

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Ketamine anesthesia is typified by cardiac and respi-ratory depression, increased blood pressure, reducedbody temperature, slow violent recoveries and pro-longed physiologic changes.

Ketamine is rarely used alone. Because of the musclerigidity produced by this drug and the inadequacy ofthe analgesia achieved, ketamine is most often usedin combination with either xylazine or diazepam.12,20

The ratio for both ketamine/diazepam orketamine/xylazine combination is 10:1 on a mg/kgbasis. Either combination provides for more rapidinduction, smoother maintenance and less violentrecovery than when ketamine is used alone.

Xylazine produces good muscle relaxation and tran-sient analgesia. It can cause bradycardia and heartblocks.20

Diazepam is an excellent sedative and provides somemuscle relaxation.20 Ketamine/diazepam combina-tions can be useful when mild restraint is required.

The dosages for the drugs to be administered incombination are calculated based on a ketamine dos-age of 5 to 30 mg/kg IM (or 2.5 mg to 5.0 mg IV) mixedwith xylazine 1.0 mg to 4.0 mg IM (or 0.25 to 0.50 mgIV). Alternatively, diazepam (0.5 mg to 2.0 mg/kg IMor IV) may be substituted for the xylazine.2,4,5,8,12,28

The two drugs chosen are mixed together and admin-istered either intramuscularly or intravenously. Re-duced doses are necessary in seriously ill, pediatricand geriatric patients and for intravenous admini-stration. Ratites require only 3 mg/kg of ketamine.Because these drugs have a narrow therapeutic in-dex and the species and individual dose responsesvary widely, clinicians are advised to start at thelower end of the dosage range. The intravenous routeis preferred, as the dose can be titrated to effect.12

Both xylazine and diazepam can be mixed in thesame syringe with ketamine. Care must be taken,especially with smaller doses, to eliminate all airpockets from the syringe and to thoroughly mix thetwo drugs. Recovery from intravenous administra-tion of these injectable anesthetic combinations maytake 15-45 minutes, while recovery from intramuscu-lar administration, especially if additional dosageshave been necessary, may take hours. Recovery maybe violent. Yohimbine has been shown to be an effec-tive reversal agent for ketamine/xylazine anesthesiain raptors. A dosage of 0.1 mg/kg yohimbine waseffective in reversing anesthesia caused by the ad-ministration of intravenous ketamine (4.4 mg/kg)/xy-lazine (2.2 mg/kg).5 Tolazoline (15 mg/kg IV) has been

used to successfully reverse ketamine/xylazine anes-thesia in turkey vultures.2 The use of these reversalagents may make the use of ketamine/xylazine saferand more practical for birds.

Etorphine has been successfully used in large birdssuch as ostriches and cassowaries. A dosage of 0.02 to0.03 mg/kg IM is utilized for restraint. This can thenbe reversed with 0.04 to 0.06 mg/kg IV of diprenor-phine.15

Midazolam (same group as diazepam) (15 mg/kg IM)was successfully used to reduce the percentage ofisoflurane necessary for general anesthesia in racingpigeons. It was then effectively reversed with thedrug flumazenil (0.1 mg/kg IM).29

Gas Anesthetic Equipment and Delivery

Anesthetic Machines and VaporizersMost of the available models of anesthetic machinesare adequate for an avian practice. What is requiredis an out-of-circuit, precision vaporizer for the admin-istration of isoflurane. The vapor pressure of isoflu-rane (261 mm Hg) is so close to halothane (243 mmHg) that the same type precision vaporizer can beused for both agents (Figure 39.2). However, onceconverted to isoflurane, a machine should no longerbe used for halothane. A vaporizer can be purchasedthat is manufactured specifically for use with isoflu-rane, or a halothane vaporizer can be cleaned withether and re-calibrated for use with isoflurane. Avaporizer cannot be used for halothane and isoflu-rane at the same time. Switching back and forth

FIG 39.2 The vapor pressure of isoflurane and halothane are simi-lar so isoflurane can be delivered through a halothane vaporizer;however, once a vaporizer has been converted to isoflurane use, itshould not be used with halothane.

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between these agents will destroy the vaporizer.Calibration of the vaporizer is necessary after a con-version has occurred from halothane to isoflurane.Once isoflurane is in use, the vaporizer should becleaned and re-calibrated on a yearly basis.

Breathing SystemsGas anesthesia can be achieved through either anopen, semi-open or semi-closed system. Open sys-tems rely on the animal’s being placed in contact withan absorbent material soaked in the anesthetic liq-uid. There are descriptions of methoxyflurane beingadministered in a drip cone system. With the highlyvolatile anesthetics like halothane and isoflurane,very high concentrations of the gas will rapidly occurin the inspired air, causing acute anesthetic overdoseand death. Tank systems used to induce anesthesiain small mammals should not be used in birds. Thesechambers prevent monitoring of the patient, create apotential for beak, head, neck or spinal trauma andrelease high concentrations of gas into the environ-ment when the top is opened (Figure 39.3).

Semi-open systems rely on an Ayres T-piece, Y-piece,Norman elbow or Kuhn circuit that prevents therebreathing of expired gases. Because of the rela-

tively low resistance to air flow present in thesesystems, they are ideal for avian patients.

Semi-closed systems rely on the complete rebreath-ing of expired gases. The resistance inherent in thecircuit makes them impractical for birds.

A non-rebreathing anesthetic system is recom-mended for patients under seven to eight kilograms(most birds). This reduces dead space and decreasesthe effort that the patient must exert in order tobreathe. This is especially important in birds, be-cause both expiration and inspiration involve activeuse of the trunk muscles. Either an Ayer’s T-piece orBain’s circuit can be effectively used with most birds.Some clinicians prefer the Bain’s circuit because intheory, the patient’s expired gases warm the in-flow-ing gases and reduce the loss of body heat. This canbe critical in birds because their small size predis-poses them to hypothermia, and respiration is one ofthe major routes through which body heat is lost. Inpatients over seven to eight kilograms, conventionalhuman pediatric supplies are adaptable, easy to ob-tain and easy to maintain. In larger avian patients(eg, ostriches), standard small animal anestheticequipment and supplies are applicable.

A standard 0.5 liter reservoir bag can be used in somelarger avian patients, but better control and monitor-ing of respiration can be achieved with a smallervolume bag specifically designed for birds. These canbe handmade from plastic bags, or an inexpensive,disposable avian anesthesia bag is commerciallyavailable (Figure 39.4).c

FIG 39.3 Tank systems should not be used for inducing anesthesiain birds.

FIG 39.4 Anesthesia bags (50 ml, 100 ml and 250 ml) are commer-cially available for use in birds. These inexpensive bags account forthe reduced tidal volumes of birds, allow for precise IPPV and aredisposable, which prevents nosocomial infections. The bags can beadapted to any Ayres T-piece-type semi-open anesthetic deliverysystem (courtesy of Exotic Animal Medical Products).

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An appropriate scavenging system is the best protec-tion for operating room personnel from secondary gasexposure. Once the scavenging system is in place, gasexposure can be reduced by quickly intubating pa-tients, minimizing the time the patient is wearing amask and keeping flow rates as low as possible toprevent gas from escaping via the pop-off valve. Endvalves placed in the reservoir bag can be venteddirectly into the scavenging system.

Endotracheal TubesNon-cuffed infant, Magill or Cole (smallest size = 2mm) endotracheal tubes can be used in medium- tolarge-sized birds (Figure 39.5). Cuffless tubes areused because birds have complete tracheal rings thatcannot expand if excessive amounts of air are intro-duced into a cuffed tube. Alternatively, some clini-cians choose to make their own endotracheal tubesout of red rubber feeding tubes. The end of the tubeis snipped off and small holes are cut in the surfaceof the tube to allow for air exchange. The tip of thetube should be blunted by heating it with a flame andpressing it on a hard surface. These tubes are lesscostly than purchased tubes and have the addedbonus of being disposable. In any situation, a tubewith the maximum internal diameter that will fit ina bird’s trachea should be used.

Face MasksThe delivery of inhalant gases from a precision va-porizer can best be achieved by manually restrainingthe patient and placing the nostrils and mouth in aface mask connected to an Ayres T-piece anestheticcircuit. Common canine or feline anesthetic masks,while not ideal, can be used for induction. Most small

animal masks fit avian patients poorly, resulting indilution of the anesthetic gas with room air. Withthese leaks, higher gas and oxygen settings are nec-essary in order to compensate for leakage (Figure39.6). To avoid nosocomial infections, a disposableplastic drinking cup, with soft paper products placedbetween the cup and the patient’s neck to prevent gasleaks, can be used as a face mask (Figure 39.7). Inbirds less than 150 g, an effective mask can be madeby covering the end of a 12 cc syringe case with asection of latex glove. The syringe case can then beslipped over an Ayres T-piece with a 50 ml anesthesianonrebreathing bag (Figure 39.8).

FIG 39.5 Non-cuffed, 2 mm endotracheal tubes are commerciallyavailable. These are generally small enough for use in birds over150 g. In smaller birds, a red rubber feeding catheter with severalholes cut in the end can be used as an endotracheal tube.

FIG 39.6 A small animal face mask can be used to induce gasanesthesia in medium and large companion birds.

FIG 39.7 Using a disposable plastic cup as an induction maskprevents the transmission of respiratory pathogens (eg, chlamy-dial, viral, fungal) between patients. If small animal face masksare used, they must be cleaned and sterilized between avianpatients.

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Care of EquipmentThe proper use and maintenance of anesthetic equip-ment is an often overlooked area.

With the large number of infectious bacterial, fungaland viral agents encountered in avian patients, anyequipment used during anesthesia, including tubingand endotracheal tubes, should be thoroughly disin-fected to reduce the chance of nosocomial infections.Equipment should not be used for other companionanimals and then used for birds without steriliza-tion. While the face mask and Ayres T-piece can beeasily disinfected in cold sterilization solutions, an-esthetic bags are much more difficult to disinfect.

Tubing, reservoir bags, face masks and endotrachealtubes should be thoroughly cleaned with soap andwater, then rinsed with clear water. They shouldthen be disinfected using a chemical disinfectant andrinsed again with clear water. Finally, they should beallowed to air-dry in a clean, dust-free location. Alter-natively, they may be sterilized using ethylene oxideor, with some endotracheal tubes, a heat autoclave.Because this cleaning regime must be used withevery anesthetic episode, a large reserve of equip-ment is necessary to handle a sizable avian patientcase load. Many clinicians feel it is more economicalto use disposable anesthetic supplies than to usetechnician time for cleaning equipment. Disposables,however, are more expensive and they contribute tothe medical waste problem.

Delivery of Inhalant Anesthetics

Two methods of anesthetic induction with isofluranehave been discussed. One method is to place the birdin a face mask and slowly increase the gas to a levelof 2.5 to 3%. However, the editors believe that therapid induction achieved by using a 5% setting in-itially, followed by a decrease to maintenance levelsof 1 to 2% is a better method. The amount of isoflu-rane delivered will vary with the patient, the individ-ual anesthetic machine and the delivery system.Some macaws, owls and Galliformes appear to beparticularly sensitive to gas anesthesia and may be-come apneic even with the use of isoflurane. Mainte-nance levels of anesthesia may be as low as 0.25% insensitive individuals.

After induction, any patient that will be anesthetizedfor more than ten minutes should be intubated withan appropriately sized endotracheal tube (Figure39.9). The amount of dead space should be minimizedby ensuring an adequate gas flow and by using tra-cheal tubes of the proper length. The appropriateendotracheal tube length can be determined bymeasuring the distance from the thoracic inlet to thetip of the beak. The laryngeal structure of birds ishighly mobile and can be manipulated from belowthe mandible to improve access for intubation.

Following intubation, the endotracheal tube can beconnected directly to the semi-open system. If thereis a possibility of regurgitation, the tongue and glot-tis should be pulled cranially, and the esophagus

FIG 39.8 A 12 cc syringe case can be cut to fit over an Ayres T-piece and covered with a latex glove to be used as a disposable face mask insmall avian patients.

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should be packed with moistened cotton to preventaspiration.

Air Sac AdministrationFor surgery of the head, trachea or syrinx, anesthe-sia can be delivered by placing a short endotrachealor red rubber tube into the clavicular or caudal tho-racic air sacs.25,26 The placement procedure is rapidand may be indicated as an emergency tactic whenan animal is presented with respiratory arrest orwhen severe dyspnea has been induced by foreignbody aspiration. To place an air sac tube, the animalis positioned with the leg extended to the rear as fora surgical sexing procedure. A small skin incision ismade over the sternal notch, and hemostats are usedto produce an entrance through the body wall andinto the left abdominal air sac (see Chapter 13). Ashortened endotracheal tube can then be insertedinto the air sacs and the Ayres T-piece connecteddirectly to the tracheal tube.

A study in pigeons and common buzzards indicatedthat isoflurane could be safely administered throughthe air sacs to maintain a surgical plane of anesthe-sia for 60 minutes. These birds were monitored forchanges in temperature, pulse rate, oxygen satura-tion, blood pressure and paCO2 levels (Table 39.1). Inthis study a persistent period of apnea was notedwhen the air sac tube was perfused with oxygen. Itwas suggested that the loss of CO2 present in thelungs and air sacs decreased the stimuli to the respi-ratory centers and induced the apnea. No assistedrespiration techniques were used during the 60-min-ute period of apnea.16

At the end of the 60-minute study, the birds wereflushed with oxygen to remove residual isofluraneand their paCO2 levels dropped to 19. This hypocap-nia was followed in four minutes by the return ofspontaneous respiration, which was associated withan increase of paCO2 levels (40 in the pigeons, 31.7 inthe buzzards). Arrhythmias were common in the pi-geons starting around 50 minutes after induction.The part that hypothermia played in inducing ar-rhythmias could not be determined. The mean recov-ery time to standing was 10 to 12 minutes. A metabo-lic alkalosis occurred throughout the anestheticepisode that was attributed to the decrease inpaCO2.16

TABLE 39.1 Mean Effects of Air Sac Anesthesia with Isoflurane16

Pigeon Buzzard

Temperature (°C) 37.3 (41.5) 38.7 (41)

ApH 7.62 (7.36) 7.67 (7.51)

paO2 426 mm Hg 360 mm Hg

paCO2 19.2 19.1

Pulse rate 93.1 (172) 232 (301)

Blood pressure 64.6 mm Hg (106) 119.7 mm Hg

O2 saturation(pulse oximeter)

98.1% 99%

Normal is listed in parenthesis. ApH = arterial pH, paO2 = partial pressure ofoxygen, paCO2 = partial pressure of carbon dioxide.

Management of theAnesthetic Patient

Patient Evaluation

Isoflurane can be used for two distinct purposes inthe avian practice. One is for long-term general an-esthesia needed to perform difficult diagnostic proce-dures and surgeries. The other is as an anesthetic toprovide short-term restraint and to facilitate theease of performing fluid administration, blood collec-tion, radiography, endoscopy or bandage changes(Figure 39.10).

The goal of a preanesthetic evaluation is to detectand correct any underlying pathology prior to induc-ing anesthesia. In some cases, several days or weeksof supportive care may be needed in order to ade-

FIG 39.9 In some birds (like this owl), it is easy to visualize theglottis for intubation. In others (many psittacine birds), it is moredifficult to visualize the glottis. Intubation can be simplified byplacing a finger in the intermandibular space and gently lifting theglottis into view.

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quately stabilize a compromised patient before anes-thesia can be safely administered. In other cases,eliminating abnormalities may not be possible, andconsequently, adjustments must be made in inducingand monitoring anesthesia to ensure a successfuloutcome.

The minimum database is designed to help the anes-thetist develop a list of risk factors associated withgeneral anesthesia in a given patient and to developevaluation methods or supportive care techniquesthat decrease the anesthetic risk. The patient evalu-ation associated with the use of isoflurane for short-duration procedures (five to ten minutes) is generallylimited to a thorough history and physical examina-tion. The theory in using isoflurane for short-termprocedures with a limited database is that this drughas a wide therapeutic index and has consistentlybeen shown to be relatively safe even in severelycompromised patients.

If a bird is going to undergo anesthesia for more thanten minutes, then in addition to the history andphysical examination, a minimum database ideallyshould include a fecal parasite check, Gram’s stain offeces and choana, PCV, TP, WBC with differential, aplatelet estimate, estimated clotting time, bile acids,AST, LDH and UA. Additional tests may be indicateddepending on the initial assessment and the type ofprocedure requiring anesthesia.

Risk ClassificationSuccessful risk classification de-pends on conservative evaluation ofthe minimum database. Practically,risk assessment allows one to esti-mate the duration of safe anesthesia,the intensity of monitoring requiredand the supportive care and techni-cal assistance needed to ensure pa-tient safety. It also provides the clini-cian with a prognostic perspective tobe discussed with the owner (see Ta-ble 39.2).

It can be successfully argued thatfew avian patients requiring anes-thesia are Class I. Most patients areClass IV and V. With careful suppor-tive care, a clinician can reduce theanesthetic risk factors of many ClassIV and V patients to those of Class IIor III patients.

A commonly encountered complica-tion of anesthesia in birds is liver

dysfunction. Hepatopathies may be suspected whenperforming the initial physical examination and con-firmed with findings of lowered protein levels, ele-vated or depressed bile acids and tissue enzyme val-ues, and radiographic findings of hepatomegaly, orconversely, a loss of liver mass. Liver dysfunctionmay reduce a patient’s ability to metabolize anes-thetic agents and may also be associated with coagu-lopathy. The use in these patients of any anestheticdrug that is dependent on the liver for metabolism iscontraindicated (most injectables, halothane,methoxyflurane). Supportive care designed to im-prove liver function may be necessary before anes-thesia. If anesthesia cannot be postponed to allow

FIG 39.10 Isoflurane is generally safe to use for short procedures (eg, radiography,endoscopy, blood collection) in patients with only a history and a physical examination. Ifa bird will be anesthetized for more than ten minutes, a complete database should beobtained to assess the stability of the patient.

TABLE 39.2 Risk Classification of Potential Anesthesia Patients

Class I(minimal risk)

Young, healthy patient undergoing an electiveprocedure.

Class II(some risk)

Young, healthy patient undergoing a non-elec-tive procedure, or a healthy patient undergoingan elective procedure.

Class III(risky)

Patient with an ongoing health problem undergo-ing a procedure for this or another problem.

Class IV(very risky)

Patient with a major health problem (unstable innature) undergoing a procedure.

Class V(moribund)

Last ditch effort to save bird’s life.

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sufficient stabilization, then anesthetic agents thatare minimally metabolized by the liver (eg, isoflu-rane) and vitamin K injections to help promote clot-ting are suggested.

Obesity is common in companion birds. Excess fatdeposits interfere with the patient’s ability to venti-late. Respiratory effort is further compromised whena bird is anesthetized and placed in abnormal bodypositions for surgery. With elective procedures, die-tary changes and treatment for underlying metabolicdisorders are indicated before general anesthesia isperformed.

Surgery is frequently required for egg-related perito-nitis, especially in small species (eg, cockatiels, love-birds, budgerigars). These patients should be care-fully stabilized prior to anesthesia. This stabilizationprocess may take weeks and in some cases rendersurgical intervention unnecessary. An abdominal tapand diuretic therapy are indicated prior to anesthe-sia to reduce the volume of fluid in the abdomen andto improve the patient’s ability to breathe.

These patients should be maintained in an uprightposition to prevent abdominal fluid and debris fromentering the lungs through rents in the air sacs. Thesurgery table should be tilted so that the patient’shead is slanted up.

In non-elective procedures on obese patients or thosewith an abdominal fluid accumulation, proper in-tubation is mandatory to ensure a patent airway.Gentle IPPV will help maintain adequate oxygena-tion. Keep in mind when providing IPPV that theavian lungs inflate minimally, and pressure placedon a breathing bag should be less than 15 mm H2O toprevent rupture of the air capillaries.

Preanesthetic Stabilization and Preparation

Nutritional TherapyFor elective procedures, inadequate diets should becorrected three to four weeks before surgery. For spe-cific nutritional requirements and nutritional supportof surgical patients, see Chapters 3, 15 and 40.

Fluid TherapyFluid therapy is an important aspect of supportivecare that should be provided to avian patients. Manysick birds presented for evaluation have been off foodand water for at least a day, often longer. With theirhigh metabolic rate, birds rapidly become dehy-drated. Correcting dehydration will dramatically im-

prove the patient’s ability to physiologically copewith anesthesia.

It has been suggested that all birds suffering fromtrauma and disease can be assumed to be at least tenpercent dehydrated, and that the following formulashould be used to calculate their fluid requirements:normal body weight (grams) x 0.1 (10%) = fluid deficitin ml. The dose for maintenance fluid is estimated at50 ml/kg/day.24

Calculated fluid requirements can be administeredin severely dehydrated patients by an intravenous orintraosseous route (see Chapter 15) (Figure 39.11).17,30

Fluids administered by oral or subcutaneous routes arenot as effective in restoring or maintaining circulatingvolume.

FIG 39.11 Placing an intraosseous cannula in the tibiotarsal boneis an excellent way to provide fluids to a patient during surgery.In comparison to catheters in peripheral vessels, intraosseouscannulas are much easier to maintain. Intraosseous cannulasplaced in the tibiotarsus can also be used in critically ill patientsfor intermittent fluid, blood or drug administration.

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Lactated Ringer’s solution is the fluid of choice. Thisbalanced electrolyte solution protects renal functionbetter than sugar solutions.23 Five percent dextroseis not a satisfactory replacement solution becausethe dextrose is metabolized, leaving free water.23 Flu-ids administered to anesthetized birds should beheated (96°F) to prevent hypothermia.

Fluids must be carefully administered to birds toprevent volume overload. The maximum acute fluidload that can be tolerated by healthy patients is 90ml/kg/hr.14 In a cockatiel this would be a maximum of9 mls in an hour or 0.15 mls per minute. Most avianpatients, however, are unstable and cannot toleratesuch a high rate and volume of fluid administration.

Electrolyte levels and acid-base balance should al-ways be of concern in the anesthetic candidate. Somenewer analyzers use small volumes (10 µl) of serum,providing clinicians access to actual values to use inassessing the status of their patients. If no means ofdetermining the bicarbonate deficit is available andthe patient is dehydrated or critically ill, the admini-stration of 1 mEq/kg of bicarbonate at 15 to 30 min-ute intervals to a maximum of 4 mEq is suggested.24

FastingRecommendations concerning fasting of birds priorto anesthesia have varied from no fasting to an over-night fast.12,13 Practically speaking, the patientshould be kept off food long enough for the uppergastrointestinal system to become empty. This proc-ess takes overnight in large birds and four to sixhours in smaller birds. One should palpate the cropand postpone surgery if it is not empty. In an emer-gency, a patient with food in the crop should be heldupright during the induction procedure, with a fingerblocking the esophagus just below the mandible.Once the animal is anesthetized, the crop can beemptied by placing a finger covered with cotton orgauze over the choanal slit to prevent food enteringthe nasal cavity, turning the bird upside down andmanually emptying the crop and esophagus. Theesophagus can then be packed with gauze, and thehead and neck positioned on an upward slant tominimize the chances of passive regurgitation. Thetrachea should be intubated using an appropriatelysized tube.

Patient Monitoring

The goal in any anesthetic episode is to maintain thelowest possible level of anesthesia to achieve neces-sary restraint. Anesthetic planes in birds are difficult

to observe from outward signs, and depth should bemonitored by combining information obtained fromheart rate monitored by either an ECG or doppler,respiratory rate and effort, toe pinch, palpebral andcorneal reflexes and wing tone. The rates will varydepending on the species (Table 39.3). A doppler canbe placed on either the cranial tibial or medial meta-tarsal arteries.

TABLE 39.3 Heart Rates and Respiratory Rates in Birds Anesthetized with Isoflurane

Beats Per Minute Breaths per Minute

Budgerigar 600-750 55-75

Cockatiel 450-604 30-40

Pigeon 93.1±5.416 15-25

Parrot 120-780 10-20

Ostriches4 60-72 2-20

Anatomic locations to evaluate the reflex response topain or touch in avian patients include palpebra,cornea, cloaca, propatagium, cere, interphalangealarea, pupils (response to light) and pectoral mus-cles.16

In a light plane of anesthesia, the patient has apalpebral, corneal and pedal reflex but has lost vol-untary motion. The ideal anesthetic level, as de-scribed in one study,16 was when the bird’s eyelidswere completely closed and mydriatic, the pupillarylight reflex (pupillary response to light) was delayedand the nictitating membrane moved slowly over theentire cornea. The muscles were relaxed and all painreflexes were absent. The loss of a corneal reflex (noreflex closure of the lid after touching the peripheralcornea with a dry swab) was considered to indicatedeep anesthesia.16

The respiratory rate should be slow and deep. If apatient becomes too deep, all reflexes will be lost andthe respiratory rate will be slow and irregular. Wingflutter is often an early indicator that an animal is

CL INICAL APPL ICAT IONSAnesthetic planes may be monitored by:

Rate and depth of respiration

ECG

Heart rate — doppler

Toe pinch

Palpebral reflex

Temperature

Wing flutter

Lid closure

Pupillary dilation

Pupillary reflex

Corneal reflex

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becoming light. An excellent plane of anesthesia formost procedures can be accomplished by reaching adepth of anesthesia where wing tone has just disap-peared. If injectable agents have been used, the tra-ditional planes of anesthesia may not be present,making evaluation of the patient more challenging.

Body TemperaturePhysiologically, birds are actually less efficient ho-motherms than mammals and as a result undergomore rapid changes in body temperature during an-esthesia. Loss of heat during surgical anesthesia is avery important factor in anesthetic survival and inthe rate of return to a physiologic normal state fol-lowing anesthesia. Besides a loss of physiologic re-sponses to reduced core temperature, hypothermia isalso induced during surgery by removal of large ar-eas of feathers to expose surgical sites, by the con-stant flow of cool anesthetic gases through the respi-ratory tract, by the liberal use of alcohol, by bodycontact with a cold conductive surface and by thelength of the procedure. Even with supplementalheat, it is not unusual to have rapid reductions incore temperature during anesthesia. Any degree ofhypothermia compromises the patient’s ability to re-cover from anesthesia. While supplemental heat willnot prevent the drop in core temperature seen withanesthesia, it does tend to reduce the speed of heatloss.

All patients undergoing long surgical proceduresshould be placed on water circulating heating pads.Keep in mind that these devices need at least a20-minute warmup period before they reach the pre-set temperature. The clinician may choose to mini-mize the amount of alcohol used in the surgical scruband instead use chlorhexidine or povidone iodine tominimize heat loss through evaporation. Body tem-perature loss may also be minimized through the useof heat lamps, heated lavage solutions, heated IVfluids or hot towels wrapped around non-rebreathingtubes. Hypothermia occurs in birds despite their be-ing placed on water circulating pads.

Body temperature (normal=105 to 107°F28) can beconstantly monitored during anesthesia to properlyevaluate the degree of heat loss. A patient underanesthesia will experience a time-related reductionin body temperature (maybe as much as 10°F), whichcan predispose to cardiac arrhythmias and increasedrecovery times. If severe hypothermia (loss of greaterthan 10°F) occurs, the patient may not recover at all.Traditional thermometers can be used to record thisdata, but they require cloacal insertion and take

three to five minutes to give an accurate reading.Electronic thermometers also require cloacal inser-tion and take two to three minutes to give a reading.A more practical option is a tympanic scanner,d whichgives a reading in five to six seconds. The monitorsare easy to use by applying the probe to the outersurface of the ear. Tympanic temperatures are con-sistently slightly higher than cloacal temperatures.21

Heart MonitoringHeart rate in avian patients can be monitored inseveral ways. Palpation at the point of maximumintensity is possible in some patients (see Table 39.3).Peripheral pulses can be used but are often difficultto detect in smaller patients. Auscultation via astethoscope is possible, although the chest may bedifficult to reach once the patient is draped for sur-gery. Esophageal stethoscopes equipped with pediat-ric tubing can be used for auscultation of the heart inavian patients the size of Amazon parrots and larger.This monitoring system allows direct auscultation ofthe heart without having to go near the surgical field.If correctly positioned, the esophageal stethoscopecan also be used for monitoring respiration. Dopplerscan be used, but are extremely positional in natureand difficult to maintain in birds (Figure 39.12).Some oximetry units provide pulse rates up to 250bpm; these units are easy to use and are not posi-tional like the doppler. In a group of cockatiels main-tained in a surgical plane of anesthesia, the heartrate remained above 450 bpm.12 In one study withpigeons and common buzzards, the pulse rates deter-mined by the oximeter were consistent with thosedetermined through a direct arterial line.16 In anemergency situation, a heart rate can be quicklyobtained by placing the doppler probe on the globe ofthe eye. An ECG is an excellent way to monitor the

FIG 39.12 A doppler probe placed on the medial metatarsal arterycan be used to monitor the heart rate during anesthesia.

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depth of avian anesthesia. As a bird gets deeper, theT-waves become smaller and may totally disappear.As the depth further increases, the R-wave will in-crease in magnitude and the S-wave is reduced.

Respiratory RateRespiratory rates during anesthesia should be slowand regular (see Table 39.3). Hyperventilation orrapid jerky motions are indications of ensuing prob-lems. An increase in the respiratory rate may indi-cate that a bird is entering a lighter plane of anesthe-sia, that the bird is having difficulty breathing(occluded tracheal tube) or that the bird has an ele-vated paCO2. Because surgical patients are draped,it is often difficult to observe respiratory effort. Di-rect visualization of chest movement as an indicationof respiration can be facilitated by using clear sterilesurgical drapes.e An anesthetic bagc designed to dealwith the lower tidal volumes of birds will also makeit easier to monitor respiration.

When using halothane or methoxyflurane, apnea andcardiac arrest may develop at the same time withoutprior warning. With isoflurane, apnea usually proceedscardiac arrest by several minutes. Halothane typicallyinduces a rapid decrease in heart rate that returns tonormal shortly after ceasing gas administration.

Apnea monitors do work in birds; however, less ex-pensive units may not be sensitive enough to detectthe respirations of smaller patients. The monitoringdevice that attaches to the endotracheal tube isheavy, and precautions must be taken to keep theweight of the monitor from kinking small diametertubes. These units also require that the patient beintubated. A unit intended for use in birds should beevaluated on avian patients prior to purchase.

Blood PressureBlood pressure can be monitored directly or indi-rectly and should remain above 100 mm Hg. Exceptin a research situation, it is unlikely that most prac-titioners are going to opt for direct blood pressuremonitoring due to the cost and invasiveness of theprocedure. Although indirect monitors that use pedi-atric cuffs are available and offer some promise for

use in avian patients, they are less reliable for smallerpatients. Appropriate responses to patients with de-creased blood pressure values include reduction of anes-thetic levels, administration of IV fluids, correction ofhypothermia and evaluation and correction of blood loss.

Blood GasesArterial blood gases can be assessed directly by run-ning arterial samples on a blood gas machine. This isnot practical for most practitioners and it may in-volve taking multiple blood samples, a procedurethat smaller patients cannot tolerate. Indirect as-sessment of blood oxygenation can be done via anoximeter. An oximeter records the percentage of cir-culating oxygenated blood via a noninvasive probe.10

The unit works by spectrometrically measuring thedifference in absorbance between reduced hemoglo-bin and oxyhemoglobin. Oximeters are not as sensi-tive at direct determination of arterial blood gases,and oximeter readings at 98% saturation are com-mon in birds that are actually 100% saturated.16 Theauthor has found that the oximeter probe can beattached to the wing web, toe, tongue or the area overthe tibiotarsal bone. The tibiotarsal area seems togive the most consistent and reliable readings. Theprobe is small and requires only one wire so it iseasily used during surgery. Additionally, manyoximeters are actually pulse oximeters that producean audible beep, allowing the anesthetist to monitorheart rate as well as oxygen saturation levels. Ide-ally, oxygen saturation levels should be above 90%. Areading below 80% should be considered life-threat-ening. Most birds will maintain an oxygen saturationbetween 80 to 85% when self-ventilating. Use ofIPPV to increase oxygen saturation is, therefore,valuable. Normal blood gas values of paCO2=19,paO2=400 and ApH=7.4 have been reported.20

Anesthetic Emergencies

With careful assessment of patients, conscientioussupportive care and thorough monitoring, many an-esthetic-related emergencies can be prevented.

Respiratory ArrestIf respiratory arrest occurs, the anesthetic systemshould be disconnected from the bird and the chestshould be lightly pressed and released to induce airintake, or fresh air can be gently delivered into thetracheal tube. If the patient is not intubated, an air sactube should be placed or the animal should be immedi-ately intubated. The practitioner must keep mind thatair sac intubation may result in apnea while the paO2

is increasing and the paCO2 is decreasing.

CL INICAL APPLICAT IONSEmergency Steps for Respiratory Arrest

Disconnect bird from anesthetic

Press on sternum 40 to 50 cycles/min

Intubate or apply air sac tube

IPPV through tube

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If respiratory arrest occurs in response to injectableanesthetics, the reversal agent should be administeredintravenously. The administration of doxapram HCl onthe tongue may help stimulate respiration. The pulserate should be carefully monitored and resuscitationshould continue until the bird is breathing unassisted.Birds that show respiratory arrest should be resched-uled for the procedure; a second or third episode ofapnea in these cases is often followed by cardiac arrest.

Cardiac ArrestCardiac arrest represents a poor prognosis. Resusci-tation efforts are often unsuccessful. If success is tobe achieved and cardiac arrest truly does exist, theclinician should be aggressive and utilize open heartmassage. The rate should be 60 or more compressionsper minute and they should be accompanied by coor-dinated artificial ventilation. These efforts should becontinued for up to five minutes. Although rare, somebirds may recover following cardiac arrest.

HemorrhageIf hemorrhage occurs during surgery, a significantportion of that loss can be replaced via fluid therapyusing isotonic solutions. If hemorrhage is severe, atransfusion will be necessary (see Chapter 15).

Postanesthetic Monitoring and Recovery

Anesthetic recovery should occur in a pre-heated envi-ronment, preferably a pediatric or avian incubator. The

safest approach to post-anesthetic monitoring of apatient is to leave all of the monitoring devices inplace until the patient absolutely will not toleratethem. Patients should be recovered where they canbe easily observed. Birds should not be left unsuper-vised until they are perching without difficulty.

Recovery from injectable anesthetics will be muchmore prolonged and if ketamine has been used, po-tentially traumatic. Anesthetic recovery is best ac-complished by wrapping the bird in a towel to pre-vent wing-flapping and self-inflicted trauma. Thelights should be dimmed and the noise level kept toa minimum to prevent violent reactions. The patientshould be rolled over every few minutes, and thepharynx should be monitored for the accumulation ofmucus or vomit. In severely depressed birds, IPPVcan be continued until the patient is no longer willingto tolerate the tracheal tube. Recovery from evenlong anesthetic episodes with isoflurane generallyrequires less than five minutes. The administrationof a reversal agent is indicated when appropriate.

Products Mentioned in the Texta. AErrane, Anaquest, Madison, WIb. IsoFlo, Solvay Animal Health, Mendota Heights, MNc. Avithesia, Exotic Animal Medical Products, Watkinsville, GAd. Tympanic Scanner, Exergin Corp, Newan, MAe. Steri-drapes, 3M, St. Paul, MN

References and Suggested Reading

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2.Allen JL, Oosterhuis JE: Effect of tola-zoline on xylazine/ketamine-inducedanesthesia in turkey vultures. J AmVet Med Assoc 189(9):1011-1016,1986.

3.Bendnarski RM, et al: Isoflurane-ni-trous oxide-oxygen anesthesia in anAndean condor. J Am Vet Med Assoc187(11):1209-1210, 1985.

4.Bruning DF, Dolensek EP: Ratite(Struthioniformes, Casuariiformes,Rheiformes, Tinaformes and Aptery-giformes). In Fowler ME (ed): Zooand Wild Animal Medicine 2nd ed.Philadelphia, WB Saunders Co, 1986,pp 277-291.

5.Degernes LA, et al: Ketamine/xy-lazine anesthesia in red-tailed hawkswith antagonism by yohimbine. JWildl Dis 24(2): 322-326, 1988.

6.Fedde MR: Avian respiratory physiol-ogy. Proc 8th Annual Vet MidwestAnes Conf, 1992.

7.Fitzgerald G, Cooper JE: Preliminarystudies on the use of propofol in thedomestic pigeon (Columba livia). ResVet Sci 49(3):334-338, 1990.

8.Flammer K: Update on avian anesthe-sia. In Kirk RW (ed): Current Ther-

apy X. Philadelphia, WB SaundersCo, 1989, pp 776-780.

9.Goelz MF, et al: Effects of halothaneand isoflurane on mean arterial bloodpressure, heart rate and respiratoryrate in adult Pekin ducks. Am J VetRes 51(3):458-460, 1990.

10.Green SA: Monitoring oxygenationand ventilation in practice-pulseoximetry and capnography. ProcACVS Vet Symp, 1991, pp 559-561.

11.Greenless KJ, et al: Effect of ha-lothane, isoflurane and pentobarbitalanesthesia on myocardial irritabilityin chickens. Am J Vet Res 51(5):757-758, 1990.

12.Harrison GJ: Evaluation and supportof the surgical patient; Anesthesiol-ogy. In Harrison GJ, Harrison LR(eds): Clinical Avian Medicine andSurgery. Philadelphia, WB SaundersCo, 1986, pp 543-559.

13.Harrison GJ: Pre-anesthetic fastingrecommended. J Assoc Avian Vet5(3):126, 1991.

14.Hubbell JAE: The case against rou-tine fluid administration. Vet Clin NoAmer Sm Anim Anes, 1992, pp 448-450.

15.Jacobson ER, et al: Ventriculostomyfor removal of multiple foreign bodiesin an ostrich. J Am Vet Med Assoc189(9):1117-1119, 1986.

16. Korbel R, et al: Aerosacular perfusionwith isoflurane - an anesthetic proce-dure for head surgery in birds. ProcEurop Assoc Avian Vet, 1993, pp 9-37.

17.Lamberski N, Daniel G: Fluid dynam-ics of intraosseous fluid administra-tion in birds. J Zoo Wildl Med 23:47-54, 1991.

18.Ludders JW, et al: Minimal anestheticconcentration and cardiopulmonarydose response of isoflurane in ducks.Vet Surg 19(4):304-307, 1990.

19.Ludders JW, et al: Isoflurane anesthe-sia in sandhill cranes (Grus canaden-sis): Minimal anesthetic concentra-tion and cardiopulmonary dose-re-sponse during spontaneous and con-trolled breathing. Anesth Analg68(4):511-516, 1989.

20.Mandsager RE, Raffe MR: Chemical re-straint techniques in dogs and cats.In Kirk RW (ed): Current VeterinaryTherapy X, Philadelphia, WB Saun-ders Co, 1989, pp 63-70.

21.Paster M: Use of tympanic tempera-ture scanner. J Assoc Avian Vet4(3):154, 1990.

22.Petrak M (ed): Diseases of Cage andAviary Birds. Phildelphia, Lea & Fe-biger, 1982, p 401.

23. Raffe MR: The case for routine fluidadministration. Vet Clin No AmerSm Anim Anes 22(2):447-448, 1992.

24.Redig PT: Fluid therapy and acidbase balance in the critically ill avianpatient. Proc Intl Conf Avian Med,1984, pp 59-73.

25.Rode JA, et al: Ventilation throughan air sac cannula during tracheal ob-struction in ducks. J Assoc Avian Vet4(2):98-102, 1990.

26.Rosskopf WJ, Woerpel RW: Abdomi-nal air sac breathing tube placementin psittacine birds and raptors: Itsuse as an emergency airway in casesof tracheal obstruction. Proc AssocAvian Vet, 1990, pp 215-217.

27.Seaman G, et al: Effects of inspiredoxygen on ventilation in birds anes-thetized with isoflurane. Proc 8th An-nual Midwest Anes Conf, 1992.

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29.Smith J, Muir WW: Cardiopulmonaryeffects of midazolam and flumazenilin racing pigeons. Proc 8th AnnualMidwest Anes Conf, 1992.

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