Avian Anesthesia

Symposium on Cage Birds

Avi an Anesthesia Alan M. Klide, V.M.D.*

There is a need to be able to anesthetize birds for various lengths of time safely. This could be for examination, surgery, or experimental procedures. The history of anesthesia for birds has developed in a manner similar to that for other animals, with a few additional features. The respiratory system of birds has been less well understood than that of mammals and therefore the use of inhalant anesthetics has been midunderstood and they have not been used advantageously. The use of local anesthetics in birds has been said to be contraindicated; however, this is not so.

LOCAL ANALGESIA The injection of local anesthetic drugs into an area to provide regional analgesia is a procedure commonly performed on humans and other mammals; however, this has rarely been done in the avian species. There are many reports in the literature stating the great danger involved in using these agents in avians. 14 • 18 • 20 • 31 In general, the cause for the increased toxicity has been attributed to a markedly increased sensitivity (of avians as compared to mammals) to local anesthetics, especially procaine. This is probably not the complete explanation or may not be the explanation at all. The actual cause of the toxicity is largely a gross overdosing of very small birds on a mg. per kg. basis; e.g., using 1 mi. of 2 per cent procaine in a 30 gm. parakeet is a dose of 667 mg. per kg. The subcutaneous LD 50 's of procaine (in mg. per kg.) in some common mammals are: guinea pig, 430; rabbit, 460; cat, 450; dog, 250. 5 • 19 Even if the sensitivity of parakeets were the same as these mammals, 1 mi. of 2 per cent procaine would be much greater than the LD 50 and even 112 mi. would be close to the LD 50 • In a small study with procaine in 18 parakeets, (A. M. Klide and W. *Associate Professor and Chief, Section of Anesthesia, Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia l'eterinar)' Clinics of North America- Vol. 3, No.2, May 1973

175

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Table 1.

M.

KLIDE

Subcutaneous Procaine Toxicity in Parakeets NO.

DRUG

Saline Procaine Procaine Procaine Procaine

CONCEN-

VOL. INJ.

STRENGTH

NO. OF

SHOWING

NO.

PER CENT

TRATION

mi.

mg./kg.

BIRDS

TOXICITY

DIED

DIED

0.3 0.3 0.3 0.3 0.3

4 2 4 4 4

0 2

()

200 40 20 10

()

()

()

0 0

0 0

0 0

0.9% 2 0.4 0.2 0.1

1

50

B. Amand, unpublished data), it seems that the subcutaneous LD 50 may be as low as 200 mg. per kg. (Table 1). In another report, 20 1 of 3 parakeets given 0.5 ml. of 2 per cent procaine subcutaneously died, indicating that the LD50 may be greater than 330 mg. per kg. if the birds weighed 30 gm.; however, the weights of the birds were not given. There may or may not be a somewhat greater sensitivity to procaine in the parakeet as compared to the mammals listed; however, there is no need to approach the possibly toxic dose of procaine in small birds. In the clinical use oflocal anesthetics, dilute the local anesthetic when using it in very small birds; 0.20 per cent procaine is probably adequate in birds the size of parakeets. The tendency to overdose on a mg. per kg. basis decreases in larger birds. The major problem with the use of local anesthetics, especially in small birds, is the restraint during the surgical procedure; however, this technique can be used to advantage in birds which are poor risks for general anesthesia, or for very short and simple procedures.

GENERAL ANESTHESIA The general anesthetics can be divided into two groups: those that are injected and those that are inhaled. Injectable anesthetics have been used in avians as in other species and this route suffers from the same disadvantages in birds as it does in other species. These are: variability of dose between species; variability of dose between individuals; the fact that the anesthetic level cannot be rapidly decreased; and the fact that most injectable anesthetics do not produce good surgical conditions without markedly depressing the bird and requiring a prolonged recovery. There is danger of gross overdosage, especially when administered by the intraperitoneal, intramuscular, subcutaneous, or oral route. The IV route gives more consistent results; however, there are problems of small vessel size and restraint of the bird for the venipuncture and injection. There are a relatively large number of reports on the use of injectable anesthetics in birds. 2 • 9 • ' 0 - 12 • 14- 18 • 20 • 25 • 28 • 31 • 32 Some of these are summarized in Table 2.

Table 2.

>

Experimental Use of Injectable Anesthetics for Birds

<:

:;::

z

DURATION OF SURGICAL SPECIES

DRUG

Aylesbury Pentobarbital Na domestic duck Methohexital Na

Herring and lesser blackbacked gull General avian

DOSE

ROUTE

30 to 60 mg. per kg.

IV

Variable

5 to 10 mg. per kg.

IV

-

Ethyl carbamate Equithesin Pentobarbital Na

15 3.0 60 1.3

mg. per kg. to 3.5 mi. per kg. mg. per mi. to 1.4 mi. per kg.

Pentobarbital Na

40 mg. per kg.

ONSET

IV IV IM

3 minutes 10 to 20 minutes

IM

1

Pentobarbital Na

16 to 60 mg. per kg.

IV

Urethane

30 to 45 mg. per kg. 1.5 gm. per kg.

IM IV

Pentobarbital Na

30 to 40 mg. per kg.

IP Pigeons IV

Equithesin

2.5 mi. per kg.

IM

/z to 5 minutes

5 to 10 minutes -

10 to 30 minutes

ANESTHESIA

COMMENTS

Variable

Excitement Death No effect; larger doses produced variable respouses Little effect 3. to 4 hours Satisfactory 95 minutes Satisfactory

Decreases Variable with decreasing size of bird 10 to 60 minutes 30 minutes Up to 9 hours Satisfactory for non-survival experiments 45 to 60 minutes 20 to 75 minutes

REF.

12

> z "'..,'" ::t:

'"

"' :;::

11 2

31 23

Successful

18

Satisfactory

16

......

o..J o..J

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M.

KLIDE

Injectable Agents

Pentobarbital Sodium. This drug has been used extensively in mammals. It has been tried in birds and reports vary as to the usefulness and safety; most stress the importance of giving the drug intravenously, slowly, in diluted solution, and to effect. Duration is less than in mammals and is shortest in the smaller birds. Thiobarbiturates. In general these have not been reported to be useful and many fatalities haYe been reported. Phenobarbital Sodium. This drug has also been tried but does not seem to be useful or safe. Onset times are long (up to l hour) with unpredictable results. Combinations. A combination of drugs which has been used in birds is a mixture of pentobarbital sodium, chloral hydrate, magnesium sulfate, propylene glycol, and ethanol.* This mixture is used for sedation and anesthesia in the horse. This mixture has been useful but suffers from the same disadvantages as other injected agents. Urethane. This long-lasting anesthetic has been used only for nonsurvival experimental procedures. It has a very long duration of anesthesia, up to 9 hours, and is cytotoxic. 23 Cyclohexylamines. This relatively new group of agents is being used in many different animal species; some of these agents may be useful in avian species. The three compounds of interest are phencyclidine,** ketamine,~ and tiletamine,t and a combination which is not yet marketed. This mixture of the cyclohexylamine, tiletamine (CI-634) and a benzodiazepine tranquilizer (CI-714) is called CI-744. These drugs may have some use in avian species. 3 There are several reports on the use of these compounds in birds.:J, 6 • 17 • 24 • 26 As with the reports of the compounds in different mammalian species, there are conflicting opinions; the basic disagreement being what is acceptable as adequate surgical conditions. There is no doubt that in many mammalian species these drugs are excellent for restraint, examinations, and minor procedures. If surgery or other pain-inducing procedure is necessary, it would be best to anesthetize the animal with an inhalant anesthetic such as halothane or methoxyflurane. This might be an appropriate procedure to follow in birds also. The dose rate reported for ketamine in birds has been from 30 to 250 mg. per kg. intramuscularly. It would be best to use the lower dose rate and if the procedure requires anesthesia, use an inhalant anesthetic. Metomidate:j: is a relatively new short-acting hypnotic which has been tried with some success in birds. 8 • 10 It has also been used for capturing wild birds. *Equisthesin, .Jensen Salsbery Laboratories, Kansas City, Missouri. **Sernylan, Bioceutic Laboratories, Inc., St. Joseph, Missouri. ~Vetalar, Parke-Davis and Co., Detroit, Michigan. tParke-Davis and Co., Detroit, Michigan. :j:Metomidate, Pitman-Moore, Inc., Washingtons Crossing, N.J.

.-\ VIAN ANESTHESIA

179

The section on injectable agents is brief; however, there are adequate references for further information. It is the belief of the author that most injectable agents are much inferior to inhalant agents for adequate safe, operating conditions.

Inhalation Anesthesia The use of inhalation anesthesia in the veterinary field had a slow start in relation to human use. However, it is now widely used in all species from armadillos to zebras. The early avian literature reports on the inability to use these agents in these species.9 • 16 • 20 • 25 Various reasons were given, including the anatomy of the avian respiratory system. There are no reasons why inhalant anesthetics cannot be used in birds as they are in mammals. The induction of, and the recovery from anesthesia with inhalant agents in birds is more rapid than in mammals. There are several possible explanations for this. The blood: gas partition coefficient may be different in avians as compared to mammals. There is even a difference between mammalian species (B. B. Cohn, unpublished data). If the coefficient were lower in birds than mammals it could account for a difference in induction and recovery time. The anatomy of the avian respiratory system allows for a more rapid equilibration of inspired concentration with arterial blood than can occur in mammalian lungs. This would allow a more rapid induction and recovery. Some ofthe problems in anesthetizing birds were caused by the very rapid induction and the attainment of too deep a plane of anesthesia too fast. There are many agents which have been used: diethyl ether, ethyl chloride, N 2 0, cyclopropane, methoxyflurane, and halothane. Ether, ethyl chloride, and cyclopropane each have some disadvantages, but the greatest disadvantage is common to all three, i.e., they are flammable and explosive. The agents in greatest use now are halothane and methoxyflurane. Halothane. 18 • 20 • 2 1. 27 • 29 • 3 1. 34 This is a relatively nonirritating, nonflammable, nonexplosive agent. It requires a precision vaporizer. The induction concentration in healthy small birds (parakeet size) is about 2 per cent. Because the blood:gas coefficient of halothane is fairly low (2.3 in mammals), and for the other reasons explained above, the induction is very rapid and if too high a concentration is used, the induction can be too fast to be controllable and the bird can become too deeply anesthetized and might have respiratory or cardiac arrest. In larger birds, a higher concentration may be needed, i.e., 2lfz to 3 per cent for induction. Inspired concentration for maintenance in relatively healthy birds not given any other drugs is l to 11/z per cent. Induction and recovery are usually quite rapid, both taking a few minutes. Methoxyflurane.* This agent can also be used with birds. 4 • 15 • 31 • 34 *Metofane, Pitman-Moore, Inc., Washingtons Crossing, N.J.

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Because it is a more soluble agent its blood:gas ratio is higher (l 0 to 13 in mammals) and the time for induction and recovery is longer. The changes in depth of anesthesia are slower, which is both an advantage and disadvantage. It proves to be a disadvantage because it takes longer to get a bird to a lighter level of anesthesia, and an advantage because it seems to be easier to maintain a stable level of anesthesia. This is deceptive because the bird gets quite deep without much obvious change in signs, thus often having a prolonged recovery.

Technique Induction of anesthesia could be with an injectable agent but is usually produced by the administration of the inhalent agent through a face (head) mask. The anesthetic delivery system for birds under l 0 pounds should be of the semi-open type (Fig. 1).a:J For larger birds, a circle system can be used. 33 There are several pieces of equipment which can be used as a mask. The common canine masks can be used by placing the rubber diaphragm of the mask over the bird's head (Fig. 2). This makes it easier to restrain the bird and induce anesthesia. The large dead space that may be present in such a mask can be overcome by using a high fresh gas flow. For small birds, the delivery end of a "Y" piece can be used as a mask. If the "Y" piece is being used, it is also the delivery system for the anesthetic. If a mask is used it can be connected to a "Y" piece or if the bird is very large, directly to a circle system. Intubation. After induction the bird should be intubated, i.e., an

Figure l. Kuhn system.

Two semi-open systems-an Ayres "T" piece with a reservoir tube and a

181

AVIAN ANESTHESIA

Fig ure 2.

Large canine face mask.

endotracheal tube placed through the glottis into the trachea (Figs. 3 and 4). Almost any bird of about 100 gm. or lar ger can be, a nd sh ould be, intubated. After intubation, the endotracheal tube is connected to the semi-open system or to a circle system, depe nding on the size of the bird. The endotracheal tubes used are those which are available for infants, children , dogs, and cats. The only modification that sometimes has

Fig ure 3.

Larynx ofa small owl.

182

ALAN

Figure 4.

M.

KLIDE

Larynx of a to ucan with non-cuffed endotracheal tube in place.

to be made is that the tube is cut so that it is shorter in length, to prevent excessive dead space (Fig. 5). It is very important to intubate anesthe tized birds (especially psittacine) because their airways become easily obstructed. In very small birds, which are not intubated , there are two procedures which aid in

Figure 5. T wo small e ndotracheal tubes which have been cut to decrease their length. One is a small cuffed tube, the other is a Cole Pediatric tube.

:\ VIAN ANESTHESIA

183

Figure 6. An endotracheal tube which had been used in a chicken not. g i,·en atropin e; the tube is completely occluded by secretions.

preventing obstruction. If a small plastic tube is placed in the esophagus it will draw up fluid by capillary action and aid in preventing this liquid from getting into the glottis. It should be reme mbered that a single visible drop of liquid can totally occlude the trachea of a parakeet. The other aid is a small smooth hook, such as can be made from a paper clip. This is used to try to keep the tongue forward to prevent it from obstructing the airway. If the bird is moderately to severely ill and there is danger of regurgitation during induction, the bird might be intubated awake, especially non psittacine birds. There are several signs of airway obstruction. Increasingly greater movements of the thorax and abdomen are usually seen. Normally the tail of a bird does not move very much as the bird breathes, but with airway obstruction the tail moves with the attempt at inspiration. This is most noticeable when a bird is in dorsal recumbancy. Often squeaking sounds may be heard if the obstruction is not complete. The bird appears to be getting more lightly anesthetized. This is the wrong time to increase the inspired anesthetic concentration; the obstruction must be cleared. Airway Secretions. Another source of obstruction is secretions into the airway. This can cause obstruction whether the bird is intubated or not (Fig. 6). If the bird is intubated the cure usually is to change the endotracheal tube, with suction of the trachea if necessary. If the fluid accumulates on the glottis of a bird which is not intubated, then it can be removed with a cotton tipped applicator. Atropine can be given by intramuscular injection 5 minutes before the induction of anesthesia to try to prevent these secretions. The common concentration of atropine is 0.5 mg. per mi. A moderate size parakeet weighs about go gm. A dose of atropine of 0.044 mg. per kg. would require the parakeet to receive 0.00132 m g., which is 0.00264 ml. of the standard solution; this is 2.64 microliters. There are microliter syringes* available which can m easure this quantity with no difficulty. A syringe like this would be useful for anyone *Microliter Syringes, Hamilton Company, P.O. Box 7500, Reno, Nevada.

184

ALAN

Table 3.

KLIDE

Oxygen Consumption and Minute Volume in Various Sized Birds

WEIGHT

Chicken Pigeon Sparrow

M.

gm.

2400 300 24

0 2 CONSUMPTION mJ. per gm. per hr. mi. per min. 0.5 0.9

3.0

20 45 1.2

RESPIRATORY MINUTE VOLUME

mi.

770 250 25

who treats small animals or mammals. If a syringe of this type is not available, then a dilute solution of atropine has to be made, remembering that the total volume injected should be reasonable. Consider that an injection of 0.3 ml. in a 30 gm. parakeet is the same as giving an injection of about 500 ml. to a 100 pound child. Oxygen Flow. There are several considerations in determining the oxygen flow to use for a particular bird. If a precision type vaporizer is used, the oxygen flow should be at least high enough so that it is in the range at which the vaporizer is accurate. For the Vapor and Flutec III, this is about 200 ml. per min. If a circle system is used there should be a relatively high flow for the first 5 minutes, and then the flow should be decreased to a maintenance level. This level should be in excess of the oxygen consumption (Table 3). If a semi-open system is used the oxygen flow should be three times the respiratory minute volume (Table 3). Temperature. Care must be taken to move birds carefully and slowly when they are anesthetized. It is very easy to apply great stress to a small bird's neck. Hypotension occurs from movement, especially in anesthetized individuals. The degree of hypotension can be great enough in an ill, hypovolemic, anesthetized patient to cause cardiac arrest. Near normal body temperature should be maintained. It is very easy for a small bird, anesthetized, lying on a cold, metal operating table, to cool markedly and rapidly. A warm water circulating pad is very useful to prevent cooling (Fig. 7). * Blood Volume. Great care must be taken to maintain hemostasis. If a small bird has a blood volume of 100 ml. per kg. then a canary of 20 gm. has a blood volume of about 2 ml. If there are 20 drops per ml. of blood, then 5 drops of blood is 1/s of the canary's blood volume and this degree of blood loss in a sick, anesthetized bird could easily cause severe hypotension ending in cardiac arrest. In larger birds, hypovolemia, hemorrhage, and dehydration can be treated by the intravenous administration of electrolyte solutions. However, in very small birds this is technically difficult. It is fortunate that birds seem to have a more efficient system than mammals for rapidly restoring blood volume.13 The bird should not be put back in the cage until it can stand by it*K-Pad, Gorman Rupp Industries, Bellville, Ohio.

185

_-\ VIAN ANESTHESIA

Figure 7. A pigeon anesthetized with halothane, intubated, attached to a semiopen system, on a warm water pad, with needle electrodes in the pectoral muscles for recording the E. K. G.

self. This does not usually take m ore than 5 to 10 minutes with halothane. Other Methods. There are other methods for administering inhalant anesthetics for birds. The liquid inhalant anesthetic can be sprayed from a syringe and n eedle into the nostril of a bird.14 • 30 This system is not very controllable, nor is an oxygen-enriched mixture supplied, and the airway is left unprotected. Another m ethod is very interesting and also provides a different method of ventilating a bird which is not breathing.7 • 34 The technique is to place a needle into the interclavicular air sac. A polyethylene cath eter is passed through th e needle into the air sac, a nd the n eedle is r em oved . Oxygen and anesthesia, halothane or methoxyflurane, are passed through the catheter. This m e thod is not r ecommended for birds under 50 gm. (parakeets and canaries). The r eport of ventilating birds by flowing air or oxygen into the air sacs7 used the posterior thoracic air sac. T hey too found that anesthesia can be produced by adding a n inhalant anesthe tic to the air or oxygen . Even though birds can be ventilated with this system, the airway is unguarded and r egurgitation r esulting in aspiration pneumonitis can still occu r.

REFERENCES I. Altman , P. L., an d Dittmer, D. S.: Respiration and Circulation. Fed er ation of Ameri-

can Societies for Experimental Biology, Washington, D.C., 1971. 2. Arnall, L. : Anesthesia and surgery in cage and aviary bi rds (I). Veterin . Rec., 73 : 134142, 196 1. 3. Beck, C. C. : C he mical restraint of exotic species. 'l'he j ournal of Zoo Animal Med icine, 3:3- 66, 1972.

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4. Bennett, R. R.: The use of metofame in experimental laboratory birds. Pract. Vet., 40:184-187, 1968. 5. Booth, N.H.: Local anesthetics. In L. M. Jones: Veterinary Pharmacology and Therapeutics, 3rd ed. Ames, Iowa, Iowa State University Press, 1965, Ch. 20. 6. Bree, M. M., and Gross, N. B.: Anesthesia of pigeons with CI-581 (ketamine) and pentobarbital. Laboratory Animal Care, 1 S/:500-502, 1969. 7. Burger, R. E., and Lorenz, F. W.: Artificial respiration in birds by unidirectional air flow. Poultry Science, 39:236-237, 1960 8. Callear, J. F. F.: Correspondence use of the hypnotic agent methoxymol (R7315) in birds of prey. Veterinary Rec., 88:242, 1971. 9. Church, L. E.: Combuthal as an anesthetic for baby chicks. Poultry Science, 36:788791, 1957. 10. Cooper, J. E.: Use of the hypnotic agent methoxymol in birds of prey. Veterin. Rec., 87:751-752, 1970. 11. Deli us, J. D.: Pentobarbital anesthesia in the herring and lesser blackbacked gull. J. Small Anim. Pract., 7:605-609, 1966. 12. Desforges, M. F., and Scott, H. A.: Use of anesthetics in the aylesbury domestic duck. Res. in Vet. Science, 12:596-598, 1971. 13. Djojosugito, A. M., Folkow, B., and Kovach, G. B.: The mechanism behind the rapid blood volume restoration after hemorrhage in birds. Acta Physiol. Scan d., 74:114122, 1968. 14. Friedburg, K. M.: Anesthesia of parakeets and canaries. J.A.V.M.A., 141:1157-1160, 1962. 15. Gandal, C. P.: Avian anesthesia. Federation Proc., 28:1533-1534, 1969. 16. Gandal, C. P.: Satisfactory general anesthesia in birds. J. Amer. Veterin. Assoc., 128:332-334, 1956. 17. Gerlach, H.: Surgical conditions in wild and pet birds. Veterin. Rec., 84:342, 1969. 18. Graham-Jones, 0.: Restraint and anesthesia of small cage birds. J. Small Anim. Prac., 6:31-39. 19. Graubard, D.]., and Peterson, M. C.: Clinical uses of intravenous procaine. Springfield, Illinois, Charles C Thomas, 1950. 20. Grono, L. R.: Anesthesia of budgerigars. Austral. Veter. J., 37:463-464, 1961. 21. .Jones·, R. S.: Halothane anesthesia in turkeys. Brit. .J. Anaesth., 38:656-658, 1966. 22 . .Jordan, F. T. W., Sanford,.J., and Wright, A.: Anesthesia in the fowl..J. Camp. Path., 70:437-449, 1960. 23. King, A. S., and Biggs, P. M.: General anesthesia in g. domesticus for non-survival laboratory experiments. Poultry Science, 36:490-495, 1957. 24. Kittle, E. L.: Ketamine HCI as an anesthetic for birds. Modern Veterinary Practice, 52:40-41, 1971. 25. Lee, C. C.: Experimental studies on the actions of several anesthetics in domestic fowls. Poultry Science, 32:624-627, 1953. 26. Mandelker, L.: Ketamine hydrochloride as an anesthetic for parakeets. Veterinary Medicine-Small Animal Clinician, 67:55-56, 1972. 27. Marley, E., and Payne, .J.P.: A method of anesthesia with halothane suitable for newborn animals. Brit. .J. Anaesth., 34:776-783, 1962. 28. McGinnis, C. H., Jr., and Ringer, R. K.: Carotid sinus reflex in the chicken. Poultry Science, 45:402-404, 1966. 29. Myers, R. E., and Stettner, L. .J.: Safe and reliable general anesthesia in birds. Physiol. and Behavior, 4:227-278, 1969. 30. Raises, M. B.: Anesthesia of cage birds. Austral. Veterin . .J., 43:594, 1967. 31. Sanford,.J.: Avian anesthesia. In Soma, L. R. (ed.): Veterinary Anesthesia. Baltimore, Williams and Wilkins, 1971, Ch. 25. 32. Sanger, V. L., and Smith, H. R.: General anesthesia in birds. J. Amer. Veterin. Assoc., 131:52-55, 1957. 33. Soma, L. R.: Systems and techniques for inhalation anesthesia. In Soma, L. R. (ed.): Veterinary Anesthesia. Baltimore, Williams and Wilkins, 1971, Ch. 17. 34. Whittow, G. C., and Ossorio, N.: A new technique for anesthestizing birds. Veterin. Rec., 73:134-142, 1961. School of Veterinary Medicine University of Pennsylvania 3800 Spruce Street Philadelphia, Pennsylvania 19174