Cardiorespiratory Effects of Isoflurane Anesthesia in ...

Cardiorespiratory Effects of Isoflurane Anesthesia in Crested Caracaras (Caracara plancus) Author(s): André Escobar, D.V.M., Ph.D., Sc.M., Roberto Thiesen, D.V.M., Ph.D., Sc.M., Sérgio N. Vitaliano, D.V.M., M.Sc., Emílio A. Belmonte, D.V.M., M.Sc., Karin Werther, D.V.M., Ph.D., and Carlos A. A. Valadão, D.V.M., Ph.D. Source: Journal of Zoo and Wildlife Medicine, 42(1):12-17. 2011. Published By: American Association of Zoo Veterinarians DOI: 10.1638/2009-0055.1 URL: http://www.bioone.org/doi/full/10.1638/2009-0055.1

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Journal of Zoo and Wildlife Medicine 42(1): 12–17, 2011 Copyright 2011 by American Association of Zoo Veterinarians

CARDIORESPIRATORY EFFECTS OF ISOFLURANE ANESTHESIA IN CRESTED CARACARAS (CARACARA PLANCUS) Andre´ Escobar, D.V.M., Ph.D., Sc.M., Roberto Thiesen, D.V.M., Ph.D., Sc.M., Se´rgio N. Vitaliano, D.V.M., M.Sc., Emı´lio A. Belmonte, D.V.M., M.Sc., Karin Werther, D.V.M., Ph.D., and Carlos A. A. Valadaõ, D.V.M., Ph.D.

Abstract: To evaluate the cardiorespiratory changes induced by isoflurane (ISO) anesthesia in the crested caracara (Caracara plancus), eight crested caracaras that weighed 1.0 kg (range 0.9–1.1 kg) were the subjects for the study. The birds were anesthetized by face mask with ISO for brachial artery catheterization. After recovery, anesthesia was re-induced and maintained with ISO with spontaneous ventilation. Electrocardiography, direct systolic arterial blood pressure (SAP), diastolic arterial blood pressure (DAP), mean arterial blood pressure (MAP), respiratory rate (RR), end-tidal carbon dioxide (PETCO2), and cloacal temperature (TuC) were measured before induction (baseline, under physical restraint) and after 5, 10, 15, 20, 25, 30, 35, and 40 min of ISO anesthesia. Arterial blood samples were collected for blood gas analysis at baseline, 10, 25, and 40 min. No cardiac arrhythmias were observed in the present study. RR, SAP, DAP, MAP, TuC and pH decreased from baseline values, whereas arterial partial pressures of oxygen and carbon dioxide, bicarbonate concentration, and PETCO2 were significantly higher than baseline. Apnea was not observed in any bird. ISO anesthesia is suitable for use in healthy members of this species despite the moderate cardiovascular and respiratory depression produced. Key words: Acid–base, anesthesia, birds, cardiorespiratory, crested caracara, Caracara plancus, isoflurane.

cardiac parameters, including heart rate (HR) and blood flow velocities, are significantly decreased in ISO anesthetized common buzzards compared with awake animals.27 The only report that investigated inhalant anesthesia in crested caracara (Caracara plancus) described that sevoflurane is a suitable protocol, despite the moderate cardiovascular and respiratory depression produced.4 The respiratory depression caused by volatile anesthetics is one of the major concerns in spontaneously breathing avian patients. Inspiration and expiration is an active muscular process in avian species. The myorelaxation caused by inhalant anesthetics may potentiate the respiratory depression caused by these agents by weakening the respiratory muscles, thereby making ventilation less effective.12 Respiratory acidosis has been described in cranes, ducks, and pigeons after ISO anesthesia during spontaneous ventilation.10,11,29 In addition, ISO caused significant progressive respiratory depression over time in spontaneously ventilating bald eagles as indicated by increased carbon dioxide partial pressure (PaCO2) values associated with a decrease in pH.8 It has been described that the ISO respiratory anesthetic index for ducks is 1.65, whereas, in dogs, it is 2.51, and, in horse, it is 2.33, which suggests that ISO is a more potent respiratory depressant in birds.10 Although mechanical ventilation effectively ameliorates hypercapnia, there are concerns regarding the potential

INTRODUCTION Birds can be very sensitive to stress induced by handling.27 Chemical immobilization or general anesthesia is commonly used in avian patients for examination and for diagnostic and surgical procedures as well as for research.18,25 Inhalant anesthesia has been considered the safest technique in birds;7 and isoflurane (ISO), which has been used since 1985, is considered the most common agent in avian patients.6 Advantages of inhalant anesthetics over injectable anesthetics include rapid induction and recovery (especially when an agent with low blood-gas solubility is used), easy control of anesthetic depth, improved oxygenation (concurrent administration of oxygen [O2]), recovery independent of systemic metabolic pathways, and reduced myocardial depression.6,15 In bald eagles (Haliaeetus leucocephalus), both ISO and sevoflurane anesthesia resulted in rapid induction and recovery, however, a high incidence of ISO-induced cardiovascular adverse effects occurred in this species.8 Doppler-derived From the Department of Veterinary Clinics and Surgery (Escobar, Thiesen, Belmonte, Valadaõ) and Veterinary Pathology (Vitaliano, Werther), Faculdade de Cieˆncias Agra´rias e Veterina´rias, Saõ Paulo State University, Via de acesso. Professor Paulo Donato Castelane, s/n, Jaboticabal, SP, 14884-900 Brazil. Correspondence should be directed to Dr. Escobar ([email protected]).

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ESCOBAR ET AL.—ISOFLURANE ANESTHESIA IN CRESTED CARACARA

detrimental effects on the cardiovascular system in birds.29 It is well known that different avian species have specific cardiorespiratory response changes to inhalant anesthetics. In addition, there are no reports of ISO anesthesia in the crested caracara. The purpose of this study was to evaluate the cardiorespiratory changes in crested caracara anesthetized with ISO during spontaneous ventilation. MATERIALS AND METHODS Animals Eight crested caracaras (Caracara plancus) that weighed 1.0 6 0.1 kg (mean 6 standard deviation [SD]) were used in this study. The animals had previously been sent to the Veterinary Hospital of Saõ Paulo State University, in Jaboticabal, where appropriate medical care was provided for various problems, including severe burns, fractured limbs, and metabolic and infectious diseases. All the birds used in this study were assessed as unreleaseable after veterinary treatment. After treatment and rehabilitation, healthy animals were selected for the current study. The birds were judged to be in good health based on a physical examination and hematologic evaluation. This study was authorized by the Instituto Brasileiro do Meio Ambiente e dos Recursos Naturais Renova´veis and was approved by the animal care committee of the authors’ institution. The animals were housed in individual cages, and water was provided ad libitum. The caracaras were fed with whole prey once a day, six times per week. Study preparation Food was withheld for 24 hr before administration of anesthetic drug. This study was undertaken by using the same methods previously described by Escobar et al.4 After 24 hr of fasting, the animals were induced with general anesthesia by using a modified mask with 5% ISO (Isothane, Zeneca, Cotia, Saõ Paulo 06707000, Brazil) in O2 at 3 L/min. Anesthetic concentrations that provided immobility and unconsciousness in most patients were chosen based on pilot studies. An anesthetic gas monitor (Dixtal 2010, Dixtal, Manaus, Amazonas 69077000, Brazil) was used to maintain a 2.5% endtidal ISO concentration, which was sufficient to anesthetize all the birds for instrumentation. The right or the left brachial artery was clipped and sterilely prepared, then cannulated with a 24-

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gauge over-the-needle catheter (BD Angiocath, BD – Brazil, Saõ Paulo, Saõ Paulo 04717-004, Brazil) through a small cutdown. The surgical wound and the catheter were sutured, and the animals were allowed to recover under physical restraint to avoid catheter removal. One hour was allowed for the re-establishment of physiological and physical parameters (HR, RR, temperature, vocalizations, leg movements, head and neck elevations, and wing flapping). Anesthesia and monitoring The birds were positioned in dorsal recumbency for collection of baseline data. A pressure transducer (Dixtal 2010, Dixtal, Manaus, Amazonas 69077-000, Brazil) was connected to the arterial catheter to record the systolic arterial blood pressure (SAP), diastolic arterial blood pressure (DAP), and mean arterial blood pressure (MAP). Arterial blood samples were collected from the catheter for blood gases and acid–base analysis (Omni C, Roche Diagnostics, Saõ Paulo, Saõ Paulo 05321-900, Brazil). Alligator clip electrocardiogram electrodes (ECGPC, TEB, Saõ Paulo, Saõ Paulo 04310-000, Brazil) were attached to the skin at the base of the right and left wings and each medial thigh region of the patient for measurement of the heart rhythm and HR by using the R-R interval. Lead II was used for measurement of R-R intervals. A tight-fitting face mask with a side stream sampling line connected to the anesthetic gas monitor was used to measure the baseline end-tidal carbon dioxide (PETCO2). Anesthesia was induced with 5% ISO in O2 at 3 L/min via face mask. The birds were induced by using the same technique described for instrumentation. Each bird was intubated with a 3-mm noncuffed endotracheal tube, and anesthesia was maintained at 2.5% end-tidal ISO concentration, with an O2 flow of 3 L/min, by using an Ayre’s Tpiece nonrebreathing circuit (JacksonRees/Baraka, J. G. Moriya, Saõ Paulo, Saõ Paulo 04225050, Brazil). The caracaras were positioned in dorsal recumbency. A minimum of 10 min was allowed for acclimation to the set inhalant concentration, and the birds were allowed to breathe spontaneously. The body temperature (TuC) was measured with the aid of an electronic probe inserted into the cloaca (Dixtal 2010, Dixtal, Manaus, Amazonas 69077-000, Brazil). A circulating water blanket (T-Pump, Gaymar, Saõ Paulo, Saõ Paulo 04616-005, Brazil) and a heat lamp were used to maintain temperature values between 39.5uC and 40.5uC.

a HR, heart rate; RR, respiratory rate; SAP, systolic arterial pressure; DAP, diastolic arterial pressure; MAP, mean arterial pressure; PETCO2, end-tidal carbon dioxide; T, body temperature. b Significantly different from baseline values (P , 0.05).

6 6 6 6 6 6 6 251 18 126 102 115 35 38.3 252 19 128 102 117 28 39

6 6 6 6 6 6 6

100 6b 26b 25b 25b 6 0.7b

250 18 129 102 116 32 38.9

6 6 6 6 6 6 6

106 7b 30b 27b 27b 8 0.7b

262 18 133 106 120 32 38.7

6 6 6 6 6 6 6

102 4b 33b 28b 30b 7 0.6b

252 17 128 104 117 32 38.6

6 6 6 6 6 6 6

94 4b 26b 26b 26b 6 0.6b

251 17 125 101 114 33 38.6

6 6 6 6 6 6 6

92 256 5b 18 29b 129 29b 102 29b 118 6 36 0.7b 38.4

6 6 6 6 6 6 6

91 6b 34b 32b 30b 8b 0.8b

251 18 125 102 114 33 38.4

6 6 6 6 6 6 6

86 5b 30b 25b 27b 7 0.9b

T40 T35 T30 T25 T20 T15

87 27 22 21 21 5 0.6 6 6 6 6 6 6 6 274 48 226 180 198 26 40

ISO produced a not statistically significant decrease in HR at all time points (Table 1), but no birds developed cardiac arrhythmias. Baseline MAP values (198 6 21 mm Hg) decreased 42% compared with T40 (115 6 26 mm Hg), and SAP, MAP, and DAP were significantly decreased over baseline during the whole anesthesia period (Table 1). Although none of the caracaras experienced apnea, the RR decreased 60% over baseline after induction at T5 (19 breaths/min) (Table 1). The PETCO2 increased at all time points (Table 1), but it was only significant at T30 (36 mm Hg) compared with baseline (26 mm Hg). In addition, the PaCO2 values increased to 41 6 5 mm Hg at T10 and to 46 6 6 mm Hg at T40 when compared with awake values (25 6 6 mm Hg),

HR (beats/min.) RR (breaths/min) SAP (mm Hg) DAP (mm Hg) MAP (mm Hg) PETCO2 (mm Hg) T (uC)

RESULTS

T10

The data were analyzed for normality by Kolmogorov–Smirnov test and are expressed as the mean 6 SD. The variables were considered normally distributed and were compared with baseline by one-way repeated measures analysis of variance followed by the Student–Newman– Keuls test. The significance level of all tests was set at 5% (P , 0.05).

T5

Data analysis

T0

All the baseline values (T0) were recorded before induction under physical restraint. The respiratory rate (RR), HR, SAP, DAP, MAP, PETCO2 and TuC were measured at T0, 5 (T5), 10 (T10), 15 (T15), 20 (T20), 25 (T25), 30 (T30), 35 (T35), and 40 (T40) min after the acclimation period. A heparinized syringe was used to collect 0.5 mL of arterial blood at T0, T10, T25, and T40 for immediate measurement of blood-gas values, which were corrected for body temperature by using a standard mammalian correction factors. Arterial blood gas and acid-base variables measured included pH, O2 partial pressure (PaO2) and PaCO2. Calculated results included bicarbonate (HCO3) and base excess (BE). After T40, the catheter was removed, the artery was tied, and the skin was sutured. The ISO vaporizer was turned off, and the animals were allowed to breath 100% O2 until extubation. Extubation was performed when the presence of the endotracheal tube elicited a swallowing or cough response. Each bird received 30 mg enrofloxacin (Flotril 10%, Schering-Plough, Cotia, Saõ Paulo 06714-050, Brazil) intramuscularly as prophylaxis against bacterial infections.

83 4b 28b 25b 26b 7 0.9b

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Table 1. Mean 6 standard deviations of changes in temperature, cardiovascular, and respiratory parameters before induction (T0) and at 5 (T5), 10 (T10), 15 (T15), 20 (T20), 25 (T25), 30 (T30), 35 (T35) and 40 (T40) minutes following isoflurane anesthesia with spontaneous ventilation.a

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Table 2. Mean 6 standard deviations of changes in arterial blood gas and acid–base balance before induction (T0) and at 10 (T10), 25 (T25), and 40 (T40) minutes following isoflurane anesthesia with spontaneous ventilation.

pH PaO2 (mm Hg) PaCO2 (mm Hg) HCO3 (mmol/L) BE (mmol/L)

T0

T10

T25

T40

7.54 6 0.08 99 6 9 25 6 6 19 6 3 21.6

7.38 6 0.04b 392 6 42b 41 6 5b 23 6 2b 21.3

7.36 6 0.04b 393 6 18b 44 6 6b 24 6 2b 21.4

7.34 6 0.04b 398 6 30b 46 6 6b 24 6 2b 21.6

a PaO2, arterial oxygen partial pressure; PaCO2, arterial carbon dioxide partial pressure; HCO3, calculated bicarbonate concentration; BE, calculated base excess. b Significantly different from baseline values (P , 0.05).

whereas the pH significantly decreased at all time points during the study (Table 2). An increase in PaO2 appropriate for the fraction of inspired O2 (FiO2) was recorded after induction during the whole study (Table 2). As expected in hypoventilated birds, ISO administration caused a compensatory significant increase in HCO3 during the anesthesia (Table 2). The mean BE values at T0 and T40 were the same, and no significant changes were recorded during the procedure (Table 2). Despite attempts to prevent a decrease in body temperature, there was a significant decrease in TuC over the course of the experiment (Table 1). DISCUSSION When considering the description of cardiac adverse effects of ISO in raptors, such as tachycardia, hypertension, and arrythmias,8 this agent was considered a reasonable option to anesthetize crested caracaras because of apparent cardiorespiratory stability. In addition, similar cardiorespiratory changes to a previous sevoflurane study in crested caracaras were found.4 Despite the fact that minimum alveolar concentration is not an appropriate index of potency for inhalation anesthetics in birds, a similar index, the minimum anesthetic concentration has been used by several research groups to determine anesthetic dose.15,16,21 The minimum anesthetic concentration for ISO in ducks is 1.3%12 and for captive thick-billed parrots (Rhynchopsitta pachyrhyncha) is 1.07%.14 A 3.5% and a 2–3% ISO clinical concentration had been reported in bald eagles and common buzzards (Buteo buteo), respectively.8,28 After pilot studies, a 2.5% end-tidal ISO concentration was considered adequate for anesthetic maintenance in the crested caracara. Many avian anesthesia studies have been conducted without the measurement of awake cardiovascular parameters.8,15,17,19,29 Birds can be

very sensitive to the stress induced by handling,27 however, the comparison between awake and anesthetized values is vital to determine the significance of the adverse effects caused by the anesthetic. Although HR values of this current study are similar to other birds at rest,13 it is possible that all baseline data differed from values encountered in unrestrained caracaras. In this study, the HR had a minor decrease and the arterial blood pressures were significantly lower during anesthesia compared with awake values. A slight increase in HR and moderate hypotension (37.5% decrease in MAP) was described in crested caracaras during sevoflurane anesthesia.4 Although awake values were not described, ISO anesthesia did not cause a significant change in the arterial blood pressures of spontaneously ventilating anesthetized hispaniolan amazon parrots (Amazona ventralis). The same study described that a decrease in HR was noted only after 45 min of anesthesia.19 As reported in mammals,26 a decrease in systemic vascular resistance caused by inhalant anesthetics seems to be the most probable cause of the hypotension observed in the current study. In bald eagles, 3.5% end-tidal ISO anesthesia is associated with a decrease in HR and cardiac arrhythmias, such as second-degree atrioventricular block, probably because of an increase in vagal tone.8 No cardiac arrhythmias were noted in this study. This observation has also been noted in this species when anesthetized by using sevoflurane.4 Premature ventricular contractions have been described in ISO-anesthetized ducks, however, the arrhythmias resolved when the ISO concentration was reduced,10 which might suggest that higher anesthetic concentrations can more easily induce arrhythmias in birds. ISO is reported to cause respiratory depression in different bird species during spontaneous ventilation.10,11,22,29 Just as is observed in mammals, inhalant anesthetics can depress the venti-

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JOURNAL OF ZOO AND WILDLIFE MEDICINE

latory response to hypercapnia because of a depression in central PaCO2 chemoreceptors and peripheral extrapulmonary O2 -sensitive chemoreceptors.6 Species-specific characteristics that make birds more sensitive to inhalant-induced respiratory depression include the absence of diaphragm,9 restriction of sternum excursions by dorsal recumbency,5 and decreased responsiveness of intrapulmonary chemoreceptors to CO2 caused by inhalant anesthetics.20 In the present study, ISO caused respiratory depression indicated by the increase in PaCO2, and decrease in RR and pH. Normal arterial pH in awake birds ranges between 7.4 and 7.6.21 In mammals, a pH below 7.2 is associated with depression of the central nervous system,3 organ damage, and failure in the activity of some enzymes, which affects the animal’s metabolism.24 Arterial pH significantly decreased (P , 0.001) during ISO anesthesia in the present study. Although the values were still within an acceptable range, a slight respiratory acidosis compared with the data described for sevoflurane anesthesia in the same species was observed.4 Similarly, spontaneously ventilating bald eagles developed respiratory acidosis during ISO anesthesia.8 Hypoventilation has been described in ducks anesthetized with ISO when FiO2 . 40%.23 PaO2 values measured in the current study were considered normal given the FiO2 of 100%. The FiO2 may have depressed the activity of the O2-sensitive chemoreceptors, further contributing to the reduced ventilatory drive. Supplemental heat is often indicated during anesthesia, especially in avian patients who have a high ratio of body surface area to body volume2 and thus a substantial decrease in body temperature over time.1 Body temperature decreased over time even though a circulating warmwater blanket and a heat lamp were used. Decrease in body temperature has been described in different avian species during ISO anesthesia,8,14 and in the crested caracara during sevoflurane anesthesia.4 ISO anesthesia resulted in minor effects on the respiratory and cardiovascular system. In spontaneously breathing crested caracara, this agent was considered a suitable anesthesia protocol, however, careful ventilatory assistance is recommended in this species. Acknowledgment: The authors thank the Conselho Nacional de Desenvolvimento Cientı´fico e Tecnolo ´ gico – CNPq for funding the authors’ scholarship.

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23. Seaman G. C, J. W. Ludders, H. N. Erb, and R. D. Gleed. 1994. Effect of low and high fractions of inspired oxygen on ventilation in ducks anesthetized with isoflurane. Am. J. Vet. Res. 55: 395–398. 24. Sherwood L. 1997. Fluid and acid-base balance. In: Sherwood, L. Human Physiology: From Cells to Systems, 3rd ed. Wadsworth Publishing Co., Belmont, California. Pp. 515–545. 25. Sinn L. C. 1994. Anesthesiology. In: Ritchie B. W, G. J. Harrison, and L. R. Harrison (eds.). Avian Medicine: Principles and Application, 1st ed. Wingers Publishing Inc., Lake Worth, Florida. Pp. 1066–1080. 26. Souza A. P, P. N. H. Guerrero, C. T. Nishimori, D. P. Paula, P. S. Santos, M. L. de Rezende, and N. Nunes. 2005. Cardiopulmonary and acid-base effects of desflurane and sevoflurane in spontaneously breathing cats. J. Fel. Med. Surg. 7: 95–100. 27. Straub J, N. Forbes, M. Pees, and M.-E. Krautwald-Junghanns. 2003. Effect of handling-induced stress on the results of spectral Doppler echocardiography in falcons. Res. Vet. Sci. 74: 119–122. 28. Straub, J., N. A. Forbes, J. Thielebein, M. Pees, and M. E. Krautwald-Junghanns. 2003. The effects of isoflurane anaesthesia on some Doppler-derived cardiac parameters in the common buzzard (Buteo buteo). Vet. J. 166: 273–276. 29. Touzot-Jourde G, S. J. Hernandez-Divers, and C. M. Trim. 2005. Cardiopulmonary effects of controlled versus spontaneous ventilation in pigeons anesthetized for coelioscopy. J. Am. Vet. Med. Assoc. 227: 1424–1428.

Received for publication 10 March 2009