Abstract

The specific aims of this study were to define the induction and constant rate infusion dosages and the cardiopulmonary effects of the intravenous anesthetic agent propofol (PropoFlo, Abbott Labs, North Chicago, IL 60064 USA) in red-tailed hawks (Buteo jamaicensis). Adult, gender unknown, red-tailed hawks (n = 6) were utilized for both phases of the study. The birds were assessed as healthy based upon findings from physical examination, hematology and plasma biochemistry values, and fecal examinations for parasites.

The goal of phase one of the study was to define the appropriate constant rate infusion of propofol for a light plane of anesthesia. A 24-ga 19-mm venous catheter (Insyte, Becton-Dickinson Infusion Therapy Systems, Inc. Sandy, UT 84070 USA) was placed in the medial metatarsal vein and 0.2 mg/kg/min propofol was given intravenously as a constant rate infusion for 30 min. Palpebral reflex, beak tone, glottal reflex to attempted intubation, toe pinch, and feather pluck were assessed at the end of this period. The infusion rate was increased 0.05 mg/kg/min every 15 min until response to all stimuli was negative. All birds were intubated once the glottal reflex was negative and were provided 100% oxygen. Heart rate and respiratory rate were monitored at each interval throughout the anesthetic period. Esophageal temperature and end tidal carbon dioxide (ETCO₂) were monitored at the same time intervals once instrumentation was possible. The infusion rate at which the response to the stimuli was negative was recorded as the appropriate constant rate infusion for the individual bird. Recovery times from the end of the infusion to extubation, standing, and standing without ataxia were recorded.

The goals of phase two of the study were to define the appropriate induction dosage for intubation and to assess the cardiopulmonary effects of propofol at the constant rate infusion defined in phase one. A minimum of 2 wk was allowed between phases of the study. Each bird was anesthetized with Sevoflurane (Sevoflo, Abbott Labs, North Chicago, IL 60064 USA) in 95-100% oxygen via mask induction and maintained using a non-cuffed endotracheal tube for instrumentation. The median ulnar artery was identified, surgically prepared, cannulated with a 23.5-ga 3-cm arterial catheter (Cook Veterinary Products, Queensland 4113, Australia) and secured with suture. The right carotid artery was cannulated in one bird. A 24-ga 19-mm catheter was placed in the medial metatarsal vein and secured with suture. Once instrumentation was complete, sevoflurane anesthesia was discontinued and the birds allowed to recover for 1 hr. Each bird was then induced with 1 mg/kg/min propofol intravenously until the animal lost its righting reflex and did not move spontaneously. Birds were then intubated and provided 100% oxygen. The appropriate constant rate infusion determined for individual birds in phase one of the study began 2 min after completion of the induction dose of propofol and was given for a total of 30 min. Systolic, diastolic, and mean arterial pressure, oxygen saturation (sPO₂), heart rate, and respiratory rate were measured in awake birds at 0, 5, 10, 15, 20, 25 and 30 min after induction and 5 min after completion of the constant rate infusion. ETCO₂ and esophageal temperature were measured at the same time intervals once the bird was induced. Arterial oxygen (PaO2) and carbon dioxide (PaCO₂) tensions, arterial pH, bicarbonate (HCO₃), and base excess were obtained in awake birds and at 0, 5, 10, 15, and 30 min after induction and 5 min after completion of the propofol infusion. Recovery times were recorded in the same manner as in phase one of the study. Statistical analysis was performed using analysis of variance and covariance with repeated measures (BMDP Statistical Software, Inc., Los Angeles, CA 90025 USA).

Results from phase one of the study found that the average constant rate infusion of propofol necessary to maintain a light plane of anesthesia for these six red-tailed hawks was 0.48 ± 0.06 (mean ± SD) mg/kg/min. Results from phase two found that the average induction dosage of propofol necessary for intubation was 3.81 ± 0.92 (mean ± SD) mg/kg. Significant elevations (P < 0.05) in PaCO₂, PaO₂, HCO₃, and ETCO₂ as well as a significant decrease in arterial pH were detected during the phase two anesthetic period when compared to measurements in awake animals. The recovery times from the end of infusion to extubation, standing, and standing without ataxia for both phases of the study are shown in Table 1. Clinical signs of central nervous system excitement such as head twitching, myoclonic activity, and opisthotonos were observed in 5/6 red-tailed hawks in phase one and 3/6 birds in phase two during the recovery period. All other measured values did not differ significantly over the anesthetic period.

Based upon the results of this study, we believe that while a constant rate infusion of propofol will allow for a light plane of anesthesia in red-tailed hawks, respiratory monitoring and ventilatory support are recommended and prolonged recovery periods may be anticipated.

Table 1. Recovery times (mean ± SD) for propofol anesthesia in red-tailed hawks (n = 6).

Acknowledgments

We would like to thank the Center for Companion Animal Health, School of Veterinary Medicine, University of California, Davis for financial support of this study.