Raptor Sedation and Anesthesia

Sedation and/or anesthesia is routinely and successfully used in raptors for a wide variety of procedures from the routine such as physical examination, radiographs, or venipuncture, to the more complex, such as orthopedic surgeries. Understanding the anatomy and physiology of raptor patients who present for care, and being fully prepared before the start of any procedure, can increase the success of anesthetic procedures. Recent advances in raptor sedation and anesthesia continue to improve the health and welfare of these avian patients.

Backyard Poultry and Waterfowl Sedation and Anesthesia

The popularity of backyard poultry (chickens, turkey, guinea fowl) and waterfowl (ducks and geese) is increasing in the United States, and these animals frequently present for veterinary care. Like other birds, these species have unique anatomy that should be clinically considered before anesthesia. A balanced approach to an injectable, inhalational, or combination anesthesia protocol must be taken to ensure a safe outcome for the patient and to achieve the procedural needs. A well-informed clinician may use both sedation and general anesthesia to care for backyard bird patients in practice.

A comparison of the pharmacodynamic effects of intravenous ketamine-xylazine with alfaxalone in mute swans (Cygnus olor) presenting at a wildlife veterinary hospital

OBJECTIVE

To compare effects of intravenous (IV) alfaxalone with ketamine-xylazine combination on anaesthetic induction, recovery and cardiopulmonary variables in mute swans.

STUDY DESIGN

Randomized, controlled, clinical study.

ANIMALS

A group of 58 mute swans.

METHODS

Swans were given either alfaxalone (10 mg kg-1; group A) or a combination of ketamine (12.5 mg kg-1) and xylazine (0.28 mg kg-1) (group KX) IV. Heart and respiratory rates, end-tidal carbon dioxide and peripheral haemoglobin oxygen saturation were recorded at 5 minute intervals during anaesthesia. Time from anaesthetic induction to intubation, from cessation of isoflurane to extubation, to lifting head, sternal recumbency and absence of head/neck ataxia were recorded. Anaesthetic and recovery quality were scored (1 = very poor; 5 = excellent). Data are presented as median (interquartile range). Significance was set at p < 0.05.

RESULTS

In group A, 44% (12/27) of swans required mechanical ventilation for 2-14 minutes versus 3.2% (1/31) of swans in group KX (p = 0.0002). Heart rate was higher in group A than in group KX [146 (127-168) versus 65.5 (56-78) beats minute-1, respectively; p < 0.0001]. The isoflurane concentration required to maintain anaesthesia was higher in group A than in group KX [2.5% (2.0-3.0%) versus 1.5% (1.0-2.0%), respectively; p = 0.0001]. Time from cessation of isoflurane administration to lifting head was significantly longer in group A than in group KX [12 (9-17) versus 6 (4-7.75) minutes, respectively; p < 0.0001]. Anaesthesia quality scores were significantly better in group KX than in group A [4 (4-5) versus 4 (3-4), respectively; p = 0.0011], as were recovery scores [4 (3-5) versus 2 (2-3), respectively; p = 0.0005].

CONCLUSIONS AND CLINICAL RELEVANCE

Alfaxalone is a suitable anaesthetic induction agent for use in mute swans. There is a greater incidence of postinduction apnoea and a higher incidence of agitation on recovery with alfaxalone than with ketamine-xylazine.

ISOFLURANE RESPIRATORY ANESTHETIC INDEX IN CHICKENS (GALLUS GALLUS DOMESTICUS)

Respiratory depression from isoflurane seems to be greater in birds than in mammals. Isoflurane respiratory anesthetic index (AI) has only been evaluated in ducks (Anas platyrhynchos), which indeed showed a lower AI compared to mammals, but the isoflurane AI for other avian species is not known. The aim of this study was to evaluate the isoflurane AI in chickens (Gallus gallus domesticus). Six adult hens were anesthetized with isoflurane for determination of the minimum anesthetic concentration (MAC) using the bracketing method. During a second anesthetic event, the isoflurane AI was determined by progressively increasing the expired fraction of isoflurane by 0.5 times MAC until apnea was achieved (ET_iso-apnea). The isoflurane AI was considered the ratio between the ET_iso-apnea and the MAC. Heart rate, systolic arterial pressure, respiratory rate, and end-tidal carbon dioxide were continuously monitored throughout both anesthetic events. Data were analyzed using a mixed-effect model with Greenhouse-Geisser correction, followed by Tukey's test. The MAC for isoflurane was 1.18% ± 0.09% (mean ± SD). The ET_iso-apnea was 3.31% ± 0.34% and the isoflurane AI was 2.80 ± 0.26. In chickens, isoflurane AI is similar to that measured in mammals, which is in contrast with published data in other avian species.

Comparison of Dorsoventral Erect and Ventrodorsal Supine Radiographic Views for the Evaluation of Intracoelomic Organs in Clinically Normal African Grey Parrots (Psittacus erithacus)

Standard positioning for radiographic evaluation may require sedation and can be deleterious in critically ill birds. A prospective crossover study was performed in 15 clinically normal African grey parrots (Psittacus erithacus) to describe an alternative, unrestrained radiographic view. Whole-body radiographs were obtained in unrestrained dorsoventral erect (DVE) views and in anesthetized ventrodorsal supine (VDS) views. Visualization of various anatomic items in each view was scored by 3 observers. The surface area of the air sacs and the width of the heart, liver, thorax, and cardiohepatic waist were measured in DVE and VDS views. Measurements were obtained by 3 observers, and 1 observer repeated the measurements twice. Intraobserver and interobserver agreement were assessed. Major rotation of the coelom and superimposition of the limbs over the coelom were, respectively, observed in 4 of 15 (27%) and 15 of 15 (100%) of the DVE views and not observed in VDS views. The evaluation of the respiratory tract structures was considered limited in DVE views compared with VDS views, and the surface areas of the air sacs were significantly smaller. The proventriculus and ventriculus were more visible in the DVE view. The visualization of the heart was not significantly different between the 2 views. The absolute measures of heart, liver, and cardiohepatic waist width were significantly larger in the DVE view compared with the VDS view. Moderate intraobserver and interobserver agreement was observed in the evaluation of the 2 views. In conclusion, the DVE view could be adequate to assess the heart and the upper digestive tract. This positioning is likely to provide clinically relevant information for cases in which general anesthesia or dorsal recumbency is contraindicated.

Advancements in Evidence-Based Anesthesia of Exotic Animals

Anesthesia and sedation of pet nondomestic species are often necessary for both invasive and noninvasive procedures. Even minimally invasive procedures can be stressful for small prey species that are not domesticated or acclimated to human contact and restraint. Recent advancements in evidence-based practice will continue to improve the field based on scientifically sound best practices and rely less on anecdotal recommendations. This article focuses on new scientific literature that has been published in the past 5 years. For ease of reading, the authors divide the article to highlight advances in anesthetic pharmacology and discoveries in anesthetic physiology and monitoring.

Penguin lungs and air sacs: implications for baroprotection, oxygen stores and buoyancy

The anatomy and volume of the penguin respiratory system contribute significantly to pulmonary baroprotection, the body O2 store, buoyancy and hence the overall diving physiology of penguins. Therefore, three-dimensional reconstructions from computerized tomographic (CT) scans of live penguins were utilized to measure lung volumes, air sac volumes, tracheobronchial volumes and total body volumes at different inflation pressures in three species with different dive capacities [Adélie (Pygoscelis adeliae), king (Aptenodytes patagonicus) and emperor (A. forsteri) penguins]. Lung volumes scaled to body mass according to published avian allometrics. Air sac volumes at 30 cm H2O (2.94 kPa) inflation pressure, the assumed maximum volume possible prior to deep dives, were two to three times allometric air sac predictions and also two to three times previously determined end-of-dive total air volumes. Although it is unknown whether penguins inhale to such high volumes prior to dives, these values were supported by (a) body density/buoyancy calculations, (b) prior air volume measurements in free-diving ducks and (c) previous suggestions that penguins may exhale air prior to the final portions of deep dives. Based upon air capillary volumes, parabronchial volumes and tracheobronchial volumes estimated from the measured lung/airway volumes and the only available morphometry study of a penguin lung, the presumed maximum air sac volumes resulted in air sac volume to air capillary/parabronchial/tracheobronchial volume ratios that were not large enough to prevent barotrauma to the non-collapsing, rigid air capillaries during the deepest dives of all three species, and during many routine dives of king and emperor penguins. We conclude that volume reduction of airways and lung air spaces, via compression, constriction or blood engorgement, must occur to provide pulmonary baroprotection at depth. It is also possible that relative air capillary and parabronchial volumes are smaller in these deeper-diving species than in the spheniscid penguin of the morphometry study. If penguins do inhale to this maximum air sac volume prior to their deepest dives, the magnitude and distribution of the body O2 store would change considerably. In emperor penguins, total body O2 would increase by 75%, and the respiratory fraction would increase from 33% to 61%. We emphasize that the maximum pre-dive respiratory air volume is still unknown in penguins. However, even lesser increases in air sac volume prior to a dive would still significantly increase the O2 store. More refined evaluations of the respiratory O2 store and baroprotective mechanisms in penguins await further investigation of species-specific lung morphometry, start-of-dive air volumes and body buoyancy, and the possibility of air exhalation during dives.

Evaluation of thermal antinociceptive effects and pharmacokinetics after intramuscular administration of butorphanol tartrate to American kestrels (Falco sparverius)

OBJECTIVE

To evaluate antinociceptive effects and pharmacokinetics of butorphanol tartrate after IM administration to American kestrels (Falco sparverius).

ANIMALS

Fifteen 2- to 3-year-old American kestrels (6 males and 9 females).

PROCEDURES

Butorphanol (1, 3, and 6 mg/kg) and saline (0.9% NaCl) solution were administered IM to birds in a crossover experimental design. Agitation-sedation scores and foot withdrawal response to a thermal stimulus were determined 30 to 60 minutes before (baseline) and 0.5, 1.5, 3, and 6 hours after treatment. For the pharmacokinetic analysis, butorphanol (6 mg/kg, IM) was administered in the pectoral muscles of each of 12 birds.

RESULTS

In male kestrels, butorphanol did not significantly increase thermal thresholds for foot withdrawal, compared with results for saline solution administration. However, at 1.5 hours after administration of 6 mg of butorphanol/kg, the thermal threshold was significantly decreased, compared with the baseline value. Foot withdrawal threshold for female kestrels after butorphanol administration did not differ significantly from that after saline solution administration. However, compared with the baseline value, withdrawal threshold was significantly increased for 1 mg/kg at 0.5 and 6 hours, 3 mg/kg at 6 hours, and 6 mg/kg at 3 hours. There were no significant differences in mean sedation-agitation scores, except for males at 1.5 hours after administration of 6 mg/kg.

CONCLUSION AND CLINICAL RELEVANCE

Butorphanol did not cause thermal antinociception suggestive of analgesia in American kestrels. Sex-dependent responses were identified. Further studies are needed to evaluate the analgesic effects of butorphanol in raptors.