Inconsistency of allometric scaling for dissociative anesthesia of wild felids

Abstract

Objective: To evaluate allometric scaling for ketamine-xylazine (KX) anesthesia in wild felids using domestic cats for reference.

Study design: Prospective single-phase non-blinded study.

Animals: Six domestic cats and 13 wild felids (five Leopardus pardalis, five Puma concolor, one Panthera onca and two Panthera leo).

Methods: Six domestic cats (4.1 ± 0.8 kg, REF1) were anesthetized by intramuscular administration of ketamine (15 mg kg(-1) ) and xylazine (1 mg kg(-1) ). Wild cats were divided into three groups based on body weight: 12.9 ± 2.4 kg (G1; n = 7), 43.0 ± 15.7 kg (G2; n = 4) and 126.0 ± 7.8 kg (G3; n = 2). Ketamine and xylazine doses were calculated based on allometric scaling of the basal metabolic rate (BMR = 70 × body mass(0.75) ). Afterwards, the six domestic cats were administered mean KX doses calculated for G1 and G2 (REF2). The heart rate, systolic arterial pressure, respiratory frequency, pH, the venous partial pressure of carbon dioxide, bicarbonate and lactate concentrations were recorded for up to 60 minutes.

Results: Additional doses were required in 12 out of the 13 wild cats. Anesthesia was not achieved in G3. Latency periods in wild felids were longer than REF1 and REF2. Anesthesia duration in REF1 was longer than that in the other groups. Recovery from anesthesia in REF1 and REF2 was longer than G1 and G2. Physiological variables remained within the range limits for the species. G1 baseline lactate concentration was higher than in the other groups.

Conclusion and clinical relevance: KX anesthesia established by allometric scaling of BMR from doses administered to domestic cats did not predict reliable anesthetic doses for wild cats. Dose rates calculated with this method must not be applied to these species.

Keywords: allometric scaling; dissociative anesthesia; ketamine; metabolic rate; xylazine.