Effects of ketamine on the minimum anesthetic concentration of isoflurane in chickens (Gallus gallus domesticus).

OBJECTIVE

To assess the effects of two continuous intravenous (IV) infusion dose rates of ketamine on the minimum anesthetic concentration (MAC) of isoflurane in chickens.

STUDY

DESIGN

Prospective, randomized, blinded, experimental crossover design.

ANIMALS: A group of eight adult ISA Brown hens weighing 2.1 ± 0.19 kg.

METHODS

Anesthesia was induced and maintained with isoflurane in oxygen and chickens were mechanically ventilated. Body temperature and partial pressure of end-expired carbon dioxide were maintained between 40 and 41 °C and 30 and 40 mmHg (4-5.3 kPa). Isoflurane MAC was determined using electrical stimulation and the bracketing technique. Subsequently, a bolus of low (LD) or high (HD) dose ketamine (5 or 10 mg kg-1 IV) was injected into the brachial vein followed by a constant rate IV infusion (5 or 10 mg kg-1 hour-1, respectively), with a 1 week washout period between treatments. Isoflurane MAC was determined again approximately 1.5 (T1.5) and 3 hours (T3) after bolus injections. Adverse events and time to extubation were recorded. Data analyses consisted of a mixed-effects model for repeated measures (MAC data).

RESULTS

Isoflurane MAC was 1.51 ± 0.18% (mean ± standard deviation). Isoflurane MAC at T1.5 and T3 was 1.45 ± 0.16% and 1.53 ± 0.15% (LD) and 1.42 ± 0.24% and 1.46 ± 0.23% (HD). Isoflurane MAC values during LD [(T1.5) p = 0.857 and (T3) p = 0.995] and HD [(T1.5) p = 0.797 and (T3) p = 0.974] ketamine infusion were not different from baseline. Extubation times after isoflurane discontinuation was 12 ± 9 minutes for the LD and 14 ± 5 minutes for the HD treatment. Overall, four animals (both treatments) developed an obstructive mucous plug in the endotracheal tube.

CONCLUSIONS AND CLINICAL RELEVANCE: Ketamine did not change isoflurane MAC in chickens. Chickens anesthetized with isoflurane and ketamine should be monitored for endotracheal tube obstruction.