Abstract
ObjectiveTo evaluate the effects of midazolam and nitrous oxide (N2O) on the minimum anesthetic concentration of isoflurane (MACISO) in ball pythons. Study designProspective, crossover, randomized, semi-blinded study. AnimalsA total of nine healthy adult female ball pythons (Python regius) weighing 2.76 ± 0.73 kg. MethodsIn each snake, three protocols were evaluated with 2 week washouts: treatment MID–O2, midazolam (1 mg kg−1) administered intramuscularly (IM) and anesthesia induced with isoflurane–oxygen; treatment SAL–O2, saline (0.2 mL kg−1) IM and anesthesia with isoflurane–oxygen; and treatment SAL–N2O, saline IM and anesthesia with isoflurane and 50% nitrous oxide (N2O):50% oxygen. In each treatment, isoflurane was administered by face mask immediately after premedication. Snakes were endotracheally intubated and inspired and end-tidal isoflurane concentrations were monitored. The study design followed a standard bracketing technique, and the MACISO was determined using logistic regression. Electrical stimulation using a Grass stimulator connected to the base of the tail (50 V, 50 Hz, 6.5 ms pulse−1) was used as the supramaximal stimulus. Blood-gas analysis was performed on cardiac blood collected immediately following intubation and after the last stimulation. Blood-gas variables were compared over time and between treatments using linear mixed models. ResultsMACISO at a body temperature of 30.1 ± 0.4 °C was 1.11% (95% confidence interval, 0.94–1.28%) in SAL–O2 and was significantly decreased to 0.48% (0.29–0.67%) in MID–O2 (p < 0.001) and to 0.92% (0.74–1.09%) in SAL–N2O (p = 0.016). PO2 was significantly lower in MID–O2 and SAL–N2O than in SAL–O2. Conclusions and clinical relevanceMidazolam significantly decreased the MACISO by 57% in ball pythons, whereas addition of N2O resulted in a modest, although significant, decrease (17%). MACISO in ball pythons was lower than those previously reported in reptiles.
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