Comparison of arterial blood pressure and quality of induction and recovery in horses anesthetized with diazepam or guaifenesin co-induction combined with xylazine and ketamine and maintained on isoflurane.

The objective of this prospective alternating crossover study was to compare quality of induction and recovery and cardiopulmonary function in horses administered guaifenesin or diazepam as co-induction drugs. Six healthy horses were anesthetized twice to undergo an MRI and surgical biopsies, with 5 wk between treatments. Horses were sedated intravenously (IV) with xylazine, 0.6 mg/kg BW, and IV induction started 4 min later. Group G received guaifenesin, 100 mg/kg BW, over 2 min and ketamine, 2 mg/kg BW, within 1 to 2 min of starting the guaifenesin. Group D received diazepam, 0.1 mg/kg BW, within 5 s and ketamine, 2 mg/kg BW, 0.5 to 1 min after and the quality of induction assessed. Horses were positioned on an MRI-compatible table, the trachea intubated, allowed to breathe spontaneously for the initial 10 min, then connected to a rebreathing circuit and anesthetic machine and mechanically ventilated under anesthesia [end-tidal isoflurane (FE'Isoflurane): 1.3 to 1.5%] during the MRI. Direct arterial blood pressure, heart rate, end-tidal CO2 (PE'CO2) and FE'Isoflurane were recorded at 10, 20, 30, and 40 min post-induction. Requirements for dobutamine and/or phenylephrine for arterial blood pressure support were recorded. A 2-way analysis of variance (ANOVA) was used to compare arterial blood pressure and a Wilcoxon matched-pairs signed rank test for comparing sedation, induction, and recovery scores (significance was set at P < 0.05). Arterial pressures were not significantly different between groups; however, systolic (P = 0.004), diastolic (P < 0.0001), and mean (P = 0.004) arterial pressures decreased significantly at 20, 30, and 40 min in Group D. Dose of dobutamine and/or phenylephrine was similar between groups. Sedation, induction, and recovery scores were similar. Induction scores were good to excellent [both groups: 0.5 (0, 2); median (range)]. In conclusion, guaifenesin and diazepam at the doses used in this study produced similar effects on arterial blood pressure and on the quality of induction and recovery.