Effects of intravenous butorphanol on cardiopulmonary function in isoflurane-anesthetized alpacas

To determine the effects of intravenous (IV) butorphanol on the cardiopulmonary system and on the bispectral index (BIS) in isoflurane-anesthetized alpacas.

Randomized, blinded cross-over experimental trial.

Eight healthy, young (3 +/- 1 SD years) adult female alpacas weighing 64 +/- 9 SD kg.

Alpacas were anesthetized with isoflurane by mask followed by tracheal intubation and maintenance of anesthesia with isoflurane in oxygen and intermittent positive pressure ventilation. Animals were assigned to two treatments, butorphanol (0.1 mg kg(-1), IV) and saline (0.01 mL kg(-1), IV) in a randomized manner allowing a 2-week interval between treatments. Cardiovascular variables included systolic, diastolic, and mean arterial blood pressure, heart rate, pulmonary arterial pressure, pulmonary arterial occlusion pressure (PAOP), central venous pressure, cardiac output, and pulmonary temperature (TEMP). Cardiac index, systemic vascular resistance (SVR), and pulmonary vascular resistance (PVR) were calculated. Bispectral index was also measured. Arterial and mixed venous blood samples were collected for blood gas analysis. All variables were recorded at baseline (time 0) and at 5, 10, 15, 30, 45 and 60 minutes following injection and were analyzed by using repeated-measures ANOVA (p < 0.05). PAOP, PVR, and BIS were analyzed by paired t-tests.

Butorphanol decreased SVR at all times when compared with the baseline, but no difference was detected between treatments. TEMP decreased with time in both treatments, but they were not different from each other. Other cardiovascular, BIS, and blood gas variables were not different between groups.

We conclude that butorphanol had minimal effects on the cardiovascular system of the alpacas, causing a mild decrease in SVR.