LAUSR

OBJECTIVE To evaluate perioperative stress-related hormones in isoflurane-anesthetized horses administered infusions of dexmedetomidine alone or with butorphanol or remifentanil, compared with ketamine-morphine. STUDY DESIGN Randomized, prospective, nonblinded clinical study. ANIMALS A total of 51 horses undergoing elective surgical procedures. METHODS Horses were premedicated with xylazine, anesthesia induced with ketamine-diazepam and maintained with isoflurane and one of four intravenous infusions. Partial intravenous anesthesia (PIVA) was achieved with dexmedetomidine (1.0 μg kg-1 hour-1; group D; 12 horses); dexmedetomidine (1.0 μg kg-1 hour-1) and butorphanol bolus (0.05 mg kg-1; group DB; 13 horses); dexmedetomidine (1.0 μg kg-1 hour-1) and remifentanil (3.0 μg kg-1 hour-1; group DR; 13 horses); or ketamine (0.6 mg kg-1 hour-1) and morphine (0.15 mg kg-1, 0.1 mg kg-1 hour-1; group KM; 13 horses). Infusions were started postinduction; butorphanol bolus was administered 10 minutes before starting surgery. Blood was collected before drugs were administered (baseline), 10 minutes after ketamine-diazepam, every 30 minutes during surgery and 1 hour after standing. Mean arterial pressure (MAP), pulse rate, end-tidal isoflurane concentration, cortisol, nonesterified fatty acids (NEFA), glucose and insulin concentrations were compared using linear mixed models. Significance was assumed when p < 0.05. RESULTS Within D, cortisol was lower at 120-180 minutes from starting surgery compared with baseline. Cortisol was higher in KM than in D at 60 minutes from starting surgery. Within all groups, glucose was higher postinduction (except DR) and 60 minutes from starting surgery, and insulin was lower during anesthesia and higher after standing compared with baseline. After standing, NEFA were higher in KM than in DB. In KM, MAP increased at 40-60 minutes from starting surgery compared with 30 minutes postinduction. CONCLUSIONS AND CLINICAL RELEVANCE Dexmedetomidine suppressed cortisol release more than dexmedetomidine-opioid and ketamine-morphine infusions. Ketamine-morphine PIVA might increase catecholamine activity.