Cardiopulmonary effects and recovery characteristics of horses anesthetized with xylazine-ketamine with midazolam or propofol.

OBJECTIVE: To evaluate cardiopulmonary and recovery characteristics of horses administered total intravenous anesthesia (TIVA) with xylazine and ketamine combined with midazolam or propofol.

STUDY DESIGN: Randomized crossover study.

ANIMALS: A group of eight adult horses, aged 7-22 years, weighing 493-740 kg.

METHODS: Horses were administered xylazine (1 mg kg-1 ) intravenously (IV), and anesthesia was induced with ketamine (2.2 mg kg-1 ) IV. Anesthesia was maintained for 45 minutes via IV infusion of xylazine (0.016 mg kg-1 minute-1 ) and ketamine (0.03 mg kg-1 minute-1 ) combined with midazolam at 0.002 mg kg-1 minute-1 (MKX), propofol at 0.05 mg kg-1 minute-1 (PKXlow ) or propofol at 0.1 mg kg-1 minute-1 (PKXhigh ). Additional ketamine was administered if a horse moved spontaneously. Cardiopulmonary variables, blood gases, lactate concentration, packed cell volume and total solids were recorded before sedation (baseline), at 10, 20, 30 and 45 minutes during TIVA and 10 minutes after standing. Recovery variables and quantitative recovery scores were compared. Significance was set at p < 0.05.

RESULTS: Additional ketamine was required for 50% of MKX horses. Systolic arterial pressure was elevated in MKX at 20 minutes compared with baseline (p = 0.043), at 10 and 20 minutes compared with PKXhigh (p = 0.007, p = 0.024) and at 20 and 30 minutes compared with PKXlow (p = 0.009, p = 0.02). MKX horses (5/8) were hypertensive compared with PKXlow (1/8; p = 0.017). All horses became hypoxemic (PaO2 ≤80 mmHg; 10.7 kPa) during TIVA. Recovery variables did not differ among treatments.

CONCLUSIONS AND CLINICAL RELEVANCE: PKXlow and PKXhigh had similar cardiopulmonary and recovery performance compared with MKX. PKX combinations provided superior quality of anesthesia to that of MKX. A combination of propofol, ketamine and xylazine administered as TIVA can be used in horses to provide anesthesia for short procedures. Supplemental oxygen is recommended.