Propofol anaesthesia for surgery in late gestation pony mares.

OBJECTIVE: To characterize propofol anaesthesia in pregnant ponies.

ANIMALS: Fourteen pony mares, at 256 ± 49 days gestation, undergoing abdominal surgery to implant fetal and maternal vascular catheters.

MATERIALS AND METHODS: Pre-anaesthetic medication with intravenous (IV) acepromazine (20 µg kg(-1)), butorphanol (20 µg kg(-1)) and detomidine (10 µg kg(-1)) was given 30 minutes before induction of anaesthesia with detomidine (10 µg kg(-1)) and ketamine (2 mg kg(-1)) IV Maternal arterial blood pressure was recorded (facial artery) throughout anaesthesia. Arterial blood gas values and plasma concentrations of glucose, lactate, cortisol and propofol were measured at 20-minute intervals. Anaesthesia was maintained with propofol infused initially at 200 µg kg(-1) minute(-1), and at 130-180 µg kg(-1) minute(-1) after 60 minutes, ventilation was controlled with oxygen and nitrous oxide to maintain PaCO2 between 5.0 and 6.0 kPa (37.6 and 45.1 mm Hg) and PaO2 between 13.3 and 20.0 kPa (100 and 150.4 mm Hg). During anaesthesia flunixin (1 mg kg(-1)), procaine penicillin (6 IU) and butorphanol 80 µg kg(-1) were given. Lactated Ringer's solution was infused at 10 mL kg(-1) hour(-1). Simultaneous fetal and maternal blood samples were withdrawn at 85-95 minutes. Recovery from anaesthesia was assisted.

RESULTS: Arterial blood gas values remained within intended limits. Plasma propofol levels stabilized after 20 minutes (range 3.5-9.1 µg kg(-1)); disposition estimates were clearance 6.13 ± 1.51 L minute(-1) (mean ± SD) and volume of distribution 117.1 ± 38.9 L (mean ± SD). Plasma cortisol increased from 193 ± 43 nmol L(-1) before anaesthesia to 421 ± 96 nmol L(-1) 60 minutes after anaesthesia. Surgical conditions were excellent. Fetal umbilical venous pH, PO2 and PCO2 were 7.35 ± 0.04, 6.5 ± 0.5 kPa (49 ± 4 mm Hg) and 6.9 ± 0.5 kPa (52 ± 4 mm Hg); fetal arterial pH, PO2 and PCO2 were 7.29 ± 0.06, 3.3 ± 0.8 kPa (25 ± 6 mm Hg) and 8.7 ± 0.9 kPa (65 ± 7 mm Hg), respectively. Recovery to standing occurred at 46 ± 17 minutes, and was generally smooth. Ponies regained normal behaviour patterns immediately.

CONCLUSIONS AND CLINICAL RELEVANCE: Propofol anaesthesia was smooth with satisfactory cardiovascular function in both mare and fetus; we believe this to be a suitable anaesthetic technique for pregnant ponies.