Real time monitoring of propofol blood concentration in ponies anaesthetized with propofol and ketamine

Abstract

This study examined the pharmacokinetics of propofol by infusion in ponies using an analyser for the rapid measurement of propofol concentrations. The analyser (Pelorus 1000; Sphere Medical Ltd., Cambridge, UK) has a measurement cycle of approximately five minutes. Ten Welsh-cross ponies (weighing 135-300 kg) undergoing minor procedures were studied after premedication with acepromazine 0.03 mg/kg and detomidine 0.015 mg/kg. Anaesthesia was induced with ketamine 2 mg/kg and diazepam 0.03 mg/kg, and maintained with an infusion of propofol at an initial rate of 0.16 mg/kg/min for the first thirty minutes, after a bolus of 0.3 mg/kg; and ketamine by infusion (20-40 μg/kg/min). Blood samples (<2 mL) were collected prior to, during and after the infusion, and on assuming standing position. Anaesthesia was uneventful; with the duration of infusion 31-89 min. Blood propofol concentrations during the infusion ranged between 1.52 and 7.65 μg/mL; pseudo-steady state concentrations 3.64-6.78 μg/mL, and concentrations on assuming standing position 0.75-1.40 μg/mL. Propofol clearance and volume of distribution were 31.4 (SD 6.1) mL/min/kg and 220.7 (132.0) mL/kg, respectively. The propofol analyser allows titration of propofol to a given concentration; and may be useful for anaesthesia in animals where kinetics are unknown; in disease states; and where intercurrent therapies affect propofol disposition.