In vitro variability in propofol absorption by different membrane oxygenators

Introduction

The sequestration of drugs, such as fentanyl [1,2], thiopental, nitroglycerine and propofol [3] in the extracorporeal circuit in vitro has been well described. This phenomenon can change the pharmacokinetic behaviour of drugs during cardiopulmonary bypass, thus potentially leading to problems in achieving adequate dosing regimens.

Objective

The aim of this in vitro laboratory study was to compare the binding of propofol to different oxygenator membranes, and to examine the effects of the type of prime solution and temperature on the rate of binding.

Methods

Samples of three types of membrane oxygenators were used: the SM-35 (polydimethylsiloxane in sheet form), the CML (polypropylene in sheet form) and the SAFE II (polypropylene in hollow fibre form). ¹⁴C-propofol in either crystalloid solution or diluted bovine blood was incubated with samples of membranes at 28°C or 37°C. Membrane samples were removed at 30, 60, 90 and 120 min and rinsed. The mass of propofol bound to the various membranes was then measured using liquid scintillation counting. This experiment was carried out for both types of prime solution at 28°C and 37°C.

Results

See Table 1. The SM-35 membrane bound significantly more propofol than the membranes from the CML and the SAFE II. Binding of propofol in diluted blood was significantly less than in crystalloid solution. Temperature had little effect on propofol binding in either prime solution type.

Table 1