Intentional [tourniquet] ischaemia and the role of propofol as an antioxidant in the attenuation of reperfusion injury

ABSTRACT

Reactive oxygen species which damage cellular components and initiate the lipid peroxidation process are known to be responsible for the ischaemia-reperfusion injury. Lipid peroxidation is a chain reaction leading to oxidation of polyunsaturated fatty acids which, in turn, disrupts the structure of biological membranes and produces toxic metabolites such as malondialdehyde [MDA]. The use of pneumatic tourniquet for bloodless limb surgerv is accepted as a good human model for the study of ischaemiareperfusion injury. Propofol [2,6 diisopropylphenol] is chemically similar to phenol based free radical scavengers. It has been shown to exhibit significant antioxidant activity. This study was carried out to study the role of propofol as an antioxidant, in the attenuation of ischaemia -reperfusion injury induced by the use of pneumatic tourniquet in lower limb surgery. Thirty adult ASA III patients scheduled for lower limb surgery were studied. Patients were randomly allocated into two equal groups. In the propofol group, anaesthesia was induced using fentanyl and propofol followed by a continuous infusion of propfol adjusted according to clinical signs and anticipated demands. In the control group, anaesthesia was induced using fentanyl and thiopentone. Inhalational maintenance was then carried out with 1-2% isoflurane in oxygen. In both groups, a pneumatic tourniquet was then applied on the limb to be operated upon. Parameters studied included heart rate, arterial blood pressure, ECG, arterial blood gases, serum potassium level, serum malondialdehyde [MDA] level, serum level of reduced glutathione [GSH], and superoxide dismutase [SOD] enzyme activity in the RBCs. In both groups tourniquet deflation was accompanied by a significant increase in heart rate, a significant decrease in arterial blood pressure, significant decrease in arterial blood pH, and a significant increase in serum potassium. In the propofol group, following tourniquet deflation, there were no significant changes in serum MDA level, serum GSH level, and SOD enzyme activity. In the control group, there was significant increase in serum MDA level, significant decrease in serum G.S.H level, and significant inhibition in SOD enzyme activity. In conclusion, propofol attenuated ischaemia-reperfusion -induced lipid peroxidation in therapeutic doses used in anaesthesia. Also, it delayed the exhaustion of naturally occurring antioxidants