Enhanced thromboxane synthesis with extradural anaesthesia

Reperfusion of limb following tourniquet ischaemia increases plasma concentration of thromboxane (TxB₂). The study examined TxB₂ production during the ischaemia and reperfusion of femoral-popliteal bypass surgery and the effect of anaesthetic technique. Patients (n = 19) were randomly allocated to receive either general (GA) or extradural (EA)anaesthesia. TxB₂ concentrations were similar both before and after anaesthesia in the two groups. Clamping the femoral artery in patients given GA resulted in a small but insignificant increase in TxB₂ concentration. However, in the EA group clamping resulted in a 10-fold increase in TxB₂ concentration (P < 0.05). To demonstrate that anaesthesia itself was not the stimulus to TxB₂ synthesis, patients undergoing inguinal herniorrhaphy (n = 13) received either GA or EA. There were no subsequent changes in TxB₂ concentration in each group. The results indicate that EA but not GA maintains collateral flow during femoral arterial clamping and provides the oxygen needed for generati9n of TxB₂ during ischaemia