Circulatory, respiratory and metabolic changes after thigh tourniquet release in combined epidural-propofol anaesthesia with preservation of spontaneous respiration.

Twelve elderly patients undergoing total knee arthroplasty received lumbar epidural anaesthesia and propofol infusion at 5 mg.kg(-1).h(-1) following a 1.5-2.0 mg.kg(-1) bolus dose with preservation of spontaneous respiration via a laryngeal mask airway. Circulatory, respiratory and metabolic variables were measured before and 1, 3, 5, 15 and 30 min after release of a pneumatic thigh tourniquet. The blood pressure was decreased at all time-points and the respiratory rate increased at 1 min. The P(a)CO(2) was increased only at 1 min. Arterial blood pH and base excess were decreased at 1 and 3 min and 1, 3 and 5 min, respectively. Arterial blood lactate levels were increased at all times. These characteristics were considered to be identical to those under regional anaesthesia with conscious spontaneous respiration, showing that spontaneous respiration under this anaesthetic regimen has a similar respiratory capacity to that of conscious spontaneous respiration.