SYMPATHETIC MUSCLE NERVE ACTIVITY, PERIPHERAL-BLOOD FLOWS, AND BARORECEPTOR REFLEXES IN HUMANS DURING PROPOFOL ANESTHESIA AND SURGERY

Background. With percutaneous recordings of muscle nerve sympathetic activity (MSA), it is possible to study interactions between the autonomic nervous system and anesthetics. This study describes the effects of propofol infusion both before and during microlaryngoscopy. Methods: Nine patients participated. MSA was recorded, muscle and skin blood flows were measured. Sodium nitroprusside-induced decreases in blood pressure were used to quantitate baroreceptor reflex sensitivity. Results. During steady state propofol anesthesia (0.1 mg . kg-1 . min-1), ''total MSA'' (MSA burst area per minute) was 37% (P < 0.05) of awake control value; leg blood flow recorded by strain-gauge plethysmography was 227% (difference not significant); and skin blood flow recorded by laser Doppler flowmetry and finger pulse plethysmography was 300% (P < 0.05) and 376% (P < 0.05) of respective awake control values. During microlaryngoscopy, when mean arterial blood pressure was controlled as close as possible to mean arterial blood pressure in the awake state by individually adjusted propofol infusion rates (average 0.33 mg . kg-1, min-1) MSA was restored to 93% of the activity before anesthesia, and leg blood flow increased further. Both cardiac and muscle sympathetic baroreflex sensitivities were depressed by propofol. During surgery the cardiac baroreflex sensitivity decreased further, whereas the muscle sympathetic baroreflex sensitivity was unchanged. Conclusions: Propofol is a potent inhibitor of sympathetic neuronal activity and decreases the sensitivity of the baroreflex. When used to control the pressor response during surgery, the vasodilatating effect of propofol overrides the neural vasoconstriction induced by surgery, and a further inhibition of the cardiac baroreflex is observed.