Upper limb blood flow during hexamethonium-induced hypotension. Studies in patients anaesthetized with halothane

We report the effect of hypotensive anaesthesia on blood flow in the upper limbs of 17 patients before the start of surgery. Under light halothane-oxygen anaesthesia, patients (n = 17) were given hexamethonium 0.5-1.0 mg kg-1. Forearm blood flow (FBF), hand blood flow (HBF) and systemic arterial pressure (AP) were measured before, and 9 and 18 min after the administration of hexamethonium. During the control period of halothane anaesthesia, HBF was AP-dependent, but FBF was not. Hexamethonium produced a statistically significant (P less than 0.001) decrease in systolic AP by 9 and 18 min, but significant reductions in FBF and HBF were seen only at 9 min. During the hypotensive period neither HBF nor FBF correlated with the systolic AP, which had decreased from an average of 98 mm Hg to an average of 65 mm Hg (range 95-50 mm Hg), but the changes in HBF and FBF did correlate with the changes in systolic AP. As a secondary factor, the control FBF correlated inversely with the reduction in FBF after hexamethonium. We concluded that hypotension induced by hexamethonium during halothane anaesthesia produced a transient reduction in limb blood flow that was dependent on the change in AP. A range of systolic AP from 95 to 50 mm Hg did not correlate with either FBF or HBF during the hypotensive period.