Hip Surgery and Venous Thrombosis: Effect of Anesthesia

To the Editor.— The article by Hull et al¹ examines the effect of a mechanical countermeasure on the incidence of postoperative venous thrombosis, a frequent complication of total hip replacement. They point out that a purported mechanism of thrombosis is a reduction in perioperative venous blood flow in the lower extremities from muscular inactivity. Sequential intermittent leg compression presumably functions as an artificial muscle facilitating blood return to the heart.

Hull et al conclude that this mechanical technique reduced the incidence of perioperative thrombosis, but they fail to report differences in anesthetic management that could have introduced statistical bias into their data. For example, general anesthetics with neuromuscular blockade and positive-pressure ventilation may impede venous return and contribute to vascular stasis. In contrast, major conduction anesthetics (eg, spinal, epidural) directly produce regional vascular dilatation and obviate the need for mechanical ventilation, perhaps augmenting venous blood flow. Some investigators have