Hypotensive Anesthesia with Isoflurane and Enflurane during Total Hip Replacement

Abstract

Catecholamine and renin-angiotensin responses to enflurane- or isoflurane-hypotensive anesthesia were compared in a randomized study. Two groups of 10 patients undergoing total hip arthroplasty were premedicated with morphine hydrochloride (0.1 mg/kg). Anesthesia was induced with thiopental and the trachea intubated after pancuronium. Equal concentrations of each volatile agent (1.3 MAC) were administered until mean arterial blood pressure decreased to 50-60 mm Hg. Hemodynamic data and blood samples for measurements of plasma renin activity (PRA) and plasma epinephrine (E) and norepinephrine (NE) concentrations were collected 1) after induction and intubation but before the start of isoflurane or enflurane; 2) 15 min (T15) after the start of isoflurane or enflurane administration; and 3) 45 min (T45) after the start of isoflurane or enflurane administration. The desired level of hypotension was achieved at T15 with isoflurane and at T45 with both anesthetics. When hypotension was achieved, cardiac index and stroke index were significantly lower in the enflurane group while systemic vascular resistance index was lower in the isoflurane group. Increases in E and NE levels above baseline levels were significantly greater in the isoflurane group than in the enflurane group. Use of isoflurane to induce hypotension is associated with more rapid induction of hypotension, less depression of cardiac output, and better preservation of homeostatic responses than is use of enflurane.