Acute Normovolemic Hemodilution and Nitroglycerin-Induced Hypotension: Comparative Effects on Tissue Oxygenation and Allogeneic Blood Transfusion Requirement in Total Hip Arthroplasty

Abstract

Study Objectives: To study the comparative effects of acute normovolemic hemodilution and nitroglycerin-induced hypotension on tissue oxygenation and blood transfusion requirement.Design: Prospective, randomized study.Patients: 30 ASA physical status I and II patients scheduled for primary total hip arthroplasty.Interventions: Patients were randomized to one of three groups of 10 patients each, to receive acute normovolemic hemodilutin (Group 1) or nitroglycerin-based hypotension (Group 2); Group 3 served as the control group. In Group 1, 2 U of blood was collected and replaced with an equal volume of hydroxyethyl starch (200/0.5 6%) immediately after anesthesia induction. In Group 2, nitroglycerin was infused at a rate sufficient to reduce mean arterial pressures to 60 to 65 mmHg before initiation of surgery. When hematocrit was reduced to 25%, at first autologous blood and then, if necessary, allogeneic blood was transfused to Group 1, and allogeneic blood was transfused to the other two groups, until hematocrit reached 30% for 5 days postoperatively.Measurements and Main Results: Total transfused allogeneic units of blood were determined by the fifth postoperative day. Arterial oxygen content (CaO<inf>2</inf>), venous oxygen content (CvO<inf>2</inf>), and oxygen extraction ratios (EO<inf>2</inf>) were calculated by standard formulas. The mean allogeneic transfusion requirement was significantly lower in Group 1 (1.3 ± 0.8 U) than in Group 2 (2.3 ± 0.8 U) or Group 3 (2.7 ± 1.1 U) (p < 0.05). In Group 1, CaO<inf>2</inf> and CvO<inf>2</inf> were decreased at all times, but EO<inf>2</inf> was significantly increased from 15 ± 3.9% to 33.3 ± 5.3% (p < 0.001). As for the other two groups, although CaO<inf>2</inf> and CvO<inf>2</inf> were decreased, EO<inf>2</inf> was not significantly increased.Conclusions: Acute normovolemic hemodilution is more effective than nitroglycerin-induced hypotension in reducing allogeneic blood transfusion requirement in total hip replacement surgery, without significant metabolic changes. Copyright (C) 1999 Elsevier Science Inc.