Acute normovolemic hemodilution and nitroglycerin-induced hypotension: Comparative effects on tissue oxygenation and allogeneic blood transfusion requirement in total hip arthroplasty

Study Objectives: To study the comparative effects of acute normovolemic he modilution and nitroglycerin-induced hypotension on tissue oxygenation and blood transfusion requirement transfusion requirement. Design: Prospective, randomized study. Patients: 30 ASA physical status I and II patients scheduled for primary to tal hip arthroplasty. Interventions: Patients were randomized to one of three groups of 10 patien ts each to receive acute normovolemic hemodilutin (Group 1) or nitroglyceri n-based hypotension (Group 2); Group 3 served as the control group. In Grou p 1, 2 U of blood was collected and replaced with an equal volume of hydrox yethyl 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 wa s reduced to 25%, at first autologous blood and then, if necessary, allogen eic blood was transfused to Group 1, and allogeneic blood was transfused to the other two groups, until hematocrit reached 30% for 5 days postoperativ ely. Measurements and Main Results: Total transfused allogeneic units of blood w ere determined by the fifth postoperative day. Arterial oxygen content (CaO 2), venous oxygen content (CvO(2)), and oxygen extraction ratios (EO2) were calculated by standard formulas. The mean allogeneic transfusion requireme nt 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, CaO2 and CvO (2) were decreased at all times, but EO2 was significantly increased from 1 5 +/- 3.9% to 33.3 +/- 5.3% (p < 0.001). As for the other two groups, altho ugh CaO2 and CvO(2) were decreased, EO2 was not significantly increased. Conclusions: Acute normovolemic hemodilution is more effective than nitrogl ycerin-induced hypotension in reducing allogeneic blood transfusion require ment in total hip replacement surgery, without significant metabolic change s.