RESUMO
BACKGROUND: Acute normovolemic hemodilution (ANH) and deliberate hypotension (DH) are methods used for reducing homologous transfusions in cases of massive intraoperative bleeding. Using the technique of combining ANH and DH, we can save more homologous blood than a single use of ANH or DH, but the risk of tissue hypoxia may increase. METHODS: Fourteen male dogs were used for this study and divided into two groups. After performing ANH by 25 ml/kg, mean arterial pressures were reduced to 60 mmHg by sodium nitroprusside (S group) or esmolol (E group). The critical oxygen delivery and the hemoglobin concentration at the critical oxygen delivery were determined by measurements of hemodynamic change, systemic oxygen delivery and systemic oxygen consumption during subsequent hemodilution. RESULTS: After performing ANH by 25 ml/kg, the cardiac output was significantly increased, and systemic vascular resistance and hemoglobin concentration were significantly decreased compared with control values. The critical oxygen deliveries were 179.6 ml/min in the S group and 169.1 ml/min in the E group. There was a difference in mean systemic oxygen consumption between the S group (123.4 +/- 16.7 ml/min) and E group (112.9 +/- 15.4 ml/min) above the critical oxygen delivery point (mean +/- SD). The hemoglobin concentrations at the critical oxygen delivery were 2.6 +/- 0.7 g/dl in S group and 4.0 +/- 1.3 g/dl in E group (mean +/- SD). CONCLSIONS: The critical oxygen delivery during hemodilution under DH by sodium nitroprusside was 179.6 ml/min and by esmolol was 169.1 ml/min. However, esmolol was higher in hemoglobin concentrations at the critical oxygen delivery than sodium nitroprusside. These results suggest thathemodilution under DH by esmolol rather than sodium nitroprusside requires more careful monitoring of systemic oxygen delivery for prevention of tissue hypoxia.