The Effects of Hemodilution on Critical Oxygen Deliveries during Deliberate Hypotension by Esmolol or Sodium Nitroprusside in Dogs / 대한마취과학회지

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.

Effects of Sodium Nitroprusside-induced Hypotension under Acute Normovolemic Hemodilution on the Cardiovascular System and Systemic Oxygen Balance in Dogs / 대한마취과학회지

BACKGROUND: To decrease homologuous transfusion and bleeding, Acute Normovolemic Hemodilution (ANH) may be combined with induced hypotension. Tissue oxygen balance may be in danger because of decreased tissue perfusion pressure by induced hypotension and reduced arterial oxygen content by ANH. Thus it is necessary to evaluate effects of induced hypotension combined with ANH on hemodynamics and systemic oxygen balance. METHODS: In 6 mongrel dogs anesthetized with N2O-O2-enflurane and paralyzed with vecuronium, ANH was performed up to half of initial level of hemoglobin with isovolemic pentastarch infusion, and then mean arterial pressure (MAP) was lowered by 30% of the initial value by intravenous administration of Sodium Nitroprusside (SNP). Various hemodynamic parameters were measured before and after ANH and 15, 30, 45 and 60 minutes after induction of hypotension and 15 minutes after the end of hypotension. RESULTS: Heart rate was not changed significantly throughout the study. Central venous pressure increased significantly after ANH but decreased to the initial value after induced hypotension. Systemic vascular resistance showed significant decrease after ANH, more significant decrease after induced hypotension and slight increase after discontinuation of SNP. Cardiac output increased markedly by ANH and maintained during induced hypotension. Oxygen flux decreased significantly after ANH but slightly increased after induced hypotension. Oxygen consumption and Oxygen extraction ratio were maintained throughout the study. There were no acidemia and hypoxemia throughout the study. CONCLUSION: The combined use of ANH and induced hypotension with SNP is safe in the aspect of cardiovascular system and systemic oxygen balance.