Effects of Esmolol-induced Hypotension under Acute Normovolemic Hemodilution on the Cardiovascular System and Systemic Oxygen Balance in Dogs

Do, Sang Hwan; Chang, Seong Ho

Abstract

BACKGREOUND: Acute normovolemic hemodilution (ANH) is one of the methods of autologous transfusion drawing much attention recently. It is economical and easy to apply to many surgeries requiring multiple transfusions. When used as a drug for induced hypotension, esmolol can avoid many drawbacks of sodium nitroprusside and reduce the amount of intraoperative bleeding with better operative field. Considering recent trend of combining ANH and induced hypotension to increase the success rate of autotransfusion, esmolol-induced hypotension with ANH will be used more frequently in the future. However, 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 cardiovascular system and systemic oxygen balance.
METHODS
In 8 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 esmolol. Various hemodynamic parameters were measured before and after ANH and 15, 30, 60 and 90 minutes after induction of hypotension and 30 minutes after the end of hypotension.
RESULTS
Heart rate began to decrease after ANH and showed significant decrease at 60 and 90 minutes after hypotension compared with initial value. Central venous pressure increased significantly after ANH and hypotension. Pulmonary arterial pressure showed significant increase at 15 and 90 minutes after hypotension. Cardiac output was increased markedly by ANH but began to decrease after hypotension and showed significant decrease at 60 minutes after hypotension. Systemic vascular resistance showed significant decrease after ANH, 15 minutes after hypotension and 30 minutes after discontinuation ofesmolol. Pulmonary capillary wedge pressure and pulmonary vascular resistance showed no significant change. Oxygen flux was decreased markedly by esmolol but recovered after discontinuation of esmolol. Oxygen consumption was maintained throughout the study. Oxygen extraction ratio was increased dly after hypotension. There were no acidemia and hypoxemia throughout the study.
CONCLUSION
In conclusion, the results of this study suggest that tissue oxygen delivery might be decreased by anemia but that systemic oxygen balance might be preserved by ANH and induced hypotension within the range used in this study.