The Effects of Isovolemic Hemodilution on Hemodynamic Changes in Myocardial Ischemia-Induced Dogs

Chang, Young Jin; Woo, Young Cheol; Koo, Gill Hoe

Abstract

BACKGROUND: Anesthesiologists often encounter patients who have acute, massive blood loss and severe hemodilution as the result of fluid therapy in the operating room. It is known that patients with normal heart function survive at hemoglobin 4 6 g/dl. Recently, the incidence of elderly patients with ischemic heart disease have been increasing progressively but studies about critical hematocrit level in patients with ischemic heart disease are rare. This study, therefore, was designed to evaluate the hemodynamic response of isovolemic hemodilution in myocardial ischemia-induced dogs.
METHODS
In 12 anesthetized dogs, a Swan-Ganz catheter and left ventricle catheter were inserted and hemodynamic parameters were measured as control values. Myocardial ischemia was induced with a left anterior descending (LAD) coronary artery ligation. Thereafter, isovolemic hemodilutions were done several times to set the hematocrit levels of 36%, 31%, 26%, 21%, 16%, and 11%. Records and samples for hemodynamic parameters were obtained after LAD ligation and at each hematocrit level.
RESULTS
There were significant decreases in diastolic blood pressures in hematocrits 21%, 16%, 11%, in mean arterial pressures in hematocrits 16%, 11% and in systolic blood pressure in hematocrit 11% (P < 0.05). Oxygen delivery progressively decreased in hematocrits 36%, 31%, 26%, 21%, 16% and 11% (P < 0.05). Oxygen extraction ratios progressively increased and were statistically significant in hematocrits 21%, 16% and 11% (P < 0.05). Arterial blood gases showed metabolic acidosis in hematocrits 16% and 11%. There was decreased PCO2 in hematocrit 11% (P < 0.05). Mixed venous blood oxy-hemoglobin saturation decreased in hematocrit 16% and 11% (P < 0.05). Other variables were not significant.
CONCLUSIONS
Blood pressure decreased at hematocrit 16% so it is necessary to maintain a hematocrit level above 21% at least in cardiac depressed dogs.