Experimental analysis of critical oxygen delivery

Departments of 1 Anesthesiology, 2 Emergency Medicine, and 3 Physiology, Virginia Commonwealth University Reanimation Engineering Shock Center, Virginia Commonwealth University, Richmond, Virginia 23298-0695 Submitted 26 August 2004 ; accepted in final form 22 October 2004 Systemic variables were evaluated with respect to O 2 delivery to test the hypothesis that critical O 2 delivery and critical Hb can be estimated by multiple variables collected simultaneously. Rats were subjected to transfusion with either fresh or stored blood and then subjected to stepwise isovolemic hemodilution. Critical levels were measured by the dual-regression method from plots of systemic variables against O 2 delivery and Hb. Delivery was calculated from cardiac index and arterial O 2 content. We found that 1 ) after hemodilution, O 2 delivery changed in a nonlinear relationship with Hb; 2 ) critical delivery calculated using 30 different systemic variables was not statistically different from each other; 3 ) critical delivery and critical Hb were correlated but were not different between animals receiving fresh or stored blood; and 4 ) similar critical levels were found using a single variable from several animals and using several variables from the same subject. The best variables to estimate critical delivery were lactate, bicarbonate, base excess, O 2 extraction ratio, expired CO 2 , pulse pressure, cardiac index, and systolic pressure. The data suggest that a multivariable analysis of critical delivery may help determine the physiological oxygenation boundary at the whole body level. This may assist in finding therapeutic triggers on an individual basis using systemic markers of the transition from aerobic to anaerobic metabolism. hemodilution; transfusion; oxygen delivery and consumption Address for reprint requests and other correspondence: I. P. Torres Filho, Dept. of Anesthesiology, MCV-VCU, 1101 East Marshall St., Rm. B1-012, PO Box 980695, Richmond, VA 23298-0695 (E-mail: itorres{at}vcu.edu )