Accuracy of carboxyhemoglobin dilution method for the measurement of circulating blood volume

Purpose: The management of circulating blood volume (BVc) is crucial in intensive care unit (ICU) patients. The purpose of this study was to verify the accuracy and precision of the carbon monoxide-labeled hemoglobin (COHb) dilution method (CO method) by comparing it with the Cr-51-labeled erythrocyte dilution method (Cr-51 method) for the measurement of BVc. Methods: A prospective study was performed in 18 patients who underwent coronary artery bypass grafting (CABG) under mild hypothermic cardiopulmonary bypass (CPB). The BVc was measured by both the CO method and the Cr-51 method at 24 hr after ICU admission in order to verify the accuracy and precision of the CO method. Paired data were assessed in absolute terms, and percentage errors were calculated by the degree of agreement. Results: Small mean differences and standard deviations between the CO method and the Cr-51 method (-70.2 +/- 184.8 mL) and small percentage errors (-0.49 +/- 1.29%) indicated the accuracy and precision of the CO method, and a close correlation was observed (r=0.97). Conclusion: The CO method can measure BVc with a similar degree of accuracy as the Cr-51 method. It is simple, repeatable and safe without the risk of exposure to radioactivity in the ICU.