ACCURACY OF A NEW BEDSIDE METHOD FOR ESTIMATION OF CIRCULATING BLOOD-VOLUME

Objective: To evaluate the accuracy of a modification of the carbon monoxide method of estimating the circulating blood volume. Design: Prospective, clinical study comparing two methods for estimating the circulating blood volume. Carbon monoxide kinetics were studied by computer simulation. Setting. Intensive care unit in a university hospital. Patients. Intensive care patients receiving intermittent positive-pressure ventilation and healthy volunteers. Measurements and Main Results. The circulating blood volume was determined from measurements of the carbon monoxide saturation of hemoglobin before and after rebreathing a gas mixture containing 20 to 50 mL of carbon monoxide for a period of 10 to 15 mins. A specially designed Water's ''to & fro'' system was developed to avoid any leakage during intermittent positive-pressure ventilation. Blood samples were taken before, during, and immediately after rebreathing. The amount of carbon monoxide administrated during each rebreathing maneuver resulted in an average increase in the carbon monoxide saturation of hemoglobin of 3.6%. The washin of carbon monoxide was completed within the first 4 to 6 mins of the rebreathing period in nine healthy subjects and within 10 mins in 12 intensive care patients. The 95% limits of agreement between the carbon monoxide method and the radioactive isotope-labeling method was +/- 540 mL (+/- 2 SD). Conclusion: Determination of circulating blood volume can be performed with sufficient accuracy using an amount of carbon monoxide that gives rise to an unharmful increase in the carboxyhemoglobin concentration.