Determination of hemoglobin mass and blood volume with CO: evaluation and application of a method.

An improved protocol was applied to the use of carboxyhemoglobin (HbCO) saturation for the estimation of body hemoglobin (Hb) mass, red blood cell volume, and blood volume and was appraised in normal volunteers. A body size-related dose of CO (50-90 ml), estimated to change HbCO saturation by 6.5%, was introduced into a low-volume (2.8 liters) closed-circuit rebreathing system and allowed to equilibrate over 10 min. Plots of venous HbCO were characterized by a plateau after 8 min, which remained stable for at least 40 min. No loss of CO from the vascular space was evident. Three estimations of Hb mass at weekly intervals in seven subjects produced a coefficient of variation of 0.8% such that, in the absence of physiological influences, changes as little as 1.5% in Hb mass are detectable. Venesection [498 +/- 16 (SE) ml] in seven subjects was associated with a measured decrease in Hb mass after 1 wk equal to the calculated loss. Blood volume was, however, largely restored by plasma expansion. The method is sensitive and precise. It can be used safely and repeatedly in normal volunteers and hospital patients.