Determination of single and repeated red cell volumes by the indicator dilution method using carbon monoxide as the indicator

The use of radioactive isotopes limits clinical applications of blood volume measurement in the ICU. We measured red cell volumes with carbon monoxide-labeled RBC in six dogs and five human volunteers. The measured values obtained on the dogs were compared with the simultaneous measurements with the 51Cr method; the ratio of the carbon monoxide to 51Cr values ranged from 0.86 to 1.17, and the mean ratio was 1.0 +/- 0.1 (SD), r = .93. We infer from these results that the carbon monoxide method has several advantages over the 51Cr method: a) the short labeling time (about 1 min), b) rapidly decreasing background levels of carbon monoxide with FIO2 1.0, and c) repeatability at intervals of several hours.