Haematocrit measurements during cardiopulmonary bypass surgery: comparison of three stat methods with a blood cell counter.

Monitoring packed cell volume (PCV) is essential to safeguard oxygen delivery to the tissues during cardiopulmonary bypass (CPB). We compared the results obtained using a PCV monitor, a blood gas analyser and a microcentrifuge with those from a laboratory-based automated blood cell counter. PCV was measured in 221 samples of 40 patients undergoing open-heart surgery. The limits of agreement (mean difference +/- 2 SD) was unacceptably wide when the results obtained with the PCV monitor and the blood gas analyser were compared with those of the automated blood cell counter. This was most pronounced when PCV was measured in low concentration samples. The microcentrifuge showed good limits of agreement regardless of sample concentration. The data suggests that measurement of PCV by either continuous monitoring or by a blood gas analyser is not an accurate alternative to an established laboratory method. The microcentrifuge is the most accurate method of the ones investigated to measure haematocrit during CPB.