Study is on haemoglobin accuracy, reliability and precision using the I-Stat point of care device.

Patients having surgery that normally involves large blood-loss and volume replacement would be included in this study. The aim of the study is to demonstrate how changes in the composition of the circulating blood volume (plasma protein levels) affect the dependability of the haematocrit as measured by the i-STAT device. This device employs the analytical technique of conductometry to measure this variable, and conductometry is known to be affected by plasma protein levels. Blood samples would be drawn from the patient at various stages of the operation, after variable but recorded quantities of fluids had been given. These blood samples would have been collected for routine monitoring purposes. The samples would then be analysed by the laboratory (routinely) to determine haematocrit, and then also by the i-STAT to measure this same parameter. Hence, we can determine how these 2 measurements of the same parameter differ from one another. Simultaneously, we would measure plasma protein levels, and determine how the i-STAT-measured haematocrit varies with these levels. Finally, each i-STAT measurement would be duplicated in order to determine how the precision of the instrument varies with changing plasma protein levels. The only requirement of this study is to measure plasma protein levels in addition to the other routine tests of haematocrit.