Measurement of total circulating blood volume following subarachnoid haemorrhage: methodological aspects

The total circulating blood volume (TCBV) and total body/venous haematocrit ratio (Htb/Hv) was determined by simultaneous measurement of the red cell volume (RCV) and the plasma volume (PV) in 10 subarachnoid haemorrhage (SAH) patients, 10 supine bedresting control patients and 20 ambulant out-patients. The mean Htb/Hv of the SAH patients, 0.866, was found to be significantly lower than that of the supine controls, 0.908, and the ambulant patients, 0.909, (p less than 0.01). Using the ratio 0.866 the total circulating blood volume of the SAH patients was calculated from either their RCV or their PV and compared with their measured TCBV. Expressed as a percentage of measured TCBV the mean errors of these single volume determinations were 2.84% and 1.76% respectively. The significance of these changes in the Htb/Hv ratio of SAH patients is discussed in relation to the circulatory disturbances they suffer.