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Canadian Journal of Anesthesia, Vol 15, 579-592, Copyright © 1968 by Canadian Anesthesiologists' Society

Blood Volume: A Comparative Study

L. A. FROSTAD M.D.1

1 Department of Anaesthesia, University Hospital, Saskatoon, Saskatchewan

A short review is presented of the various means available to determine blood volume in man. On the basis of our findings, it is clear that there is no reliable way of clinically assessing the adequacy or otherwise of the circulating blood volume. No relationship could be demonstrated between serum proteins, serum electrolytes, creatinine, or central venous pressure and blood volume. Haemoglobin and haematocrit determinations by themselves also are of limited value, but if their changes are related to baseline readings, which include a reliable blood volume determination, then certain conclusions can be drawn from changing haematocrit and haemoglobin. The chlorpromazine test also fails to be a reliable index of blood volume in that it may not affect the arterial blood pressure in cases of moderate hypovolaemia and on the other hand may cause hypotension in the presence of a normal circulating volume. This latter effect can be explained most readily by the multiplicity of the pharmacological impact of that agent.

The only reliable methods of determining circulating volume (and this also has its limitations) are those based on indicators of which the RIHSA technique by means of the Volemetron is the simplest. This method allows calculation of plasma and red cell volume indirectly through the determination of mixed venous haematocrit. For all practical purposes therefore this is the method of choice at the present time, bearing in mind that the accuracy of results will depend upon adequate mixing, which under some clinical conditions cannot be assured. Of course, blood volume determined by whatever method must be related to a "normal predicted value" for that particular individual. There still is much controversy whether the normal predicted value should be based on present weight, on past weight in the case of weight loss, or on ideal weight with corrections being made for any deviation from that ideal. Until this question is resolved any percentage deviations from predicted normals are open to serious doubt.

In view of the fact that clinical impressions are so misleading it is recommended that blood volume determinations be carried out in all cases in which there is the slightest doubt as to the state of the circulating blood volume.

Note:

Presented as part of the Residents' Program at the Annual Meeting of the Canadian Anaesthetists' Society at Ottawa, Ontario, May 1968.






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Copyright © 1968 by the Canadian Anesthesiologists' Society.