The use and limitations of isotope studies in clinical shock.

Blood volume measurements can only be of value in the treatment of clinical shock if the results are obtained quickly. In a changing situation, such as continuing haemorrhage, erroneous conclusions are inevitable. Assumptions which are commonly made concerning tracer loss rates and mixing rates may be invalid. Semi-automated machines can introduce new sources of error. The measurement of blood volume should be regarded as an aid to assessing the relative contributions of intravascular volume and vascular tone to the resulting intravascular pressures.