CLINICAL STUDIES OF THE BLOOD VOLUME. I. CLINICAL APPLICATION OF A METHOD EMPLOYING THE AZO DYE “EVANS BLUE” AND THE SPECTROPHOTOMETER

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Abstract
The application of a method for determining the plasma and total blood vol. employing the blue dye Evans Blue and the spectrophotometer to the investigation of clinical problems is described. Colorimetric errors inherent in earlier methods due to turbidity of plasma, lipemia, residual dye in repeated determinations and hemolysis of samples are minimized by the use of the spectrophotometer, and a spectrophotometric method of correcting for hemolysis is descr. Errors due to variations in dye mixing time ocqurring in different clinical states, and possible dilution of injected dye by lymph are eliminated by calculating the plasma vol. from a value obtained by extrapolation of the slope of disappearance of the dye from the blood stream, as detd. by multiple samples taken over a period of at least 30 min. after dye inj., to the time of inj. By the "direct" method of repeated single dets., vol. changes of clinical significance in the same individual can be reliably measured at frequent intervals. By the "indirect method" changes in vol. can be continuously followed for periods of from a few mins. to several hrs. Certain factors affecting the accuracy of the indirect method are discussed. A physiological response to serial blood sampling consisting of a transient and variable decrease in the circulating plasma and red cell vol. renders accurate estimation of the rate of disappearance of dye from the blood stream difficult. Exptl. procedures may alter the intrinsic color of the serum and rate of dye disappearance.

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