POSTURE AND APPARENT PLASMA VOLUME IN LATE PREGNANCY

Abstract

Summary Two consecutive measurements were made of the T‐1824 space (apparent plasma volume) in each of 37 women in late pregnancy, one after lying supine for an hour and the other after lying on one side for an hour. Most of the patients were alternated with regard to the initial position. The supine position had three effects. (1) It usually decreased the apparent plasma volume. (2) Mixing of the dye often was not complete within the first ten minutes. (3) After the women turned on to their sides the optical densities of their sera usually increased, sometimes markedly. When the women lay on their sides their apparent plasma volumes usually were greater than while they lay supine and mixing of the dye was complete within ten minutes. The first two effects of the supine position vitiate estimates of the plasma volume during late pregnancy if they are made while the patient is lying on her back and they may explain, in part, the alleged decrease in plasma volume during the last weeks of gestation.