SIMULTANEOUS DETERMINATION OF PLASMA VOLUME AND TRANSCAPILLARY ESCAPE RATE WITH 131 I-LABELLED ALBUMIN AND T-1824 IN THE NEWBORN

A new micro method for plasma volume determination with T-1824 was investigated in 10 newborn infants. Dye concentration was measured with a two wavelength spectrophotometric method. The method was found to be easy, rapid to perform and requires only 150 μl plasma. Thus several plasma samples could be obtained and the dye loss during mixing time calculated and corrected for. This is of special importance in the newborn due to the high transcapillary albumin loss mentioned below. Plasma volume was determined with ¹³¹I human serum albumin (RIHSA) serving as reference. Identical results were obtained, mean 43 ml/kg. Consequently it is concluded that the dye method, being a non-radioactive method, should be preferred for plasma volume determination in the newborn. Transcapillary escape rate of albumin (fraction of intra-vascular mass of albumin escaping to the extravascular space per unit time) was determined from the disappearance of intravenously injected RIHSA and T-1824 during the first hour after the injection. The mean transcapillary escape rate with RIHSA was: 18.4%/hour, with T-1824: 20.7%/hour (p<0.1). These values are 3 to 4 times higher than those obtained in adults thus indicating a high capillary permeability to albumin in newborns.