Plasma arginine vasopressin, diuresis, and neonatal respiratory distress syndrome

The pathogenesis of the diuresis that precedes the recovery from respiratory distress syndrome (RDS) in preterm infants has not been clearly delineated. To define the role of Arginine Vasopressin (AVP) or Antidiuretic Hormone in the diuretic phase of RDS, we obtained plasma AVP levels (radioimmunoassay) and sequential time-urine-plasma collections during the first, the third and the fifth days of life in twelve premature ventilated newborns. AVP levels were persistently elevated (12.7 +/- 7.6; 9 +/- 4.7 and 10.4 +/- 6.6 pg/ml, respectively) despite normal plasma sodium and osmolality. Maximum diuresis (output/intake greater than 0.72) occurred at 72 hours and preceded the improvement in FiO2/PaO2, significant on 5th day (p less than 0.01), and associated with a 10.6% decrease in body weight. These results suggest a nonosmotic release of AVP in ventilated newborns, and show a hypervasopressinemia unrelated to the diuresis associated with the recovery phase of RDS.