Urinary Arginine Vasopressin Excretion and Hyponatremia in the Sick Neonates

ABSTRACT

We attempted to clarify the renal physiologic response to arginine vasopressin (AVP) in the 12 sick neonates: three with respiratory distress syndrome (RDS), three with meconium aspiration syndrome, two with transient tachypnea of the newborn, two with neonatal asphyxia, and two low birthweight infants during the first 2 days of life. Plasma atrial natriuretic factor (ANF), urinary AVP, osmolality, free water clearance and cre-atinine clearance (C_cr) were measured at 8 to 16 hours of life (stage 1) and 24 to 32 hours of I ife (stage 2). Urinary AVP was expressed as the ratio of AVP to C_cr (urine AVP/C_cr). These subjects were divided into two groups: group A represented five infants with a urine AVP/ C_cr ratio of 2000 or higher and group B, seven infants with a ratio of less than 2000 at stage 1. Hyponatremia occurred in two infants of group A at stage 2. Number of infants on mechanical ventilation was four in group A and one in group B. There were no significant differences in gestational age, birthweight, Apgar scores at 1 and 5 minutes, blood gas pH and mean arterial blood pressure between groups A and B. A good correlation was observed between logarithm of urine AVP/C_cr ratio and urinary osmolality (p < 0.01). A negative correlation was observed between logarithm of urine AVP/C_cr ratio and free water clearance (p < 0.01). Body weight of infants of group A at stage 2 was greater than at stage 1 (p < 0.05). Higher plasma ANF concentrations were observed in infants of group A at stage 2 when compared with those at stage 1 (p < 0.1). These results suggest that the syndrome of inappropriate excretion of antidiuretic hormone may occur in the early neonatal age.