Vasopressin and pneumothorax in the neonate.

The release of vasopressin (AVP) was assessed by measuring urinary excretion of the hormone in ten neonates who had an acute and symptomatic pneumothorax in the first three days after birth. AVP excretion rose significantly (paired t analysis) after the pneumothorax occurred. When apparent re-expansion of the lungs occurred after treatment, excretion of AVP returned to prepneumothorax levels within eight to 16 hours. If the pneumothorax persisted or worsened. AVP excretion remained elevated. Urine osmolality rose significantly (paired t analysis) after pneumothorax, presumably in response to the increased AVP levels. Two of the ten infants had hyponatremia in the period studied, while in a state of sodium balance. It was concluded that AVP release is increased after a pneumothorax occurs. This increase is apparently not due to osmoregulatory requirements. Fluid intake in these infants may need adjustment to prevent an inappropriate positive water balance.