Normal plasma-urine osmolality relationship in preterm infants on positive pressure mechanical ventilation

Mechanical ventilation with positive pressure has been implicated in the inappropriate release of vasopressin. To examine whether such a phenomenon occurs in infancy, 26 preterm neonates with Respiratory Distress Syndrome were studied. Simultaneous urine and plasma were collected for osmolality determination during mechanical ventilation with positive end expiratory pressure of 4-8 cmH2O. Results were plotted onto our previously described nomogram. The data show normal distribution of plasma to urine osmolality ratio in 25 out of 26 infants. These results do not support the common belief that positive pressure mechanical ventilation in the newborn with RDS provokes inappropriate secretion of vasopressin.