Adrenocortical function in the very low birth weight infant: improved testing sensitivity and association with neonatal outcome.
OBJECTIVE: To evaluate adrenocortical function in ill preterm infants and investigate potential relationships between plasma cortisol concentrations and major neonatal outcomes. STUDY DESIGN: Randomized trial of adrenocorticotropic hormone (1-24ACTH) stimulation testing, followed by a chart review. SETTING: Two level III neonatal intensive care units, Sacramento, Calif. PARTICIPANTS: Sixty-seven very low birth weight infants, born at 32 weeks of gestation or earlier weighing 1500 gm or less, who had endotracheal intubation and indwelling arterial access. RESULTS: Most infants (76%) had baseline cortisol concentrations < 414 nmol/L (15.0 micrograms/dl), and of those, only 36% responded to stimulation with 1-24ACTH, 0.1 microgram/kg. Raising the 1-24ACTH dose to 0.2 microgram/kg resulted in a response rate of 67% (p = 0.09) but decreased the sensitivity of the test. An elevated mean 11-deoxycortisol/cortisol ratio indicated that decreased 11 beta-hydroxylase activity may limit cortisol production in some infants. Infants with baseline cortisol concentrations less than 414 nmol/L (15.0 micrograms/dl) were more likely to have chronic lung disease (p < 0.002) and less likely to have severe intraventricular hemorrhage (p < 0.02). Response to 1-24ACTH was not associated with a detectable difference in outcome. CONCLUSION: Many very low birth weight infants have low cortisol and ACTH concentrations and are unable to mount a cortisol response to physiologic doses (0.1 microgram/kg) of 1-24ACTH. These findings suggest that delayed maturation of adrenal response may result in physiologically inadequate cortisol concentrations in stressed very low birth weight infants. This delayed maturation may contribute to the development of chronic lung disease.