Stress, severity of illness, and outcome in ventilated preterm infants

To determine physiological and hormonal stress responses in ventilated preterm infants.

Physiological and hormonal stress responses were studied in 47 ventilated preterm infants who were judged clinically to require sedation. The correlation between the stress response and severity of illness was examined, and responses were compared between infants with different clinical outcomes.

Stress hormone concentrations were significantly correlated with severity of illness, assessed using the arterial: alveolar oxygen partial pressure ratio. Noradrenaline showed the strongest correlation, with an exponential pattern of increased secretion. Catecholamine concentrations before sedation were significantly higher among infants who subsequently died (n = 15, at a median age of 6 days) than among survivors: median noradrenaline 4.31 vs 2.16 nmol/l, median adrenaline 0.69 vs 0.31 nmol/l. The observed fall in noradrenaline with sedation was lower among those who died than survivors (median fall 2% vs 40%).

Preterm infants are capable of hormonal stress responses appropriate for the severity of their illness. Extreme catecholamine responses, in the sickest infants, are associated with the worst outcome.