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Changes in plasma cortisol with ventilation and analgesia in preterm infants

Presented at the Neonatal Society 2002 Summer Meeting (programme).

Wong CM, Boyle EM, Laing IA, Yorke J, Armstrong J, Smith J, Midgley PC, McIntosh N

Neonatal Unit, Simpson Centre for Reproductive Health, Royal Infirmary of Edinburgh, Edinburgh EH16 4SA, UK

Background: Plasma cortisol can be used as a marker of pain and stress in neonates1. Preterm infants often require assisted ventilation but analgesia is not used routinely.

Aims: To investigate the effect of ventilation on plasma cortisol levels in preterm infants, and to see if analgesia affects these levels.

Methods: From July 2000 to December 2001, longitudinal once-daily morning blood samples were collected from 88 neonates ≤ 32 weeks gestation. Plasma cortisol was measured by a direct in-house radioimmunoassay. Infants with painful conditions were excluded. No infant received postnatal steroids. Results were analysed by Mann-Whitney U test.

Results: Median cortisol values (nmol/L) are tabulated. Table 1 shows results from the 88 neonates grouped by ventilation. All the ventilated babies are shown in Table 2 grouped by analgesia. Within this ventilated cohort was a subgroup of infants randomised in the NEOPAIN Trial to morphine or placebo infusions. Samples taken during assisted ventilation showed significantly higher cortisol levels. However, there was no significant difference in cortisol levels between the groups receiving analgesia or no analgesia. Similar results were obtained with samples from the subgroup of NEOPAIN infants. There was no difference in gestation or birth weight between those who received analgesia and those who did not.

Conclusions: Assisted ventilation is associated with raised plasma cortisol levels in preterm infants. This could be due to the underlying cause of the need for ventilation, or the pain or stress of ventilation itself. However, analgesia has no effect on these levels in ventilated infants, suggesting either that morphine is ineffective in ameliorating pain, or that the stress of ventilation is not related to pain.

1. Anand KJ. NEJM 1992; 326(1):1-9

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