In this retrospective analysis by Crawford et al.8 ACTH levels were found to be significantly lower post-CPB compared to preoperative levels. This may be secondary to a blunted HPA axis caused by preoperative methylprednisolone (all patients received), which could result in transient, iatrogenic AI. Serum cytokines were not significantly different in patients exhibiting AI compared to those with a normal adrenal response indicating that increased inflammation was not primarily responsible for the development of AI. Higher methylprednisolone levels result in higher cortisol levels due to cross-reactivity of the assays; patients with higher baseline postoperative cortisol levels demonstrated a blunted response to cosyntropin suggesting that these patients may have higher blood concentrations of methylprednisolone and its metabolites, thereby leading to more inhibition of the HPA axis. Taken together, these two studies demonstrate that AI occurs at high frequency after neonatal CPB and that AI is associated with deleterious outcomes. While postoperative hydrocortisone improves outcomes in neonates with AI, the investigator cannot exclude preoperative methylprednisolone as a cause of iatrogenic AI. Other investigators have shown in children treated with dexamethasone prior to surgery, that higher measured levels of dexamethasone were associated with postoperative AI9.