Little is known regarding the incidence and clinical impact of AI in neonates during the acute postoperative period following separation from CPB. In a randomized control pilot study performed by the UAB CVICU research team, prophylactic post-CPB hydrocortisone infusions improved some postoperative outcomes, especially in those that acquired AI7. In an attempt to further explore post-CPB AI, a retrospective analysis of data from this study was performed. Of the 40 neonates included in the study, one-third (32.5%) developed AI following CPB (as determined by low-dose, 1 µg, cosyntropin stimulation test). Almost all of these subjects had normal response to cosyntropin stimulation pre-CPB. Subjects that developed AI demonstrated more hemodynamic instability, increased serum lactate and required more colloid resuscitation in the immediate post-CPB period in the operating room. Recent evidence has begun to highlight potential morbidity associated with perioperative steroid administration. Our cardiac surgery program is changing clinical practice and ceasing to give preoperative steroids to all patients (previously only neonatal CPB patients received preoperative methylprednisolone). With the possibility that preoperative steroid administration, and not CPB, primarily causes the high incidence of AI, it is prudent to further investigate the benefit and/or harm of perioperative steroid administration