Opiate Blunting of Perioperative Stress Responses in Infants.Integration of nociceptive pathways and cardiovascular control centers in the neonatal brain stem are quite well developed as demonstrated by marked hormonal, metabolic, and cardiovascular responses to painful and stressful stimulation. During surgical procedures, the hormonal and metabolic responses to pain are extreme in the neonate and may be deleterious. Increases in levels ofβ‐endorphins, catecholamines, growth hormone, cortisol, and glucagon in neonates during major surgical procedures are greater than those seen in adults. These increased levels produce a substantial catabolic drive intraoperatively and postoperatively characterized by increased levels of oxygen consumption, glucose, lactate, pyruvate, tissue glycogen, and protein metabolism that are poorly tolerated by the fragile neonate. In contrast to other anesthetic agents, these extreme hormonal and metabolic stress responses to surgically‐induced pain can be at least partially attenuated by high‐dose opiates. Such high‐dose opiates have additional benefits such as increases in the threshold for ventricular fibrillation, but opiates also produce marked respiratory depression requiring a period of mechanical ventilation. In addition, high‐dose opiates blunt pulmonary vascular reactivity and decrease pulmonary hypertensive crises in infants with pulmonary hypertension. Further understanding of the integration of pain and cardiovascular responses in the neonate is needed to further improve our abilities to control thes