Comparison of perioperative changes in the plasma adrenaline and blood glucose concentrations between the fentanyl (solid line, n = 8) and nonfentanyl (dashed line, n = 8) anesthesia groups. Modified and reprinted with permission from Anand KJ, Sippell WG, Aynsley-Green A: Randomised Trial of Fentanyl Anesthesia in Preterm Babies Undergoing Surgery: Effects on the Stress Response. Lancet 1987; 1:243–8.