Perioperative changes in alpha 1-acid glycoprotein concentrations in infants undergoing major surgery.

alpha 1-Acid glycoprotein (AAG) is an acute phase protein that is responsible for binding basic drugs such as bupivacaine. In order to determine how AAG concentrations change in response to surgical stress, arterial blood samples were obtained from 50 infants undergoing major surgery, at induction of anaesthesia and daily for the next 7 days. AAG concentrations were measured using a rate nephelometric technique. The overall mean preoperative AAG concentration was 0.38 (SD 0.16) mg ml-1, although concentrations were significantly greater in infants undergoing urgent surgery compared with those undergoing elective surgery (P = 0.02). There were no significant correlations between gestational or postnatal age and preoperative AAG concentration. Mean AAG concentrations increased to 0.76 (0.18) mg ml-1 by day 4 after surgery and stayed at that concentration thereafter. Infants with preoperative AAG concentrations < 0.38 mg ml-1 showed a greater percentage increase in postoperative AAG concentrations than did infants with preoperative AAG concentrations > 0.38 mg ml-1 (P = 0.001). We conclude that preoperative measurement of AAG may identify those infants most at risk of drug toxicity in the early postoperative period.