Is hyperglycemia seen in children during cardiopulmonary bypass a result of hyperoxia?

Objective: We sought to identify whether elevated Pao(2) itself can directl y cause hyperglycemia in newborns and to document any additional effects of cardiopulmonary bypass on this response. Methods: Piglets were exposed to either normoxia (88 +/- 6 mm Hg) or hypero xia (470 +/- 28 mm Hg) in the following studies. Anesthetized 3-day-old neo natal pigs were either ventilated for 2 hours of normoxia (n = 5) or hypero xia (n = 5) or placed on normothermic, normoxic cardiopulmonary bypass (n = 6) and then randomly assigned to either undergo a 2-hour normoxic period o r a 1-hour hyperoxic episode, followed by a return to normoxia for an addit ional hour. Blood glucose levels were measured in all animals. Results: No significant changes were observed in blood glucose levels in ne onatal pigs that underwent 2 hours of normoxic ventilation (5.0 +/- 0.6 mmo l/L) or cardiopulmonary bypass (6.6 +/- 1.6 mmol/L). However, the ventilato ry model showed a significant and sustained (P <.001) hyperglycemic respons e after both 1 hour (8.6 +/- 1.0 mmol/L) and 2 hours (9.8 +/- 1.6 mmol/L) o f hyperoxia. In the cardiopulmonary bypass model, exposure to I hour of hyp eroxia elicited a significant (P <.05) hyperglycemic response (10.3 +/- 1.2 mmol/L), followed by a return to normal blood glucose levels (6.6 +/- 1.6 mmol/L) with a return to normoxia. This hyperoxia-mediated hyperglycemic re sponse was confirmed when data examined from children undergoing cardiopulm onary bypass for primary repair of their congenital defects also identified a significant positive correlation (r = 0.72, P =.02) between oxygen level s and blood glucose levels measured before and at the end of cardiopulmonar y bypass. Conclusions: Hyperoxia triggers a hyperglycemic response in both ventilator y and bypass models. Cardiopulmonary bypass does not exacerbate this respon se, as shown by the similar levels of hyperglycemia sustained for the durat ion of the hyperoxic exposure in both experimental models. Therefore, not o nly may hyperoxia play a crucial role in the hyperglycemic response seen du ring neonatal cardiopulmonary bypass, but its effect on glucose homeostasis should be considered whenever children are exposed to hyperoxia.