Hormonal and metabolic responses during coronary artery bypass surgery: role of infused glucose

Anesthesia, surgery, and hypothermia are conventionally considered the major stress factors in the metabolic and hormonal responses to cardiac surgery. We compared these responses in 14 nondiabetics during and for 24 h after coronary artery bypass surgery; 8 received cardioplegic solutions (C+), and 6 did not (C-). The mean intraoperative glucose load in C+ was 106 g compared to 32 g in C-; postoperatively both groups received 50 g. Marked hyperglycemia (31.8 +/- 4.8 mmol/L) occurred during hypothermia in C+, but dropped to 18.9 mmol/L before surgery ended and to 11.2 +/- 1.1 mmol/L by 2 h postop. In contrast, C- showed constant mild hyperglycemia of 8.3-9.8 mmol/L throughout, significantly less than C+ until 1 h postop. Insulin was suppressed by 55% only during hypothermia, peaking with rewarming in C+ at 2,849 +/- 911 vs. 639 +/- 251 pmol/L in C- (P less than 0.05); as with glycemia, values were comparable after 2 h postop. The pancreatic beta-cell thus responded to hyperglycemia during restoration of normothermia, resulting in a rapid decline in glycemia. This occurred despite elevations in antiinsulin factors in both groups; GH was 14 +/- 4 micrograms/L, cortisol was 607 +/- 38.6 nmol/L, norepinephrine was 11.5 +/- 3.7 nmol/L, epinephrine was 13,863 +/- 3,875 pmol/L, and FFA were 0.36 +/- 0.05 g/L. Early postop, a secondary rise in stress hormones occurred in both groups. Maximal cortisol values were at 4 h (1,186 +/- 140 nmol/L) and peaks of norepinephrine (6.50 +/- 1.66 nmol/L), epinephrine (7,969 +/- 3,602 pmol/L), and FFA (0.27 +/- 0.03 g/L) occurred. The only significant glucagon elevation was at 24 h (C+, 464 +/- 53 ng/L; C-, 350 +/- 241 ng/L; P less than 0.02), Thus, 1) many metabolic responses during coronary artery bypass surgery are influenced by the glucose-containing cardioplegic solution; 2) hypothermia suppresses insulin secretion, but it responds thereafter despite marked elevations of catecholamines, and is associated with decreasing glycemia despite elevated antiinsulin factors; 3) a lesser but highly significant stress response corresponds to awakening from anesthesia; and 4) glucagon plays a minor role in intraoperative hyperglycemia; the rise at 24 h is unexplained.