Glucose and insulin administration while maintaining normoglycemia inhibits whole body protein breakdown and synthesis after cardiac surgery.

We investigated the effect of insulin administered as part of a hyperinsulinemic-normoglycemic clamp on protein metabolism after coronary artery bypass grafting (CABG) surgery. Eighteen patients were studied, with nine patients in the control group receiving standard metabolic care and nine patients receiving insulin (5 mU·kg(-1)·min(-1)). Whole body glucose production, protein breakdown, synthesis, and oxidation were determined using stable isotope tracer kinetics (l-[1-(13)C]leucine, [6,6-(2)H2]glucose) before and 6 h after the procedure. Plasma amino acids, cortisol, and lactate were also measured. Endogenous glucose production (preoperatively 10.0 ± 1.6, postoperatively 3.7 ± 2.5 µmol·kg(-1)·min(-1); P = 0.0001), protein breakdown (preoperatively 105.3 ± 9.8, postoperatively 85.2 ± 9.2 mmol·kg(-1)·h(-1); P = 0.0005) and synthesis (preoperatively 88.7 ± 8.7, postoperatively 72.4 ± 8.4 mmol·kg(-1)·h(-1); P = 0.0005) decreased in the presence of hyperinsulinemia, whereas both parameters remained unchanged in the control group. A positive correlation between endogenous glucose production and protein breakdown was observed in the insulin group (r(2) = 0.385). Whole body protein oxidation and balance decreased after surgery in patients receiving insulin without reaching statistical significance. In the insulin group the plasma concentrations of 13 of 20 essential and nonessential amino acids decreased to a significantly greater extent than in the control group. In summary, supraphysiological hyperinsulinemia, while maintaining normoglycemia, decreased whole body protein breakdown and synthesis in patients undergoing CABG surgery. However, net protein balance remained negative.

Albumin synthesis in surgical patients.

Albumin plasma concentrations are being used as indicators of nutritional status and hepatic function based on the assumption that plasma levels reflect the rate of albumin synthesis. However, it has been shown that albumin levels are not reliable markers of albumin synthesis under a variety of clinical conditions including inflammation, malnutrition, diabetes mellitus, liver disease, and surgical tissue trauma. To date, only a few studies have measured albumin synthesis in surgical and critically ill patients. This review summarizes the findings from these studies, which used different tracer methodology in various surgical or critically ill patient populations. The results indicate that the fractional synthesis rate of albumin appears to decrease during surgery, followed by an increase during the postoperative phase. In the early postoperative phase, albumin fractional synthesis rate can be stimulated by perioperative nutrition, if enough amino acids are being provided and if nutrition is being initiated before the operation. The physiologic meaning of albumin synthesis after surgery, however, still needs to be further clarified.