• protein balance [ Time Frame: two days after surgery ] [ Designated as safety issue: No ]
  

• albumin synthesis, fibrinogen synthesis, total plasma protein synthesis, mRNA expression of ubiquitin [ Time Frame: two days after surgery ] [ Designated as safety issue: No ]
  

The major objective of the nutritional management of surgical patients is to accelerate wound healing and increase resistance to infection while preventing wastage of functional and structural proteins. Parenteral nutrition represents a useful strategy to achieve this goal, particularly in patients undergoing major abdominal procedures with temporary intolerance to oral feeding. At present administration of large, hypercaloric amounts of glucose together with amino acids is the only nutritional modality to establish a positive protein balance (anabolism) after surgery. The fact that hyperalimentation requires central venous cannulation, causes hyperglycemia and is associated with increased morbidity is an impediment to its routine use. Attempts to induce anabolism by diminishing the glucose load to iso- or hypocaloric quantities failed because of

• failure to control for type and quality of perioperative analgesia
• inadequate assessment of the patient`s catabolic status prior to surgery with subsequent
• lack of individualization of energy and substrate supply.

We recently demonstrated that segmental pain relief by epidural analgesia facilitates oxidative glucose utilization thereby decreasing the amount of glucose necessary to attenuate protein losses after surgery. Hypocaloric glucose and epidural analgesia prevented the postoperative increase in protein oxidation, but only if preoperative fasting was avoided, i.e. the glucose infusion was started 24 hours before surgery. We also showed that patients with epidural analgesia could be rendered anabolic by short term administration of glucose and amino acids. Based on our findings of anti-catabolic and anabolic effects of epidural analgesia in the presence of energy and substrate supply we now propose that epidural analgesia and hypocaloric parenteral nutrition initiated 24 hours before colorectal surgery will produce a more positive postoperative protein balance including a greater muscle protein synthesis than when initiated with skin incision.

In order to test the validity of this assumption, patients scheduled for elective colorectal cancer surgery will be randomly assigned to an "early" or "late" feeding protocol. "Early" nutrition will start 24 hours prior to surgery, "late" nutrition will commence with surgical skin incision. Nutrition will be adjusted to provide 50% of the patient`s actual energy expenditure as glucose and 20% as amino acids. The stable isotope tracer L-[1-13C]leucine will be applied to assess whole body protein breakdown, amino acid oxidation and protein synthesis. A positive protein balance (difference between protein synthesis and protein breakdown) will be used as an indicator of anabolism. Because whole body protein kinetics provide no insight into metabolic processes at organ level (muscle, liver), the fractional synthesis rates of albumin, fibrinogen and muscle protein will also be determined after surgery.

The demonstration of anabolic effects of epidural analgesia and nutrition with less than half the commonly used energy would have a valuable practical application. If the nutrient load can be decreased, use can be made of peripheral veins and hyperglycemia can be avoided, thus making nutritional therapy more efficacious, safer and available to more patients.