NUTRITIONAL PRESCRIPTION
Prescribing nutritional support for surgical patients during the
perioperative period (parenteral or enteral) requires knowledge of the patient's
requirements for calories and protein. To accurately predict a patient's proteincalorie
requirements, the physician must know the patient's current state of nutritional
health and current predicted calorie requirements. The previous sections discussed
the assessment of nutritional defects measuring caloric use with indirect calorimetry
and the calculation of REE and measurement of protein requirements by nitrogen balance
studies.
Parenteral versus Enteral Nutrition
Nutritional requirements for perioperative surgical patients can
be administered enterally through the gut or parenterally through a vein.[146]
[147]
Both routes have their indications and advocates.
Enteral feeding through a fine-bore nasogastric tube or bypassing the stomach with
a feeding enterostomy tube in the distal gastrointestinal tract has the advantage
of the use of normal routes for nutrient absorption as well as a decreased risk of
infection. Although enterostomy tubes provide a convenient
simple route for nutrition, they must be carefully monitored for function. If the
stoma breaks down or the tube becomes misplaced, the patient is at risk for peritonitis
from leakage of gut contents or tube feedings into the peritoneal space.
Enteral feeding decreases the atrophy of the luminal brush border
of the gut and may decrease bacterial translocation from the intestinal lumen to
the bloodstream.[148]
However, enteral feeding
intolerance was associated with an increased mortality in a study by Chang and colleagues.
[149]
This complication was aggravated by delayed
recognition of enteral feeding intolerance and a period of starvation before the
commencement of intravenous nutrition. Enteral feeding intolerance is manifested
by diarrhea, bowel distention from unabsorbed feedings, high residual volume aspirated
from the catheter, and failure to reverse signs of malnutrition. It is not immediately
apparent whether the route of nutrition caused the mortality observed by Chang and
coworkers[149]
or merely heralded a more profound
systemic disease. Because the efficacy of perioperative nutritional support is generally
effective only to reverse specific nutritional deficits,[150]
[151]
[152]
[153]
it is unlikely that any route of nutrition would reverse an otherwise inexorable,
downhill clinical course.
Perioperative starvation impairs wound healing[154]
and causes excessive protein catabolism, but routine TPN to all surgical patients
is not cost-effective because well-nourished surgical patients with brief perioperative
fasting periods do not demonstrate a therapeutic effect of TPN.[154]
[155]
[156]
[157]
Cancer patients frequently represent a group of patients who benefit from TPN[158]
[159]
to replace specific nutritional deficits.
The use of enteral feedings administered through a tube distal to the pylorus allows
an increasing use of nutrition support for surgical patients, including cancer patients.
Enteral feeding is associated with fewer complications and less expense than TPN,
but it must be monitored carefully to avoid the complications noted by Chang and
associates.[149]
Appropriately monitored enteral
feedings can be successfully administered into the small bowel of most postsurgical
and trauma patients, including those who have undergone abdominal surgery and patients
with pancreatitis.[160]
Parenteral nutrition through
a central vein provides nutritional support in patients with a nonfunctioning gastrointestinal
tract. Ten years ago, there was a general consensus among critical care medicine
physicians that enteral feeding was superior to TPN.[161]
[162]
However, the pendulum has recently swung
back
to the middle, with most recent recommendations advising early TPN if the patient's
gut function is inadequate. The complication rates for TPN and total enteral nutrition
are similar.[163]
[164]
[165]
[166]
[167]
[168]
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