Parenteral nutrition in the critically ill
Chief dietician, John Radcliffe Hospital, Oxford
Focus on parenteral nutrition
At the current time, in the absence of contraindication, the critical care literature strongly favours adopting enteral nutrition as the first line method for feeding ICU patients. The ESPEN 2006 guidelines suggest avoidance of parenteral nutrition in patients who tolerate enteral nutrition and can be fed approximately to target enteral feeding values. In the critical care setting parenteral nutrition is used to either supplement enteral nutrition if patients cannot be fed sufficiently via the enteral route, or as a sole nutritional technique.
Parenteral nutrition is often indicated when the gastrointestinal tract is either not working, not available, or not appropriate:
Non functioning gut e.g. paralytic ileus
Malnourished patients in whom the use of the intestine is not anticipated for >7 days after major abdominal surgery
Severe mucositis following systemic chemotherapy, upper gastrointestinal strictures or fistulae and severe acute pancreatitis where jejunal feeding is contraindicated
In those patients with major resections of the small intestine (short bowel syndrome) before compensatory adaptation occurs
The duration of parenteral nutrition is commonly determined by the return of normal gut function. Longer-term parenteral nutrition may be required in a small number of patients for various reasons. Examples would include:
Extreme short bowel syndrome of any aetiology
Other causes of prolonged intestinal failure e.g atresia, radiation enteritis, some inflammatory or motility disorders
Focus on parenteral nutrition composition
Parenteral nutrition protein is provided in the form of amino acids.
Carbohydrate and lipid
Total energy intake is best given as a mixture of glucose and lipid, usually in a ratio of 60:40 or 50:50. The exact ratio can be varied if clinically important glucose intolerance develops, or if there is a requirement for a lipid free bag. The energy in parenteral nutrition is described as non-protein calories.
The overall aim is to provide all fluid volume requirements via parenteral nutrition, including losses from wounds, drains, stomas and fistulae. However, if these losses are large or highly variable, they should be replaced and managed separately.
These are modified according to clinical requirements with particular regard to extra-renal losses. Frequent monitoring is needed.
Vitamins, minerals and trace elements
These are added routinely on a daily basis. Extra Zinc or Selenium may be required in patients with large gastrointestinal losses. Patients on long-term parenteral nutrition require routine micronutrient screening.
Focus on the use of IV glutamine with parenteral nutrition
Glutamine is considered a conditionally essential immunonutrient that is derived from muscle protein breakdown. It has been suggested that IV glutamine should be routinely given if an ICU patient is being fed entirely by the parental route. The theory behind this is that the catabolic status associated with critical illness increases consumption of glutamine. This leads to a critical depletion of muscle glutamine stores with the following theoretical consequnces:
- Increased translocation of bacteria or bacterial toxins
- Decreased activity of macrophages and killer cells in the intestinal wall
- Increased risk of sepsis
- Increased morbidity and mortality
- Prolonged stay at the intensive care unit or in the hospital
However, at the current time supplementation with IV glutamine on the ICU is not routine. This is in part due to lack of clinical evidence of improved outcome and in part cost.
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Should immunonutrition become routine in critically ill patients? A systematic review of the evidence.
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Meta-analysis of parenteral nutrition versus enteral nutrition in patients with acute pancreatitis.
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Parenteral vs. enteral nutrition in the critically ill patient: a meta-analysis of trials using the intention to treat principle.
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