Title: The management of critically ill patients with enteral and parenteral nutrition
Key words: malnutrition, protein-calorie, surgery, shock, trauma, burns, sepsis, critically ill, enteral, parenteral nutrition, nutritional support, gut permeability, gut mucosal atrophy, gut permeability, secretory immunoglobulins, gastrointestinal hormones, gut translocation, immunosuppression, postoperative sepsis, immunonutrition, immunomodulators, cytokine, arginine, glutamine, nucleotides, gastroduodenal motility, regurgitation, pneumonia, mortality rate, ventilated patients, ICU, TPN, soybean, emulsions, triglycerides, omega-3, PUFAs, polyunsaturated fatty acids, line infections, secondary infections, bowel paresis,
Date: Oct 2006
Category: Special diets
Author: Morgan, G
The management of critically ill patients with enteral and parenteral nutrition
Severe protein-calorie malnutrition is a major problem in the critically ill patient, especially following surgery, trauma, shock, burns or sepsis. Amongst surgical patients, for example, the rate of malnutrition has been found to be tripled (Gallagher-Allred 1996), with serious immunologic, metabolic and physiological consequences. The use of enteral and parenteral nutrition has been found useful in addressing these issues. This review will look at the advantages and disadvantages of these two forms of nutritional support in the critically ill.
The concept that enteral nutrition is the preferred form of nutritional support in the critically ill rests on much clinical research and has led to the maxim “if the gut works, use it”(Baskin 1992). In contrast to enteral nutrition, parenteral nutrition leads to gut mucosal atrophy, the loss of secretory immunoglobulins and gastrointestinal hormones, and increased gut permeability (Lara 1998). Although there is no direct evidence that these changes lead to gut translocation, bacterial antigenic transfer occurring via the mucosa is part of the process that occurs during the bacterial translocation and immunosuppression taking place during septic infection in these critically ill patients (Lara 1998). Immunological suppression in the context of surgery, trauma and malnutrition, is the major factor leading to sepsis in the critically ill (Bozzetti 1999).
A review in 1991 (Moore 1991) comparing enteral versus parenteral nutrition on the rate of postoperative sepsis, which showed a reduction from 35% to 18%, has been followed by several other analytic reviews confirming significant reduction in infection rates in such groups treated with enteral nutrition (Suchner 2000, Grimble 2001, Sacks 2003). Earlier enteral nutrition in these groups appears to yield improved results (Braga 1999, Marik 2001). These results are mirrored in much research which demonstrates the beneficial effects of immunonutrition formulae, such as Impact, containing immunomodulators, such as omega-3 fatty acids, arginine, glutamine and nucleotides, on the body’s cytokine, prostaglandin and immunologic profile (Senkal 1995, Kemen 1995, Gianotti 2000). The downside to enteral nutrition is that protocol targets are rarely met, particularly in the critically ill, largely due to diminished gastroduodenal motility and regurgitation (Griffiths 2003). In one series of ventilated medical ICU patients (Ibrahim 2002), only 28% achieved target nutrition due to upper gastrointestinal intolerance. A major concern has been the increased rate of pneumonia in such series, with, in one study (Mentec 2001), an increased mortality rate. It has been argued that increased pneumonia rates may counteract the beneficial nutritional and immunologic effects of enteral nutrition in the critically ill leading to impaired mortality (Griffiths 2003).
In the most recent analyses, the benefits are much less clearcut in these groups (Wischmeyer 2001), with some evidence for an increased mortality rate (Heyland 2001). In the less critically ill, the consensus is that enteral nutrition carries with it a lower rate of sepsis and is to be preferred (Jolliet 1999). However, a more discriminating use of parenteral nutrition in recent years coupled with more effective TPN formulae has progressively improved the results of parenteral nutrition. The original soybean-based emulsions were shown to possess negative immunologic properties (Battistella 1997, Dupont 1999) and have now been replaced with emulsions containing omega-3 PUFAs, medium chain triglycerides, arginine, glutamine and nucleotides, with positive nutritional and immunologic profiles (Chan 1998, Griffiths 2003).
The use of glutamine has attracted especial interest. Its use enterally has led to significant reductions in pneumonia rates, though not to mortality rates (Conejero 2002). By contrast, intravenous use has led to pronounced reductions in line infections, pneumonia, secondary infections, and other complications leading to improved mortality figures in the critically ill (Griffiths 2001, Dechelotte 2002).
In summary, both enteral and parenteral nutrition have a place in the management of the critically ill. Both help to provide an energy-dense form of nutrition to a depleted nutritional and immune system, reducing the rate of septic complications and length of hospital stay. The beneficial effects of enteral nutrition on the gastrointestinal tract, and in terms of reduced sepsis rate and cost, make it the route of choice in the less critically ill. Bowel paresis is only a relative contraindication to its use. In the most seriously ill, parenteral nutrition remains the route of choice: target rates are more easily met, pneumonia, secondary infection and complication rates are reduced, and overall mortality improved.
Patient selection is of prime importance, with those undergoing major elective abdominal surgery being candidates for enteral nutrition, and those with more severe nutritional deficiencies and clinical status, in an ICU setting, being candidates for parenteral nutrition. The expertise of the medical team is also of prime importance in such management decisions.
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