TPN in Critical Care by Bharesh Dedhia

TPN in Critical Care - Bharesh DedhiaIn general, the enteral route is preferred over the parenteral route, as the former is more physiologic, is less likely to be associated with biliary stasis and hyperglycemia, and is significantly less expensive.9 Many studies have purported to show that total parenteral nutrition (TPN) is associated with higher infection rates than is enteral feeding, although this has not been confirmed when equivalent calories have been administered by each route and when overfeeding with TPN is avoided.Contraindications to enteral feeding include diffuse peritonitis, intestinal obstruction, intractable vomiting, paralytic ileus, and severe diarrhea. Hypotension with hemodynamic instability is associated with reduced intestinal blood flow, and low tolerance to enteral feeding is the rule.TPN plays an important role in patients in whom the gut cannot be used. Administration of 25 kcal/kg of usual body weight is adequate for most patients with normal BMI. In most patients this goal approximates the one calculated from the Harris Benedict equation. With BMI <> 100 mg/dL might be an indication to decrease nitrogen intake, although this is not well validated in the acute illness setting. A more usual issue in feeding the patient with acute renal failure is that volume restrictions limit the quantity of feeding. In persons with chronic renal insufficiency, 0.8 g/kg/d of protein is sufficient. Another possible indication for limiting protein consumption in TPN occurs in persons in whom hepatic encephalopathy is a major clinical problem. Reducing the amino acid load or using a high quantity of branched-chain amino acids (BCAAs) have been shown to improve mental status.The lipid component of TPN consists of omega-6-polyunsaturated fatty acids that may be administered separately from the dextrose/protein or as part of a three-in-one solution. Theoretical concerns with overfeeding of lipids include injury to the reticuloendothelial system, which might lead to immunosuppression and can negate the beneficial effect of nutrition support. However, limiting fat calories to 30% of total calories is unlikely to lead to this complication, especially when the fat is infused slowly as with the three-in-one solution. Triglyceride levels > 400 mg/dL are a relative contraindication to adding lipids.Carbohydrates should constitute the remainder of the total calories at between 3 and 5 g/kg/d,8 however, the specific amount should be adjusted appropriately to maintain a blood glucose level <> 220 mg/dL) has been shown to increase the risk of nosocomial infection to a degree that nullifies the benefits of nutritional repletion.16 Severe stress (eg, postoperative patients) is accompanied by rising plasma levels of the counterregulatory hormones glucagon, epinephrine, and cortisol, and thus, postoperative patients are most at risk from TPN-induced hyperglycemia.Fluid restriction is often vital in cardiac, pulmonary, postoperative, and renal patients in the ICU. For such patients, TPN can be restricted to 1 L. Maximally concentrating nutrients allows the provision of 1,000 kcal and 70 g of protein per liter, which is often a substantial percentage of the weight-based feeding goal. Vitamins and trace elements are usually administered as components of the TPN. In addition, a number of medications, such as histamine-2 receptor antagonists and metaclopramide, can be mixed in with the TPN solution.Bharesh Dedhia