Nutrition in the ICU

Patients in the intensive care unit (ICU) are at increased risk of malnutrition, and few can feed themselves. Route, timing, rate, and formulation of nutritional support are important to consider.

Enteral nutrition, via a tube directly into the gastrointestinal tract, is the mainstay of nutritional support. Parenteral nutrition, delivered intravenously via peripheral or central vein, is an option for patients unable to be fed enterally.

Contraindications to enteral nutrition include:

• severe hemodynamic instability

• increased risk of bowel ischemia, ileus, bowel obstruction, gastrointestinal bleeding
  
  

Timing of nutritional support is an important factor in ICU patients. Although data are inconclusive, early enteral feeding (within 48 hours of ICU admission) is thought to decrease the risk of infection. However, no evidence of benefit exists for starting parenteral nutrition early.

• In one study, 90-day mortality in patients started on early (within 48 hours) or late (after day 7) parenteral nutrition was similar. However, early IV nutrition was associated with increased risk of infection and a longer hospital stay. In practice, when enteral feeding is not an option, most patients are not started on IV nutrition until day 7−10 in the ICU.

• In a 2018 study, no differences in mortality or secondary infections were found between early enteral versus early parenteral nutrition in ventilated patients with shock. However, early enteral feeding was associated with increased risk of bowel ischemia. (Note that in this study, nutrition was initiated at target rate, which is not done in practice).
  
  

Rate: The recommendation in critically ill patients is to initiate feeding at 20%−30% of metabolic need during the first week in the ICU. Metabolic requirements can be calculated from one of many online calculators (e.g., ClinCalc, SurgicalCriticalCare.net). Standard practice is to initiate early enteral nutrition when a patient can tolerate it.

Refeeding syndrome: When starting artificial nutrition, it is important to monitor for refeeding syndrome (e.g., hypophosphatemia, hypokalemia, and hypomagnesemia, as well as vitamin deficiencies).

Stress ulcers: Patients in the ICU are at increased risk for stress ulcers. Risk factors include shock, sepsis, and mechanical ventilation. To prevent stress-related gastrointestinal bleeding, patients are frequently started on prophylactic acid suppressive medications. In a 2018 study, regular pantoprazole use was not associated with a benefit in 30-day mortality. However, pantoprazole did reduce GI bleeding and therefore, should be used in high-risk patients.

Glycemic management in the ICU setting: Hyperglycemia is associated with critical illness due many different factors including increased cortisol secretion, gluconeogenesis, and insulin resistance. Hyperglycemia is associated with poor outcomes and insulin therapy for glucose control is the standard of care. Several studies have investigated the optimal blood glucose goals in critically ill patients. In the NICE-SUGAR trial, a more-stringent blood glucose target of 81—108 mg per deciliter was associated with increased mortality in adult patients admitted to the ICU, as compared with blood glucose target of 180 mg or less per deciliter. As a result, insulin therapy for glucose control to a more liberal blood glucose target range of 140-180 mg per deciliter is often the goal in critically ill adults.