Nutritional Support in Surgical Patients

Surgery increases the risk of malnutrition, which can increase morbidity in the perioperative setting. Therefore, surgical patients should be carefully assessed for malnutrition and the need for enteral or parenteral nutritional support. In this section, we briefly review the following topics:

• Nutritional and Metabolic Changes in Acute Illness

  • Assessment of Malnutrition

  • Determination of Nutritional Requirements

  • Indications for Supplemental Nutrition

• Enteral Nutrition

• Parenteral Nutrition

• Risks Associated with Supplemental Nutrition

• Considerations in Special Patient Populations

Nutritional and Metabolic Changes in Acute Illness

Malnutrition affects as many as 50% of inpatients, leading to increased risk for complications and mortality, longer hospital stay, and higher hospital costs. The acute stress of surgery further increases the risk of malnutrition and leads to global metabolic changes that include increased catabolism during acute illness and anabolism during subsequent recovery. These metabolic changes cause a negative nitrogen balance with protein breakdown, resulting in as much as 5% loss of muscle mass per day. In critically ill patients, the loss of muscle mass can lead to delayed ambulation perioperatively and compromise of respiratory muscles.

Preoperative fasting also creates metabolic stress associated with greater risk of postoperative complications. Providing preoperative nutritional supplementation to increase total energy and protein intake has been shown to reduce mortality in critically ill patients and lower the complication rate in surgical patients.

Assessment of Malnutrition

History and physical examination: A focused and thorough history and examination are key to diagnosing malnutrition.

• The history should include evaluation of the following markers of nutrition:

  • food and nutritional intake

  • recent weight loss

  • gastrointestinal symptoms

  • functional capacity

• The physical exam can reveal the following findings associated with malnutrition:

  • loss of muscle mass or subcutaneous fat

  • resultant fluid accumulation with edema or ascites

  • weakened handgrip strength suggesting poor functional status

Assessment tools: A number of tools have been developed to assess for malnutrition, including the following:

• Nutritional Risk Screening (NRS) Tool

• Nutrition Risk in the Critically Ill (NUTRIC) Score

  • ASPEN recommends using either NRS or NUTRIC to assess nutrition risk.

  • Head-to-head comparisons have suggested that NRS is a more sensitive tool but that NUTRIC may have better discriminatory ability.

  • NUTRIC has been validated in more patient populations and is associated with mortality risk and prognostication in critical care settings.

• Nutrition Risk Index (NRI)

Laboratory testing should not be used to diagnose malnutrition but can be useful for identifying sequelae of malnutrition and for nutritional planning by consulting nutritional support teams. Although albumin and prealbumin were historically used as biomarkers of malnutrition, they have more recently been shown to correlate poorly with protein-energy malnutrition.

Determination of Nutritional Requirements

• Indirect calorimetry remains the gold standard for determining nutritional requirements.

  • Indirect calorimetry is easily performed in ventilated patients in whom exhaled carbon dioxide (CO₂) can easily be measured.

• Equations have been developed to predict nutritional requirements. Although the accuracy of these equations is more variable than indirect calorimetry, they can be used to estimate caloric needs.

  • The Harris-Benedict equation estimates resting energy expenditure based on weight, height, and age.

  • The Penn State equation estimates resting metabolic rate from minute ventilation and body temperature.

Indications for Supplemental Nutrition

A number of societies have published guidelines for nutritional support in critically ill patients, including the American Society for Parenteral and Enteral Nutrition (ASPEN), European Society for Clinical Nutrition and Metabolism (ESPEN), Canadian Critical Care Clinical Practice Guidelines Committee, and Society of Critical Care Medicine (SCCM). Early consultation with the nutrition team can assist with nutritional monitoring, decision-making, and titration of supplementation for each patient.

Recommendations for indications for supplemental nutrition:

• Critically ill patients should be considered for early nutrition as soon as possible within 48 hours of admission to the intensive care unit (ICU).

• Patients at high risk for malnutrition (NRS-2002 >5 or NUTRIC score ≥5) should be started on supplemental nutrition early, with preference for enteral nutrition over parenteral nutrition if tolerated.

• Patients at low risk for malnutrition (NRS-2002 ≤3 or NUTRIC score ≤5) and low disease severity can defer supplemental nutrition for one week.

• Postoperative surgical patients often experience poor oral intake due to the underlying disease process or postoperative recovery. Therefore, history of oral intake should be elicited after one week to determine the need for supplemental nutrition.

Enteral Nutrition

Enteral nutrition is preferred over parenteral nutrition whenever tolerated, fulfilling the maxim: “If the gut works, use it.” If the patient can tolerate oral nutrition, poor intake can be supplemented orally with nutritional shakes.

• Feeding tube placement: If oral intake is contraindicated or poorly tolerated, enteral access for nutrition may be obtained with orogastric, nasogastric, or postpyloric (nasoduodenal or nasojejunal) tubes.

  • Feeding tube placement may be complicated by aspiration of gastric contents on placement and placement into the lung with resultant bronchial injury or pneumothorax.

    • An instructional video on nasogastric tube placement can be found here.

    • All feeding tube placements should be confirmed radiographically prior to administration of feeds, fluids, or medications via the tube.

  • Gastrostomy or jejunostomy tubes may be placed surgically or endoscopically in patients requiring long-term supplementation.

    • The most significant risks associated with surgical or endoscopic tube placement include intestinal injury or perforation and accidental dislodgement, which may cause intra-abdominal sepsis requiring exploratory laparotomy.

    • The risk-benefit profile for each patient should be discussed with the appropriate interventional team.

• Assessing risk of aspiration: Patients receiving enteral nutrition should be assessed for risk of aspiration.

  • Patients at high risk of aspiration should be considered for postpyloric access to avoid distending the stomach with feeds.

  • Gastric residual volumes were traditionally used to assess risk of aspiration. However, current guidelines recommend against this practice to determine continuation of enteral nutrition. Gastric residual volumes have not been shown to accurately predict incidence of aspiration pneumonia or mortality and can lead to inappropriate discontinuation of enteral nutrition and inadequate nutritional supplementation.

• Assessing tolerance of enteral nutrition: Patients should be assessed on an individual basis to determine if “the gut works” and enteral nutrition is tolerated based on the following characteristics:

  • presence of bowel function (passage of flatus or bowel movements)

  • symptoms of nausea or emesis

  • signs of abdominal distention or tympany on exam

  • significant gastric or intestinal dilation on imaging suggestive of ileus or obstruction with correlating signs and symptoms

• Composition of enteral nutrition: The composition of enteral nutrition is created by specialists on nutritional support teams and individualized for each patient’s unique requirements. The macronutrient composition detailed below may serve as a basic guide.

• Administration of tube feeds:

  • Tube feeds may be initiated with trophic or “trickle” feeds (10-20 cc/hr) to prevent mucosal atrophy and maintain gut integrity before uptitrating to goal rates to meet caloric needs (typically increased by 10 cc/hr every 4-6 hours as tolerated).

  • Gastric tube feeds may be administered on a continuous basis, cycled overnight, or as bolus feeds on a schedule because the stomach can store a significant reserve of feeds.

  • Due to risk of intestinal overdistention, postpyloric feeds should not be administered as a bolus but rather continuously or in a cycled fashion.

Parenteral Nutrition

Surgical patients are frequently unable to tolerate enteral nutrition for several reasons, including obstruction, ileus, delayed gastric emptying, gastrointestinal (GI) fistulas, short gut syndrome, and feeding tube complications. Parenteral nutrition should be instituted for adequately nourished patients who are not expected to take adequate enteral nutrition for 7 days, and sooner for patients with existing malnutrition.

• Options for parenteral nutrition:

  • Total parenteral nutrition (TPN) is more concentrated and requires central access due to high osmolarity and causticity to peripheral veins. Patients who are expected to require parenteral nutrition for more than 7 to 10 days should be initiated on TPN.

  • Partial parenteral nutrition (PPN) has limited osmolarity and may not adequately provide caloric content.

• Composition of parenteral nutrition:

  • Parenteral nutrition consists of 20-25% protein, 10-30% lipid, and 50-60% carbohydrate by calories.

  • Electrolyte and acid-base abnormalities can be corrected by adjusting the electrolyte balance in the solution.

  • Finer adjustments can be made for patients with kidney disease, liver disease, hyperglycemia, or electrolyte derangements.

• Administration of parenteral nutrition:

  • Parenteral nutrition may be administered on a continuous basis or cycled overnight, typically at a rate that obviates the need for additional maintenance fluids.

  • As patients begin to tolerate enteral nutrition, calorie counts should be employed to determine continued need for parenteral nutrition and the proportion of caloric intake received via parenteral nutrition gradually weaned.

Risks Associated with Supplemental Nutrition

Enteral nutrition

• Enteral nutrition should not be initiated in critically ill patients when there is concern for bowel ischemia.

  • Although hemodynamic instability has traditionally been considered a contraindication to enteral nutrition, recent studies demonstrate that patients on vasopressors can safely receive enteral nutrition and benefit from early nutrition.

• Enteral nutrition is contraindicated in patients with obstructive processes.

• Patients receiving enteral nutrition should be evaluated for risk of aspiration with consideration of postpyloric enteral access or initiation of parenteral nutrition for high-risk patients.

  • Although postpyloric tubes have traditionally been recommended for patients with high risk of aspiration, they have not been shown to reduce risk of aspiration or mortality.

Parenteral nutrition

• Parenteral nutrition carries risk of electrolyte derangements and metabolic acidosis, as well as dyslipidemia and cholestatic liver injury due to its lipid content.

  • For this reason, a lipid and triglyceride panel should be obtained prior to initiation and monitored at least weekly during the course of parenteral nutrition.

• Avoid line-associated infections in patients who require longer-term parenteral nutrition, particularly through central venous lines.

  • Central line placement may also be complicated by vascular injury, pneumothorax, or hemothorax particularly with subclavian lines.

    • Long-term patients on parenteral nutrition may develop central venous stenosis. In patients who may require long-term hemodialysis access, nephrology should be consulted prior to placement of indwelling central lines.

  • For these reasons, peripherally inserted central catheters (PICC) are preferred in patients requiring parenteral nutrition of short or unknown duration.

Refeeding syndrome

• Severely malnourished patients who are newly initiated on supplemental nutrition should be closely monitored for refeeding syndrome, which can cause hypokalemia, hypomagnesemia, and hypophosphatemia and can lead to life-threatening cardiac arrhythmias.

• Patients with refeeding syndrome require close monitoring of electrolytes, aggressive correction of metabolic derangements, and cautious initiation and advancement of supplemental nutrition.

Considerations in Special Patient Populations

• Trauma

  • Trauma patients in critical condition, like all ICU patients, should be considered for early enteral nutrition as tolerated, once stabilized from a hemodynamic standpoint.

  • Severe trauma and burn patients likely have higher protein requirements (1.5-2.0 g/kg/day).

• GI malignancies

  • Patients with gastrointestinal malignancies (particularly patients with esophageal malignancy) may suffer from prolonged malnutrition preoperatively and benefit from enteric access at time of resection.

  • Routine placement of jejunostomy tubes during Whipple procedures for pancreatic malignancies has been linked to delayed gastric emptying and perioperative morbidity.

• Pancreatitis

  • Patients with severe pancreatitis benefit from early enteral nutrition.

    • No strong evidence of benefit exists for postpyloric enteral feeding versus gastric feeding in patients with pancreatitis.