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INTRODUCTION — Malnutrition in hospitalized patients is well documented with rates up to 50 percent in certain populations . Nutritional support may be indicated for malnourished individuals requiring surgical intervention, or for healthy individuals undergoing major surgery with an anticipated lengthy recovery time to return of normal gastrointestinal function; however, it can be unclear when it is appropriate to intervene. The notion that malnutrition can affect outcomes in surgical patients was first reported in 1936 in a study showing that malnourished patients undergoing ulcer surgery had a 33 percent mortality rate compared with 3.5 percent in well-nourished individuals . A prospective study of 500 patients, including 200 surgical patients, admitted to a teaching hospital in England found that 40 percent of patients were undernourished on presentation, and patients lost an average of 5.4 percent of their body weight during their hospital stay .
The nutritional assessment of surgical patients, options for and potential benefits of nutritional support are reviewed here. An overview of parenteral and enteral nutrition and issues related to nutritional support in critically ill patients, and other specific populations (eg, cancer, burns, lung disease) are discussed in separate topic reviews.
CONSEQUENCES OF MALNUTRITION IN SURGICAL PATIENTS — Reduced food intake results in loss of fat, muscle, skin, and ultimately bone and viscera, with subsequent weight loss, and expansion of the extracellular fluid compartment . Nutritional requirements fall as an individual's body mass decreases, probably reflecting more efficient utilization of ingested food and a reduction in work capacity at the cellular level. However, the combination of decreased tissue mass and reduced work capacity impedes normal homeostatic responses to stressors such as surgery or critical illness .
The stress of surgery or trauma creates a hypermetabolic state, increasing protein and energy requirements. Macronutrients (fat, protein, and glycogen) from the labile reserves of fat tissue and skeletal muscle are redistributed to more metabolically active tissues such as the liver and visceral organs. This response can lead to the onset of protein calorie malnutrition (defined as a negative balance of 100 g of nitrogen and 10,000 kcal) within a few days . The rate of development of postoperative malnutrition in a given individual depends upon their preexisting nutritional status, nature and complexity of the surgical procedure, and the degree of hypermetabolism.
Malnutrition causes a number of negative consequences, including [4,5,7,8]:
●Increased susceptibility to infection
●Poor wound healing
●Increased frequency of decubitus ulcers
●Overgrowth of bacteria in the gastrointestinal tract
●Abnormal nutrient losses through the stool
Of particular concern for patients undergoing surgery are the risks of postoperative infection and poor wound healing. Malnutrition leads to immune system dysfunction by impairing complement activation and production, bacterial opsonization, and the function of neutrophils, macrophages, and lymphocytes . One series of underfed patients identified subnormal skin reactions to Candida and low levels of antibodies to various phytomitogens, suggesting that humoral and cell-mediated immunity are affected . (See "Secondary immunodeficiency due to underlying disease states, environmental exposures, and miscellaneous causes", section on 'Malnutrition'.)
Patients with protein energy malnutrition also have slower rates of wound healing , although most wounds will eventually heal on their own . Additional adverse effects associated with malnutrition were identified in a study of 2743 patients undergoing cardiothoracic surgery . Patients with preoperative hypoalbuminemia alone or in association with chronic liver disease or heart failure were more likely to have postoperative organ dysfunction (cardiac, pulmonary, renal, hepatic, neurologic), gastrointestinal bleeding, nosocomial infections, increased days on mechanical ventilation and length of stay in the intensive care unit, and inpatient death. A body mass index (BMI) <20 kg/m2 was associated with lower morbidity and mortality compared with a higher BMI; however, this finding in this study contrasts with other studies. BMI is an imperfect measure of nutritional status and should be used in conjunction with other clinical indicators.
NUTRITIONAL ASSESSMENT IN THE SURGICAL PATIENT — The first task when considering perioperative nutritional recommendations is to assess whether or not the patient has malnutrition. The basic principle of dietary and nutritional assessment in the general population is discussed elsewhere. Important aspects of nutritional assessment that pertain to surgical patients are reviewed below. (See "Dietary assessment in adults".)
Based upon expert consensus, a diagnosis of malnutrition requires that the patient exhibit two or more of the following [13,14]:
●Insufficient energy intake
●Loss of muscle mass
●Loss of subcutaneous fat
●Localized or generalized fluid accumulation that may sometimes mask weight loss
●Diminished functional status as measured by handgrip strength
History and physical — Several aspects of the past medical history are of particular importance, including chronic disease (particularly diabetes), infection, recent hospitalization, and prior surgery (particularly gastrointestinal surgery).
On review of systems, a history of weight loss or gain is important. Any recent losses or gains (and whether they were purposeful or not) prior to the hospital stay should be assessed. The details of the current hospitalization also play a central role. Newly admitted trauma patients who are otherwise well have drastically different needs from patients who have had surgery several weeks in the past but have remained hospitalized due to complications.
In addition to collecting information on current medications, nonprescription medicines and other supplements should be noted. The use of dietary supplements, such as protein shakes, should also be determined. Lastly, any allergies or food intolerances should also be noted. A diet history should be collected from the patient, family, or care facility. Although there are several methods of dietary assessment, the most useful and straightforward may be to assess the usual intake on an average day before hospitalization or before the onset of the current illness .
In addition to vital signs and a general physical examination, the following should be noted:
●General: Loss of subcutaneous fat, any generalized fluid accumulation
●Head and neck exam: Hair loss, bitemporal wasting, conjunctival pallor, xerosis, glossitis, bleeding or sores on the gums and oral mucosa, angular cheilosis or stomatitis, dentition
●Cardiovascular: Evidence of heart failure or high-output state
●Extremities: Edema, loss of muscle mass
●Neurologic: Evidence of peripheral neuropathy, reflexes, tetany, mental status, handgrip strength
●Skin: Ecchymoses, petechiae, pallor, pressure ulcers, assessment of surgical wound healing and signs of surgical site infection (if postoperative).
Signs of specific nutritional deficiencies should also be sought. Some of these are given in the table (table 1). Appropriate micronutrient levels should be investigated depending on clinical exam findings. (See 'Other laboratory studies' below.)
Several clinical tools are available to quickly assess and score nutrition status. The Subjective Global Assessment of Nutritional Status is a brief tool that includes history and physical examination findings, and allows standardized assessment . The Nutritional Risk Screening tool (NRS 2002) can be applied rapidly and used to screen for poor baseline nutritional status . A study that assessed the ability of the NRS 2002 score to predict the incidence and severity of postoperative complications found the overall incidence of nutritional risk was 14 percent among 608 patients undergoing gastrointestinal surgery . A significantly higher overall complication rate was found in patients at nutritional risk compared with those with a normal NRS 2002 risk score (40 versus 15 percent). Severe complications were also significantly higher in patients at nutritional risk (54 versus 15 percent).
Assessing protein status — Assessing protein status is particularly important in the surgical patient because of the close relationship between protein status and wound healing, and because protein-calorie malnutrition can be treated with supplementation as discussed below [19,20]. Protein status is affected by previous intake, muscle mass, duration of current illness, blood loss, wound healing, infections, and gastrointestinal absorption.
Three serum measures of protein status have differing half-lives. These serum components do not directly indicate nutritional status, but rather reflect the severity of illness and must be used in conjunction with other clinical data such as the duration of the current surgical illness to be useful in determining therapy. Although decreased levels for these protein markers correlate with adverse outcomes, improvements in these markers with nutritional supplementation are not reliably associated with a clinical benefit . (See 'Outcomes for nutritional intervention' below.)
●Serum albumin has the longest half-life at 18 to 20 days and is the most extensively used parameter. Low serum albumin (<2.2 g/dL) is a marker of a negative catabolic state, and a predictor of poor outcome . Surgical stress, other acute stresses, hepatic disease, and renal disease decrease serum albumin levels.
●Serum transferrin has an intermediate half-life of eight to nine days, reflecting protein status over the past two to four weeks. Transferrin also reflects iron status, and low transferrin should be considered an indicator of protein status only in the setting of normal serum iron.
●Serum prealbumin (transthyretin) has the shortest half-life at two to three days. Although prealbumin responds quickly to the onset of malnutrition and rises rapidly with adequate protein intake, the level can be altered in the acute phase response due to acute or chronic inflammation. In general, inflammatory cytokines reduce the level of prealbumin synthesis by the liver, and it can also be reduced with renal and hepatic disease. Therefore, serum prealbumin is the least helpful of the three for assessing overall nutritional status.
Other laboratory studies — In addition to assessing protein status, a few other laboratory studies may be helpful. Electrolytes, glucose, and BUN/creatinine help assess overall clinical and fluid volume status and need to be obtained if parenteral (intravenous) nutrition will be instituted. Iron levels should be measured in the setting of unexplained anemia, as should specific vitamin levels if clinically indicated (eg, B12/folate in macrocytic anemias, others based upon specific physical signs). Serum calcium, magnesium, and phosphorous should also be assessed periodically, particularly in the setting of poor oral intake or diarrhea .
NUTRITIONAL INTERVENTIONS — Once the presence of malnutrition is established, or it becomes clear that the patient will not be able to maintain adequate nutrition, nutritional intervention may include oral supplementation, enteral (tube) feeding, or parenteral (intravenous) feeding. Enteral support is recommended over parenteral support because of its relative simplicity, safety, reduced complications, and lower cost, as well as its ability to maintain mucosal barrier function.
●Enteral nutrition – Enteral nutrition support refers to the provision of calories, protein, electrolytes, vitamins, minerals, trace elements, and fluids via an intestinal route, either orally or via a feeding tube.
•Oral supplementation – There is a wide variety of supplements available for oral supplementation in a wide range of styles (juice, yogurt, milk shakes), formats (liquid, powder, pudding, pre-thickened), types (high protein, fiber-containing, low volume), energy densities (1 to 2.4 Kcal/mL), and flavors. Most oral supplements provide 300 Kcal, 12 g protein, and a full range of vitamins and minerals. Specific types of oral supplements may benefit certain groups. In general, high protein oral supplements are most suitable for patients with wounds, and those with malignancy. Prethickened supplements and puddings are helpful for providing nutritional support to individuals with dysphagia and those with neurological conditions.
•Tube feeding – Enteral nutrition may be delivered in a gastric or postpyloric fashion. The available formulations, components, and delivery of enteral nutrition are reviewed elsewhere. (See "Nutrition support in critically ill patients: An overview" and "Nutrition support in critically ill patients: Enteral nutrition".)
●Parenteral nutrition – Parenteral nutrition is an intravenous solution that contains dextrose, amino acids, electrolytes, vitamins, minerals, and trace elements. The available formulations, components, and delivery of parenteral nutrition are reviewed elsewhere. (See "Nutrition support in critically ill patients: An overview" and "Nutrition support in critically ill patients: Parenteral nutrition".)
As the complex interactions between nutrition, mucosal barrier function, immunoregulation, and severe illness have become clearer, tailored forms of enteral nutritional support for specific disease states have been developed. Many enteral and parenteral formulas contain nutrients previously considered nonessential, such as arginine, glutamine, RNA nucleotides, and omega-3 fatty acids. During an episode of critical illness, these nutrients may become "conditionally essential." Formulas that are supplemented with these components are often referred to as immune-enhancing nutritional supplements, or simply immunonutrition. (See "Nutrition support in critically ill patients: An overview" and 'Immune-enhancing nutritional supplements' below.)
INDICATIONS — The general indications for nutritional support include preexisting nutritional deprivation, anticipated or actual inadequate energy intake by mouth, and significant multiorgan system disease. Among patients undergoing surgery, patients who undergo gastrointestinal surgery may be at a greater nutritional disadvantage if the return of intestinal function is significantly delayed [24-30].
Early enteral feeding (oral, tube feeding) can be instituted following many types of surgery [30,31]. A Cochrane review and metaanalysis updated in 2011 identified no obvious advantage to the routine practice of maintaining patients “nil per os” (ie, NPO) postoperatively . The review identified 14 trials that included 1224 patients undergoing predominantly colorectal surgery. No significant differences were identified in the risk of intraabdominal abscess, anastomotic leak/dehiscence, or pneumonia for patients started on early oral nutrition (initiated within 24 hours of surgery) compared with traditional surgical care (ie, no nutrition or oral nutrition when tolerated). Length of hospital stay and the incidence of postoperative wound infection were also similar. A metaanalysis of six of the trials found a slightly increased risk of vomiting (risk ratio 1.27, 95% CI, 1.01-1.61). The higher incidence of vomiting reported in the early feeding group did not appear to be related to oral intake compared with tube feeding. No additional information was given regarding the type of surgery (open versus laparoscopic), or perioperative pain management (eg, opioid or antiemetic use). A later systematic review and metaanalysis that focused on colorectal surgery found similar results; there was a reduced length of hospital stay, but no significant difference in the rate of vomiting between those who received early oral feeding compared with those who did not .
Some patients, such as those with inflammatory bowel disease, have an increased risk of being malnourished when undergoing surgical procedures. A period of bowel rest (nil per os) may be appropriate for patients with disease that is severe enough to require surgical intervention. (See "Nutrition and dietary interventions in adults with inflammatory bowel disease".)
Parenteral support is indicated in postoperative patients who are unable to receive adequate enteral nutrition by postoperative days 10 to 14 [26,34]. Earlier enteral support may be appropriate in patients who are malnourished at baseline, or who have a complicated postoperative course [23,35]. In patients undergoing bowel surgery for gastrointestinal malignancy, malignancy-related metabolic changes may also suggest the need for earlier intervention.
OUTCOMES FOR NUTRITIONAL INTERVENTION — The majority of trials evaluating the potential benefits of perioperative nutritional support are small, and comparisons are difficult due to the wide variety of surgeries studied, variability in methodology, and a lack of standard definitions and measures of malnutrition used. The risks associated with each route of nutritional support, plus the added cost, need to be taken into account, along with the potential benefits, when assessing the need for perioperative nutritional support.
Preoperative nutritional support — Patients with severe malnutrition may derive some benefit from delaying surgery to be fed, but are at an increased risk for infectious complications if treated with total parenteral nutrition. Patients will benefit more from enteral feeding whenever it is possible. For patients who are adequately nourished or who have mild-to-moderate malnutrition, surgery need not be delayed for preoperative parenteral or enteral supplementation [24,25,35]. (See 'Indications' above.)
A multicenter cohort study evaluated the effect of preoperative nutritional support in 512 patients undergoing abdominal surgery who were at nutritional risk as defined by the Nutritional Risk Screening Tool 2002 (NRS-2002) . Of the 120 patients with an NRS score ≥5, the complication rate was significantly lower in the preoperative nutrition group compared with the control group (25.6 versus 50.6 percent). The length of hospital stay was significantly shorter in the preoperative nutrition group than in the control group (13.7 versus 17.9 ± 11.3 days). No significant differences were seen for lesser NRS scores.
Oral supplementation — A systematic review that focused on preoperative nutrition in patients undergoing gastrointestinal surgery included three studies comparing preoperative liquid oral supplementation with usual care or dietary advice . No significant differences were found in the overall incidence of complications, infectious complications, or length of stay. Each of the trials evaluated a different oral supplement.
Parenteral feeding — Several metaanalyses have evaluated preoperative parenteral nutrition, but have reached inconsistent conclusions [37-39].
One systematic review found that preoperative parenteral nutrition (13 randomized trials) decreased postoperative complications by 10 percent, while postoperative parenteral nutrition alone (8 randomized trials) resulted in a 10 percent increase in complication rates . These findings were not verified by a subsequent larger metaanalysis that included 41 trials of parenteral nutrition provided before and/or after surgery . Parenteral nutrition had no effect on postoperative mortality and there was no significant effect on postoperative complication rates, although trends for all evaluated outcomes favored parenteral nutrition over no nutrition.
Another metaanalysis (26 randomized trials, although 3 were not in surgical patients) found that parenteral nutrition decreased hospital complications in studies where lipid-free solutions were used, and for patients who were malnourished (not consistently defined) . These findings were also not confirmed in the larger metaanalysis, which found greater benefit for total parenteral nutrition in trials where lipids were used, and in trials evaluating well-nourished patients .
Studies have also focused on whether particular subgroups might benefit from preoperative parenteral feeding.
●An early study suggested that parenteral nutrition was beneficial in patients with upper gastrointestinal malignancies [40,41]. Mortality and postoperative complications were decreased in a group of patients with gastrointestinal malignancies and weight loss (minimum 10 percent) who received 10 days of preoperative parenteral nutrition and 9 days of postoperative total parenteral nutrition, compared with control patients who did not receive preoperative parenteral nutrition and were only partially supplemented postoperatively . Preoperative treatment with parenteral nutrition also decreased morbidity in a group of patients undergoing resection for hepatocellular cancer . (See "The role of parenteral and enteral/oral nutritional support in patients with cancer".)
●The VA Cooperative study randomly assigned patients to parenteral nutrition for seven days preoperatively and three days postoperatively or to control groups who either received no nutrition or were fed enterally . Overall, patients who received parenteral nutrition had a higher rate of infectious complications (14.1 versus 6.4 percent), but mortality rates were not significantly different (7.3 and 4.9 percent at 30 days). However, in the severely malnourished subgroup, those treated with parenteral nutrition had fewer major postoperative complications than controls (20 to 25 percent versus 40 to 50 percent).
●In a later systematic review (discussed above) that focused on patients undergoing gastrointestinal surgery, preoperative parenteral nutrition significantly reduced the risk for major complications (relative risk 0.64, 95% CI 0.46-087). However, no difference was observed for infectious complications .
Postoperative nutritional support — For many postoperative patients, early enteral nutrition (<24 hours) is possible and is associated with beneficial effects. Enteral nutrition (oral or tube feeds) rather than parenteral nutrition should be instituted whenever possible. For patients with a delayed return of intestinal function, postoperative parenteral nutrition is indicated only if return of bowel function is not anticipated for more than 10 days. Earlier intervention may be appropriate in patients who are severely malnourished at baseline, or who have a complicated postoperative course. (See 'Indications' above.)
Early enteral feeding — Early postoperative enteral nutritional support may decrease the incidence of infectious complications, but does not impact other outcomes. Early nutrition is a component of most enhanced recovery after surgery protocols (ERAS) [45-47].
●A metaanalysis evaluated 44 randomized trials of perioperative enteral nutrition (predominantly postoperative support) . Trials were grouped into three comparisons: enteral nutrition versus no artificial nutrition, enteral nutrition versus parenteral nutrition, and volitional nutritional supplements (oral supplemental feeding) versus no artificial nutrition. There were no mortality differences for any of the comparator groups. Compared with no artificial nutrition, patients receiving enteral nutrition had fewer infections (absolute risk -11 percent, 95% CI -20 to -1 percent), but there was no significant impact on duration of hospitalization or the incidence of wound complications. Patients who received postoperative oral nutritional supplements, compared with no supplements, also had a decreased infection rate (absolute risk difference -10 percent 95% CI -19 to -1), and a shorter length of hospital stay by two days (95% CI -3.37 to -0.72).
●Another metaanalysis comparing enteral nutrition within 24 hours of gastrointestinal surgery with traditional postoperative management showed a 45 percent decrease in the risk of overall postoperative complications in those patients receiving early postoperative feeding. There were no differences in the incidence of anastomotic dehiscence, length of stay, or mortality .
Total parenteral nutrition — Patients who are unable to tolerate enteral nutritional support will require intravenous fluid and total parenteral nutrition at the discretion of the treating team until such time as they can be transitioned to enteral nutrition. The outcomes of total parenteral nutrition in critically-ill postoperative patients, and following burn and cancer surgery, are discussed elsewhere. (See "Nutrition support in critically ill patients: An overview" and "Overview of nutritional support for moderate to severe burn patients" and "The role of parenteral and enteral/oral nutritional support in patients with cancer".)
Immune-enhancing nutritional supplements — The role for immune-enhancing nutritional supplements, also referred to as immunonutrition, remains unclear. There is insufficient high quality evidence to suggest any specific amino acid or other supplementation for all surgical patients. (See 'Nutritional interventions' above.)
Several metaanalyses have evaluated immunonutrition (ie, enteral or parenteral supplementation with arginine, glutamine, nonessential fatty acids, branched chain fatty acids, or RNA) in surgical patients [36,50-52]. Reductions in infectious complications and length of hospital stay have been found, but without an effect on mortality. A 2012 Cochrane review and metaanalysis of preoperative nutritional support found that immunonutrition (six trials) significantly decreased the risk of complications (noninfectious and infectious) (relative risk 0.67, 95% CI 0.53-0.84) . The various metaanalyses have been inconsistent in their results and are without sufficient strength to make clinical recommendations [50,51,53,54]. The authors of these metaanalyses have noted methodological flaws in the individual studies. It is worth noting that surgical patients at the highest risk for postoperative complications have been excluded from the majority of studies on immunonutrition. Thus, until higher quality data demonstrating unequivocal benefit are available, immunonutrition cannot be recommended as a routine addition to nutritional supplementation in surgical patients.
Studies of individual and combinations of components of immunonutrition have demonstrated some benefit but no effect on survival in surgical patients [15,50,51,54-65]. Separate metaanalyses have found a significantly reduced incidence of infectious complications and reduced length of hospital stay for patients receiving supplemental glutamine , or arginine . However, a later multicenter trial randomly assigned 150 intensive care unit patients requiring parenteral nutrition after gastrointestinal, vascular, or cardiac surgery to receive standard glutamine-free parenteral nutrition or alanyl-glutamine dipeptide parenteral nutrition . There were no significant differences between the groups for cumulative mortality at six months, the incidence of bloodstream infection, or any other adverse event. However, this study was likely underpowered to fully assess these outcomes.
SUMMARY AND RECOMMENDATIONS
●Malnutrition is a prevalent condition with important implications for patients undergoing surgery. When evaluating the patient for possible intervention, the patient's nutritional status should be assessed by performing a history and physical examination. Judicious use of laboratory tests aimed at assessing protein status is useful. (See 'Consequences of malnutrition in surgical patients' above and 'Nutritional assessment in the surgical patient' above and "Dietary assessment in adults".)
●Studies regarding outcomes of nutritional interventions in the perioperative period are numerous but are often of low quality, and comparisons are difficult given the broad range of surgical settings and interventions. However, our general recommendations are as follows: (see 'Nutritional interventions' above and 'Outcomes for nutritional intervention' above)
•For patients who are not malnourished or who have mild-to-moderate malnutrition, surgery should not be delayed for preoperative enteral or parenteral feeding.
•Patients with severe malnutrition may derive some benefit from delaying surgery to be fed.
•Patients clearly benefit more from enteral feeding, whenever possible, rather than total parenteral nutrition (TPN), as TPN is associated with an increased risk for infectious complications.
•For many patients undergoing surgery, early enteral nutrition (<24 hours) is possible and is associated with beneficial effects. Whenever possible, enteral nutrition (oral or tube feeds) should be instituted, unless there is a specific contraindication.
•For patients with a delayed return of gut function, postoperative parenteral nutrition is not indicated unless bowel function is not anticipated to return for more than 10 days. Earlier intervention may be appropriate in patients who are severely malnourished at baseline, or who have a complicated postoperative course.
•The role for immunonutrition is unclear. Thus far, there is insufficient high quality evidence to suggest any specific amino acid or other supplementation for surgical patients.
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