INTRODUCTION — Malnutrition in hospitalized patients is well documented, with rates up to 50 percent in certain populations [1]. Nutrition support may be indicated for individuals with malnutrition who require a 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 [2]. In the 1990s, a prospective study of 500 patients admitted to a teaching hospital in England (including 200 surgical patients) noted that 40 percent were undernourished on admission [3]. Furthermore, patients in this study lost an average of 5.4 percent of their body weight during their hospital stay.
An overview of nutrition support in the perioperative period, including options and potential benefits, are reviewed here. Clinical assessment and monitoring and the role of parenteral nutrition support in surgical patients, and nutrition support issues in critically ill patients and other specific populations are discussed separately. (See "Clinical assessment and monitoring of nutrition support in adult surgical patients" and "Postoperative parenteral nutrition in adults" and "Nutrition support in critically ill patients: An overview".)
CONSEQUENCES OF MALNUTRITION IN SURGICAL PATIENTS — Reduced caloric intake results in loss of fat, muscle, skin, and ultimately bone and viscera, with subsequent weight loss, and expansion of the extracellular fluid compartment [4]. Nutritional requirements decrease as an individual's body mass decreases, 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 [5].
The stress of surgery or trauma creates a catabolic state, increasing protein and energy utilization. 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 [6]. The rate of development of postoperative malnutrition for a given individual depends upon their preexisting nutritional status, the nature and complexity of the surgical procedure, the degree of postoperative hypermetabolism, and their ability to consume an optimal number of calories.
Malnutrition is associated with 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 [8]. One series reported that patients with malnutrition had subnormal skin reactions to Candida and low levels of antibodies to various phytomitogens, suggesting that humoral and cell-mediated immunity are affected [9]. Patients with protein energy malnutrition are also reported to have slower rates of wound healing, although most wounds will eventually heal on their own [10,11]. Additional adverse effects associated with malnutrition were identified in a study of 2743 patients undergoing cardiothoracic surgery [12].
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 [12]. 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 the patient has malnutrition.
The clinical assessment of the surgical patient includes a complete history and physical examination on admission, assessment of protein status and may include other laboratory studies. These are discussed in detail separately. (See "Clinical assessment and monitoring of nutrition support in adult surgical patients", section on 'History and physical'.)
Briefly, a nutritional assessment should include:
●Past medical history, noting chronic disease, infection, recent hospitalization, and prior surgery.
●Assessment of recent weight losses or gains and whether they were purposeful or not.
●Identification of current medications including nonprescription medicines and other supplements and any allergies or food intolerances (See "Overview of herbal medicine and dietary supplements".)
●Dietary history
●A complete physical examination that includes vital signs, height and weight, and calculation of body mass index [BMI] ((calculator 1)(figure 1).
●Signs of specific nutritional deficiencies (table 1).
NUTRITIONAL INTERVENTIONS — Once 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.
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 patients. 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 nutrition 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 "Postoperative parenteral nutrition in adults".)
INDICATIONS — The general indications for nutrition 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 [13-19].
Early enteral feeding (oral, tube feeding) can be instituted following many types of surgery [19-21]. A Cochrane review and meta-analysis updated in 2011 identified no obvious advantage to the routine practice of maintaining patients "nil per os" (ie, NPO) in the postoperative period after gastrointestinal surgery [22]. (See 'Early enteral feeding' below.)
Some patients, such as those with inflammatory bowel disease, have an increased risk of having malnutrition 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 management for 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 [15,23]. Earlier enteral support may be appropriate in patients having malnutrition at baseline, or who have a complicated postoperative course [24,25]. In patients undergoing bowel surgery for gastrointestinal malignancy, malignancy-related metabolic changes may also suggest the need for earlier intervention. (See "Postoperative parenteral nutrition in adults".)
OUTCOMES FOR NUTRITIONAL INTERVENTION — The majority of trials evaluating the potential benefits of perioperative nutrition support are small, and comparisons are difficult due to the wide variety of operations studied, variability in methodology, and a lack of standard definitions and measures of malnutrition. The risks associated with each route of nutrition support, plus the added cost, need to be taken into account, along with the potential benefits, when assessing the need for perioperative nutrition support.
Preoperative nutrition support — For patients who are adequately nourished or who have mild-to-moderate malnutrition, surgery need not be delayed for preoperative parenteral or enteral supplementation. Patients with severe malnutrition may derive some benefit from delaying surgery to be fed, but the data on which these recommendations come from observational studies that are flawed [13,14,25]. Patients will benefit more from enteral than parenteral feeding whenever it is possible; parenteral nutrition increases risk for infectious complications.
Whether patients with severe malnutrition benefit or suffer harm from prolonged delay of surgery for preoperative nutrition support, particularly when the malnutrition is due to the surgical disease, is unknown. However, if the malnutrition is largely the result of catabolic wasting, concerns regarding significant delay of surgery include exposing the patient to further wasting and increasing surgical risk, since such wasting does not respond to nourishment.
There is no question that surgical outcomes are less favorable in patients with malnutrition. A multicenter cohort study evaluated the effect of preoperative nutrition support in 512 patients undergoing abdominal surgery who were at nutritional risk as defined by the Nutritional Risk Screening Tool 2002 (NRS-2002) [25]. 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 [26]. 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 nutrition — Most randomized trials of perioperative parenteral nutrition have been designed as "disease modifying," which is to say that all patients with a particular condition were randomly assigned to receive parenteral nutrition or no artificial nutrition. As a result, much of the data are not helpful to guide decisions related to the individual patient who cannot receive nourishment in any manner other than parenterally. Several meta-analyses have evaluated preoperative parenteral nutrition but have reached inconsistent conclusions [27-29].
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 [29]. These findings were not verified by a subsequent larger meta-analysis that included 41 trials of parenteral nutrition provided before and/or after surgery [28]. 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 meta-analysis (26 randomized trials, although 3 were not in surgical patients) found a trend toward decreased complications in studies where lipid-free solutions were used (relative risk [RR] 0.80, 95% CI 0.63-1.02), and for patients who had malnutrition (not consistently defined) [27]. These findings were also not confirmed in the larger meta-analysis, which found greater benefit for parenteral nutrition in trials where lipids were used, and in trials evaluating well-nourished patients [28].
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 [30,31]. 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 parenteral nutrition, compared with control patients who did not receive preoperative parenteral nutrition and were only partially supplemented postoperatively [32]. Preoperative treatment with parenteral nutrition also decreased morbidity in a group of patients undergoing resection for hepatocellular cancer [33]. (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 [34]. 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). In a post hoc analysis of the subgroup with the most severe malnutrition, approximately 5 percent of the total cohort, 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 0.46-0.87). However, no difference was observed for infectious complications [26].
Postoperative nutrition support — For many postoperative patients, early oral or 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 have severe malnutrition at baseline, or who have a complicated postoperative course. (See 'Indications' above.)
Early enteral feeding — Early postoperative enteral nutrition 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 (ERAS) protocols [35-37].
●A meta-analysis evaluated 44 randomized trials of perioperative enteral nutrition (predominantly postoperative support) [38]. 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 meta-analysis 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 [39].
●By comparison, a Cochrane review and meta-analysis updated in 2011 identified 14 trials that included 1224 patients undergoing predominantly colorectal surgery [22]. No significant differences were identified in the risk of intra-abdominal 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 meta-analysis 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 meta-analysis 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 [40].
Whether the route of enteral administration has any clinically important effect for surgeries other than colorectal surgery, which is the basis for much of the literature on postoperative nutrition, is less certain. As an example, for pancreaticoduodenectomy, a systematic review of early enteral nutrition did not show any differences in complication rates for five differing routes of administration, including an oral route; enteral nutrition via either a nasojejunal tube, gastrostomy, or jejunostomy; or parenteral nutrition (seven randomized trials, seven observational studies) [41]. A later trial that randomly assigned 42 patients to a nasoenteric tube or jejunostomy tube following pancreaticoduodenectomy also found no significant difference in complication rates [42]. However, the nasoenteral group required introduction of parenteral therapy significantly more frequently than the jejunostomy group. In a trial comparing early nasojejunal tube feedings with early parenteral nutrition support, the overall incidence of complications was higher for nasojejunal feedings (76 versus 64 percent) due to a higher incidence of postoperative pancreatic fistula and delay in resumption of oral diet [43]. There were no significant differences in the incidence of infectious complications or length of postoperative stay. (See "Surgical resection of lesions of the head of the pancreas", section on 'Nutrition support'.)
Parenteral nutrition — Patients who are unable to tolerate enteral nutrition support will require intravenous fluid and parenteral nutrition at the discretion of the treating team until such time as they can be transitioned to enteral nutrition. (See "Postoperative parenteral nutrition in adults".)
Immune-enhancing nutritional supplements — The role for immune-enhancing nutritional supplements, also referred to as immunonutrition (ie, enteral or parenteral supplementation with arginine, glutamine, nonessential fatty acids, branched chain fatty acids, nucleotides, or RNA), remains unclear. There is insufficient high-quality evidence to suggest any specific supplementation for all surgical patients. (See 'Nutritional interventions' above.)
Studies of individual and combinations of components of immunonutrition have demonstrated no effect on survival in surgical patients [44-60]. Several meta-analyses have evaluated immunonutrition [26,45-48,61-65]. Reductions in infectious complications and length of hospital stay have been found, but without an effect on mortality. In a large review and meta-analysis of immunonutrition (including trials of glutamine, arginine, omega-3 fatty acids, RNA, and nucleotides), there was no effect on perioperative mortality associated with major abdominal surgery. Compared with control groups, immunonutrition reduced the risk of overall complications (odds ratio [OR] 0.79, 95% CI 0.66-0.94, 41 trials) and infectious complications (OR 0.58, 95% CI 0.51-0.66, 66 trials), and shortened hospital stay (mean difference -1.79 days, 95% CI -2.39 to -1.19, 52 trials) [48]. However, when excluding three trials judged by the authors to have a high or unclear risk of bias, these effects were no longer seen. The authors of these meta-analyses 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. A later systematic review and metanalysis evaluated the utility of immunonutrition in surgical patients treated for cancer [61]. As demonstrated for other populations, infectious complications were reduced, as was the risk for intestinal anastomotic complications; however, the rates of sepsis and mortality were similar between the groups. Some of the limitations of this review include different types and stages of surgical cancers and the lack of standard dosing or route of immunonutrition formula. Thus, until higher-quality data demonstrating unequivocal benefit are available, immunonutrition cannot be recommended as a routine addition to nutritional supplementation in all surgical patients.
Probiotics/synbiotics — In addition to supplementation of calories or using immune-enhancing treatments, it has been speculated that probiotics or synbiotics administered in the perioperative period may improve surgical outcomes. Probiotics are living microorganisms believed to convey health benefits to the host. Synbiotics are nutritional supplementations combining probiotics with prebiotics, which are ingredients (eg, fermentable fiber) that stimulate the growth and/or function of beneficial intestinal microorganisms. Probiotics or synbiotics can be administered preoperatively, postoperatively, or both, and via oral or enteral routes.
Whether perioperative administration of probiotics/synbiotics improves outcomes of abdominal surgery is unclear. Routine use of probiotics/synbiotics has not been uniformly adopted by the surgical community or within enhanced recovery protocols, but several systematic reviews and meta-analyses have suggested a variety of possible benefits [66-70]. The latest of these was a systematic review that identified 34 trials in patients who predominantly underwent gastrointestinal or other abdominal (eg, pancreatic) surgeries [71]. Among 20 trials, patients who received a variety of perioperative probiotics/synbiotics (n = 825) had a significantly lower risk of surgical site infection compared with those who received valid control treatment (n = 424; relative risk [RR] 0.65; 95% CI 0.51-0.84). Among the included trials evaluating other outcomes, probiotics/synbiotics were also associated with shortened time to first postoperative bowel movement, a reduced incidence of other infectious complications such as pneumonia (RR 0.63, 95% CI 0.42-0.92) and urinary tract infection (RR 0.43, 95% CI 0.25-0.72), shortened duration of antibiotic therapy, and shortened intensive care unit stay and hospital stay.
While these overall results appear promising, the trials were small, heterogeneous, and often at high risk of bias, and the long delay from the last study analyzed until publication is a concern. Further study is needed to confirm these findings and determine the optimal agents (species, strains), dosing (timing, route, duration), and clinical settings for use of probiotics or synbiotics. Because of episodes of fungemia in some critically ill patients due to the organism supplemented, and worse outcomes in severe pancreatitis [72,73], the Society of Critical Care Medicine and the American Society of Parenteral and Enteral Nutrition in guidelines for adult critically ill patients were unable to make a generalized recommendation for their use [74].
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Nutrition support (parenteral and enteral nutrition) in adults".)
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 for determining prognosis but does not reflect protein intake. (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 for 10 to 14 days to be fed.
•Enteral nutrition is associated with fewer complications compared with parenteral nutrition. Patients benefit more from enteral feeding, whenever possible, rather than parenteral nutrition, as parenteral nutrition is associated with an increased risk for infectious complications.
•For many patients, early postoperative 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.
ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Kathleen M Fairfield, MD, DrPH, who contributed to an earlier version of this topic review.
