INTRODUCTION — Nutrition support refers to enteral or parenteral provision of calories, protein, electrolytes, vitamins, minerals, trace elements, and fluids. The fundamentals of nutrition support for critically ill patients will be reviewed here, including the goals, outcomes, indications, contraindications, and daily nutritional requirements. Access, formulations, prescribing, monitoring, and complications of enteral and parenteral nutrition are discussed separately. (See "Nutrition support in critically ill patients: Enteral nutrition" and "Nutrition support in critically ill patients: Parenteral nutrition".)
GOALS — Nutritional needs in the critically ill are poorly understood and vary with the phase of critical illness. Although outcomes have not been adequately studied in randomized trials, the primary goal of nutrition support is to alter the course and outcome of the critical illness. Major goals are determined by the following principles:
●Acute critical illness is traditionally thought to be characterized by catabolism exceeding anabolism [1-3]. However, with better management of ventilatory failure, fever, anxiety, and pain, calorie consumption, as measured by calorimetry, has been dramatically reduced [4].
●Carbohydrates are believed to be the preferred energy source during this period because fat mobilization is impaired [5].
●The basis of protein prescriptions is the hope for mitigation of the breakdown of muscle proteins into amino acids, which then serve as the substrate for gluconeogenesis, as reflected in a favorable nitrogen balance [6]. Studies do not support a beneficial role for providing supplemental protein to critically ill patients, and more modest goals have been recommended [7]. There is concern, particularly in the absence of strong evidence of significant clinical outcomes benefits, that supplementation of protein may have detrimental impact on outcomes [8-10].
●The phase of recovery, which begins as critical illness resolves, is characterized by anabolism exceeding catabolism. Nutrition support provides substrate for the anabolic state, during which the body corrects hypoproteinemia, repairs muscle loss, and replenishes other nutritional stores [11]. Persistence of these in the face of adequate nourishment should be viewed as an indicator of continued catabolism and not inadequacy of nourishment.
OUTCOMES — Enteral and parenteral nutrition do not appear to impact clinical outcomes differently in critically ill patients [7].
Adequately nourished patients — Historically, most of the evidence related to nutrition support is from patients who are adequately nourished when they enter the study since clinical trials have typically excluded patients with malnutrition.
Enteral nutrition — Historically, enteral nutrition has been thought to have the potential to decrease the incidence of infection in critically ill patients if provided early in the course of critical illness, although data are conflicting [12-17]. This effect has been demonstrated in clinical trials that compared patients who received early enteral nutrition with patients who received either delayed enteral nutrition or intravenous fluids only. Early and delayed have been variably defined in clinical trials, but, roughly speaking, early enteral nutrition is initiated within 48 hours and delayed enteral nutrition is initiated later.
An initial meta-analysis of three randomized trials (133 patients) found a non-statistically significant reduction in the incidence of infectious complications among patients who received early enteral nutrition (25 versus 41 percent; relative risk 0.66, 95% CI 0.36-1.22) [13]. In an unpublished update of the meta-analysis, seven randomized trials (440 additional patients) were added and the reduction in the incidence of infectious complications became statistically significant (43 versus 58 percent; relative risk 0.76, 95% CI 0.59-0.98) [18]. These meta-analyses are limited by the methodologic flaws of the included randomized trials [19].
The mechanisms by which enteral nutrition decreases infectious complications are unknown. However, preservation of gut immune function and reduction of inflammation have been proposed [20,21].
Whether early enteral nutrition decreases mortality in critically ill patients is uncertain [13,18,22,23]. In a meta-analysis of eight randomized trials (317 patients) that compared early enteral nutrition with either delayed enteral nutrition or intravenous fluids, there was a non-statistically significant mortality reduction among the patients who received early enteral nutrition (6 versus 15 percent; relative risk 0.52, 95% CI 0.25-1.08) [13]. In an unpublished update of the meta-analysis, 14 randomized trials (670 additional patients) were added [18]. The reduction of mortality was almost statistically significant (10 versus 20 percent; relative risk 0.68, 95% CI 0.46-1.01). However, a randomized trial of 78 critically ill patients was stopped early due to greater mortality in patients receiving very early (within six hours of hemodynamic stability) and aggressive (>75 percent of goal) enteral nutrition compared with patients who received standard nutritional support [16].
A systematic review and meta-analysis of 15 prospective randomized trials that compared early enteral nutrition with either no enteral nutrition or delayed enteral nutrition reported that the benefit of early enteral nutrition could be attributed to the effect of risk of bias within the studies [24]. Thus, the benefits of early feeding in this population may be overestimated.
In another systematic review comparing early enteral nutrition with late enteral nutrition and early parenteral nutrition in a mix of surgical and medically critically ill patients, no difference was found in mortality (odds ratio [OR] 1.01, 95% C, 0.86-1.18) [25]. However, there was a significant reduction in pneumonia (OR 0.75, 95% CI 0.60-0.94). When subgroups were compared, there was a reduction in mortality (OR 0.45, 95% CI 0.21-0.95) when early enteral was compared with late enteral but, interestingly, no difference when early enteral was compared with parenteral (OR 1.04, 95% CI 0.89-1.22). There was a significant reduction in pneumonia (OR 0.27, 95% CI 0.10-0.70) when early enteral was compared with late enteral, but there was only a nonsignificant trend toward a reduction in pneumonia when early enteral was compared with parenteral nutrition (OR 0.80, 95% CI 0.63-1.00). However, additional subsequent meta-analyses failed to show any difference in outcomes between enteral and parenteral nutrition when patients able to receive enteral were randomized to enteral or parenteral nutrition [7].
In balance, the evidence supports a clinically important reduction in infections and, specifically, pneumonia when enteral nutrition is administered early to critically ill patients, versus no feeding, as well as a potentially important reduction in mortality. We believe that the potential benefit of early enteral nutrition outweighs the likelihood of harm and that it should be prescribed for most critically ill patients who do not have contraindications to enteral feeding. We recognize that the evidence for this approach is somewhat weak overall and is higher quality for patients with surgical problems than for medical problems: Surgical patients (eg, trauma, peritonitis, pancreatitis, burns) were the main focus of the randomized trials and meta-analyses described above [13,18,25], whereas medical patients have primarily been studied in observational studies [22,26].
It is important to note that while early enteral nutrition appears to have benefit, there are data from randomized studies that suggest that attempting to achieve 100 percent of estimated caloric goals in the first week of critical illness may be harmful. There are also data that when enteral nutrition alone cannot meet caloric goals, the addition of parenteral nutrition in the first week of intensive care unit (ICU) care to reach those caloric goals (those goals) does not alter outcomes [7]. Therefore, the goal should be the initiation of enteral nutrition within 48 to 72 hours of entry into the ICU but should not be the aggressive provision of goal calories and protein within the first week of critical illness. (See "Nutrition support in critically ill patients: Enteral nutrition".)
The administration of concentrated feedings does not appear to confer benefit when compared with standard formulations [27]. Further details on concentrated feedings are provided separately. (See "Nutrition support in critically ill patients: Enteral nutrition", section on 'Concentrated'.)
Parenteral nutrition — The provision of early parenteral nutrition (up to 48 hours from start of critical illness or surgery) to patients with absolute or relative contraindications to enteral nutrition does not alter mortality [28-31]. Additionally, there is no consistent evidence in critically ill patients suggesting that early parenteral nutrition improves the number of ventilator-free days or length of stay in the ICU or hospital. On the other hand, there was no difference in any outcome when patients were randomized to early enteral nutrition or parenteral nutrition [7]. On balance, evidence suggests that early parenteral nutrition in well-nourished critically ill patients, whether given as the sole therapy or supplemental to enteral nutrition, does not reduce mortality. The optimal time for starting parenteral nutrition in critically ill patients is unknown. However, based upon this data, we typically do not start feeding parenterally before one to two weeks in well-nourished patients (sooner in those with antecedent starvation). Given new data [7], we are no longer reluctant to start parenteral nutrition earlier in the ICU stay.
Earlier evidence, for the most part observational, suggests early parenteral nutrition may increase the risk of infection [28-30,32]. One randomized study of 4640 critically patients [29] and a meta-analysis of 69 randomized trials (3750 patients, critically ill and noncritically ill) [28] reported that patients who received parenteral nutrition had a 4 to 5 percent increase in the incidence of infection [28]. Data since then refutes these findings [7], and better safety practices may account for comparable outcomes between enteral nutrition and parenteral nutrition. The use of parenteral nutrition as an adjunct to enteral nutrition (to improve provision of calories and protein) has shown some benefits in individual studies [29,33] but not in the aggregate [7].
Enteral versus parenteral — Direct comparisons of enteral nutrition with parenteral nutrition in critically ill patients from randomized trials indicate that outcomes in patient receiving enteral or parenteral nutrition are comparable [7].
Patients with malnutrition — Most clinical trials have excluded patients with malnutrition. In clinical practice, however, malnutrition may exist at the time of admission or as a consequence of ongoing catabolism and/or receiving little or no nutritional intake for an extended period (eg, two weeks) during the hospitalization. Importantly, the term malnutrition is somewhat confusing in that it includes both the impact of starvation and the catabolic effects (wasting, insulin resistance, hypoproteinemias, immune suppression) due to systemic inflammation [34,35]. Nourishment strategies have no impact on the latter [36], and studies have not been forthcoming in proving a mortality benefit [37].
A post hoc analysis of data from a large prospective randomized trial (EFFORT) demonstrated that systemic inflammation is a negative determinant for response to nourishment (ie, the higher the C-reactive protein, the less likely nourishment is to benefit the patient) [38]. Another post hoc analysis demonstrated that none of the six nutrition screening tools or diagnostic criteria for malnutrition predicted response to nutritional interventions [39]. Since so much of what is assessed in nutritional screening is due to inflammation, this is not surprising.
We believe that enteral and parenteral nutrition is beneficial to patients with prolonged periods of inadequate intake since there is no controversy that chronic starvation is deleterious. Some clinicians will also cite observational evidence that a progressive caloric deficit is associated with increased morbidity in critically ill patients, as well as the indirect evidence described above from adequately nourished patients [11]. However, the conclusion from these data (that prevention of mild to moderate starvation in critically ill patients will improve outcomes) has not been supported by randomized studies [15,37] and there are data suggesting potential harm (eg, increased mortality) from early and aggressive feeding [16]. Thus, the more acutely ill the patient, the more cautious we are to avoid trying to treat malnutrition with aggressive nourishment.
Patients with obesity — Data regarding the impact of nutritional support on clinical outcomes (eg, mortality and length of ICU stay) in critically ill patients with obesity (body mass index ≥30 kg/m2) are limited to small observational series and inadequately powered randomized trials that have had mixed results [7,40-47]. Additionally, the presence of malnutrition in patients with obesity may confound the effect of obesity on measured outcomes [46]. Some trials suggest that hypocaloric high-protein regimens are associated with a trend toward reduced length of stay in this population without an effect on mortality [40-45,48]. In contrast, a large observational study reported mixed effect on 60-day mortality in those given a hypocaloric low-protein diet [49]. Some clinicians prefer a high-protein and low-calorie approach in critically ill patients with obesity [50]. However, until the clinical impact of alternative diets is better elucidated, we suggest that nutritional support in the critically ill obese parallel that of the adequately nourished patient. Additional studies are warranted.
COMPLICATIONS — The most common complications associated with enteral nutrition are aspiration, diarrhea, metabolic abnormalities, and mechanical complications. These may or may not be causally related to enteral nutrition and are discussed separately. (See "Nutrition support in critically ill patients: Enteral nutrition", section on 'Complications'.)
The most common complications of parenteral nutrition are bloodstream infection, metabolic abnormalities, and problems related to venous access. These complications are also reviewed elsewhere. (See "Nutrition support in critically ill patients: Parenteral nutrition", section on 'Complications'.)
PATIENT SELECTION
Indications — Our usual approach to selecting critically ill patients for nutrition support is as follows [13,15,18,51-53]:
●For patients without contraindications to enteral nutrition, we begin early enteral feeding (ie, within 48 hours) because we believe that the potential benefits of early enteral feeding (eg, fewer infections, possibly lower mortality) outweigh its risks (see 'Enteral nutrition' above). During the first five to seven days of critical illness, we do not exceed 20 to 30 percent of feeding goal, unless the patient is quite stable.
●For adequately nourished patients who have contraindications or intolerance to enteral nutrition, we do not initiate early parenteral nutrition and typically do not start feeding parenterally before one week has elapsed. This reflects the lack of evidence or benefit from early parenteral nutrition, while recognizing new data that outcomes are the same in patients receiving early enteral or parenteral nutrition [7]. (See 'Parenteral nutrition' above.)
●For patients with antecedent starvation and/or wasting who have contraindications to enteral nutrition that are expected to persist for a week or more, we will, at times, initiate parenteral nutrition before one to two weeks have elapsed. We recognize that the effects of parenteral nutrition in such patients are unknown; however, our rationale is that failure to treat the starvation in patients with little reserve will result in a worsening of their state of frailty, which is associated with increased morbidity. Supplemental parenteral nutrition may be administered to patients receiving enteral nutrition who are chronically unable to meet their needs by a significant margin. This, however, does not apply to patients during at least the first week of intensive care unit care. (See 'Patients with malnutrition' above.)
●For patients with obesity (body mass index [BMI] ≥30 kg/m2), we recommend using the same indications for enteral and parenteral nutrition as for the adequately nourished critically ill patient. The patient who is chronically starved and/or wasted but who remains obese is likely to be sicker and at higher risk for complications related to undernourishment, despite obesity, than were they not starved or wasted and may need to be considered the same as other inadequately nourished patients.
Criteria for diagnosing malnutrition have been published [34,35] and have been validated to predict length of stay and mortality in the critically ill [54]. The terminology remains confusing as the syndrome of malnutrition includes both the consequences of starvation as well as the consequences of catabolic wasting. The former is malnourishment; the latter is not. Evidence that a patient has malnutrition includes poor nutritional intake accompanied by unintentional weight loss or low body weight. Sample criteria (arbitrarily chosen and not validated) include a BMI less than 18.5 kg/m2, the unintentional loss of more than 2.3 kg (5 lb) or 5 percent of body weight over one month, or the unintentional loss of more than 4.5 kg (10 lb) or 10 percent of body weight over six months [55]. Temporal muscle wasting, sunken supraclavicular fossae, decreased adipose stores, and signs of vitamin deficiencies may also be apparent (table 1). While such findings may be suggestive of starvation, they are just as likely to be a consequence of the catabolic effect of underlying illness. Nutritional surrogates, particularly serum proteins (eg, albumin, prealbumin/transthyretin), are similarly susceptible to the effects of systemic inflammatory illness and are not responsive to nutrient intake. While these identify patients with catabolic illness as at higher risk for medical and surgical complications and death, they should not be used to detect malnourishment in critically ill patients [56,57].
It is assumed that malnutrition due to malnourishment is impending when there has been a prolonged period of poor nutritional intake. The precise duration necessary for malnourishment- or starvation-related malnutrition to develop is unknown and probably varies among patients. As a general guideline, it is reasonable to assume that starvation-related malnutrition is impending in any patient who has had little or no nutritional intake for two weeks. One week or less may be more accurate for patients with antecedent undernourishment, with the precise duration depending on the severity of the undernourishment. Inflammation-related malnutrition may develop indolently, as does starvation-related malnutrition, but may also develop far more quickly, in hours to days, depending on the severity of illness.
Contraindications — Guidelines discourage early enteral nutrition in critically ill patients who are both hemodynamically unstable and have not had their intravascular volume fully resuscitated since such patients may be predisposed to bowel ischemia [7,58]. Hemodynamic instability by itself, unless severe, is not a contraindication for enteral nutrition if there is evidence for adequate volume resuscitation and tissue perfusion [59]. Other contraindications to enteral nutrition include bowel obstruction, severe and protracted ileus, major upper gastrointestinal bleeding, intractable vomiting or diarrhea, severe hemodynamic instability, gastrointestinal ischemia, and a high-output fistula.
Some conditions previously considered contraindications to enteral nutrition are no longer considered as such. Examples include hyperemesis gravidarum and the absence of bowel sounds or flatus following routine colorectal surgery or surgery for bowel perforation [12,60-64]. While such patients remain at increased risk for vomiting, enteral nutrition may confer an overall benefit since it may decrease the risk of infection [12,63]. In addition, a new gastrointestinal anastomosis distal to the infusion site that the surgeon feels is at risk of dehiscence was once considered a contraindication until more recent data indicated that early feeding strengthens anastomoses [65]. Whether this applies to all anastomoses is unknown, and when the anastomoses are felt to be tenuous, we defer to the surgeon's judgement as to whether enteral nutrition should be started.
Contraindications to parenteral nutrition include hyperosmolality, severe hyperglycemia, severe electrolyte abnormalities, volume overload, inadequate intravenous access, and inadequate attempts to feed enterally.
Relative contraindications to parenteral nutrition are not well defined. However, parenteral nutrition is often avoided in sepsis and systemic inflammatory response syndrome. In situations where contraindications to enteral nutrition are expected to resolve quickly, such as minor vomiting, gastrointestinal bleeding, and short-term mechanical ventilation, parenteral nutrition is usually delayed.
Enteral and parenteral nutrition must be initiated slowly and with strict monitoring in patients at risk for "refeeding syndrome." We also suggest review of antecedent laboratory tests, when available, for episodes of hypokalemia or hypophosphatemia as we believe those patients with recently low levels to be at risk for refeeding syndrome, irrespective of supplementation. Patients with chronic undernourishment should receive supplemental thiamine prior to initiation of artificial nourishment to prevent Wernicke syndrome. (See "Eating disorders: Overview of prevention and treatment", section on 'Refeeding syndrome'.)
NUTRITIONAL REQUIREMENTS — Once it has been determined that a critically ill patient will receive nutrition support, the patient's nutritional requirements must be determined. These requirements are used to select the appropriate formulation and rate of administration. (See "Nutrition support in critically ill patients: Enteral nutrition" and "Nutrition support in critically ill patients: Parenteral nutrition".)
Randomized trials evaluating the optimal quantity of caloric intake and/or protein intake are unlikely to be performed with adequate precision because the anticipated sample sizes required to detect outcome differences are prohibitively large. Small trials have been performed, but their results are equivocal. Trials that compare the measurement of caloric or protein intake with the estimation of caloric or protein intake (eg, formulas, tables) are similarly unlikely to be performed. Thus, clinical decisions must be based upon observational evidence and clinical experience.
There is little consensus among clinicians regarding how to adjust energy requirements for critically ill patients with obesity. Adjustments can be made based upon an estimate of the individual's resting energy expenditure (REE) or their body weight. Indirect calorimetry and predictive equations can be used in this population to estimate the REE. Although most experts agree that indirect calorimetry is the best method for REE measurement [66], calorimeters are not widely available, calorie prescription based on calorimetry has not been adequately tested, and some patients do not meet valid testing criteria. Therefore, predictive equations are more commonly used [48,67,68]. Alternatively, weight-based adjustments in the patient with obesity can be performed, as outlined below. Additional guidelines for the assessment of REE for critically ill patients can be found at the American Society for Parenteral and Enteral Nutrition [48].
Dosing weight — When prescribing enteral or parenteral nutrition, the appropriate body weight from which to calculate caloric and protein intake (ie, the dosing weight) must first be determined.
For patients who are underweight (body mass index [BMI] <18.5 kg/m2), we suggest using the current weight as the initial dosing weight. Calculation of caloric intake based on ideal body weight could lead to the administration of excess initial calories and induce refeeding syndrome [69] (see "Eating disorders: Overview of prevention and treatment", section on 'Refeeding syndrome'). Calories may be increased to attempt weight gain once the patient is stable.
For patients whose weight is normal (BMI 18.5 to 24.9 kg/m2) or who are overweight (BMI 25 to 29.9 kg/m2), we suggest using the current weight as the dosing weight. An effort should be made to subtract the estimated weight of any peripheral edema.
For patients who are obese (BMI ≥30 kg/m2), guidelines recommend use of current weight and use of the Penn State University 2010 predictive equation [48]. If neither expertise with this equation or calorimetry is available, we suggest that the dosing weight be adjusted. The purpose of adjusting the dosing weight of patients who are obese is to account for the absence of metabolic requirements by fat tissues:
●The most commonly employed method is to add 0.4 times the difference between the ideal body weight (IBW) and the actual body weight (ABW) to the IBW. In other words:
Dosing weight = IBW + 0.4 (ABW – IBW)
●An alternative method is to use 110 percent of the IBW. In other words:
Dosing weight = 1.1 × IBW
For either equation, the IBW can be determined from the calculator (calculator 1).
For patients who are volume overloaded (eg, liver failure), an estimate of dry body weight can be used.
Calories — Energy expenditure is approximately equal to REE in the properly treated critically ill patient.
In the past, providing fewer calories than needed to meet energy needs was controversial [70-72]. However, there has since been evidence that, in the first week of critical illness, this approach is not harmful and may have some benefits (eg, less gastrointestinal intolerance, fewer infections), such that it has become routine practice in most intensive care units [73-75]. As examples:
●In one randomized trial of 1000 mechanically ventilated patients with acute lung injury (EDEN), low-calorie feeding (mean caloric intake 400 kcal per day) for the first six days, compared with full enteral feeding (mean caloric intake 1300 kcal per day), did not change ventilator-free days, 60-day mortality, or infectious complications but was associated with less gastrointestinal intolerance [73].
●In another randomized trial of 894 critically ill patients (medical, surgical, trauma) (PermiT), compared with standard enteral feeding (70 to 100 percent of calculated caloric requirements), 14 days of permissive underfeeding (40 to 60 percent of the calculated caloric requirements with similar amounts of protein to the standard formula) was not associated with a difference in mortality, gastrointestinal intolerance, infectious complications, or length of hospital stay [75]. This effect was maintained in adequately nourished as well as malnourished critically ill patients [76].
●One meta-analysis of 15 trials reported a favorable benefit on mortality (ICU and 30-day), length of hospital and ICU stay, duration of mechanical ventilation, and rate of infectious complications from hypocaloric feeding [77]; however, there was low confidence in the results since estimates ranged from beneficial to harmful.
We believe that a safe starting point for most critically ill patients is approximately 8 to 10 kcal/kg per day [73]. Attempting to achieve a goal of 25 to 30 kcal/kg of dosing weight per day after one week is reasonable for most stable patients. A goal of 35 kcal/kg per day is an acceptable goal if weight gain is desired in a relatively stable patient; weight gain should not be attempted until the patient is stable and in a lower inflammatory state. We keep the caloric goal at 25 kcal/kg per day or less if extubation is imminent.
Protein — Guidelines promote the hypothesis that protein requirements increase as illness becomes more severe. This is based solely on nitrogen excretion and not on outcomes studies except in burns. Practice is to give patients with only mild to moderate illness 0.8 to 1.2 g/kg protein per day. Critically ill patients are generally prescribed 1.2 to 1.5 g/kg per day [78], and patients with severe burns may benefit from as much as 2 g/kg per day. An ongoing assessment of the patient's clinical condition as it impacts protein prescription estimates is suggested. (See 'Goals' above.)
ADMINISTRATION — Administration of nutrition support requires that appropriate access is established and that the composition and rate of delivery be determined. Once started, nutrition support must be monitored for tolerance and complications. These issues are different for enteral and parenteral nutrition, which are discussed separately. (See "Nutrition support in critically ill patients: Enteral nutrition" and "Nutrition support in critically ill patients: Parenteral nutrition".)
CORONAVIRUS DISEASE 2019 — In patients with coronavirus disease 2019 (COVID-19) who develop critical illness, the same data that instruct our care of all critically ill patients should guide our nutrition support approaches until specific data from COVID-19 patients emerge [79]. However, select issues deserve attention. (See "COVID-19: Management of the intubated adult".)
●Early parenteral nutrition – Randomized trials have not demonstrated net harm from early parenteral nutrition, compared with early enteral nutrition, in patients who are critically ill [7]. There is no evidence to suggest that this would be otherwise in patients with COVID-19. For critically ill patients with malnutrition in whom enteral nutrition fails, consideration of early parenteral nutrition has been suggested by consensus but without supportive data [7]. Data to support these are provided separately. (See 'Parenteral nutrition' above.)
●Enteral nutrition while proning – Many patients with COVID-19 need prone positioning to successfully improve oxygenation. Several studies have demonstrated the safety of enteral tube feeding in the prone position, as well as the safety of continuing feeding during changes in position [80-83]. Use of nasal bridles to secure nasal feeding tubes is reasonable. (See "Prone ventilation for adult patients with acute respiratory distress syndrome".)
●Malnutrition – The diagnosis of malnutrition is more likely to occur in patients with chronic illness. Due to the acuity of COVID-19, it is likely that malnutrition is less prevalent in these patients when they are first admitted to the hospital. However, because the critical illness associated with COVID-19 seems to be prolonged and the disease is so highly inflammatory, it is possible that malnutrition may be more evident at a later point in the illness. Thus, reevaluation of nutritional status later in the course of illness is prudent. (See 'Patients with malnutrition' above.)
●Protein supplementation – The widespread use of the sedative propofol, which is administered in a lipid emulsion infusion (that provides calories but no protein), has led to an increased effort to supplement protein in ventilated patients. We believe that protein supplementation is not necessary and that goals for protein intake should be similar to that administered to non-COVID-19 patients. Evidence supporting supplementation of protein in critically ill patients is largely observational and not supported by robust outcomes. In addition, measures to provide protein supplementation that increase nursing interaction with patients are of particular concern for increasing risks to the provider without well-established benefit to the patient. (See 'Protein' above and 'Goals' above and "Nutrition support in critically ill patients: Enteral nutrition", section on 'Protein'.)
●Nutrient supplementation – The use of nutrient supplementation has long been of interest for modulating disease outcomes in the critically ill. While there are weak data suggesting the possibility of benefits of high-dose vitamin C [84,85], they do not warrant a recommendation for use in patients with COVID-19. Vitamin D levels are associated with adverse outcomes in the critically ill, but supplementation has failed to improve outcomes in several randomized control trials [86,87]. While trace element levels are decreased and associated with critical illness outcomes [88], there are no data to support a benefit in the critically ill. (See "Nutrition support in critically ill patients: Enteral nutrition", section on 'Vitamins and trace elements'.)
●Shortages and ethics – There is the potential for shortages of tube feeding pumps and feeding products. Decisions for utilizing any nutrition intervention should account for the strength of data, probability of benefit, risk of creating critical shortages, and risk to providers. (See "COVID-19: Management of the intubated adult", section on 'Surge capacity and resource allocation'.)
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
●Nutrition support refers to the enteral or parenteral provision of calories, protein, electrolytes, vitamins, minerals, and fluids. (See 'Introduction' above.)
●Critically ill patients are selected for nutrition support on the basis of whether they have contraindications to enteral nutrition, as well as whether the patient is adequately nourished or malnourished:
•For critically ill surgical patients without contraindications to enteral nutrition, we recommend early (eg, within 48 hours) enteral nutrition (Grade 1B). For critically ill medical patients without contraindications to enteral nutrition, we suggest early enteral nutrition (Grade 2C). (See 'Enteral nutrition' above and 'Patient selection' above.)
•For critically ill patients who are hemodynamically unstable and have not had their intravascular volume fully resuscitated, early enteral nutrition is contraindicated (Grade 2C). (See 'Contraindications' above.)
•For adequately nourished patients who have contraindications to enteral nutrition, we suggest not initiating early parenteral nutrition (Grade 2C). While the optimal time for starting parenteral nutrition in these patients is unknown, we typically do not start parenteral feeding before one to two weeks have elapsed. (See 'Parenteral nutrition' above and 'Patient selection' above.)
•For patients with malnutrition who have contraindications to enteral nutrition that are expected to persist one week or less, we suggest not initiating parenteral nutrition (Grade 2C). For patients with malnutrition who have contraindications to enteral nutrition that are expected to persist greater than one week, we suggest parenteral nutrition (Grade 2C). (See 'Patients with malnutrition' above and 'Patient selection' above.)
•For patients with obesity (body mass index ≥30 kg/m2), the optimal approach to nutrition is unknown. We prefer that enteral and parenteral nutrition and choice of nutrition in this population be the same as for the adequately nourished critically ill patient. (See 'Patients with obesity' above.)
●An acceptable initial nutritional goal is 8 to 10 kcal of calories/kg per day and then 18 to 25 kcal and 1.5 grams of protein/kg per day after five to seven days, although these targets have not been rigorously validated. (See 'Nutritional requirements' above.)
