Nutrition support in intubated critically ill adult patients: Initial evaluation and prescription

INTRODUCTION — Nutrition support refers to the enteral or parenteral provision of calories, protein, electrolytes, vitamins, minerals, trace elements, and fluids. Acute critical illness is characterized by catabolism exceeding anabolism [1-3]. In contrast, the phase of recovery is characterized by anabolism exceeding catabolism. Understanding the importance of nutrition is critical when managing all phases of critical illness.

Indications, contraindications, and appropriate prescription of nutrition in critically ill patients are discussed in this topic. Our usual approach is, for the most part, supported by several international guidelines, although differences may exist as new data emerge [4-7].

Aspects that are specific to enteral and parenteral nutrition are discussed separately. (See "Nutrition support in intubated critically ill adult patients: Enteral nutrition" and "Nutrition support in intubated critically ill adult patients: Parenteral nutrition".)

INITIAL EVALUATION — Once a patient is admitted to the intensive care unit (ICU), we assess the patient's nutritional status, need for nutritional support, and the presence of any contraindications to select modes of delivery. In general, oral feeding is preferred over enteral support, and enteral feeding preferred over parenteral support. However, individual morbidities may impact this choice. In the ICU, where many patients are intubated or on noninvasive modes of ventilation, oral feeding is not typically a reasonable option. Thus, by default, enteral feeding is our usual mode of nutritional support unless contraindications exist (eg, small bowel obstruction). (See 'Adequately nourished patients' below.)

Assess nutritional status — Our approach to assessing nutritional status is the following:

●Dry body weight and body mass index (BMI) – We perform an initial evaluation of nutritional status that involves measuring the current dry body weight and calculating the BMI (calculator 1). Patients can be categorized as the following:

•Normal weight – BMI between 18.5 to 24.9 kg/m²

•Overweight – BMI 25 to 29.9 kg/m²

•Underweight – BMI <18.5 kg/m²

•Obese – BMI ≥30 kg/m²

●Signs of malnutrition – We also examine patients for signs of malnutrition. Criteria for diagnosing malnutrition have been published [8-11] and have been validated to predict length of stay, ICU readmission, and mortality in critically ill patients [10,12]. The syndrome of malnutrition includes both of the following:

•Wasting due to starvation (also known as malnourishment) – Patients with wasting due to starvation are malnourished and responsive to nourishment.

•Wasting due to catabolism – Wasting due to catabolism is common in critically ill adults (inflammation-related muscle wasting, insulin resistance, hypoproteinemias, immune suppression) [8,9]. Patients with wasting due to catabolism are not malnourished and are not responsive to nourishment [13-15]. However, patients with catabolism are also more likely to also have starvation and may also be malnourished.

Evidence that a patient has malnutrition includes poor nutritional intake accompanied by unintentional weight loss or low body weight. Examples include the following [16]:

•A BMI less than 18.5 kg/m²

•Unintentional loss of more than 2.3 kg (5 lbs) or 5 percent of body weight over one month

•Unintentional loss of more than 4.5 kg (10 lbs) or 10 percent of body weight over six months

•Others include muscle wasting (eg, temporal muscle wasting, sunken supraclavicular fossae, scaphoid abdomen), decreased adipose stores, and signs of vitamin deficiencies (table 1)

The precise duration necessary for malnourishment 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. For patients with antecedent undernourishment, one week or less may be more accurate. Inflammation-related malnutrition may develop indolently but may also develop in hours to days with severe illness. Thus, reassessment of nutritional status is important during critical illness.

●Laboratory assessment – Although nutritional chemistries are often measured and are prognostic indicators of poor outcome, we and other experts are not proponents of this approach [17,18]. Such surrogates, particularly reduced serum proteins (eg, albumin, prealbumin/transthyretin), are nonspecific and should be assumed to be due to systemic inflammatory critical illness. In addition, they are not responsive to nutrient intake and therefore, cannot be used as therapeutic biomarkers.

Assess indications and contraindications

Indications — Once a patient is admitted into the ICU, we assess the need for nutritional support.

●Extubation expected within 36 hours – Adequately nourished patients who are expected to be extubated within 24 to 36 hours of admission and are likely able to eat after extubation typically do not need enteral or parenteral support since oral nutrition is considered optimal.

●Mechanical ventilation expected beyond 36 hours – This population needs nutritional support, typically enteral support, unless contraindications exist, in which case we consider parenteral support (see 'Contraindications' below). In situations where contraindications to enteral nutrition (EN) are expected to resolve quickly, such as minor vomiting or gastrointestinal bleeding, parenteral nutrition (PN) may be administered until enteral feeding is deemed safe or the patient is extubated and can eat safely.

Contraindications — Contraindications to enteral and parenteral feeding are listed in the table (table 2).

●Enteral nutrition (EN) — General contraindications to enteral feeding include the following:

•Hemodynamic instability/shock – We generally do not administer EN to 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 [6,19,20]. Thus, many patients with critical illness are not candidates for EN immediately after ICU admission. As an example, one randomized trial reported that in critically ill adults with shock, early EN did not reduce mortality or infections and was associated with a greater risk of digestive complications compared with early PN [20].

If there is evidence for adequate volume resuscitation and tissue perfusion, hemodynamic instability by itself, unless severe, is not a contraindication for EN [21]. Similarly, enteral feeding does not necessarily need to be stopped for transient, mild periods of hemodynamic instability, which can commonly punctuate a patient's course during critical illness. Recurrent unnecessary holding of tube feeding can result in large calorie deficits and should be avoided when possible.

•Others – Other contraindications to EN include the following:

-Bowel obstruction

-Severe and protracted ileus

-Major upper gastrointestinal bleeding

-Intractable vomiting

-Gastrointestinal ischemia

-High-output gastrointestinal fistula

-Abdominal compartment syndrome

Some conditions previously considered contraindications to EN 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 [22-27]. While such patients remain at increased risk for vomiting, enteral feeding does not appear to impart an increased risk for infection or pneumonia.

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 data indicated that early feeding strengthens anastomoses [28]. Whether this applies to all anastomoses is unknown, and when the anastomoses are felt to be tenuous (eg, gastric bypass surgery), we defer to the surgeon's judgement as to whether EN should be started.

High gastric residual volume (GRV) is not an absolute contraindication to enteral feeding, although holding feeding when residual volumes are >500 mL is acceptable. Management of high GRV is discussed in detail separately. (See "Nutrition support in intubated critically ill adult patients: Enteral nutrition", section on 'Measure gastric residual volume'.)

●Parenteral nutrition (PN) — Contraindications to PN include the following:

•Severe hyperglycemia

•Severe electrolyte abnormalities

•Volume overload

•Inadequate intravenous access

•Inadequate attempts to feed enterally

ADEQUATELY NOURISHED PATIENTS — Most patients who are admitted to the intensive care unit (ICU) are adequately nourished. This section discusses timing and optimal type of nutrition support for patients who are adequately nourished or have not developed disease-related malnutrition prior to becoming critically ill. Historically, most of the evidence related to nutrition support is derived from patients who are adequately nourished since clinical trials have typically excluded patients with malnutrition. Generally, enteral, rather than parenteral, feeding and early (eg, 36 to 48 hours), rather than delayed, support is preferred.

Timing and type of nutrition

Patients without contraindications to enteral nutrition — For adequately nourished critically ill patients without contraindications to enteral nutrition (EN), we suggest early rather than delayed EN. (See 'Early enteral nutrition' below.)

Early enteral nutrition — Support for early EN is derived from evidence in critically ill patients that supports a possible mortality benefit and reduction in infections when early EN (eg, 48 to 36 hours) is compared with delayed EN. However, the evidence for this approach is limited, often conflicting, and lower quality for patients with medical conditions compared with surgical conditions (eg, trauma, peritonitis, pancreatitis, burns).

●Early versus delayed EN – Evidence on the impact of early EN on the rate of infectious complications and mortality suggest a possible benefit when compared with delayed EN [4,20,29-31]. As an example, a 2018 meta-analysis of 16 trials totaling 3225 medical and surgical critically ill patients compared early EN with delayed EN [30]. Early EN resulted in a significant reduction in pneumonia when compared with delayed EN (odds ratio [OR] 0.75, 95% CI 0.60-0.94). However, there were few events (21 episodes of pneumonia), limiting the certainty of this finding. Data from six trials (236 patients) reported a reduction in mortality when early EN was compared with delayed EN (OR 0.45, 95% CI 0.21-0.95) [30]. However, there were also few events (33 total deaths), limiting the certainty of this finding. An earlier meta-analysis of 11 trials reached a similar conclusion [4].

●Early EN versus early PN – In the same 2018 meta-analysis, while infectious rates were lower when early EN was compared with early parenteral nutrition (PN), the finding was not statistically significant (OR 0.80, 95% CI 0.63-1) [30]. Similarly, no mortality difference was found when early EN was compared with early PN (OR 1.04, 95% CI 0.89-1.22).

In addition, two large randomized trials (only one of which was included in the meta-analysis) reported similar outcomes when early enteral and early parenteral feeding strategies were compared in critically ill adults [20,29]. These trials are discussed in detail below. (See 'Early parenteral nutrition' below.)

Very early and aggressive feeding does not appear to be of benefit and may be harmful. One 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) EN compared with patients who received standard nutritional support [31]. Another randomized trial of 3044 ventilated patients with shock also reported no mortality benefit associated with early feeding within 24 hours of intubation [32].

For patients who do not meet their caloric and protein goals during the first week of critical illness, we do not administer supplemental PN in order to reach those caloric goals since it does not alter outcomes [6]. While small individual studies reported a possible benefit [33,34], a meta-analysis of five studies reported similar outcomes when EN plus supplemental PN was compared with early EN without supplementation [6].

The calculation of caloric needs is described separately. (See 'Calorie prescription' below.)

Patients with contraindications to enteral feeding — For adequately nourished patients with contraindications to EN (table 2), we suggest early PN (eg, 36 to 48 hours) rather than delaying nutrition. This approach is based on indirect data suggesting that when PN is administered in the short-term (ie, the first week of critical illness) with a view to transitioning to EN later, outcomes are the same as patients receiving early EN [6,20,29]. It is unknown if this recommendation applies to patients who cannot transition to EN and have a potential need for PN beyond the first week of critical illness. These data are discussed below. (See 'Early parenteral nutrition' below.)

Early parenteral nutrition — While delayed PN was preferred in the past, data now suggest that the provision of early PN (up to 36 hours from the start of critical illness or surgery) does not alter mortality when compared with early EN or late PN, although there may be a positive impact of early PN on infectious risk when compared with early EN [4,6,20,29].

●Early EN versus late PN – There are limited data suggesting that early PN is not associated with harm, may be no different when compared with late PN, and may improve the number of ventilator-free days or length of stay in the ICU or hospital [33,35,36]. However, a mortality benefit has not been shown and data are inconsistent.

●Early PN versus early EN – Indirect evidence suggests early PN has similar outcomes when compared with EN:

•One 2017 meta-analysis of seven randomized trials that compared early EN with early PN reported similar mortality rates (risk ratio [RR] 0.95, 95% CI 0.76-1.19; moderate certainty) but a reduced risk of infections with early PN (RR 0.55, 95% CI 0.35-0.86; low certainty) [4]. However, patients were unselected and mostly surgical, the risk of bias was high, and there was significant heterogeneity among the included trials.

•Two large randomized trials (one of which was included in the above meta-analysis) compared early EN with early PN, starting within 36 hours of admission or 24 hours after intubation [20,29]. In one study, patients on PN were allowed to transition to EN after three days if the underlying critical illness was resolving [20], and in the other study, the intervention continued for five days only [29]. Both studies found similar 30- or 90-day mortality but, as expected, also found an increased incidence of gastrointestinal side effects in the enteral feeding group (eg, vomiting). Adverse events, including infection rates, were similar. However, the studies were not blinded and one was stopped early for futility.

Supplemental PN in patients receiving early EN (to improve provision of calories and protein) does not appear beneficial and is discussed separately. (See 'Early enteral nutrition' above.)

Calculating calorie and protein requirements in adequately nourished patients — Once it has been determined that a critically ill patient will receive nutrition support, the patient's nutritional requirements must be determined. For most adequately nourished patients who have a normal body weight (body mass index [BMI] 18.5 to 24.9 kg/m²) or who are overweight (BMI 25 to 29.9 kg/m²), we use the current weight as the dosing weight (see 'Dosing weight' below). We target 25 to 30 kilocalories (kcal)/kg (see 'Calorie prescription' below); 1.2 to 2.0 g/kg of protein per day (ie, high-protein diet) (see 'Protein prescription' below); and the recommended daily allowance of electrolytes, vitamins, minerals, and trace elements (see 'Electrolytes, vitamins, minerals, trace elements' below). We initiate feeding at 12 kcal/kg of dosing weight per day and slowly increase to the target over the ensuing three to seven days, shorter if on PN (eg, two to three days).

These requirements are used to select the appropriate formulation and rate of administration. Formulations for EN and PN are discussed separately. (See "Nutrition support in intubated critically ill adult patients: Enteral nutrition" and "Nutrition support in intubated critically ill adult patients: Parenteral nutrition".)

Dosing weight — For adequately nourished patients who have a normal body weight (BMI 18.5 to 24.9 kg/m²) or who are overweight (BMI 25 to 29.9 kg/m²), we use the current weight as the dosing weight. Definition and dosing weight for patients who are underweight (<18.5 kg/m²) or have obesity (BMI ≥30 kg/m²) are discussed below. (See 'Assess nutritional status' above and 'Patients with malnutrition' below and 'Patients with obesity' below.)

Calories and protein needs are calculated based upon the dry body weight of the individual patient (ie, the "dosing weight"). Estimating the dry body weight is not an exact science and can be challenging in the critically ill patient due to hyper- or hypovolemia. For example, we sometimes compare current with admission or previous body weight to facilitate estimation of dry body weight.

While some experts calculate calorie prescription based upon measured resting energy expenditure (eg, using indirect calorimetry), this is impractical for most settings due to cost of equipment and maintenance of expertise.

Calorie prescription — For adequately nourished critically ill patients, we initially provide 12 kcal/kg of dosing weight per day (see 'Dosing weight' above) and slowly increase to 25 to 30 kcal/kg in the next seven days, shorter for those on PN (eg, two to three days). While guidelines suggest a starting range between 12 and 25 kcal/kg of dosing weight per day [6], there is clinical equipoise regarding the optimal approach. We prefer to start at the lower end of this range to avoid potential harm from overfeeding and intolerance.

Hypocaloric feeding (eg, 8 to 10 kcal/kg dosing weight) during the first week of critical illness has been controversial [37-39]. Early trials suggested benefit (eg, less gastrointestinal intolerance, fewer infections) compared with normocaloric feeding [40-42], resulting in a paradigm shift in practice towards hypocaloric feeding in the 2000s. Since then, meta-analyses and guideline groups have reported similar outcomes when hypocaloric or normocaloric strategies are used during the first week of critical illness [6,40,42-44]. However, the effect is uncertain due in part to the broad range of imprecision in studies suggesting that outcomes may be beneficial or harmful when hypocaloric or aggressive feeding is used. It should also be noted that existing studies often focus on the first week of critical illness, but the impact of such a calorie prescription in those with prolonged critical illness is unknown.

Best supporting a normocaloric strategy is a 2022 meta-analysis of 14 trials that compared higher with lower energy intake. The analysis reported similar 28-day mortality (risk difference [RD] 0, 95% CI -0.02 to 0.02); ICU mortality (RD 0, 95% CI -0.03 to 0.03); and other outcomes including length of stay, infectious complications (eg, bacteremia or pneumonia, any infection), and ventilator days [6]. However, there was very low confidence in the results due to a significant degree of clinical heterogeneity, high risk of bias, inconsistency, and imprecision. An earlier meta-analysis showed similar findings [43].

Protein prescription — In critically ill patients, we prescribe 1.2 to 2.0 g/kg of protein per day (ie, high-protein diet). For most patients, amounts on the lower end of this range may be sufficient while patients with severe burns, trauma, or obesity may benefit from rates on the higher end. We do not reduce the amount of protein in patients with kidney disease since clinical trials have shown that critically ill patients with kidney failure can tolerate protein intake as high as 2.5 g/kg per day [45]. We perform an ongoing assessment of the patient's clinical condition as it impacts protein prescription estimates over the course of their illness.

This approach is based upon limited data in unselected critically ill patients and indirect data derived from patients with burns or obesity that support improved surrogate outcomes, such as hand grip strength or muscle mass with a high protein strategy [46-50]. This approach is also supported by the practical observation that most patients actually receive an amount significantly less than that prescribed due to frequent feeding difficulties encountered in this population [46] and that protein requirements increase as the illness becomes more severe [51]. Thus, it is thought that this strategy mitigates further muscle protein loss incurred by severe critical illness itself.

Data suggest no meaningful mortality benefit when high-dose versus low-dose prescriptions for protein in critically ill patients are compared, although data are flawed:

●A multicenter, single-blinded randomized trial of 1301 mechanically ventilated patients (most of whom had a medical condition, most often respiratory failure) who were considered at high nutritional risk compared treatment with a high protein prescription (≥2·2 g/kg per day) with the usual dose protein prescription (≤1.2 g/kg per day) [52]. High nutritional risk was defined as low BMI (≤25 kg/m²), high BMI (≥35 kg/m²), moderate to severe malnutrition, frailty, sarcopenia, or projected duration of mechanical ventilation of more than four days beyond the point of screening. Feeding was started within 96 hours of ICU admission and continued for up to 28 days or death or transition to oral feeding. Despite appropriate separation in protein dosing, similar rates of survival to hospital discharge (46 versus 50 percent) and 60-day mortality (35 versus 32 percent) were reported. It should be noted that, common to similar studies, delivery to each group was significantly less than that prescribed (1.6 versus 0.9 g/kg per day, respectively). Subgroup analysis may have suggested a possible benefit favoring the usual dosing regimen in those with acute kidney failure and high illness severity scores. However, interpretation is limited due to the lack of blinding and poor recruitment, which underpowered the trial.

●One meta-analysis of four trials (637 patients and which did not include the trial above) that compared higher with lower prescriptions of protein reported similar ICU mortality (RD -0.01, 95% CI -0.06 to 0.04) and hospital mortality (RD -0.02, 95% CI -0.07 to 0.04) [6]. (See "Overview of nutrition support in burn patients".)

Electrolytes, vitamins, minerals, trace elements — Daily requirements of electrolytes, vitamins, minerals, trace elements are typically prescribed in the absence of known deficiency. Further details are provided separately. (See "Nutrition support in intubated critically ill adult patients: Enteral nutrition", section on 'Other (vitamins, minerals, trace elements, fiber)' and "Nutrition support in intubated critically ill adult patients: Parenteral nutrition", section on 'Electrolytes' and "Nutrition support in intubated critically ill adult patients: Parenteral nutrition", section on 'Vitamins, minerals, and trace elements'.)

PATIENTS WITH MALNUTRITION — The definition of malnutrition is described above. (See 'Assess nutritional status' above.)

●Timing and type of nutrition support – The ideal approach in patients with malnutrition is unknown. In this population, we adopt the same principles as in adequately nourished patients (ie, early enteral nutrition [EN] or parenteral nutrition [PN] at 36 to 48 hours). (See 'Adequately nourished patients' above.)

We do not aggressively administer feeding within the first few hours of admission due to limited data that suggest potential harm in adequately nourished patients with this approach (eg, increased mortality) [31,53] and the potential risk of refeeding syndrome, which is high in this population. (See "Anorexia nervosa in adults and adolescents: The refeeding syndrome".)

●Nutritional prescription – For patients who are underweight (body mass index <18.5 kg/m²), we use 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 or worsen refeeding syndrome [54]. (See "Anorexia nervosa in adults and adolescents: The refeeding syndrome".)

We also suggest a similar prescription of calories and protein to that described in adequately nourished patients, although we sometimes increase the eventual target goal to 35 kilocalories (kcal)/kg of body weight per day but only in a relatively stable patient considered to be in a lower inflammatory state (ie, in early recovery phase of critical illness) (see 'Calculating calorie and protein requirements in adequately nourished patients' above). If goals cannot be met after 7 to 10 days of EN, we sometimes supplement EN with PN.

We also administer thiamine supplementation in patients with malnutrition to prevent Wernicke encephalopathy. (See "Wernicke encephalopathy".)

Ideal prescriptions for patients who are chronically ill in the intensive care unit are unknown. In general, we choose a set target of 25 to 30 kcal/kg and/or perform calorimetry to facilitate goal setting.

●Efficacy – Data to support this approach are limited since most clinical trials have excluded patients with malnutrition. Recommendations are generally based upon the biologic plausibility that excess caloric deficit is associated with increased morbidity in critically ill patients [55], indirect evidence of a potential benefit from early nutrition derived from the adequately nourished patient population (see 'Adequately nourished patients' above), and post-hoc data in patients at high nutritional risk that report similar outcomes when hypocaloric feeding is compared with normocaloric regimens [44].

PATIENTS WITH OBESITY

●Timing and type of nutrition – Most patients with obesity are adequately nourished while others may be inadequately nourished. For most patients with obesity (body mass index ≥30 kg/m²), the optimal approach to nutrition is unknown. As an initial strategy, we typically choose the same approach as that described for adequately nourished critically ill patients (ie, early enteral nutrition or parenteral nutrition at 36 to 48 hours). (See 'Adequately nourished patients' above.)

However, for malnourished patients with obesity, we may use the principles of malnourishment to drive prescription (eg, calorie prescription may be slightly higher than for the adequately nourished patient). (See 'Patients with malnutrition' above.)

●Nutritional prescription – For critically ill patients with obesity, there is little consensus among clinicians regarding the appropriate dosing weight.

•In this population, we prefer to estimate nutritional needs based upon the individual's resting energy expenditure (REE) rather than their actual body weight (ABW) or ideal body weight (IBW). Although most experts agree that indirect calorimetry is the best method for REE measurement [56], we typically use predictive equations, such as the Penn State University 2010 predictive equation [57-59] since calorimeters are not widely available and calorie prescription based on calorimetry has not been adequately tested.

•Alternatively, IBW-based adjustments can be performed. The purpose of adjusting the dosing weight of patients who are obese is to account for the absence of metabolic requirements by fat tissues:

●Efficacy – Data regarding the impact of nutritional support on clinical outcomes in critically ill patients with obesity are limited to small observational series and inadequately powered randomized trials that have had mixed results [6,60-67]. Additionally, the presence of disease-related malnutrition in patients with obesity may confound the effect of obesity on measured outcomes [66]. Some trials suggest that hypocaloric, high-protein regimens are associated with a trend toward reduced length of stay in this population when compared with normocaloric strategies [59-65]. However, additional studies are warranted in this population before we would change our approach.

Additional guidelines for nutritional support of critically ill patients who have obesity can be found at the American Society for Parenteral and Enteral Nutrition [59].

CORONAVIRUS DISEASE 2019 — In patients with coronavirus disease 2019 (COVID-19) who develop critical illness, we use the same data that instruct nutrition support in all critically ill patients [68]. Select issues deserve attention (see "COVID-19: Management of the intubated adult"):

●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 continued feeding during changes in position [69-72]. Many experts temporarily stop tube feeding and empty the stomach before positioning to the supine or prone position and then promptly resume feeding. Our practice is to continue the feeding. Use of nasal bridles (figure 1) to secure nasal feeding tubes is reasonable, though infrequently used. (See "Prone ventilation for adult patients with acute respiratory distress syndrome".)

●Malnutrition – Because in the initial phases of the pandemic the critical illness associated with acute COVID-19 was prolonged and the disease highly inflammatory, it is possible that malnutrition may have been more evident at a later point in the illness. However, whether a prolonged critical illness course still applies to COVID-19 due to evolving variants is unclear. (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), led to an increased effort to supplement protein over and above the routine amounts administered to critically ill non-COVID-19 patients. However, we believe that goals for protein intake should parallel that administered to non-COVID-19 patients. (See 'Protein prescription' above and "Nutrition support in intubated critically ill adult 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 possible benefit of high-dose vitamin C in COVID-19 [73,74], limited data in non-COVID-19 patients suggest no benefit [75]. We do not support routine use of any nutrient supplementation in any critically ill patient, unless they have a known deficiency prior to admission.

Low vitamin D levels are associated with adverse outcomes in the critically ill, but these are likely disease epiphenomena as opposed to a true deficiency. Supplementation has failed to improve outcomes in several randomized control trials of critically ill patients without COVID-19 [76,77] and those with moderate to severe COVID-19 [78-80], except possibly those with severe vitamin D deficiency [81,82]. While trace element levels are decreased and associated with critical illness outcomes [83], there are no data to support a benefit in the critically ill COVID-19 patient or any other patient.

Further data in non-COVID-19 patients are provided separately. (See "Nutrition support in intubated critically ill adult patients: Enteral nutrition", section on 'Extra supplements of no proven benefit'.)

ADMINISTRATION AND MONITORING — Administration of nutrition support requires that appropriate access is established and that the formulation, composition, delivery strategy, and delivery rate be determined. Once started, nutrition support must be monitored for tolerance and complications. These issues are different for enteral and parenteral nutrition and are discussed separately. (See "Nutrition support in intubated critically ill adult patients: Enteral nutrition" and "Nutrition support in intubated critically ill adult patients: Parenteral nutrition".)

We monitor all patients for "refeeding syndrome." Patients with malnutrition, patients with antecedent episodes of hypokalemia and hypophosphatemia, and those with conditions that predispose to electrolyte losses are likely to be at higher risk for refeeding syndrome. Further details on refeeding syndrome are provided separately. (See "Anorexia nervosa in adults and adolescents: The refeeding syndrome".)

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".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Malnutrition (The Basics)" and "Patient education: Malnutrition – Discharge instructions (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Initial evaluation – Nutrition support refers to the enteral or parenteral provision of calories, protein, electrolytes, vitamins, minerals, and fluids. Once an intubated patient is admitted to the intensive care unit, we assess their nutritional status, the need for nutritional support, and the presence of any contraindications to select modes of delivery. (See 'Introduction' above and 'Initial evaluation' above.)

●Adequately nourished patients – Adequately nourished patients who are expected to be extubated within 24 to 36 hours of admission are likely able to eat after extubation and do not need nutrition support. For patients mechanically ventilated for longer than 36 hours, our approach is the following (see 'Adequately nourished patients' above):

•No contraindications to enteral nutrition (EN) – For adequately nourished, intubated, critically ill patients without contraindications to enteral nutrition (EN), we suggest early (eg, 36 to 48 hours) rather than delayed EN (Grade 2B). Support for this approach is derived from limited data that suggest fewer episodes of infectious pneumonia and a possible mortality benefit when early EN is compared with delayed EN. (See 'Patients without contraindications to enteral nutrition' above.)

•Contraindications to EN – For adequately nourished, critically ill patients with contraindications to EN (table 2), we suggest early parenteral nutrition (PN; eg, 36 to 48 hours) rather than delaying nutrition support (Grade 2C). While in the past our practice was to administer PN later in critical illness, data since then suggest that outcomes are similar when early PN is compared with late PN. Patients who are expected to need long term PN (ie, beyond critical illness) should also start their feeding early since it is assumed that the same benefit associated with short term feeding applies to those who require longer term feeding with PN.(See 'Patients with contraindications to enteral feeding' above.)

•Prescription – For adequately nourished patients who have a normal body weight (body mass index [BMI] 18.5 to 24.9 kg/m²) or who are overweight (BMI 25 to 29.9 kg/m²), their current weight is used as the dosing weight. We suggest the following targets for the initial prescription(Grade 2C) (see 'Calculating calorie and protein requirements in adequately nourished patients' above and 'Electrolytes, vitamins, minerals, trace elements' above):

-Total calories – 25 to 30 kilocalories (kcal)/kg administered at 12 kcal/kg of dosing weight per day and slowly increase to the target, typically 25 to 30 kcal/kg, over the next three to seven days, shorter if on PN (eg, two to three days)

-Protein – 1.2 to 2.0 g/kg of protein per day (ie, high-protein diet)

-Daily supplements – Recommended daily allowance of electrolytes, vitamins, minerals, and trace elements

●Patients with malnourishment – In this population, we adopt the same principles as in adequately nourished patients (ie, early EN or PN within 36 to 48 hours and current weight as the initial dosing weight). However, if the patient is stable and in recovery, an increase in the target goal to 35 kcal/kg of their body weight per day may be needed. Importantly, aggressively administering early feeding should be avoided due to the potential risk of refeeding syndrome. (See 'Patients with malnutrition' above.)

●Patients with obesity – For patients with obesity (BMI ≥30 kg/m²), the timing and choice of nutrition should be the same as for the adequately nourished critically ill patient. (See 'Patients with obesity' above.)

They key difference is that in patients with obesity, the nutritional needs are estimated based upon the individual's resting energy expenditure (REE; eg, indirect calorimetry) rather than their actual body weight (ABW) or ideal body weight (IBW), although the latter can be used if REE measurements are not available. Common IBW calculations include the following:

or

●Administration – Administration of nutrition support requires that appropriate access is established and that the formulation, composition, delivery strategy, and delivery rate be determined. Once started, nutrition support must be monitored for tolerance and complications. These issues are different for EN and PN and are discussed separately. (See "Nutrition support in intubated critically ill adult patients: Enteral nutrition" and "Nutrition support in intubated critically ill adult patients: Parenteral nutrition".)