Nutrition
Nour Ghazi Batarseh MD, Tara Humphrey MD, Ramzy Husam Rimawi MD.
Introduction:
The importance of nutrition in the hospital setting, most precisely in the intensive care unit (ICU), cannot be overemphasized [1]. As a response to critical illness, the patients develop a systemic inflammatory response, which puts them in a catabolic stress state. This response causes increased infectious morbidity, multi-organ dysfunction, prolonged hospitalization, and disproportionate mortality [1,2,3]. Radical advances have occurred over the past three decades in the understanding of the molecular and biological effects of nutrients in stabilizing and improving the critical illness the patients are in. Nutrition is not regarded as adjunctive care to provide fuel to aid patients during this stressful state anymore. Traditionally the aim of nutrition was to preserve lean body mass, to maintain immune function, and to avert metabolic complications [1,2]. Recently nutrition is regarded as therapy on its own; it helps attenuate the metabolic response to stress, to prevent oxidative cellular injury, and to favorably modulate the immune response [1].
Nutrition Support:
If not monitored carefully, inadequate nutrition can have various complications, including [1,2,3]:
The concept that nutrition should not be thought of just as supportive means has been rightfully put forward and that, it is actually a therapy on its own right, that could change the course and outcome of critical illnesses [1,2,3] . Nutrition education in US medical schools may be inadequate and students are reported on average to receive less than twenty hours of nutrition education. Nevertheless, it is an integral part of patient care and early identification of those most at risk for malnutrition is essential [1,2,3]. In critical illnesses, patients are in a catabolic state due to the hormonal and cytokine milieu created by the inflammatory process, thus calorie consumption is high. Better management of mechanical ventilation, fever, anxiety, and pain help reduce the consumption rate, however nutrition should reverse the balance and address the patients anabolic needs to prevent the risk of protein-calorie malnutrition [1,2].
Adult under nutrition is multifactorial and is a consequence of decreased intake, increased requirements, as well as impaired absorption [3]. Treatment with adequate nutrition support supplies the substrates required for the anabolic state, subsequently facilitating the correction of hypoproteinemia, muscle loss, and depletion of nutritional stores [1,2,3].
Nutritional assessment is the first step in nutrition support and should be performed early to detect malnourishment and process in management [3]. One can proactively decrease the disease severity with a thorough assessment. The initial assessment requires a complete history, physical examination, and careful consideration of laboratory values [1,2,3]. This assessment can be used to calculate both the energy and protein requirements needed to set nutrition goals for patients, and thus initiate nutritional intervention [1]. Nutritional needs vary throughout the course of the critical illness therefore regular frequent nutritional assessment is prudent to evaluate the efficacy of current treatment and adjust support if needed [1,2,3].
Specific patient data needs to be obtained to create an appropriate metabolic and nutritional profile. The initial approach to a complete nutritional assessment encompasses the patient interview and a thorough clinical history from the patient if possible [1,2,3]. Attention should be given to the current disease state, duration of illness, intake of nutrients, weight loss, and any gastrointestinal complaints (nausea, vomiting, and diarrhea) [2,3]. Several aspects of the medical and surgical history are also particularly important, including diabetes mellitus, inflammatory bowel disease, infections, and previous hospitalizations or surgeries [2,3].
Furthermore, family history of diabetes or glucose intolerance, cardiovascular disease, inflammatory bowel disease or obesity should be determined [2,3]. Important aspects of the social history including socioeconomic status and education can help give an idea of food selection, and use of substances including alcohol, tobacco, and other drugs. In addition to accurate documentation of the medications the patients take, the consultant should elicit the patient's history regarding vitamin or mineral (especially calcium) supplementation. Any allergies or food intolerance/aversions should be reported. A thorough history about weight changes prior to hospitalization is essential. For women, menstrual history is important to document [2,3].
A physical exam should be performed as it can be used to characterize subcutaneous fat and skeletal muscle stores objectively [2,3]. In addition to the general physical appearance, important findings suggestive of improper dietary adherence may include cachexia, fluid retention, temporal wasting, jaundice, obesity, hair loss, pallor, xerosis, glossitis, mucosal bleeding, poor dentition, thyromegaly, and peripheral edema [2,3]. Other objective data such as fever or hypothermia or nonspecific signs of systemic inflammatory response such as tachycardia or hyperglycemia may help facilitate an etiological based diagnosis of malnutrition [2].
Since there is no single parameter that is definitive for adult malnutrition, a minimum of two or more of the following six characteristics is recommended for diagnosis of malnutrition and should be evaluated in all patients [3]:
1. Insufficient energy intake : Patients in critical illness have high energy requirements and calorie consumption. Malnutrition occurs when there is inadequate supply or food intake compared to the required demands. The clinician may obtain or review the food and nutrition history, estimate optimum energy needs, compare them with estimates of energy consumed and report inadequate intake as a percentage of estimated energy requirements over time.
2. Weight loss: Weight can be easily determined usually by the nursing staff. Weight must be evaluated in the light of under or over hydration. The clinician may assess weight change over time.
3. Loss of muscle mass: regular daily physical exam can determine the muscle mass. Some of the muscles that can noted by physical exam are the following : wasting of the temples [temporalis muscle]; clavicles [pectoralis and deltoids]; shoulders [deltoids]; interosseous muscles; scapula [latissimus dorsi, trapezious, deltoids]; thigh [quadriceps] and calf [gastrocnemius].
4. Loss of subcutaneous fat: Loss of subcutaneous fat (eg. orbital, triceps, fat overlying the ribs).
5. Localized or generalized fluid may sometimes mask weight loss: The clinician may evaluate generalized or localized fluid accumulation evident on exam (extremities; vulvar/scrotal edema or ascites). Weight loss is often masked by generalized fluid retention (edema) and weight gain may be observed.
6. Diminished functional status as measured by hand grip strength.
These characteristics should be assessed routinely and evaluated frequently throughout the patient’s stay in the hospital in acute, chronic, or transitional care settings.
Anthropometric data including weight, height, and BMI can be helpful. Weight loss and underweight status are well-validated indicators of malnutrition [3].
Body Mass Index (BMI) is calculated using weight (kg) divided by height (meters squared).
classifications for BMI adopted by National Institute of Health (NIH) and World Health organization (WHO) for Caucasian, Hispanic and Black individuals are [4]:
Laboratory values
In the critical care setting, traditional protein markers (albumin, prealbumin) are a reflection of the acute phase response (increases in vascular permeability and reprioritization of hepatic protein synthesis) and do not accurately represent nutrition status for multiple reasons (guidelines recommend a nutritional assessment based on comorbidities, function of the GI tract, and the risk for aspiration). Serum albumin has been studied most extensively, likely due to its’ long half-life (18 to 20 days). Low serum albumin (< 2.2 g/dL) is a marker of a catabolic state, and a predictor of poor outcome. Surgery decreases serum albumin levels, as do other acute stressors as well as hepatic and renal diseases. Serum prealbumin (transthyretin) has the shortest half-life (2-3 days) but is also influenced by renal and hepatic disease and is a reflection of the acute phase response. Albumin and prealbumin therefore are not good indicators of nutritional status but are good predictors of mortality and morbidity for critically ill patients [1].
Calculation of nutritional needs
Nutritional needs include the need for energy, protein, hydration, vitamins and electrolytes [1].
To assess the calorie or energy needs of a patient three methods can be used: Indirect calorimetry (IC), a published predictive equation or a simplistic weight-based equation (25–30 kcal/kg/d) to determine energy requirements [5,6,7].
IC calculates the heat produced either by measuring the submission of carbon dioxide and nitrogen waste as ammonia or the rate of oxygen consumption. This usually requires specific masks and equipment which are usually not available in many hospital settings. Therefore, energy needs are usually assessed by either a predictive equation or as simply as this weight based equation (25-30 kcal/Kg/d) [1].
Metabolic needs change constantly in critical illness, thus finding one standardized predicative equation for all patients is challenging [3,4,5,6]. Currently there is no strong evidence for one prediction equation over the other so selecting an equation is up to the clinician and can provide a useful starting point. The Harris-Benedict formula was previously used to predict calorie requirements in acutely ill hospitalized patients, however it can be more unreliable in a malnourished patient. The 1998 and 2003 Penn State equations, the 1992 Ireton-Jones equation, and the Swinamer equation are worthy of consideration.
Currently the Penn state equation or a kcals/kg equation is commonly used in practice [5]:
REE = BEE (0.85) + VE ( 32) + Tmax (140) - 5340
REE = Resting energy expenditure
BEE= Basal energy expenditure
BEE (men): 66 + 13.8 (wt in kg) + 5 (ht in cm) – 6.8 (age in yrs)
BEE (women): 655 + 9.6 (wt in kg) + 1.8 (ht in cm) – 4.7 (age in yrs)
VE= minute ventilation (L/min)
T max= maximum temperature (C)
REE is a good starting point for the total calorie needed by the patient, and clinicians can advance and accelerate the rate according to patients tolerance.
After determining the REE, the patient’s protein requirement needs to be established. Certain disease states have different protein requirements. Current recommendations are to give patients with mild to moderate illness 0.8 to 1.2 g/kg protein per day. Critically ill patients are generally prescribed 1.2 to 2 g/kg per day and more than 2 g/kg per day is needed for patients with severe burns [5,6].
Hydration or fluid needs must be addressed within each nutritional assessment because it can affect laboratory interpretations and nutritional interventions [1].
Once appropriate nutritional therapy has been initiated, it is important for the clinician to monitor for the development of refeeding syndrome. Refeeding syndrome can occur in malnourished patients receiving artificial nutrition therapy (enterally or parenterally) due to the potentially fatal shifts in fluids and electrolytes once nutrition has been resumed. These shifts result from hormonal and metabolic changes and may cause serious clinical complications. The hallmark biochemical feature of refeeding syndrome is hypophosphataemia. However, the syndrome is complex and may also feature abnormal sodium and fluid balance; changes in glucose, protein, and fat metabolism; thiamine deficiency; hypokalaemia; and hypomagnesaemia. For patients at high risk of developing refeeding syndrome (severely malnourished, or has not have any intake for more than 5 days), nutritional repletion of energy should be started slowly and should be tailored to each patient. It can then be increased to meet or exceed full needs over four to seven days [7,8].
Route of feeding
Enteral vs parenteral
Enteral nutrition (EN) support refers to the provision of calories, protein, electrolytes, vitamins, minerals, trace elements, and fluids via an intestinal route. For patients without contraindications to enteral nutrition, early enteral feeding (i.e., within 24-48 hours) is the preferred route of feeding [1]. Studies have shown that early enteral feeding in the first 24-48hrs can reduce risk of infections [9].
Hemodynamic instability is considered a contraindication of enteral feeding, and enteral feeding should be held while the patient is being resuscitated. Enteral feeding can be resumed with caution for patients that are being withdrawn from vasopressors [1].
Enteral feeding can be either gastric or post-pyloric [9,10,11] . Intragastric feeding is usually well tolerated by patients. The stomach has to be structurally and functionally intact prior to initiating intragastric feeding [1]. Additionally, the lower esophageal sphincter should have adequate tone and function and gastric motility must be intact with adequate gastric emptying [9,10]. Intragastric feeding is the closest to the physiological normality which allows the usual processing of nutrients. Furthermore, an orogastric or nasogastric tube insertion is a relatively safe procedure, requires minimal training, and usually done at the bedside [10]. The stomach is usually able to tolerate a larger volume and higher osmotic load than the upper small intestine [9,10]. Any factor that may delay gastric emptying should be taken into account prior to a trial of intragastric feeds. A radiographic imaging should be done to ensure the proper positioning of the feeding tube as it may be misplaced into an airway [9].
Although enteral nutrition is most commonly delivered into the stomach, it can also be administered further distal into the alimentary tract. An enteral access tube can be placed in the small bowel and is called post-pyloric enteral feeding [9,10]. Patients that are at high risk for aspiration or intolerant to gastric feeding such as having repeated high gastric residual volumes (>500cc) despite trials of promotility agents should be considered for post-pyloric enteral feeding [1].
Other indications for post-pyloric feeding include esophageal dysmotility, reflux, pancreatitis, delayed gastric emptying, emesis, trauma, gastric outlet/duodenal obstruction, gastric or duodenal fistula or anatomical anomaly [9,10].
Of note, there is no difference in the risk of pulmonary aspiration between gastric and postpyloric feeding for patients with normal gastric motility [1].
To reduce the risk of aspiration, the following measures should be taken [1]:
Regular and routine monitoring of tolerance of feeding is required. Interruption of feeding should be avoided unless patients are not tolerating it or are getting hemodynamically unstable [1].
Parenteral nutrition support refers to the provision of calories, amino acids, electrolytes, vitamins, minerals, trace elements, and fluids via a parenteral route. If enteral feeding is not feasible then parenteral feeding may be necessary [1].
Early parenteral nutrition may increase the risk of infection and prolong mechanical ventilation, ICU stay, and hospital stay and is not recommended [12]. Enteral nutrition is preferred over parenteral nutrition because it helps maintain gut integrity, modulate stress and systemic immune response, and attenuate disease severity [13]. Instead, parenteral nutrition should be initiated after 7 days if patient is unable to receive enteral therapy by then [14]. Complications of parenteral feeding include bloodstream infections, metabolic derangements such as hyperglycemia and hypophosphatemia, hepatic dysfunction, refeeding syndrome [13,14,15].
In summary, nutritional support in the ICU is a major determinant of morbidity and mortality in hospitalized patients, particularly critically ill patients and post-surgical patients. The goals of nutrition therapy are to support protein synthesis and enhance immune function in a system that is under extreme stress. Providers should be cognizant in avoiding starvation, stress metabolism, and overfeeding. Routine assistance of dietitians in the ICU can help curtail these problems and providers should assess efficacy of ongoing nutrition therapy and evaluate nutritional goals on a daily basis.
Key Points
The importance of nutrition in the hospital setting, most precisely in the intensive care unit (ICU), cannot be overemphasized [1]. As a response to critical illness, the patients develop a systemic inflammatory response, which puts them in a catabolic stress state. This response causes increased infectious morbidity, multi-organ dysfunction, prolonged hospitalization, and disproportionate mortality [1,2,3]. Radical advances have occurred over the past three decades in the understanding of the molecular and biological effects of nutrients in stabilizing and improving the critical illness the patients are in. Nutrition is not regarded as adjunctive care to provide fuel to aid patients during this stressful state anymore. Traditionally the aim of nutrition was to preserve lean body mass, to maintain immune function, and to avert metabolic complications [1,2]. Recently nutrition is regarded as therapy on its own; it helps attenuate the metabolic response to stress, to prevent oxidative cellular injury, and to favorably modulate the immune response [1].
Nutrition Support:
If not monitored carefully, inadequate nutrition can have various complications, including [1,2,3]:
- Loss of fat, muscle, skin, bone, and viscera, with consequential weight loss and an increase in extracellular fluid volume
- Increased susceptibility to infection
- Poor wound healing
- Increased frequency of pressure ulcers
- Overgrowth of bacteria in the gastrointestinal tract
The concept that nutrition should not be thought of just as supportive means has been rightfully put forward and that, it is actually a therapy on its own right, that could change the course and outcome of critical illnesses [1,2,3] . Nutrition education in US medical schools may be inadequate and students are reported on average to receive less than twenty hours of nutrition education. Nevertheless, it is an integral part of patient care and early identification of those most at risk for malnutrition is essential [1,2,3]. In critical illnesses, patients are in a catabolic state due to the hormonal and cytokine milieu created by the inflammatory process, thus calorie consumption is high. Better management of mechanical ventilation, fever, anxiety, and pain help reduce the consumption rate, however nutrition should reverse the balance and address the patients anabolic needs to prevent the risk of protein-calorie malnutrition [1,2].
Adult under nutrition is multifactorial and is a consequence of decreased intake, increased requirements, as well as impaired absorption [3]. Treatment with adequate nutrition support supplies the substrates required for the anabolic state, subsequently facilitating the correction of hypoproteinemia, muscle loss, and depletion of nutritional stores [1,2,3].
Nutritional assessment is the first step in nutrition support and should be performed early to detect malnourishment and process in management [3]. One can proactively decrease the disease severity with a thorough assessment. The initial assessment requires a complete history, physical examination, and careful consideration of laboratory values [1,2,3]. This assessment can be used to calculate both the energy and protein requirements needed to set nutrition goals for patients, and thus initiate nutritional intervention [1]. Nutritional needs vary throughout the course of the critical illness therefore regular frequent nutritional assessment is prudent to evaluate the efficacy of current treatment and adjust support if needed [1,2,3].
Specific patient data needs to be obtained to create an appropriate metabolic and nutritional profile. The initial approach to a complete nutritional assessment encompasses the patient interview and a thorough clinical history from the patient if possible [1,2,3]. Attention should be given to the current disease state, duration of illness, intake of nutrients, weight loss, and any gastrointestinal complaints (nausea, vomiting, and diarrhea) [2,3]. Several aspects of the medical and surgical history are also particularly important, including diabetes mellitus, inflammatory bowel disease, infections, and previous hospitalizations or surgeries [2,3].
Furthermore, family history of diabetes or glucose intolerance, cardiovascular disease, inflammatory bowel disease or obesity should be determined [2,3]. Important aspects of the social history including socioeconomic status and education can help give an idea of food selection, and use of substances including alcohol, tobacco, and other drugs. In addition to accurate documentation of the medications the patients take, the consultant should elicit the patient's history regarding vitamin or mineral (especially calcium) supplementation. Any allergies or food intolerance/aversions should be reported. A thorough history about weight changes prior to hospitalization is essential. For women, menstrual history is important to document [2,3].
A physical exam should be performed as it can be used to characterize subcutaneous fat and skeletal muscle stores objectively [2,3]. In addition to the general physical appearance, important findings suggestive of improper dietary adherence may include cachexia, fluid retention, temporal wasting, jaundice, obesity, hair loss, pallor, xerosis, glossitis, mucosal bleeding, poor dentition, thyromegaly, and peripheral edema [2,3]. Other objective data such as fever or hypothermia or nonspecific signs of systemic inflammatory response such as tachycardia or hyperglycemia may help facilitate an etiological based diagnosis of malnutrition [2].
Since there is no single parameter that is definitive for adult malnutrition, a minimum of two or more of the following six characteristics is recommended for diagnosis of malnutrition and should be evaluated in all patients [3]:
1. Insufficient energy intake : Patients in critical illness have high energy requirements and calorie consumption. Malnutrition occurs when there is inadequate supply or food intake compared to the required demands. The clinician may obtain or review the food and nutrition history, estimate optimum energy needs, compare them with estimates of energy consumed and report inadequate intake as a percentage of estimated energy requirements over time.
2. Weight loss: Weight can be easily determined usually by the nursing staff. Weight must be evaluated in the light of under or over hydration. The clinician may assess weight change over time.
3. Loss of muscle mass: regular daily physical exam can determine the muscle mass. Some of the muscles that can noted by physical exam are the following : wasting of the temples [temporalis muscle]; clavicles [pectoralis and deltoids]; shoulders [deltoids]; interosseous muscles; scapula [latissimus dorsi, trapezious, deltoids]; thigh [quadriceps] and calf [gastrocnemius].
4. Loss of subcutaneous fat: Loss of subcutaneous fat (eg. orbital, triceps, fat overlying the ribs).
5. Localized or generalized fluid may sometimes mask weight loss: The clinician may evaluate generalized or localized fluid accumulation evident on exam (extremities; vulvar/scrotal edema or ascites). Weight loss is often masked by generalized fluid retention (edema) and weight gain may be observed.
6. Diminished functional status as measured by hand grip strength.
These characteristics should be assessed routinely and evaluated frequently throughout the patient’s stay in the hospital in acute, chronic, or transitional care settings.
Anthropometric data including weight, height, and BMI can be helpful. Weight loss and underweight status are well-validated indicators of malnutrition [3].
Body Mass Index (BMI) is calculated using weight (kg) divided by height (meters squared).
classifications for BMI adopted by National Institute of Health (NIH) and World Health organization (WHO) for Caucasian, Hispanic and Black individuals are [4]:
- Underweight- BMI < 18.5 kg/M2
- Normal weight - BMI ≥ 18.5 to 24.9 kg/m2.
- Overweight - BMI ≥ 25 to 29.9kg/m2.
- Obesity - BMI ≥ 30 kg/m2.
- Obesity class 1- BMI of 30 to 34.9 kg/m2
- Obesity class 2 - BMI of 35 to 39.9 kg/m2.
- Obesity class 3 - BMI ≥ 40 kg/m2.
Laboratory values
In the critical care setting, traditional protein markers (albumin, prealbumin) are a reflection of the acute phase response (increases in vascular permeability and reprioritization of hepatic protein synthesis) and do not accurately represent nutrition status for multiple reasons (guidelines recommend a nutritional assessment based on comorbidities, function of the GI tract, and the risk for aspiration). Serum albumin has been studied most extensively, likely due to its’ long half-life (18 to 20 days). Low serum albumin (< 2.2 g/dL) is a marker of a catabolic state, and a predictor of poor outcome. Surgery decreases serum albumin levels, as do other acute stressors as well as hepatic and renal diseases. Serum prealbumin (transthyretin) has the shortest half-life (2-3 days) but is also influenced by renal and hepatic disease and is a reflection of the acute phase response. Albumin and prealbumin therefore are not good indicators of nutritional status but are good predictors of mortality and morbidity for critically ill patients [1].
Calculation of nutritional needs
Nutritional needs include the need for energy, protein, hydration, vitamins and electrolytes [1].
To assess the calorie or energy needs of a patient three methods can be used: Indirect calorimetry (IC), a published predictive equation or a simplistic weight-based equation (25–30 kcal/kg/d) to determine energy requirements [5,6,7].
IC calculates the heat produced either by measuring the submission of carbon dioxide and nitrogen waste as ammonia or the rate of oxygen consumption. This usually requires specific masks and equipment which are usually not available in many hospital settings. Therefore, energy needs are usually assessed by either a predictive equation or as simply as this weight based equation (25-30 kcal/Kg/d) [1].
Metabolic needs change constantly in critical illness, thus finding one standardized predicative equation for all patients is challenging [3,4,5,6]. Currently there is no strong evidence for one prediction equation over the other so selecting an equation is up to the clinician and can provide a useful starting point. The Harris-Benedict formula was previously used to predict calorie requirements in acutely ill hospitalized patients, however it can be more unreliable in a malnourished patient. The 1998 and 2003 Penn State equations, the 1992 Ireton-Jones equation, and the Swinamer equation are worthy of consideration.
Currently the Penn state equation or a kcals/kg equation is commonly used in practice [5]:
REE = BEE (0.85) + VE ( 32) + Tmax (140) - 5340
REE = Resting energy expenditure
BEE= Basal energy expenditure
BEE (men): 66 + 13.8 (wt in kg) + 5 (ht in cm) – 6.8 (age in yrs)
BEE (women): 655 + 9.6 (wt in kg) + 1.8 (ht in cm) – 4.7 (age in yrs)
VE= minute ventilation (L/min)
T max= maximum temperature (C)
REE is a good starting point for the total calorie needed by the patient, and clinicians can advance and accelerate the rate according to patients tolerance.
After determining the REE, the patient’s protein requirement needs to be established. Certain disease states have different protein requirements. Current recommendations are to give patients with mild to moderate illness 0.8 to 1.2 g/kg protein per day. Critically ill patients are generally prescribed 1.2 to 2 g/kg per day and more than 2 g/kg per day is needed for patients with severe burns [5,6].
Hydration or fluid needs must be addressed within each nutritional assessment because it can affect laboratory interpretations and nutritional interventions [1].
Once appropriate nutritional therapy has been initiated, it is important for the clinician to monitor for the development of refeeding syndrome. Refeeding syndrome can occur in malnourished patients receiving artificial nutrition therapy (enterally or parenterally) due to the potentially fatal shifts in fluids and electrolytes once nutrition has been resumed. These shifts result from hormonal and metabolic changes and may cause serious clinical complications. The hallmark biochemical feature of refeeding syndrome is hypophosphataemia. However, the syndrome is complex and may also feature abnormal sodium and fluid balance; changes in glucose, protein, and fat metabolism; thiamine deficiency; hypokalaemia; and hypomagnesaemia. For patients at high risk of developing refeeding syndrome (severely malnourished, or has not have any intake for more than 5 days), nutritional repletion of energy should be started slowly and should be tailored to each patient. It can then be increased to meet or exceed full needs over four to seven days [7,8].
Route of feeding
Enteral vs parenteral
Enteral nutrition (EN) support refers to the provision of calories, protein, electrolytes, vitamins, minerals, trace elements, and fluids via an intestinal route. For patients without contraindications to enteral nutrition, early enteral feeding (i.e., within 24-48 hours) is the preferred route of feeding [1]. Studies have shown that early enteral feeding in the first 24-48hrs can reduce risk of infections [9].
Hemodynamic instability is considered a contraindication of enteral feeding, and enteral feeding should be held while the patient is being resuscitated. Enteral feeding can be resumed with caution for patients that are being withdrawn from vasopressors [1].
Enteral feeding can be either gastric or post-pyloric [9,10,11] . Intragastric feeding is usually well tolerated by patients. The stomach has to be structurally and functionally intact prior to initiating intragastric feeding [1]. Additionally, the lower esophageal sphincter should have adequate tone and function and gastric motility must be intact with adequate gastric emptying [9,10]. Intragastric feeding is the closest to the physiological normality which allows the usual processing of nutrients. Furthermore, an orogastric or nasogastric tube insertion is a relatively safe procedure, requires minimal training, and usually done at the bedside [10]. The stomach is usually able to tolerate a larger volume and higher osmotic load than the upper small intestine [9,10]. Any factor that may delay gastric emptying should be taken into account prior to a trial of intragastric feeds. A radiographic imaging should be done to ensure the proper positioning of the feeding tube as it may be misplaced into an airway [9].
Although enteral nutrition is most commonly delivered into the stomach, it can also be administered further distal into the alimentary tract. An enteral access tube can be placed in the small bowel and is called post-pyloric enteral feeding [9,10]. Patients that are at high risk for aspiration or intolerant to gastric feeding such as having repeated high gastric residual volumes (>500cc) despite trials of promotility agents should be considered for post-pyloric enteral feeding [1].
Other indications for post-pyloric feeding include esophageal dysmotility, reflux, pancreatitis, delayed gastric emptying, emesis, trauma, gastric outlet/duodenal obstruction, gastric or duodenal fistula or anatomical anomaly [9,10].
Of note, there is no difference in the risk of pulmonary aspiration between gastric and postpyloric feeding for patients with normal gastric motility [1].
To reduce the risk of aspiration, the following measures should be taken [1]:
- Target residual volumes of less than 500cc
- Head of the bed should be elevated 30°-45°.
- EN should be delivered via continuous infusion.
- Prokinetic drugs (metoclopramide and erythromycin) or narcotic antagonists (naloxone and alvimopan) should be initiated where clinically feasible and needed.
- Diverting the level of feeding by post-pyloric tube placement can be considered.
Regular and routine monitoring of tolerance of feeding is required. Interruption of feeding should be avoided unless patients are not tolerating it or are getting hemodynamically unstable [1].
Parenteral nutrition support refers to the provision of calories, amino acids, electrolytes, vitamins, minerals, trace elements, and fluids via a parenteral route. If enteral feeding is not feasible then parenteral feeding may be necessary [1].
Early parenteral nutrition may increase the risk of infection and prolong mechanical ventilation, ICU stay, and hospital stay and is not recommended [12]. Enteral nutrition is preferred over parenteral nutrition because it helps maintain gut integrity, modulate stress and systemic immune response, and attenuate disease severity [13]. Instead, parenteral nutrition should be initiated after 7 days if patient is unable to receive enteral therapy by then [14]. Complications of parenteral feeding include bloodstream infections, metabolic derangements such as hyperglycemia and hypophosphatemia, hepatic dysfunction, refeeding syndrome [13,14,15].
In summary, nutritional support in the ICU is a major determinant of morbidity and mortality in hospitalized patients, particularly critically ill patients and post-surgical patients. The goals of nutrition therapy are to support protein synthesis and enhance immune function in a system that is under extreme stress. Providers should be cognizant in avoiding starvation, stress metabolism, and overfeeding. Routine assistance of dietitians in the ICU can help curtail these problems and providers should assess efficacy of ongoing nutrition therapy and evaluate nutritional goals on a daily basis.
Key Points
- Nutrition therapy in the critically ill can be optimized with careful monitoring of the patient’s nutritional status and daily evaluation of energy and protein requirements.
- Malnutrition contributes significantly to increased morbidity and mortality, increased frequency of hospitalizations as well as length of hospital stay, and consequently overall higher healthcare costs.
- Malnourished patients often have higher rates of infections and pressure ulcers (and consequently require greater nursing care), require more medications, are less independent due to muscle loss and consequently have longer lengths of hospital stay.
- Early enteral nutrition (within 48hrs) is associated with significant reductions in infectious morbidity and hospital length of stay.
- Enteral feeding is preferred over parenteral nutrition.
- Late parenteral nutrition (>8 days) is associated with fewer infections, shorter mechanical ventilation days, lower healthcare costs, and reduced duration of renal replacement therapy. Parenteral feeding should be avoided unless enteral is contraindicated.
- General nutritional goals: 25-30 kcal/kg/day total calories; 1.2-2.0 gm/kg/day protein.
References
- McClave SA, Martindale RG, Vanek VW, et al. Guidelines for the Provision and Assessment of Nutrition Support Therapy In the Adult Critically Ill Patient: Society of Critical Care Medicine (SCCM) and American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.) Journal of Parenteral and Enteral Nutrition (2016); 40 (2): (159-211).
- Barker L.Gout, B.Hospital Malnutrition: Prevalence, Identification and Impact on Patients and the Healthcare System. Int J Environ Res Public Health. 2011 Feb; 8(2): 514–52.
- White J. Guenter P. Consensus statement of the academy of nutrition and dietetics/ American Society for parenteral and Enteral nutrition; characteristics recommended for the identification and documentation of adult malnutrition ( Undernutrition). Jounral of the Academy of nutrition and dietetics.J Acad Nutr Diet. 2012;112:730-738.
- Clinical Guidelines on the identification, evaluation, and treatment of overweight and obesity in adults- The evidence report. National Institutes of health. Obes Res. 1998 Sep : 6 Suppl 2: 5 1S-209S.
- Dvir D. cohen J. computerized energy balance and complications in critically ill patients.Clin Nutr. 2006 Feb;25(1):37-44.
- Pirat A, Tucker AM. Comparison of measured versus predicted energy requirement in critical ill cancer patients. Respir Care. 2009 Apr;54(4):487-94.
- Mehanna HM, Moledina J, Travis. Refeeding syndrome: what it is, and how to prevent and treat it. BMJ (2008); volume 336(7659):1495-8.
- Crook MA, Hally V, Panteli JV. The importance of the refeeding syndrome. Nutrition (2001); 17: 632-637.
- Stroud M, Duncan H, Nightingale J. Guidelines for enteral feeding in adult hospital patients. Gut 2003; 52: vii1-vii12.
- Kirby DF, DeLegge MH, Fleming CR. American Gastroenterological Association technical review on tube feeding for enteral nutrition. Gastroenterology 1995; 108; 1282-1301.
- Shankar B, Daphnee DK, Ramakrishnan N, Venkataraman R. Feasibility, safety, and outcome of very early enteral nutrition in critically ill patients: Results of an observational study. J Crit Care (2015); 30(3):473-5.
- Saarnio J, Pohju A, Ahtola H. Indications and execution of enteral nutrition. Uodecim (2014); 130(21):2239-44.
- Brisard L, Le Gouge A, Lascarrou JB, et al. Impact of early enteral versus parenteral nutrition on mortality in patients requiring mechanical ventilation and catecholamines: study protocol for a randomized controlled trial (NUTRIREA-2). Trials. (2014); 15:507.
- Doig GS, Simpson F, Sweetman EA, et al. Early parenteral nutrition in critically ill patients with short-term relative contraindications to early enteral nutrition: a randomized controlled trial. JAMA (2013); 309(20):2130-8.
- Ochoa Gautier JB, Machado FR. Early nutrition in critically ill patients: feed carefully and in moderation. JAMA (2013); 309(20):2165-6.