|Year : 2012 | Volume
| Issue : 1 | Page : 9-16
Critical nutritional aspects in intensive care patients
Sukhminder Jit Singh Bajwa, Ashish Kulshrestha
Department of Anaesthesiology and Intensive Care, Gian Sagar Medical College and Hospital, Ram Nagar, Banur, Punjab, India
|Date of Web Publication
Sukhminder Jit Singh Bajwa
Department of Anaesthesiology and Intensive Care, Gian Sagar Medical College and Hospital, Ram Nagar, Banur, Punjab - 147 001
Source of Support: None, Conflict of Interest: None
Nutrition in the critically ill patients has always been a difficult task for the intensivist. Unlike normal subjects, various physiological and pathological aspects have to be taken into consideration before initiating the nutrition in this subset of patients. The associated morbidities in critically sick patient not only pose clinical difficulties to maintain a normal nutritional status but also create various limitations in selection of a particular nutrient. Various diseases commonly found in intensive care patients produces stress on the body and bring about changes in substrate metabolism thus leading to the deficiency of various nutrients. Numerous tools and methodologies are available nowadays to predict the assessment, screening, and monitoring of the nutritional status in critically ill patients. However, the nutritional status is a big decisive factor in predicting the outcome and malnutrition has been strongly associated with increased mortality and morbidity in these patients. The nutritional requirement also varies with regards to age, body mass index, co-morbid disease, duration in ICU, and many other factors and as such the calculation for nutritional supplementation has to be done strictly on an individual basis. In all these patients, it is also vital to achieve a strict glycemic control by using insulin so as to prevent any increase in morbidity and mortality. Enteral and parenteral nutritional controversies are as old as the concept of nutrition in Intensive Care Unit (ICU). Besides therapeutic merits, both enteral and parenteral nutrition are also associated with complications which can be prevented by set protocols as well as by education of nursing personnel involved in the care of critically ill. This article reviews all these aspects concerned with nutrition in critically ill patients so as to make an effort to build a comprehensive approach and strategies for designing the nutritional supplementation.
Keywords: Body mass index, calorie requirement, critically ill, enteral nutrition, micronutrients, parenteral nutrition
|How to cite this article:
Bajwa SS, Kulshrestha A. Critical nutritional aspects in intensive care patients. J Med Nutr Nutraceut 2012;1:9-16
|How to cite this URL:
Bajwa SS, Kulshrestha A. Critical nutritional aspects in intensive care patients. J Med Nutr Nutraceut [serial online] 2012 [cited 2024 Mar 2];1:9-16. Available from: http://www.jmnn.org/text.asp?2012/1/1/9/94628
"A slender and restricted diet is always dangerous in chronic and in acute diseases"
-Hippocrates 400 B.C.
With the advancement in the field of medicine over the last few decades, it has been made possible to cure many diseases which were considered incurable previously. But along with these great advancements, the number of patients requiring the facilities of intensive care unit (ICU) has increased tremendously and so is the patients admitted with varying critical pathologies. The type of patients admitted to ICU range from post-surgical patients to the patients admitted for medical emergencies like sepsis, respiratory failure, cardiac failure, acute respiratory distress syndrome (ARDS), status epilepticus, renal failure, and so on. These patients show variations with respect to age and prior nutritional status and are also prone to develop malnutrition states during their course of ICU stay. Malnutrition has been strongly associated with increased mortality and morbidity in these patients and so nutritional support is an essential component of the wholesome care given to such patients in the ICU. 
Etiology of malnutrition in critically ill
Various diseases commonly found in intensive care patients causes stress on the body and bring about changes in substrate metabolism thus leading to the deficiency of various nutrients [Table 1]. The incidence of malnutrition in critically ill is particularly high in at risk patients.  During this period of stress-induced hypermetabolism, body tries to compensate for the increased demand of glucose, the principle substrate required by tissues, by mobilizing the fat and glycogen stores by the process of gluconeogenesis. Due to excess demand of substrate in critically ill, the proteins are also broken down to provide energy by gluconeogenesis and thus the wasting of muscles ensues. However, even the provision of excess calories does not prevent the muscle breakdown seen in the long stay intensive care patients. 
|Table 1: Showing the common causes of malnutrition in critically ill and at risk patients
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Assessing the malnutrition in critically ill
Malnutrition is an alteration of body composition due to the deficiency of either total energy or of proteins (and other nutrients) that results in reduced body cell mass, organ dysfunction, and abnormal serum chemistry values. It usually results due to the adaptive changes induced by the body in response to the stress created by the critical illness to maintain a normal homeostasis.  The incidence of malnutrition although difficult to estimate but various studies have demonstrated 15-70% of under or malnourishment among patients admitted to hospital. It has also been shown that malnutrition is poorly assessed in majority of the hospitals and this undiagnosed endemic remains untreated in almost 2/3 of the patients. ,,,,,, The demographic factors such as socio-economic status and co-morbid diseases are important predictors and determinants of malnutrition thereby leading to a higher morbidity and mortality in developing nations. , Studies have established that the prevalence of malnutrition is particularly high in at risk elderly patients especially with impaired mental and cognitive functions. , This subset of patients also have higher prevalence of co-morbid diseases related to respiratory, cardiac, hepatic, renal, and other body organs. As such, protein energy malnutrition in elderly and critically ill patients is an important independent determinant for higher morbidity and mortality. ,,,
The initial step in providing nutritional support in critically ill is the assessment of degree of nutritional deficit. Assessment is a tedious task and takes various factors into account such as the severity of the present illness, underlying disease, current medications, various organ functions, and so on. The clinical assessment should also include the type of nutritional deficiency, hydration status, edema, hemodynamic parameters, body temperature, and functioning of the gastro-intestinal tract. An accurate assessment makes the task of intensivist easier in planning, providing and monitoring the nutritional therapy in critically ill patients. The general loss of body weight is considered to be a gross indicator of nutritional deficit which can be assessed using the body mass index (BMI) as:
Body Mass Index (BMI): Weight (kg)/height 2 (cm)
However, as malnutrition is often accompanied with gross edema and accurate weight estimation is not possible in critically ill, so it is not of much clinical importance. Unintentional weight loss of more than 10% within last six months has been found to correlate well with clinical outcome. ,
Anthropometric measurements of the skin fold thickness and skeletal muscle mass have been described but carry less clinical importance in the ICU.
Biochemical parameters include measurement of serum albumin, transferrin, retinol-binding protein, and prealbumin. The serum albumin concentrations, however, are considered to be poor indicator of nutritional status due to a compensatory decrease in its production by liver in response to systemic stress of critical illness and an increase in production of acute phase proteins. Hence, it is considered to be an indicator of injury and metabolic stress. 
Delayed hypersensitivity response to a variety of antigens also suggests a nutrient deficient state but its utility in the setting of intensive care is questionable.
Screening for malnutrition
The challenges are multifold in screening for malnutrition as there are no universally acceptable criterions for determination of malnutrition in critically ill patients. Numerous formulas and tools have been developed to calculate the nutritional and energy requirements in critically ill patients over the last three decades but no such tool are complete in itself. These tools are particularly very helpful in when nutritional decisions have to be made for a larger percentage of critically ill population. The selection of these tools is based on numerous factors such as demographic characteristics, co-morbid diseases, underlying disorder, training, and knowledge of the ICU staff, and past experience with such methodologies. Although various tools are available, the application of these tools does not show much inter-individual difference in predicting the outcome in critically ill patients  [Table 2].
|Table 2: Showing the various tools to assess nutritional status in critically ill patients
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Goals of nutritional support
The American College of Chest Physicians have laid down certain goals which are very essential for deciding the nutritional support in intensive care patients and should include: 
- to provide nutrition support consistent with the patient's medical condition and the available route of administration,
- to prevent development of deficiencies of various macro and micronutrients,
- to supplement various nutrients in the doses sufficient for the existing medical condition,
- to prevent any complications that may be related to the route of delivery and
- to improve patient outcome and subsequent reduction in mortality and morbidity.
Calculating the nutritional needs
The first step in calculating the nutritional requirements of a critically ill patient is the total fluid requirement. This is estimated to be around 30 to 40 ml/kg/day or 1 ml of water per calories in an adult but has to be supplemented in cases of excessive fluid requirements. The losses can be divided into overt losses (excessive upper gastrointestinal losses, diarrhea, or excess urine formation) and insensible or evaporative losses. The excessive insensible losses may result due to on-going pyrexia, tachypnea, or excessive sweating.
The caloric requirements are estimated rather than calculated by measuring the basal metabolic rate using the Harris Benedict Equation:
BMR = 13.75 × weight (kg) + 5 × height (cm) - 6.78 × Age (yrs) + 66
BMR = 9.56 × weight (kg) + 1.85 × height (cm) - 4.68 × Age (yrs) + 655
This is estimated in a healthy, afebrile individual and gives a result of around 25 kcal/kg/day and has to be modified accordingly.
Pyrexia increases BMR by 10% for each 1 degree rise in temperature above 37°C
Sepsis increases BMR by 9% regardless of temperature
Burns increases BMR by 100% if surface area involved is more than 30%
These estimated calories can be supplemented in three forms:
- Carbohydrates: These should provide 30% to 70% of the total calories required and is usually given in the form of glucose but fructose and sorbitol are also utilized. It should be noted that insulin may be required to maintain normoglycemia as resistance to insulin is usually induces during stress. One gram of carbohydrate provides about 3.75 kcal of energy.
- Fats: These should provide 20% to 50% of the total calories required as the critically ill patients utilize fats better than carbohydrates during acute periods of stress. Polyunsaturated fatty acids (PUFA) should also be included to prevent essential fatty acid deficiency. One gram of fat provides around 9.3 kcal of energy.
- Proteins: These should provide 15% to 20% of the total calories required and can be given as complex proteins or amino acids depending on the route used. The total daily requirement of proteins is estimated to be about 1.5 to 2 g/kg/day. 
These include various electrolytes such as sodium and potassium which are required at 1 mmol/kg/day but increased requirements are seen in excessive gastrointestinal losses and increased sweating. Other micronutrients required in smaller amounts include magnesium, phosphorus, iron, copper, zinc, and selenium and are also important in maintaining normal homeostasis.
Need for nutritional monitoring
The monitoring of nutritional status is a very important step in providing wholesome intensive care to critically ill. The monitoring of nutritional status is important both to identify the patients at risk of malnutrition as well as to assess the effectiveness of nutrition therapy. An important and sensitive indicator of adequate nutrition therapy is considered to be the pre-albumin levels which should be monitored weekly.  The most important pitfalls in the nutrition therapy are underfeeding characterized by dehydration and continued malnutrition, and overfeeding characterized by protein, fat, and fluid overload. However, the nutrition therapy should be modified according to the patient's metabolic requirements and the state of critical illness. The various parameters in nutrition monitoring are summarized in [Table 3].
|Table 3: Showing parameters of nutrition and their respective indicators during nutrition monitoring
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Administration of nutrients
Two important routes of administration are used to provide nutritional support to patients in intensive care unit:
The various methods of providing enteral feeding are as follows.
- Nasogastric: This the most common route used in critically ill where a feeding tube in inserted into the stomach through the nostrils. However, it can be associated with potential problems such as malposition, nasal tissue erosion, sinusitis, and difficulty in insertion and is contraindicated in the patients with fracture of base of skull.
- Orogastric: This route is used when the nasogastric route is contraindicated and in sedated patients to reduce incidence of sinusitis which can be an important risk factor for the development of ventilator associated pneumonia. However, this route is not tolerated by awake patients.
- Enterostomy: It involves gastrostomy and jejunostomy where a small feeding tube is inserted directly into the stomach or jejunum and is brought out through the peritoneal cavity. The problems can arise such as malposition, displacement, and infection and are usually preferred in patients who are suspected to require nutritional support for more than 4 weeks.
- Post-pyloric: The feeding tube is placed in the jejunum through the nostril thus bypassing the stomach. It is indicated in patients with high risk of aspiration, after major intrabdominal surgery and patients who do not tolerate gastric feeding.
Enteral feeding is considered to be preferred route of feeding as it maintains the functional and structural integrity of gut and delay in initiating the enteral feeding can bring changes in the gut associated lymphatic system (GALT) which can bring about inflammatory changes in gut mucosa rendering it susceptible to infection. In addition, due to breach in structural integrity of the gut, translocation of bacteria can induce peritonitis.  There is lot of literary evidence that enteral feeding reduce the incidence of infection but its impact on reducing the mortality is still controversial. 
The disadvantages in using enteral feeding include inadequate calorie intake due to interruptions in feeding to allow gastric emptying, abdominal distension leading to respiratory embarrassment and diarrhea which may be associated with Clostridium difficile enterocolitis. It is also suggested that enteral feeding increases the incidence of ventilator associated pneumonia (VAP) probably due to an increase in gastric pH and gastric colonization.  It should be noted, however, that the absence of bowel sounds does not preclude from initiating enteral feeding especially if post-pyloric feeding is instituted.
The various types of enteral feeds used are as follows.
- Polymeric preparations: This type of feed usually contains intact proteins, complex carbohydrates, and fats in addition to the trace elements, vitamins, minerals, and fiber. Fiber is an important constituent of such feeds as it maintains the structural integrity of the gut enterocytes. These feeds are usually made lactose free as lactose intolerance is common in critically ill patients. This type of feed is easily prepared in a hospital and can be given to majority of critically ill patients.
- Elemental preparations: The various macronutrients are present in a readily absorbable form e.g. proteins in the form of peptides or amino acids, fats in the form of medium chain triglycerides, and carbohydrates in the form of mono or disaccharides. It is indicated in patients with severe form of malabsorption states.
This route is usually employed in patients with gastrointestinal failure and when all attempts at initiation of enteral feeding fail. It is indicated in diffuse peritonitis, intestinal obstruction, intractable vomiting, paralytic ileus and severe diarrhea. This route of feeding may also be used in addition to the enteral route as several studies indicate that the enteral feeding is associated with considerable incidence of underfeeding. ,, Underfeeding in patients who receive less than 25% of target feed has been shown to have higher risk of nosocomial pneumonia.  It is suggested that all attempts should be made to start enteral nutrition initially and parenteral nutrition should be reserved for patients with absolute indications and in cases of failure of enteral nutrition.
Parenteral nutrition is usually given through central venous lines but can also be given through peripheral venous lines depending on the osmolality of the solution used. Thus, the complications are more frequent with parenteral route and are associated with catheter insertion and infection.
Central venous lines meant for parenteral nutrition should be inserted under strict aseptic conditions and a dedicated line should be used for this purpose and interruptions and reconnections should be limited and if required should be done with aseptic precautions.
Parenteral nutrition is usually given as sterile emulsion of water, protein, lipid, carbohydrate, vitamins, minerals, and trace elements. It contains
- Proteins: It is present in the form of amino acids in a soluble form and should include essential amino acids i.e. those which cannot be synthesized inside the body. It should contain equal proportions of both essential and non-essential amino acids.
- Fats: It is usually given in the form of "intralipid" which is an emulsion made from soya with chylomicron-sized particles. The lipids not only act as source of energy but also supplement essential fatty acids and also help in absorption of fat-soluble vitamins.
- Carbohydrates: This is given in the form of glucose which is readily absorbed and is an important source of energy in various vital organs.
- Electrolytes and Micronutrients: These may be included in the emulsion or may have to be provided separately. The requirements of these electrolytes and trace elements depend upon the disease and the condition of the patient
Challenges of nutritional support in specific disorders
There are few clinical scenarios where an intensivist is faced with challenging situations in providing a wholesome nutritional support to critically sick patients. Few alterations can be done in the constitution of the nutritional supplements given to critically ill patients depending on specific disease processes so as to overcome the specific deficiency states. Some of the most common diseases are discussed.
Sepsis and septicemia
This is characterized by a severe catabolic process requiring an additional 10-20% increase in calorie requirement and so is the requirement of proteins which also has to be increased owing to accelerated protein breakdown. The electrolyte and trace element requirements are also increased and close monitoring is required. Hyperglycemia can be a common finding and may require inclusion of insulin infusion. Lipids, however, may have to be decreased due to increased incidence of hypertriglyceridemia leading to lipemic serum.
Deranged hepatic functions
Patients with liver failure may have severe electrolyte abnormalities such that hyponatremia, hypokalemia, and hypomagnesemia very common and the parenteral preparations should have these deficient electrolytes. The hepatic failure patients are edematous with the presence of ascites and so the fluid restriction is employed to prevent formation of further ascites.
Acute hepatic failure results in an acute rise in ammonia due to defective urea cycle leading to encephalopathy and these patients should have restriction of certain amino acids while these should be replaced with branched chain and aromatic amino acids.
Deranged respiratory dynamics
These patients have compromised respiratory functions and difficulty in eliminating carbon dioxide. The feeds with high respiratory quotient i.e. the ratio of carbon dioxide production to the oxygen consumption are not tolerated by these patients especially during weaning. These patients require feeds with low respiratory quotient but should be provided with minimum calories required. 
The nutritional support in these patients has to be altered as these patients have to be fluid restricted due to decreased urine production. Special precautions should be taken in supplementing the electrolytes such as potassium, magnesium, and phosphate with frequent electrolyte monitoring. Low volume and low salt preparations with a reduced total nitrogen intake of 0.5-0.8 gm/kg/day should be provided.
Historically, it has been suggested that initiating feeding in these patients can worsen the disease by stimulating the release of pancreatic enzymes and thus parenteral nutrition is the only type of nutrition suggested in these patients. Some recent studies show that jejunal feeds are well tolerated in patients with acute pancreatitis,  but such feeds usually result in providing less than required calorie needs of the patient.
Role of nutritional additives
There are some substances whose addition to the various types of feeds has shown to be beneficial in overall survival of critically ill patients. These include:
Arginine, an amino acid, has been found to be important in various metabolic processes like urea cycle, lymphocyte proliferation, and an important factor in wound healing. It is also thought to modulate blood flow through its role in nitric oxide production and thus given to post-operative patients have found to be beneficial. ,
Glutamine is another amino acid considered "essential" due to an integral part of glutathione, an antioxidant compound. It is also considered to be a substrate for metabolism by leucocytes and enterocytes and thus supplementation may augment lymphocytic and macrophage functions. Various trials have shown that glutamine added as nutrient supplement in critically ill patients can reduce the incidence of catheter related infections but its effect on the overall mortality is still controversial. ,,
Omega-3 polyunsaturated fatty acids also have been shown to act as an immunomodulator as well as an anti-inflammatory agent when added to the nutrition.
Combination of immunonutrients as a supplement to the enteral feed has been studied recently and has been found to reduce incidence of infections and duration of mechanical ventilation. ,,,
It is known that growth hormone is released by the body in response to the stress but exogenous administration of growth hormone to the feed has been shown to increase protein synthesis and improve immune responsiveness especially in burn patients and critically ill children. However, its role in reducing mortality is controversial. 
Common complications of nutritional support
Although nutritional support is an essential element in the care of critically ill, it is also associated with some complications:
This syndrome is usually seen if the period of fasting exceeds 5 days or more and is seen within 4 days of restarting the feed. During prolonged fasting, the body tries to conserve the protein and muscle breakdown by reducing the rate of gluconeogenesis in liver and switching to ketone bodies as a source of energy. There is severe intracellular deficiency of electrolytes and minerals although the serum levels may be normal.
During resumption of feeding with the onset of normoglycemia, there is an increased synthesis of fat, glycogen, and protein. The various minerals and electrolytes especially potassium, magnesium, and phosphates are rapidly used up leading to their acute deficiency. There is depletion of intracellular ATPs and 2, 3-diphosphoglycerate in red blood cells leading to cellular hypoxia and inadequate oxygen delivery to vital organs. This leads to cardiac failure, arrhythmias, confusion, coma, convulsions, and respiratory failure. 
High degree of suspicion and early intervention is must to prevent this condition. Energy intake is restricted to about 50-70% of the total energy requirements during first 3-5 days. Close monitoring of the electrolytes is very essential and multivitamins are usually given accordingly. ,,
Increasing the calories in an attempt to overcome the catabolic process of critical illness has given negative results and moreover it can cause other problems like uremia, hyperglycemia, hepatic steatosis, hypercapnia, and fluid overload. Overfeeding has been associated with parenteral nutrition and is not seen with enteral nutrition. It has been suggested that slight underfeeding is beneficial in such patients.
Insulin resistance usually develops in critical illness as a part of stress response and strict control of blood sugars has been shown to significantly lower the mortality and length of stay in intensive care. , However, it should be noted that neither underfeeding nor omitting lipids in the parenteral preparations prevents infectious complications and it is the use of insulin which is essential in tight glycemic control. 
Complications of enteral nutrition
As already discussed, aspiration is the most common complication leading to pneumonia which can be prevented by various measures including nursing education and good oral hygiene.  Another important complication is diarrhea; however, it is not an indication to interrupt feeding and can be easily managed.
Complications of parenteral nutrition
The most common complications are catheter related and include pneumothorax, hemothorax, arterial and nerve injury, and the infection. It has been suggested that more complications arise due to overfeeding and hyperglycemia rather than parenteral nutrition itself. Nevertheless, infection is a dreaded complication and all measures should be taken to prevent the infection.
Parenteral nutrition can also predispose to fatty liver, cholestasis, acalculous cholecystitis, and electrolyte imbalances and thus regular monitoring of various blood investigations is mandatory to prevent such complications especially in patients with long stay in intensive care.
Malnutrition is a common problem in critically ill patients and is associated with a poor outcome. Enteral nutrition should be started initially and as soon as possible in all the patients in which it is safe to do so. Parenteral nutrition should be reserved for the patients in whom enteral nutrition cannot be started but overfeeding should be avoided. Both types of nutrition are associated with complications which can be prevented by set protocols and by education of nursing personnel involved in the care of critically ill. In all these patients, it is vital to achieve strict glycemic control by using insulin.
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[Table 1], [Table 2], [Table 3]