|Year : 2013 | Volume
| Issue : 2 | Page : 77-83
Controversies, principles and essentials of enteral and parenteral nutrition in critically ill-patients
Sukhminder Jit Singh Bajwa, Sachin Gupta
Department of Anesthesiology and Intensive Care, Gian Sagar Medical College and Hospital, Banur, Punjab, India
|Date of Web Publication||6-Jul-2013|
Sukhminder Jit Singh Bajwa
Department of Anesthesiology and Intensive Care, Gian Sagar Medical College and Hospital, Ram Nagar, Banur, House No-27-A, Ratan Nagar, Tripuri, Patiala - 147 001, Punjab
Source of Support: None, Conflict of Interest: None
Nutritional management in critically ill-patients is always a challenging task as malnutrition can have a direct impact on the prognosis. Besides assessing for nutritional requirement, the underlying severe illness and co-morbidities have to be given due consideration. Nutritional assessment has to be individualized, and nutritional plan should be formulated by involving a dedicated nutritionist. Early initiation of nutrition definitely improves the outcome in critically ill patients. Facts and principles of enteral and parenteral nutrition must be disseminated among all physicians and nursing staff working in intensive care units. Majority of old controversies related to parenteral and enteral nutrition have been settled with the intervention of various national and international committees such as Alliance and Espen. Nutritional disorders such as malnutrition, overfeeding and negative energy balance are highly associated with increased morbidity and mortality. Enteral nutrition though always preferred can always be supplemented with parenteral nutrition so as to optimize nutrition and energy status in critically ill patients.
Keywords: Critically ill-patients, enteral nutrition, parenteral nutrition
|How to cite this article:|
Bajwa SJ, Gupta S. Controversies, principles and essentials of enteral and parenteral nutrition in critically ill-patients. J Med Nutr Nutraceut 2013;2:77-83
|How to cite this URL:|
Bajwa SJ, Gupta S. Controversies, principles and essentials of enteral and parenteral nutrition in critically ill-patients. J Med Nutr Nutraceut [serial online] 2013 [cited 2020 Oct 30];2:77-83. Available from: https://www.jmnn.org/text.asp?2013/2/2/77/114731
| Introduction|| |
A good nutrition is the essence of survival and well-being in critically ill-patients. In developing countries like India, many diseases occur due to the direct consequence of malnutrition. This clinical scenario gets accentuated in critically ill-patients. Malnutrition is prevalent in hospitalized adults of all ages in the range of 20-69% with prevalence increasing to 40% in critically ill-patients. ,,, Malnutrition is not just limited to the type and severity of disease, the time patient stays in hospital has a direct impact on the risk of malnutrition. ,,, Infection, injury and sepsis lead to a hyper-catabolic state in critically ill-patients. The clinical situation is worsened by a specific or multiple organ failure leading to increase in energy requirements. ,,, The problem is compounded by the fact that patients are not able to utilize energy substrates provided to them due to metabolic abnormalities leading rapid loss of body weight in general and loss of lean body mass in particular. 
As a matter of fact, the role of nutritional support in critically ill-patients should not be under-estimated. It has been deduced from various clinical studies that loss of lean muscle mass of 10% is considered significant, loss of 20% is critical, and loss of 30% is invariably lethal.  Lack or inadequate nutrition leads to a state of starvation. The major nutritional insult is borne by the skeletal muscles as they are the first to be catabolized for gluconeogenesis to generate the much needed energy. Metabolically active tissue synthesizes important proteins such as liver enzyme proteins, renal tubular enzymes and protein in the gastro-intestinal mucosa which helps in providing further nutritional support.  This endogenous mechanism helps to tide over mild to moderate crisis during the initial part of critical illness, but in severe debilitating illness, this very mechanism becomes counterproductive and may in fact contribute to increased morbidity and mortality. 
| Principles of Nutritional Management in Critically Ill|| |
The methodology of nutritional maintenance in critically ill-patients has gone sea change in last two decades, the concept of hyper-alimentation has gradually faded and has given way to a more pragmatic and restricted feed concept. The current nutritional approaches are guided by principles based on evidence and can be briefly summarized as follows:
- Enteral nutrition is the most preferred route whenever possible. Even if, enteral route does not fulfill all the energy requirements, gut is still used for nutrition. 
- Parenteral nutrition can always be used as a supplement if the gut is malfunctioning. As a matter of fact, maintaining structural and functional integrity in critically ill is of paramount importance. 
- It has to be kept in consideration that parenteral or enteral nutrition has no anabolic effects. These routes of nutrition only reduce or blunt the effects of hyper-catabolic state, which is invariably encountered in critically ill patients. 
- The caloric balance can be maintained by providing 1500-2100 calories/day instead of the routinely practiced concept of providing excessive calories intake up to 3500-4500 cal/day. 
- It is always better to adopt the pro-active approach in preventing starvation rather than treat it later on. Therefore, early nutrition should invariably be started. In fact, it has been established that providing nutrition supplementation prior to surgery in severely malnourished patients can reduce post op complications. 
- Nutrition should be personalized for each patient taking into consideration the state of disease and the present nutritional status of the patient.
- Patient's nutritional adequacy and possible side effects should be assessed on time to time basis.
| Clinical Effects of Malnutrition in Critically Ill-Patients|| |
Malnutrition can have a drastic impact on the overall physiological and clinical status of critically ill-patients. However, morbidity of malnutrition can be described in terms of specific and non-specific effects on the health of a critically ill patient. ,,, These facts include but are not limited to:
- Specific effects
- Wound dehiscence
- Poor healing
- Breakdown of surgical anastomosis
- Poor immune response to infection.
- Non-specific effects
- Central nervous system: Apathy, drowsiness, inability to clear secretions. This could be due to alteration in amino acid composition resulting from nutritional deprivation.
- Lean muscle mass: Due to neo-glucogenesis, substantial loss of muscle mass occurs which leads to increased of work of breathing. It can lead to a clinical challenging situation of ventilator dependency.
- Sepsis: Nutritional deprivation in the setting of sepsis can lead to multi-organ dysfunction syndrome and failure and maximum brunt is borne by the liver and kidney.
| Metabolic Effects of Nutritional Deprivation|| |
A hyper-catabolic state prevails during times of stress such as sepsis, trauma and critical illness. To counter these pathophysiological states, an increased secretion of catecholamines and glucagon occurs which leads to a relative state of insulin resistance.  The resulting glucose intolerance leads to a poor uptake and utilization of glucose substrate. The body responds by deriving energy from protein breakdown rather than from carbohydrates and fats. Finally, gluconeogenesis and lipolysis sets in to provide glucose from muscle breakdown. Ketone bodies are also formed during this period as it is derived from free fatty acids. Another important factor contributing to breakdown of lean body mass is failure of the liver to manufacture ketone bodies and utilize fatty acids for calorie production. ,
| Appropriate Timing for Nutritional Support|| |
The right time to initiate nutritional support in Intensive Care Unit (ICU) is very important in maintaining the physiological milieu. The following recommendations are based on scientific support, which determines the right time to start nutritional supplementation in critically ill-patients. ,
- According to current recommendations early nutritional support is advocated in critically ill patients.
- Stabilization of hemodynamics, correction of fluids, electrolytes and acid base abnormalities should be given priority over nutrition
- Normally, an average adult <60 years can withstand 14 days of poor nutrition with minimal derangement
- For short periods of inadequate nutrition avoid parenteral nutrition because of inherent risks and dangerous iatrogenic complications
- Usual policy is to start with enteral nutrition. If not feasible or not able to provide complete nutrition, parenteral nutrition is started to supplement enteral nutrition.
| Objectives of Nutritional Supplementation in Icu|| |
The main objectives are derived from American College of chest physician, which states that:
- To provide support taken in lieu of patient's medical problem, nutritional state and route of nutrient administration.
- To prevent or treat macronutrients and micronutrients deficiencies.
- To provide nutrition to substantiate patient's metabolism.
- To improve patient outcome.
| Nutritional Assessment|| |
Before elaborating on enteral and parenteral nutrition, it is essential to focus on very important areas of nutritional assessment. Nutritional assessment is very important so as to avoid harmful effects of over-feeding or under-feeding. , It mainly comprises of combination of clinical evaluation and laboratory findings such as:
- History and clinical examination
- Medical and surgical background of current and past illness.
- Evidence of protein energy malnutrition, anemia, vitamin deficiencies etc.
- Anthropometric measurements
- Includes measurement of height and body weight.
- Critically ill patients may have normal weight in spite of significant lean muscle mass loss because of water retention.
- Biochemical data
- Serum albumin-indicator of visceral and somatic protein stores. Remember, S. albumin can decrease due to rapid i.v., infusion/over hydration. Secondly, plasma level do not rise for 4-5 weeks following nutritional replacement, so albumin is not a good marker for improved nutritional state following initiation of nutritional support.
| Nutritional Requirements|| |
After assessment of nutritional parameters, nutritional and calorie requirements are also essential. Average daily requirement is 25-35 kcal/kg ideal body weight per day. Commonly used a mathematical formula for calculating resting metabolic expenditure is the Harris-Benedict equation [Table 1].
|Table 1: The calculation of resting metabolic expenditure as per Harris-Benedict equation |
Click here to view
Calorie requirements can increase in stressful and catabolic conditions. Calvin Long stress factors are needed to calculate the exact requirement in these conditions as in clinical states like sepsis and major surgery, the calorie requirement is 1.3 times the HB whereas it is 1.5 times HB for complicated sepsis and burns <20%. However in clinical practice, these stress factors can overestimate the calorie requirement occasionally. ,
This requires measurement of patient's oxygen consumption (VO 2 ), the carbon dioxide production (VCO 2 ) and the minute ventilation. The resting energy expenditure is thus calculated as REE (kcal/min) = 3.94 (VO 2 ) + 1.1 (VCO 2 ) and REE (kcal/day) = REE × 1440.
It provides quite accurate method for measuring calorie needs though it is expensive and time consuming. At high FiO 2 (0.6), this method can be unreliable. In actual practice one initially starts with 25 kcal/kg/day of which 20% are protein, 30% are fats and 50% are carbohydrates. Proteins and carbohydrates provide 4 kcal/g and fats provide 9 kcal/g.
| Methods of Nutritional Support|| |
Enteral and parenteral nutrition methods have been used extensively ever since the concept of nutritional support started in ICU. Both methods can fulfill patient's need for nutrition, but enteral mode is generally preferred. , Some decisive key points to be considered while initiating the patient nutrition are:
- Parenteral nutrition alters body composition and increases blood flow to the gut.
- Steatosis is quite frequent with parenteral nutrition.
- Due to lack of gut stimulation, there can be damage to functional and structural integrity and reduced immune function. IgA is also decreased in parenterally fed patients.
- Parenteral feed should be stopped as soon as enteral feed is accepted by the patient.
| Enteral Feeding|| |
Enteral feeding is the preferred method of nutritional support in critically ill-patients. However, in some circumstances, enteral nutrition may not be feasible and patients have to be supported with parenteral nutrition. A few common indications of enteral nutrition can be enumerated as under.
| Indications for Enteral Feeding|| |
Broadly speaking, main indications of enteral nutrition can be enumerated as: ,
- Adequately nourished, adult patient with poor oral intake for 7-10 days.
- Undernourished patients with poor oral intake for 3-5 days.
- Patient not able to take adequate feed orally.
- Enterocutaneous fistula with output <500 ml/day.
- Patients with a minor degree of burns.
- Following upper GI surgery, e.g., total esophagectomy/total gastrectomy.
- Following necrotizing, suppurative pancreatitis - initially start with TPN following with jejunal feed.
One shall judiciously give enteral feed in ionotropic support dependent patients as there are chances of bowel infarction due to poor perfusion.
| Contraindications|| |
Certain contraindications have to be kept in mind before initiating enteral nutrition such as:
- Generalized suppurative peritonitis.
- Complete intestinal obstruction.
- Bowel ischemia.
- Patients with severe shock.
- Enterocutaneous fistula with large input.
- Acute fulminant necrotizing pancreatitis.
| Establishing Access for Enteral Nutrition|| |
Enteral nutrition can be given into stomach, duodenum or jejunum depending upon the severity of illness and health status of the gut. It can also be given via naso-gastric tube, naso-duodenal or naso-jejunal tube, percutaneous feeding, i.e., gastrostomy or jejunostomy. ,,
Gastric feeding is quite beneficial as the stomach is the primary organ which helps in initiating digestion. Besides helping in sterilizing the gastric contents, gastric secretions also help in diluting the gastric load to make it iso-osmolar. However, gastric atony and a higher risk of developing aspiration pneumonitis are few disadvantages associated with gastric feeding.
This method of feeding is very comfortable to the patient and also reduces the risk of reflux and aspiration pneumonia. The possible displacement of new, narrow tubes used these days easily into the trachea-bronchial tree is one of its primary limitations.
It is the most commonly used enteral feeding method all over the world. It allows the full use of gut despite ileus involving the stomach and large bowel. Main disadvantage in establishing the jejunal feeding access being the difficulty in guiding the fine bore tubes through the pylorus into the small bowel. This limitation can be easily overcome by preferably doing the procedure under fluoroscopic guidance.
Initiation of enteral nutrition
To begin with infuse normal saline equivalent to hourly feed that is proposed to be given over 1 h. Then clamp the NG tube for 30 min following which do the aspiration. If the aspirate is <50%, one can safely start NG feed. It is better to give test volume by infusion rather than bolus to prevent gastric distension.
It is preferable to give enteral nutrition by continuous infusion rather than by intermittent boluses. Both calories and infusion rate are increased over time and desired level is reached over few days so as to prevent diarrhea. This method is all the more important in case of jejunostomy or naso-jejunal tube as there is no reservoir (stomach). It is started at 25 ml/h and can be increased by 25 ml every hour.
Type of enteral feed
Formulations that provide 1 kcal/ml and are isotonic to plasma are best suited for enteral feed. Normally 1500 ml of feed is divided into six servings and will provide 1500 kcal with 54 g proteins, 54 g fats and 20 g carbohydrates. High density feed, i.e. 1.5-2 kcal/ml are administered when fluid intake is to be restricted. They should be given preferably into the stomach. ,
Liquefied or blenderized feed
This type of enteral feed contains milk, whey, curd, fruit juice, protein powder, glucose and liquidized potatoes, rice and vegetables. Water is added to make desired volume and the patient are fed 200 ml every two hourly. Diarrhea can be a problem but can be easily controllable.
| Complications of Enteral Feeding|| |
Enteral feed is not free without its associated complications which have to be kept in consideration during initiation and maintenance phase of feeding in critically ill patients. [32 ] These include:
- Gastric retention, vomiting and aspiration pneumonia.
- Diarrhea; however it can be controlled by reducing the amount by half and also by minimizing lactose in feed, avoiding bolus feed and use of isotonic feed. Feeding should never be stopped completely rather should be continued by giving small amounts.
- Mechanical problems - small bore tubes can get easily obstructed and are difficult to secure in obese patients. 
| Parenteral Nutrition|| |
Parenteral nutrition has been used very selectively because of so many myths, controversies and complications associated with its use. However, the scientific data has quelled majority of these concerns, and as such, it has become an inseparable part of modern day intensive care nutritional practices. The judicious use of parenteral nutrition is associated with a good outcome in critically ill patients but indications of parenteral nutrition should be followed on a strict basis.
| Indications for Parenteral Nutrition|| |
Parenteral nutrition is given preference in the following clinical states: ,,
- When gut does not function
- Surgery on the gut which prevents enteral feed
- Short bowel syndrome
- Enterocutaneous fistula >500 ml
- Necrotizing/suppurative pancreatitis
- Prolonged ileus
- Major burns.
| Establishing Access for Parenteral Nutrition|| |
Parenteral nutrition is given generally through central vein. It is always better to keep dedicated line for total parenteral nutrition (TPN). Peripheral veins can be used for administration of TPN but carries a higher risk of thrombo-phlebitis due to hyperosmolarity of TPN solutions.
| Types of Solutes for Use as TPN|| |
- Dextrose-supplies 4 kcal/g. It forms the carbohydrate component of TPN.
- Lipid solution-supplies 9 kcal/g. The chief source of fatty acids is soya bean. It is available as 10% or 20% fat emulsion.
- Amino acids (AA) solutions contain 40-50% of essential AA and 50-60% of non-essential AA. The protein content is calculated by multiplying nitrogen content in g by 6.2. Patients with hepatic encephalopathy are given the high concentration of branched chain AAs. Patients with renal failure are given solutions rich in concentrated AA and L-Histidine.
| Administration of TPN|| |
All three constituents can be given separately or all in one solution. Two-in-one solution with fat infused separately is also available. Osmolarity of 3-in-one is very high and is approximately 980 mosmol/l.
| Monitoring the Patient During TPN|| |
It is mandatory to monitor the patient during administration of TPN as it can lead to various potential complications. Therefore, monitoring of the following parameters is highly essential during administration of TPN in critically ill patients.
- Vital signs.
- Basal biochemical profile, full blood count, platelet count.
- S. calcium, phosphorus, alkaline phosphate, pH and arterial blood gas analysis (ABG).
- Once weekly serum level of transferrrin, prealbumin and retinol binding protein.
| Complications of Parenteral Nutrition|| |
Appropriate precautionary measures have to be taken during TPN administration as it is also associated with some potential complications such as: 
- Metabolic complication
- Hyperglycemia - it is the most frequent complication. It is more common when 50% dextrose solutions are used. It is better to start insulin infusion in a separate line to keep blood glucose between 150 mg/dl and 200 mg/dl. Uncontrolled hyperglycemia can lead to hyperosmolar non-ketotic coma in the form of mental obtundation without acidosis and a blood sugar levels between 450 mg/dl and 1000 mg/dl.
- Hypoglycemia can occur if TPN is suddenly stopped. As a result, it should always be slowly tampered off.
- Hypophosphatemia - can lead to mental obtundation and coma. It can also cause hemolysis, rhabdomyolysis and heart failure.
- Hepatic dysfunction
Rise in serum transaminase and alkaline phosphatase invariably occurs. Hepatic dysfunction can be attributed to breakdown products of AA and bacterial endotoxins, excessive carbohydrate administration, presence of complicating sepsis.
- Catheter related infection
Catheter related sepsis is the most disastrous complication which can be bacterial, fungal or both. Thrombosis of subclavian vein can also occur which has incidence of 2-5%. Hypertonic solution can aggravate the clinical situation. Polyvinyl catheters are more likely to cause thrombosis than silicon catheter. Co-existing diseases like sepsis or malignancy can lead to hypercoagulable state that promote thrombosis.
| Nutritional Support in Special Situations|| |
Nutritional support in ICU is highly challenging as there is high variability in pathophysiologies and co-morbidities of critically ill patients. Besides looking at the indications for enteral or parenteral nutrition, other factors have to be considered depending upon the organ functional status. Nutritional concepts in various disease pathologies can be summarized as follows:
- Renal failure: Nutrition should be initiated early as the patient is in hypercatabolic state and should be combined with hemodialysis or hemofiltration. Restrict protein intake to 0.5 g/kg/day and fluid to 0.8-1 l/day. Protein intake can be increased to 1 g/kg/day once dialysis begins. In enteral feeds, use carbohydrate: fat ratio of 60:40. Replenish the losses during hemodialysis as there is loss of 6-12 g of AA and 25-30 g of glucose. Essential Amino acid formulation is given to patients who are not able to undergo dialysis. However, it is mandatory to keep protein intake to 0.3 g/kg/day. ,
- Hepatic failure: In patients with hepatic dysfunction, keep protein intake to 1 g/kg/day if encephalopathy is not present and decrease it to 0.3 g/kg/day if encephalopathy is present. Also, carbohydrate: Fat intake ratio has to be kept at 60:40. 
- Respiratory failure: The primary aim of nutritional support in patients with respiratory compromise is to improve the muscle strength for successful weaning from ventilator support. Carbohydrate rich diet should be avoided in patients with chronic obstructive pulmonary disease.  The ratio of carbohydrate: Fat has to be kept at 40:60. Conversely, in patients with acute respiratory distress syndrome lipid emulsions should be avoided and carbohydrate: fat ratio to be kept at 65:35.
- Cardiac failure: In patients with cardiac failure, restrict salt and water intake. Carbohydrate: Fat ratio is to be kept at 60:40. TPN is to be given over 3-4 days with half of the total calorie requirements. 
- Pancreatitis: Preference is to be given to enteral feed in comparison to parenteral feed if possible. Peptide based jejunal feed should be given in such patients. In ileus and necrotizing pancreatitis, there is no other alternative but to give TPN. 
- Thermal injury: Patients with thermal injuries require 30-35 kcal/kg/24 h and high protein intake of 2-2.5 g/kg/day.
- Metabolic stress syndrome and diabetes: Elevated blood glucose can occur even in non-diabetics in ICU setup due to increase in counter regulatory hormones. Management of critically ill diabetic patients in ICU is a huge challenging task.  Though tight blood glucose control is controversial but in patients with co-morbidities, a blood glucose level of 110-140 mg/dl is an acceptable option. Effective control of blood glucose is associated with decreased morbidity and mortality. Diabetic patients, those particularly receiving TPN are difficult to manage as TPN frequently leads to hyperglycemia and electrolyte imbalance. Glucose intake has to be restricted to 150 g/24 h and insulin should be added directly to TPN solution. The dose of insulin added to TPN solution can be adjusted to quarter to half of the daily requirement. 
| Conclusion|| |
Nutritional issues are of prime importance in critically ill-patients as they directly and indirectly influence the outcome in such subset of the population. Enteral nutrition is always the preferred method of nutrition in critically ill-patients but may fail to achieve the desired nutritional goals. As such supplementation with parenteral nutrition becomes a dire necessity in the majority of the critically ill-patients. Energy and calorie intake assessment are also highly essential to prevent any over or underfeeding in critically ill patients which can also have an impact on morbidity and mortality outcome.
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