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Indian Pediatrics 2001; 38: 256-263  

Enteral Nutrition for Critically Ill Patients

Manju Salaria
Sunit Singhi

From the Department of Pediatrics, Post Graduate Institute of Medical Education and Research, Chandigarh 160 012, India.

Correspondence to: Dr. Sunit Singhi, Additional Professor, Department of Pediatrics, Post Graduate Institute of Medical Education and Research, Chandigarh 160 012, India.

Nutritional support is an important issue in the management of critically ill patients. Integrity and functioning of most of the cells of the body depends on continuous delivery of nutrients. In critically ill patients, there is interference with storage and mobilization of nutrients because of organ dysfunction. In addition, fasting can compromise gut function, the gut barrier, mesenteric blood flow, immune function, protein synthesis, wound healing, liver function and renal functions(1).

The two main routes for providing nutrition in critically ill patients are enteral feeding and parenetral nutrition. Enteral feeding is being preferred now-a-days because of ease of administration, decreased cost, decreased risk of infection, no need for central venous access and improved gastrointestinal function(2).

The major advantages of enteral nutrition are:

1. Enteral feeds lead to decrease in infection rate in critically ill patients(3,4). It main-tains integrity of gastrointestinal mucosal structure and function(5). In experimental animals, enteral nutrition is associated with higher secretion of secretary IgA and decreased secretion of catabolic hor-mones(6,7). In addition, enteral feeding also causes decrease in bacterial leak through the intestinal mucosa. All these factors result in decreased mortality rate after a septic or hypotensive insult.

2. Experimental studies have also shown that enteral nutrition results in better wound healing after abdominal surgery and there is reduced hyper-metabolic as well as catabolic phase after burn injury in experimental animals(8,9).

Any patient with intact gastrointestinal tract, is a candidate for receiving enteral nutrition. Intestinal obstruction and intestinal fistulas are the only contraindications for enteral feeding. In contrast to the usual belief, presence of bowel sounds is not a prerequisite for starting enteral feeds(10). It has been documented that 90% of critically ill adult patients tolerate feeds irrespective of presence of bowel sounds(3).

Enteral feeding can even be administered in the presence of gastrointestinal hemorrhage. A protective role of enteral feeding in gastrointestinal hemorrhage (GIH) has been shown in crtically ill patients on mechanical ventilation. GIH was defined as strongly positive hematest of nasogastric aspirates on 3 consecutive readings, frankly bloody gastric aspirate, hematemesis or malena. Various mechanisms proposed for the beneficial effect of enteral feeding in prevention of GIH are dilutional alkalinization as well as the role of positive nitrogen balance in maintenance and reparative process of gastric mucosa(11).

Minor gastrointestinal problems e.g., bloating, vomiting and diarrhea should not be taken as absolute contraindications to enteral feeds. These are potentially manageable by changing the feeding volume and rate, using gastric motility agents and change in fiber content of the feed(12). In adults, routine nursing procedures like changing of bed linens, changing infusion bags and management of tracheostomy tubes were associated with cessation of enteral feed in 30% of patients. In this study, there was delay of as long as two hours in restarting feed after a diagnostic test like CT scan, ultrasonography and roent-genograms(13). Therefore, clear instructions regarding timing of enteral feeds should be given to the nursing staff working in the Intesive Care Unit. To conclude, any patient who is not able to eat is a candidate to receive enteral feeds(14).

Following are the various categories of feeding mixtures from which selection should be made for a given patient.

1. Elemental Diets

These are monomeric formulas of low molecular weight which require minimal digestive effort and are easily absorbed without leaving much residue. Carbohydrates are present in these diets as oligosaccharides, sucrose and glucose. Proteins are present in form of short chain peptides and fat is usually present in the form of medium chain tri-glycerides along with small amounts of essential fatty acids(15). As these diets are predigested, they are easily absorbed and are ideal for patients with pancreatic insufficiency or short bowel.

2. Polymeric Formulas

These diets consist of intact proteins, complex carbohydrates, fat and residue. The various types of polymeric formulas include milk based diets and lactose free diets which are preferred in critically ill patients and in lactose-intolerant patients. Polymeric diets are of high molecular weight and are of relatively low osmolality. Therefore, they are preferred for duodenal and jejunal administration(15).

3. Modular Diets

These formulas are available as individual nutrients. Various nutrients can be mixed according to the need of the patient.

Various enteral formulas used at our center are shown in Table 1. Table II enlists few examples of commercially available formulas.

1. Sepsis, Trauma and Burns

Stress caused by sepsis, burns and trauma, results in release of various hormones in the body. These hormones cause skeletal muscle proteolysis and hydrolysis of branched chain amino acids (BCAA). Therefore, in such stress conditions, formulas rich in BCAAs are preferred(15).

2. Pulmonary Compromise

Increase intake of carbohydrates can lead to increase in CO2 production and oxygen consumption, which can complicate and delay weaning in artificially ventilated patients. Therefore, in patients with pulmonary com-promise, a formula containing decreased carbohydrate calories should be selected(15).

3. Hepatic Failure

High concentration of BCAA and low concentration of aromatic amino acids may help in normalizing the altered aminto acid profile in patients with hepatic encephalo-pathy(15, 16).

4. Renal Failure

Diets for patients with renal failure should contain high concentrations of essential amino acids combined with a large calorie to nitrogen ratio(15).

Septic, injured and other critically ill patients have immunosuppression, manifesting as infections. It has been seen that early administration of enteral feeds may be asso-ciated with decreased frequency of hospital-acquired infections. Certain nutrients have the potential to alter cellular responses to inflam-matory mediators(17). To obtain this effect, these nutrients are required in doses higher than those required for general nutritional support. Use of these nutrients is called immuno-nutrition(18). Various nutrients known to enhance immune function are dietary peptides, arginine, glutamine, Vitamin C, Vitamin A, Vitamin E and nucleic acids(19). Most of the trials on immunonutrition have used formula containing intact proteins and have added arginine, RNA and mixture of W-3 and W-6 polyunsaturated fatty acids. In a meta-analysis it was concluded that immunonutrition causes decrease in duration of hospital stay, rate of infections and ventilatory days(2).

If enteric nutrition is needed for a short period, nasoenteric feed is preferred because of its temporary nature, ease of administration and simple technique of insertion. Among all nasoenteric routes, nasogastric is the preferred site. If there is increased risk of aspiration, feeding can be administered into distal duodenum or jejunum. Tubes can be passed beyond the pylorus, i.e., nasoduodenal or naso-jejunal along with the peristaltic movements. If peristalsis is not successful, tubes can be passed through pylorus endoscopically under fluoroscopic guidance(15).

If requirement for enteral nutrition is expected for more than 4 weeks, these routes are chosen. In the past, these tubes were being inserted at the time of surgery. However, nowadays percutaneous insertion techniques are available using local anesthesia(15).

Methods of Enteral Feeding(21)

These include the following:

Bolus Feeding
It has advantages of requiring less amount of time and equipment and reduced risk of contamination. However, there are more chances of aspiration after a bolus feed. Patients with short bowel or malabsorption who run the risk of physiologic intolerance to the bolus of carbohydrate/protein or fat do not tolerate this type of feeding.

Intermittent Feeding
This is given as 2 ml/kg every 4-6 hourly, each time for 20-45 minutes. This type of feed is usually well tolerated.

Continuous Drip Feeding
This type of feeding has the advantage of leaving smallest residual volume, has least potential for aspiration, bloating and diarrhea. However, it requires close monitoring and has danger of causing bacterial overgrowth. In small bowel, continuous drip-feeding is preferred, whereas jejunal feed may be given by smaller but more frequent feeding increment than being given into the stomach(21). Feed should be started with small volumes, 1 ml/kg/h of half strength formula. If tolerated for 24 h, it can be increased by 0.5 ml/kg/h until the desired volume is delivered. Once the required volume is achieved, concentration can be increased to full strength.

The initiation and success of enteral feeding requires help of clinical nutritionist, gastroenterologist and dietician. A specific, yet flexible plan should be made for each patient before starting enteral feeds. There should be a written estimation of fluid, caloric and electrolyte requirements for that particular patient. The protocol for patient’s monitoring should be clearly defined before initiating enteral feeds. The selected formula should initially be used at one quarter to half strength; at a volume approximately half of the required 24 h volume and further increments in volume and strength should be made gradually.

The frequency of monitoring of patients on enteral feeds depends on nutritional and clinical condition. The suggested monitoring schedule is shown in Table III.

1. Pulmonary Aspiration of Gastric Contents

This complication is usually due to prolongation of gastric emptying time, which may lead to vomiting resulting in aspiration. The causes of delayed gastric emptying in critically ill patients include response to stress and pain, poor gastric perfusion and use of catecholamines and dopamine. Cisapride (0.2 mg/kg qid), a gastrointestinal prokinetic drug has been shown to increase gastric emptying (22,23). We find it very useful in our patients. Other methods, which help to decrease the risk of vomiting are elevation of the patient’s head to approximately 30 degrees and administration of enteral feeds beyond the pylorus(15). It is not practical to arbitrarily select a significant gastric volume or aspirate as a predictor, because no study has reported a correlation of gastric residual volumes with occurrence of pulmonary aspirates.

2. Diarrhea

It is a frequent problem in patients on enteral formula. The causes of diarrhea include use of hyperosomolar formula, rapid feeding of large volumes, contamination of the feed, low serum albumin, concurrent antibiotic therapy or administration of lactose containing formulas to lactose deficient patients. If these factors can be taken care of, diarrhea does not remain an absolute contraindication for enteral feeds.

3. Other Adverse Gastrointestinal Effects

These include nausea, vomiting, cramping and abdominal pain which can be caused by rapid administration of hypertonic feeds or by use of inappropriate formula. Therefore, increment in formula strength, volume and rate of administration must be made gradually(15).

4. Nutrient Deficiencies

There is a risk of development of excess or deficiencies of various nutrients and electrolytes. To overcome this, there should be a strict and accurate recording of all the sources of fluids, electrolytes and nutrients(15).

Occlusion and displacement of feeding tubes can be avoided by taking proper monitoring precautions as mentioned earlier(15).

Adequate nutrition should be a part of management protocol for critically ill patients. Enteral nutrition is as good as parentral nutrition with added advantages of being less costly and easier to administer. A proper protocol and adequate monitoring are key points for ensuring successful enteral feeding.

The authors are thankful to Mrs. Madhu Sharma, Assistant Dietician in our Dietetic Department for providing a list of enetral formulas being used at our center.

Contributors: MS conceptualised the manuscript, reviewed the literature and drafted the paper. SS was responsible for critical appraisal and co-drafting; he will act as the guaranter for the paper.

Competing interests: None stated.
Funding: None.

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