Enteral nutrition is a process of being fed with a medical device called a feeding tube. A feeding tube for enteral nutrition is mainly used by patients who have a moderate-to-severe neurological impairment that might compromise the swallowing coordination and hence exposes the patients to the risk of aspiration. Clinicians also use enteral feeding in patients with requirements for additional nutritional supplementation. Using a feeding tube to deliver nutrition or supplement to a patient is known as tube feeding, enteral feeding, or gavage.
Parenteral and enteral nutrition dates back to as far 3500 BC to the time of ancient Chinese, Egyptians and Indians. The concept of enteral feeding has existed since the time of Hippocrates, Avicenna and Celsius, and Plato. These ancient physicians prescribed special food for sick patients in the recovery phase of an acute or chronic illness. Around the latter part of the 19th century, the concepts of “dietetics “ was coined. Erasistratus and Herophilus first described the notion of the circulatory system Galen later refined it. Ibn Zur constructed the first model of parenteral nutrition and Capivacceus in the 16th century placed the first tube for enteral nutrition.
At the beginning of the 20 century, physicians pondered on the problem of feeding patients incapable of eating either because of protracted illness or its severity.
Clouston in 1872 described a method of intragastric feeding that included a cocktail of milk, egg, jelly, and alcohol. In 1882, Bless tried to use the rectal route to deliver nutrition. At the beginning of the 20th century, advances were made in the formulation of mixtures used for enteral feeding. The early and late 50s heralded the start of the space age when cosiderable research on food and nutrition mixtures for astronauts was done. In 1937, Elma was the first person to use hydrolyzed casein as a form of intravenous food for a sick patient. After that, 2 schools of thought developed:
In Sweden, there was a successful infusion intravenously of hydrolyzed casein as a source of protein together with glucose and lipids. They later replaced this with crystalline amino acid as a source of protein.
United States of America
In Philadelphia, Aubaniac was able to successfully infuse hypertonic glucose and nitrogen via a central venous catheter. Wilmore and Dudrick in 1967 reported a case of successfully providing parenteral nutrition for an infant for 6 weeks. Parenteral nutrition was in vogue until about 25 years ago when enteral nutrition was again gradually reintroduced as the best mode of feeding patient.
Enteral nutrition has continued to develop in leaps and bounds because clinicians were able to establish malnutrition as an independent risk factor for mortality. The malnourished patient is more prone to have prolonged hospital, increased the length of stay in the intensive care unit (ICU), more days on mechanical ventilation, prolonged wound healing. and a higher risk of mortality.
In the early 80s, chemically-defined and organ-specific diets were developed. Scientists made new advances in the feeding tube. Access to the gut also improved with advances in endoscopic technique and interventional radiology. Wilmore et al. proposed that translocation of bacteria from the gastrointestinal (GI) tract is a major cause of and trigger for sepsis. Current research focuses on looking at the GI tract as an organ with hormonal, immune, and metabolic functions that acts a major barrier to pathogens and intraluminal toxins.
Goals of Enteral Nutrition
Patients that are critically ill are prone to go into a catabolic state of metabolism. This can cause the breakdown of protein in the body leading to a loss lean body mass. Proteins are the building block of enzymes and hormones in the body. The dis-balance created by the breakdown of protein can cause wound dehiscence in surgical patients or impair the host response to infection.
Enteral nutrition serves the following purposes:
Indications for Enteral Feeding
Enteral tube feeding is indicated in patients who cannot main adequate oral intake of food or nutrition to meet their metabolic demands. Healthcare professionals commonly use enteral feeding in patients with dysphagia. Patients with dysphagia sometimes cannot meet their daily nutritional needs even with modification of food texture and or consistency.
For enteral feeding to be successful, the GI tract should be accessible and functional. Inaccessible GI tracts, malabsorption, and severe GI losses might make enteral feeding a challenge. The alternative is parenteral feeding.
Enteral Nutrition in Critical Illness
In patients that are critically ill, there is overwhelming evidence that enteral feeding is the best approach for nutrition in critically ill patients. The GRADE system working group came up with the following recommendation based on the level of evidence 16.
Energy consumption is calculated using the indirect calorimetry method. This is the best method to calculat the caloric requirements in patients requiring enteral feeding. When indirect calorimetry is not available, approximately 25 kkal/kg per day is the approximate energy requirement. Clinicians can calculate caloric intake for patients on mechanical ventilation by using the Penn State equation.
Carbohydrate intake should be approximately 4 gm/kg per day with a target glucose level below 180 mg/dl. Lipid intake should be between 0.7 to 1.5 gm/kg per day. Amino acid should be adjusted to 1 to 1.8 g/kg per day with an adequate supply of micronutrients.
Hypocaloric enteral intake is beneficial at the initial stage of critical illness as this can help to prevent hyperglycemia which is linked to a higher risk of mortality. Some authorities recommend around 80% of nutritional needs in the first 7 to 8 days of illness which can then be gradually increased during the phase of recovery.
Enteral nutrition is contraindicated in some special cases.
Acute Kidney Injury
In acute kidney injury (AKI), nutritional support is geared toward conserving the lean body mass, energy reserve, and preventing of malnutrition.
Patients with AKI and renal failure might be in a non-hypercatabolic or hypercatabolic state with excessive sodium, potassium, and phosphate load. In a non-hypercatabolic state, high-energy enteral nutrition with normal protein content and a low sodium, potassium and phosphate load is recommended. In AKI with a hypercatabolic phase, a low protein (2 to 2.5g/kg per day), a low electrolyte enteral nutrition is recommended. Apart from monitoring electrolytes like sodium, potassium, phosphorus, and calcium, clinicians should pay special attention to micronutrients like zinc, selenium, thiamin, folic acid, and vitamins A, C, and D.
Acute Liver Failure and Liver Transplantation
Liver failure is associated with loss of the synthetic function of the liver. Liver failure patients also have an impaired ability to synthesize clotting factors. Enteral feeding should be approached with caution in patients with liver failure because of the inherent risk gastrointestinal bleeding from varices and coagulopathy. In acute liver failure, parenteral nutrition might be better if the gut is not viable and or if the risk of hepatic encephalopathy is high. If enteral feeding is used, a balanced mixture of energy supply from carbohydrate and protein is recommended. Caloric intake should be around 25 kcal/kg per day. Enteral feeds should contain an adequate quantity of potassium, magnesium, and zinc. In liver transplant patient, early enteral feeding via a transpyloric approach is recommended.
Acute Lung Injury (ALI), Acute Respiratory Distress Syndrome (ARDS)
This is one of the most common reasons for admission into the intensive care unit (ICU). Daily protein intake should be around 1 to 1.8 g/kg per day. Use of high fat, low carbohydrate is not indicated. ALI and ARDS require an enteral diet rich in omega-3 fatty acid and antioxidants.
A patient who sustained multiple trauma should be started early enteral feeding. We recommend starting trauma patient should be started on a total caloric intake of about 25 to 30 kkal/kg per day. We also recommend arginine, omega in patients with multiple trauma.
The nutritional needs of patients with abdominal surgeryare similar to the needs of other critically ill patients. Surgery causes both inflammatory and metabolic changes in the body. A post-surgical patient with malnutrition might have delayed wound healing and dehiscence and a decrease in immunological functions placing the patient at risk for infectious and cardiopulmonary complications. This can prolong hospital stay and cause a higher rate of mortality.
Inflammation of the pancreas can provoke a systemic inflammatory response syndrome. This causes a hypermetabolic, hyperdynamic, and catabolic state. Classically acute pancreatitis is treated with bowel rest and parenteral nutrition. It has been shown that this approach is associated with high morbidity and mortality. In acute pancreatitis, there is intestinal barrier dysfunction which is associated with multiple organ failure, pancreatic necrosis, and mortality. Based on these facts, the current recommendation is to start early enteral feeding via the jejunum within 48 hours of hospitalization.
Types of Enteral Feeding Tubes
There are several types of enteral feeding tubes. They are usually made of polyurethane or silicone. Feeding tube diameters are measured in French units (Fr). Each French unit is equivalent to 0.33 millimeters. Feeding tubes are usually denoted or classified by the site of placement.
Tubes can be placed:
Nasogastric tube (NG) is mainly utilized for patients with no issues with vomiting, gastroesophageal reflux (GER), poor gastric emptying, and with no evidence of ileus, small or large bowel obstruction. NG tube is risky in patients with poor swallowing coordination or reflex. Fine bore 5 to 8 Fr NG is usually recommended. If there is a need for nasogastric decompression, a larger bore NG can be used. For patient’s safety, the recommendation is that a well-trained and qualified medical personnel places the feeding tube. After the placement, the position should be verified by auscultation or x-ray. Although not routinely recommended, an x-ray is used to confirm NG tube placement for high-risk patient population, specifically, intensive care and neonatal patients. The National Patient Safety Agency advocates for the analysis of gastric aspirate with pH graded paper to confirm proper position. The pH should be less than 5.5 before feeding is started.
Nasoduodenal and Nasojejunal Tube
These are enteral feeding tubes placed with the tip in the duodenum or jejunum. Placement can be done at the bedside or with fluoroscopy guidance
The feeding tube passes through the anterior abdominal wall into the gastric cavity. A gastrostomy tube is utilized for patients who require long-term feeding. It can be placed via endoscopy percutaneous endoscopic gastrostomy (PEG). PEG tubes are for patients who require long-term nutritional support. PEG tube with jejunal extension is associated with tube dislocation and dysfunction. Gastrostomy feeding tube can also be placed radiologically or surgically or via endoscopy.
This feeding tube passed through the anterior abdominal wall into the jejunum. It can be placed surgically or radiologically via extending through the pylorus into the jejunum. Endoscopically a percutaneous endoscopic gastrojejunostomy (PEGJ) can be placed. Placement of direct percutaneous endoscopic jejunostomy tubes is less commonly performed, but PEGJs are more robust and less likely to be dislocated.
Nutritional Support Team
An interprofessional approach is the best way to manage patients who require enteral feeding using the current protocol and guidelines. A nutrition support team is made up of the physician, nurse, clinical pharmacist, and the nutritionist. Provision of optimal enteral nutrition can be achieved by:
Services that the nutrition support team can offer include:
There are several modalities of delivery of enteral feeds. Traditionally, we usually start enteral feeding about 12 to 24 hours after placement of PEG. This is to allow for a better seal to develop at the site of insertion of the PEG tube. More recent studies have shown that enteral feeding can be initiated from 3 to 4 hours after the insertion of the PEG.
Bolus Intermittent Feeding with a Bulb or Syringe
Enteral feeding is delivered in volumes of about 100 to 400 ml over 5 to 10 minutes. It is mostly used in ambulatory settings. The risk of aspiration is high.
Cyclic Intermittent Feeding
This method is used for patients in a semi-recumbent position. Enteral feeding is delivered via a pump or gravity. Enteral feedings are delivered over an 8- to 16-hour period
This is popular for home enteral feeding. Approximately 1.5 to 2 liters of feeding can be delivered over an 8 to 16 hours period overnight. Feeding is delivered via gravity or pump.
This method is used for bedridden patients. Feeding is usually delivered via gravity or pump. The head is inclined at an angle of 45% to reduce aspiration or regurgitation.
Tube placement for enteral feeding might cause mechanical complications. Some mechanical complication form tube feeding are listed below.
Tube for enteral feeding can be inserted nasally, guided percutaneous application, or surgical technique.
Nasoenteral insertion is mostly done blindly by the bedside with about 0.5% to 16% mispositioning in the pleura, trachea or bronchial trees. This can cause the infusion of enteral feeds in the tracheobronchial tree causing a pulmonary abscess or pneumothorax. Instillation of air or auscultation is not an accurate method of determining proper tube placement. The best confirmation is with radiography. Failure of bedside nasoenteral tube placement is an indication for fluoroscopy or endoscopy-guided tube insertion.
Tube placement in enteral feeding is sometimes associated with infectious processes listed above. Aspiration pneumonia is reported in closed 89% of patients on enteral feeding with no clear benefit of nasoenteric feeding over nasogastric. Distal duodenal or jejunal feeding might prevent regurgitation of enteral feeds.
Complications from the enteral feeding tube also depend on:
Spark et al. critically reviewed pulmonary complications from nasoenteric tube placement. In 9931 cases of tube placement, there was 1.9% (187) malposition in the tracheobronchial tree. The 187 misplaced tubes resulted in 35 pneumothoraxes (18.7%) with at least 5 mortalities.
Enteral feeding is associated with several GI complications
Nausea and vomiting are common after the initiation of enteral feeding about 20% to 30% incidence. Non-occlusive bowel necrosis and aspiration can also occur. This is associated with high mortality.
This is the most gastrointestinal complication seen in enteral feeding. Diarrhea occurs in about 30% of patients admitted to the medical or surgical wards and in about 80% in patients in the ICU.
Diarrhea in enteral feeding is as a result of many factors. Using antibiotics and other medications in enteral feeding is a common cause of diarrhea. Medications like antacids, oral magnesium or phosphate, antacids, and prokinetic agents. Use of oral and intravenous antibiotics can also favor the growth of Clostridium difficile, Escherichia coli, and Klebsiella. The sorbitol-containing solution can also trigger profuse diarrhea in patients on enteral feeding. Use of fiber based on the result of meta-analysis has been found to be able to significantly reduce the incidence of enteral feeding associated diarrhea especially in high-risk patients both post-surgically and in the critically ill.
This is a less common complication that is associated with enteral feeding. Constipation is more common in patients on long-term enteral feeds. Some studies suggest that use of fiber supplementation might help reduce the percentage of patients reporting constipation in enteral feeding.
This is a potentially life-threatening complication from enteral feeding. It occurs because of aspiration of oral secretion and or gastric with enteric secretions. Aspiration is more common when patients are fed via a nasogastric tube in a supine position. The cause of aspiration pneumonia in enteral feeding are multifactorial.
Enteral feeding is associated with metabolic complications. A common complication seen in malnourished or undernourished patients is refeeding syndrome. This phenomenon was first described in Far East prisoners during the Second World War.
Patients with anorexia nervosa, hyperemesis, alcoholism, and malabsorption syndrome like short bowel syndrome who are started on enteral feeding are prone to develop the re-feeding syndrome.
The pathophysiology of the refeeding syndrome is still poorly understood. In a period of starvation, the cellular membrane system downregulates with loss of intracellular potassium, phosphorus, magnesium, and calcium. The total body content of these ions is depleted. Intake of sodium and water by the cell is also increased. The sudden reversal of malnutrition with enteral feeding is due to an uptake of potassium, phosphorus, magnesium, and calcium back by the cell with simultaneous movement of water and sodium out of the cells. The undernourished kidney is also impaired and cannot handle the sodium and water load.
Hypophosphataemia is the hallmark of re-feeding syndrome. Hypophosphatemia can cause rhabdomyolysis, cardiac failure, arrhythmia, muscular weakness, leukocyte dysfunction, seizure, coma, and sudden death.
The phenomenon is more common in enteral than parenteral feeding.
Awareness of the syndrome is the key to treatment and prevention.
Patients at Risk for Re-feeding Syndrome
To manage refeeding syndrome, the cardiovascular status of the patient should be monitored closely preferably in the ICU. Judicious monitoring of electrolytes and micronutrients should also be implemented.
Goal caloric intake should target about 50% to 75% of daily requirements.
Sodium should be restricted, I mmol/kg of body weight per day or 1.5 g per day, but adequate amount of phosphorus, magnesium, and potassium should be given.
Magnesium (0.8 to 1.6mmol/L)
For hypomagnesemia, start 0.5 mmol/kg per day over 24 hours, then 0.25 mmol/kg of body weight per day for 5 days
Maintenance 0.2 mmol/kg per day intravenous or 0.5 mmol/kg per day oral
A normal range is 0.85 per 1.40mmol/L
For mild hypophosphatemia (0.6 to 0.85 mmol/L) start at 0.3 to 0.6 mmol/kg of body weight per day
For moderate hypophosphatemia (0.3 to 0.6 mmol/L) start at 0.3 to 0.6 mmol/kg of body weight per day
Complications Associated with PEG Placement
Peristomal Wound Infection
Wound infection occurs after PEG placement with an incidence of about 3 to 70%. Wound site infection can be caused by the technique of placement, obesity, malnutrition, steroid, or immunosuppressive therapy. Prophylactic antimicrobial therapy has been shown to reduce the incidence of wound infection after placement of PEG. First-generation cephalosporins or penicillin gives adequate coverage.
Clogged Feeding Tube
The incidence of clogging of feeding tubes can be as high as 25%. Clogging occurs when very thick feeds and medications are delivered through a relatively thin feeding tube. Repeated gastric aspiration is discouraged since the low pH of gastric fluid can promote protein coagulation. Feeding tube should be flushed with about 40 to 50 mL of water after delivering thick feeds or medications. A clogged feeding tube can also be cleared mechanically using various endoscopic catheters, braided quid wires or plastic brushes.
This is also a complication of PEG tube placement for enteral feeding. Several factors can contribute to leakage. Excessive pulling and tugging, increased gastric secretion are factors that inhibit wound healing like malnutrition, diabetes, and immunodeficiency. This can be prevented by using antisecretory agents like proton pump inhibitors (PPI). Skin protectant and barrier creams can also be used.
The incidence of bleeding is about 2.5% after placement of PEG. This might be secondary to mucosal tear or damage to a local vessel. Risk factor for bleeding includes the use of antiplatelet or anticoagulation therapy. Based on current recommendation aspirin can be continued in a high-risk patient. Warfarin is recommended to be discontinued, and unfractionated heparin can be used as a bridge.
Misplacement of PEG for enteral feeding might lead to the formation of gastrocolic, colocutaneous and gastro colocutaneous fistulae. A gastrocolic fistula is a connection between the wall of the stomach and the colon. Gastro colocutaneous fistula is an epithelial connection between the wall of the stomach, colon and the skin that can occur because of iatrogenic puncture or direct erosion of the PEG into the wall of the colon and the skin.
To prevent colonic misplacement, the gastroscope should be transilluminated through the anterior abdominal wall, and the endoscopically visible imprint of a finger or needle on the is considered a “condition sine qua non” before introducing the needle through the stomach. Clinically the presence of a fistula is associated with watery diarrhea around the site of the PEG or the presence of stool around the site of insertion of the PEG. In rare instances, fistulae formation can cause peritonitis, infection or fasciitis.injection of contrast into the PEG can establish the diagnosis. Management can be conservative with the removal of PEG and awaiting the spontaneous closure of fistulae. For more severe cases, endoscopic intervention or invasive laparotomy with colonic exploration might be necessary.
Clinical significance cannot be overemphasized. The benefits of enteral feeding include effects far outweighing the administration of macronutrients and macronutrients. Utilization of the gut to provide nutrients helps in the maintenance of the gut integrity, stimulation, and modulation of the immunological properties of the GI tract.
To improve the outcome in enteral feeding requires an interprofessional approach. Enteral feeding requires coordination amongst the nutritional support team.
The nutrition support team is made up of:
The clinician coordinates and directs the care related to enteral feeding. The clinician determines the optimal feeding regimen for the patient
Nutrition nurse specialist is primarily responsible for educating the patient on the use of the feeding tube. The nurse also supervises the care of the tube and notifies the clinician if there any complications that develop.
The dietician manages the evaluation of the nutritional requirement of the patient including the calculation of the daily caloric need and the optimal feeding regimen for patients.
The pharmacist provides the enteral feed and can mix and compound parenteral nutrition. The pharmacist advises on the compatibility of nutrients and interaction
Other ancillary staff includes the social worker, physical therapist, occupational therapist.
In the United Kingdom, the National Institution for Clinical and Health Excellence recommends that an interprofessional team should provide nutritional support.