How Does Enteral Nutrition Impact Wound Healing of Pressure Ulcers?

Chronic wounds, such as pressure ulcers, place higher energy and nutrient demands on the body to support healing processes through a delayed inflammatory stage. Pressure ulcers are lesions resulting from sustained or unrelieved pressure on any part of the body, such as in bedridden patients. Affected areas include bony prominences, e.g., the scapula, occiput, elbows, sacrum, and ischium. Pressure ulcers occur over six stages of severity, ranging from intact skin with non-blanchable erythema (Stage 1) to deep-tissue injuries completely covered in eschar or slough (Stage 6/unstageable). 

The Impact of Nutrition on Wound Healing

Malnutrition is a significant contributor to wound chronicity as it directly affects immune function, wound tensile strength, and collagen synthesis. According to the WHO, malnutrition is a deficiency, imbalance, or excess in the intake of energy or nutrients. The main classes of malnutrition are protein-energy malnutrition (PEM) and protein-calorie malnutrition (PCM). PEM is common in children and primarily caused by a deficiency of dietary proteins, energy, and micronutrients. PEM symptoms include underweight, acute weight loss, stunted growth, and kwashiorkor. Secondarily, PEM can result from a prolonged illness or treatments that affect the appetite, digestion, or metabolism of the individual. PCM, on the other hand, is due to an inadequate intake of proteins, calories, and essential macronutrients, which can result in mild to severe changes in body composition and function. In patients with chronic wounds, enteral feeding may be beneficial in providing nutritional support to facilitate wound healing. 

The prevention and management of chronic non-healing wounds, such as pressure ulcers in critically ill patients or those with decreased appetite, can be challenging due to nutritional deficiencies. Enteral nutrition, also known as tube feeding, may promote faster wound healing in these classes of patients by temporarily improving their nutritional status. 

What is Enteral Nutrition?

Enteral nutrition, aka tube feeding, is a method of delivering food in a person through the gastrointestinal tract. The procedure involves inserting a nasogastric or orogastric tube through the nose or mouth directly into the stomach. Enteral feeding is suitable for all categories of patients, including minors, adults, and geriatrics. Note, however, that effective nutritional management aimed at halting the progression of pressure ulcers at long-term care facilities may involve a team effort between qualified dieticians/nutritionists and wound care specialists. The role of dieticians or nutritionists is to diagnose eating disorders and/or symptoms of malnutrition in patients and recommend enteral feeding formulations to restore nutritional status. Wound care teams carry out the management of ulcers, including re-positioning, wound disinfection, debridement, and application of wound dressings. 

Types of Enteral Formulations

Enteral formulations fall into the following categories:

• Standardized or polymeric: Contain intact proteins, long-chain triglycerides, and complex carbohydrates that require digestive functions to break down. Patients can rely on these formulations for up to six months under close medical supervision. 
• Elemental: Contain all the nutritional elements necessary to maintain sustenance and require minimal digestive function. Under close medical supervision, patients can rely on these formulations as a sole source of energy and nutrients for up to three weeks.
• Semi-elemental: These formulations contain amino acids, fats, and simple carbohydrates that are partially digested. 
• Disease-specific: These are nutritionally-complete formulations designed to cater to patients with specific health conditions.

Essential Micronutrients and Macronutrients for Wound Healing

Enteral feeding formulations should contain essential micronutrients and macronutrients in the right quantities to enhance the nutritional status of the patient. The following nutrients provide various benefits through multiple phases of wound healing:

• Vitamins A and C: Vitamin A aids the proliferation of fibroblasts, melanocytes, epithelial cells, and endothelial cells by binding itself to retinoic acid receptors. This micronutrient is ideal for all stages of pressure ulcers and also increases the number of macrophages and monocytes in the wound bed. Vitamin C deficiency causes impaired immune response while a healthy intake can promote fibroblast production required for collagen synthesis. 
• Carbohydrates: Carbohydrates are essential for insulin production and meet energy needs to facilitate inflammation, angiogenesis, collagen synthesis, and cellular activity for wound healing. The National Pressure Ulcer Advisory Panel (NPUAP) recommends a daily intake of 30 to 35 calories per kilogram (Cal/kg) of body weight, up to a maximum of 40 Cal/kg. Carbohydrates make up about 35 - 50% of most enteral feeding formulations. 
• Proteins: Protein supplementation in chronic wounds aids collagen synthesis and fibroblast proliferation. In enteral formulations, they are available in intact, hydrolyzed, and amino acid forms. The NPUAP recommends a daily intake of 1.25 to 1.5g per kilogram of body weight for patients with stages 1 and 2 pressure ulcers. Higher quantities, between 1.5 to 2.0g per kilogram of body weight are adequate for stages 3 and 4. Overconsumption of protein should, however, be avoided as it is a risk factor for dehydration in patients that have low fluid intake. 
• Fats: The fat content of enteral formulations consists of medium and long-chain triglycerides. Fats provide energy that may help to meet higher demands of the inflammatory phase of wound healing. The recommended daily caloric intake is unspecified and depends on the severity or stage of the pressure ulcer.

Risks

Some potential complications for enteral feeding in patients with pressure ulcers include:

• Refeeding syndrome in severely malnourished patients
• Food entering into the trachea/lungs
• Diarrhea 
• Tube dislodgement or blockage
• Localized infection at the tube insertion site
• Immobility of the patient, which can further worsen pressure ulcers