CKD patients, especially those with diabetes, may be at increased risk for developing non-healing wounds. Wounds of any type (surgical, diabetic foot wounds, access site infections, and so on) may take longer to heal if patients are under nourished or have chronically high blood glucose concentrations. Non-healing wounds can impact patients’ quality of life, physical functioning, and nutritional status.
Tissue regeneration in CKD patients
Wound healing is a complicated process which, depending on the severity of the wound, involves inflammation, proliferation, and remodeling of the injured tissue, according to an online report by Robert H. Demling, MD, in Open Access Journal of Plastic Surgery (2009;9). Wounds trigger an inflammatory response that will vary in duration and severity; however, wounds involving more than one layer of tissue, such as both the epidermis and dermis layers, or chronic non-healing wounds stimulate a stronger response and result in a catabolic state. Repercussions of a catabolic state on nutrient utilization can be extreme, especially in fragile or elderly patients.
In a non-stressed body, carbohydrates and fats are the primary substrates or fuel sources for daily living. If a patient is in a state of starvation, the body will slow down its metabolic processes and continue to use these primary substrates (carbohydrates and fats) to preserve lean body mass and organ tissue. In a stressed or catabolic state, the body shifts substrate utilization to protein.
This is sometimes referred to as a hypermetabolic-catabolic state. When insufficient dietary protein is consumed, lean body mass is broken down into amino acids for glucose production. The pathway used to degrade proteins changes from the usual lysosomal pathway to an ubiquitin pathway. The use of the ubiquitin pathway increases during sepsis, cancer, and trauma (Advanced Nutrition and Human Metabolism 5th ed. 2009).
Optimal protein and energy needed
CKD patients are already at risk for protein-energy wasting (PEW) due to decreased dietary intake, increased inflammation, and metabolic acidosis (Kidney Int. 2008;73:391-398). Thus, when a wound occurs, it is an additional stressor to an already stressed body. Wounds need protein, energy, and micronutrients to heal, and the body will give priority to the wound for the nutrients needed unless a substantial amount of lean body mass loss occurs (e.g. greater than 15%).
According to Dr. Demling’s report, lean body mass losses of 15% will impair wound healing. If the loss is great than 15%, a healing deficit will occur. For these reasons, providing optimal protein and energy to allow for minimal lean body loss and maximal wound healing is necessary.
Providing the optimal amount of protein and energy is a challenge. In CKD patients prior to renal replacement therapy (RRT), dietary protein may be reduced due to either uremic symptoms or dietary restriction. Clinicians will want to carefully balance a high-energy intake for protein sparing with good sources of high biological protein to promote anabolism.
Careful monitoring of the wound, glomerular filtration rate, total weight, and lean body mass in the form of mid-arm muscle measurements or global indices (such as subjective global assessment or the malnutrition inflammation score) will help clinicians assess whether the correct amount of nutrients are being consumed.
Balancing high-protein needs
Patients receiving RRT have high-protein needs without any additional stressors, 1.2 g/kg body weight/day. With the additional stress of wound healing, the protein recommendations may be more, for example, in the range of 1.5-2.0 g/kg body weight/day. As in the pre-RRT setting, sufficient energy needs to be consumed for protein spearing and weight maintenance and outcomes such as total weight, lean body mass, and the wound need to be monitored carefully. If a patient is losing weight or lean body mass, additional nutrition should be provided to preserve lean tissue and promote healing.
In the non-CKD population, glutamine, arginine, and omega-3 fatty acid supplementation have been recommended for their antioxidant and pro-immune properties to assist in wound healing. No data related to supplementation with these nutrients in the CKD population are available, however. Additionally, in the non-CKD population, vitamins and minerals have been suggested for wound healing.
These include vitamins A and C, zinc, copper, and manganese, all of which play a part in collagen formation. Vitamin A supplementation is not recommended for patients with CKD, but a supplement with vitamin C, zinc, copper, and manganese at the level of their daily recommended intake may be beneficial. Overall, the goal is to provide optimal energy, protein, and micronutrients to prevent PEW, and promote wound healing.
Dr. Steiber is Coordinator of the Dietetic Internship/Master’s Degree Program at Case Western Reserve University in Cleveland.