Nutritional Management of Hemodialysis Patients

Introduction

One of the most encountered complications of end-stage kidney disease (ESKD), especially for patients undergoing maintenance hemodialysis (MHD), is the subtle but clinically important progressive deterioration of nutritional status. Advanced chronic kidney disease (CKD) is associated with a unique state of metabolic and nutritional derangements, more aptly called protein-energy wasting (PEW). PEW is closely associated with major adverse clinical outcomes, such as increased rates of hospitalization and death in MHD patients. PEW is complicated and includes a number of clinically relevant aspects that require special attention. These include, but are not limited to, how to appropriately screen and assess nutritional status, implement preventive measures, and prescribe effective interventions.

Screening and Assessment of Nutritional Status in Maintenance Hemodialysis

A clinically meaningful assessment of nutrition and metabolic status should be able to identify and risk-stratify patients with PEW, distinguishing the causes and consequences of both PEW and the underlying disease states, and determine whether there is potential benefit from nutritional or metabolic interventions. Therefore, no single nutritional marker is likely to adequately phenotype this highly complicated comorbid state requiring several concurrent or consecutive measurements ( Table 34.1 ). It is recommended that MHD patients should undergo routine screening tests that are easy to perform, readily available, and inexpensive. Screening parameters should be collected routinely in clinical practice by any health professional and mostly provide a trigger to conduct a more extensive assessment to confirm or establish the diagnosis and determine the best course of treatment if needed. The most commonly used screening tests in MHD patients are serum albumin concentration and assessment of body weight, especially immediately following hemodialysis (i.e., estimated dry weight). Any clinically meaningful change in these metrics is adequate to initiate a more thorough workup. Nutritional assessment generally requires extensive training, provides comprehensive information to make a nutritional diagnosis, aid in intervention and monitoring planning, and should be performed by qualified individuals, preferably dietitians. The most commonly used tests in MHD patients include serum prealbumin concentration, assessment of dietary nutrient intake, anthropometric measures, and subjective global assessment (SGA). These tests should also be used for guiding nutritional therapies once the patient is deemed to be at risk or has overt PEW. A diagnosis of PEW necessitates confirmation by several tools and can be as strict as the requirement of multiple findings as suggested by the International Society of Renal Nutrition and Metabolism (ISRNM) criteria or could be less specific as suggested by others. It is also important that a number of considerations must be made on the unique situation of CKD patients for appropriate screening and assessment of their nutritional status. Some of these include the fluid status of the patient, which could alter body composition and biochemical markers; presence of systemic inflammation that could change serum concentrations of acute-phase proteins; presence and extent of proteinuria, a major determinant of serum albumin concentrations; and the level of residual kidney function, which could influence serum concentration of some biochemical markers such as prealbumin that are cleared by the kidneys. A simplified four-step PEW scoring, including serum creatinine/body surface area (Scr/BSA) and normalized protein nitrogen appearance (nPNA), was also suggested as an easy measure for nutritional assessment. In addition to biochemistry, body composition analysis via preferably by dual-energy x-ray absorptiometry can also be applied to selected patients, especially those whose volume status is unstable.

Epidemiology of Protein-Energy Wasting in Maintenance Hemodialysis Patients

Virtually every study evaluating the nutritional status of MHD patients reports some degree of protein and energy depletion. The clinical relevance of these observations is that practically every nutritional marker used in this patient population has been associated with hospitalization and death risk. Of note, most of the epidemiologic reports on nutrition in MHD patients have been mainly based on serum albumin concentrations, especially studies in large cohorts. Smaller studies using other nutritional markers such as serum prealbumin and SGA also are suggestive of increased risk associated with poor nutritional status in MHD patients. These observations are reproducible irrespective of patient demographics and geographic area. Because of the many different diagnostic tools utilized in separate studies, the prevalence of PEW in this patient population varies widely among different reports, ranging from 20% to 60%. Although there is evidence of improvement in nutritional parameters within 3 to 6 months following initiation of MHD, PEW is still present in up to 40% or more of those patients, and the prevalence seems to increase as the time on dialysis extends. Epidemiologic data also indicate a survival benefit with improvement in these markers over time.

A comprehensive meta-analysis composed of 90 studies from 34 countries reported a heterogeneous global distribution of PEW prevalence in MHD patients ranging from 28% to 54% throughout the world. Crude prevalence in the United States was reported to be as high as 80%, whereas most studies from Europe reported PEW in approximately 50% of patients with CKD. There was a wide range reported in Asia, 18%–>80%, probably due to the methods used to define PEW. Of note, the geographical region was identified as a significant determinant explaining 23% of heterogeneity worldwide.

In addition to mortality, a number of studies show significant associations between nutritional markers and several patient-reported outcomes such as fatigue, physical performance, and frailty. Studies reported that serum albumin levels are negatively correlated with fatigue and lower muscle mass. Low body mass index (BMI) is also associated with muscle loss and sarcopenia in MHD patients. Overall, epidemiological data suggest that inadequate nutrition stores are associated with frailty and decreased quality of life in MHD patients.

Etiology and Prevention of Protein-Energy Wasting in Maintenance Hemodialysis Patients

Multiple factors affect nutritional and metabolic status in patients undergoing MHD that lead to adverse consequences ( Fig. 34.1 ). Accordingly, prevention and treatment of PEW in patients on MHD should involve an integrated approach to reduce protein and energy depletion along with interventions that will avoid further losses and replenish already wasted stores.