Hemodynamic criteria for adequacy of volume regulation and prevention of myocardial impairment in chronic hemodialysis patients

Can Malnutrition be Prevented? Nutrition and Dialysis Adequacy

As chronic renal failure (CRF) worsens, the nutritional balance is disrupt ed at several different levels that are normally responsible for maintaining metabolic homeostasis (1–3). These abnormalities may remain constant, improve, or worsen once dialysis is initiated. The success of dialytic intervention in correcting these abnormalities depends not only on the actual dose of delivered therapy, but also on the availability of nutrient substrate and the ease of modulating body composition.

In the general population body composition has long been used as a predictor for mortality (4). Several different approaches have been taken to identify individuals at risk for a poor outcome (5). These techniques may examine specific serological parameters or actual components of body composition thought to more precisely depict nutritional balance.

Historically, many reports have stressed the link between serum albumin levels and patient survival for both hemodialysis and peritoneal dialysis (6–11). However, some authors have questioned the usefulness of this marker (12–14). Based on these concerns, defining nutritional status through body composition measurements may offer a more meaningful assessment than standard serological parameters. Furthermore, in the setting of uremia the ability to successfully modulate body composition may denote the essence of what aptimal dialysis should signify. Conceptually, optimal dialysis represents the therapeutic return of an individual to nutritional balance, with an expected survival comparable to that of age, gender, and disease-matched nonuremic individuals. Because of the complexity of maintaining nutrient balance, the definition of adequate dialysis should be re-evaluated. Contemporary dialysis practice should extend beyond solely quantitating dialysis to include an understanding of nutrient balance, regulation of food intake, and the application of surveillance tools for identifying abnormalities in body composition. Only through expanding the end points of adequate dialysis can we move closer to optimal dialysis synonymous with long-term treatment survival.

Clinical case-based approach to understanding intradialytic hypotension

The approach to end-stage renal disease (ESRD) patients who develop intradialytic hypotension (IDH) encompasses an understanding of the pathophysiology, appropriate dialysis prescription modification, application of newer pharmacologic therapies, and development of strategies for prevention. Patients should have a "minimal data set" as part of their predialysis assessment. This information is critical to prescription modifications that may help decrease the risk for IDH. Individuals at "high risk" for IDH should be kept to a "safe zone" for dialysis ultrafiltration (</=3% of body weight). Specific maneuvers that may decrease the risk for IDH include adjustment of the dialysate sodium or calcium concentration and dialysate temperature. The first priority for patients developing IDH should be the stabilization of the blood pressure and improvement in the patient's symptomology. Pharmacologic intervention should be considered for patients who require repeat interventions for IDH. "At-risk" patients with a strong cardiac history should undergo an assessment of their cardiovascular status if IDH episodes occur. The use of pharmacologic therapy, ie, midodrine, alone or in combination with prescription modification, can be helpful in decreasing interventions required for IDH. Noncompliance and high interdialytic weight gain in the setting of left ventricular hypertrophy (LVH) and diastolic dysfunction can increase the risk of IDH. Assessment of antihypertensive medications should be performed on a regular basis to determine the correct dosing schedule for patients with hypertension who develop IDH. Coronary flow reserve may be compromised in patients with LVH, adding to the risk for perfusion injury with low blood pressure. Increasing the dialysate calcium concentration may decrease the incidence of arrhythmogenicity in certain patients. Patients with low body temperature may benefit most from cool dialysate. Unit personnel should be aware of the potential link between hypotension and the increased relative risk for death in ESRD patients. Clinical training sessions on IDH risk recognition and appropriate treatment should be implemented within the dialysis unit. Because repeated bouts of IDH can be disruptive to the smooth efficiency of unit operations, attention to prevention as well as acute intervention of IDH is important. Preventive strategies can be developed in each unit to decrease the number of future IDH events. Considering the importance of hypotension in overall patient survival, attention to identifying the percentage of patients in each unit who experience IDH and/or who present with low blood pressure (systolic <110 mm Hg) should be tracked as a quality assurance initiative.

Setting the stage

Intradialytic hypotension (IDH) occurs during 25% to 50% of end-stage renal disease (ESRD) hemodialysis (HD) treatments. The development of IDH signals both technology- and patient-dependent limitations expressed across a broad range of symptoms, from nausea and muscle cramps to ischemic injury. While traditional thinking has emphasized the link between hypertension and cardio-cerebrovascular injury, more recent studies of ESRD patients have stimulated significant interest in hypotension and poor outcomes. Theoretically, hypotension can contribute to the increased relative risk of death in ESRD by several mechanisms, which include acute coronary syndrome, autoregulation dysfunction, ischemia, and arrhythmogenicity. Endothelial abnormalities (increased procoagulation, thrombogenecity risk, and alterations in coronary flow reserve) and altered vascular distribution within the myocardium provide an environment for vascular injury. The current symposia will examine the pathophysiology of IDH, the specific HD prescription modifications to prevent IDH, and newer pharmacologic interventions to treat IDH and will highlight the approach to several clinical cases based on the information presented. It is becoming increasingly important to identify patients at "high risk" for IDH, to customize the HD prescription to the individual patient, to use drug therapy to prevent IDH events, and to track the prevalence of chronic hypotension and the incidence of IDH complications in the dialysis unit.