The following sections have been prepared to ensure that the state of the art and science related to CVD includes novel concepts, therapeutic strategies, and emerging areas of pathophysiological and practical importance to the care of dialysis patients.
The reader will notice that the format of this section is different, reflecting its different perspective: namely, the relative lack of evidence on which to base plausible guideline statements. The evidence that does exist, and is cited in this section, is either completely in nondialysis populations, or is purely associative information, with no intervention in any population yet tested. Thus, it would be a problem to include guideline statements or recommendations.
Nonetheless, this section describes the current status of knowledge with respect to risk factors and biomarkers, and represents an overview of key areas for future clinical trials. The reader is encouraged to review this section, and examine his or her current understanding and practice within the context of these highlights.
The literature review has been conducted using the same systematic strategy as for the previous guidelines in this document. The reviews presented here have been thoughtfully constructed so that clinicians can adopt different practices based on them. However, for reasons cited above, the ability to truly recommend or suggest changes in practice would be premature at this time.
The Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults were published in 1998 to address the increasing problem of overweight and obesity in the United States498. This document reports strong evidence that overweight and obesity increases morbidity from hypertension, dyslipidemia, type 2 diabetes, CHD, stroke, gall bladder disease, osteoarthritis, sleep apnea and respiratory problems, and endometrial, breast, prostate and colon cancers. Overweight and obesity also increase all-cause mortality.
There is strong evidence that weight loss in overweight and obese individuals reduces risk factors for diabetes and CVD. Weight loss has been associated with reductions in blood pressure, reductions in triglycerides, total cholesterol and LDL cholesterol, increases in HDL cholesterol, reductions in blood glucose in overweight and obese persons without diabetes, and reductions in blood glucose and HbA1c in some patients with type 2 diabetes. No prospective trials exist to show that weight loss changes mortality.
In the NIH Guidelines, the definition of overweight is a body mass index (BMI) of 25–29.9 Kg/m2 and obesity as a BMI of >30 Kg/m2. The panel also suggested that waist circumference should be used as a marker of abdominal fat, with measurements of >102 cm in men and >88 cm in women indicating high risk. These measurements are not direct measures of body composition (i.e., fat mass and lean body mass), which are more accurately measured using total body water, total body potassium, bioelectrical impedance, dual energy X-ray absorptiometry (DEXA) (see the chapter on Malnutrition in this document), MRI, and computed tomography. In epidemiological studies, BMI is the favored measure of excess weight to estimate relative risk of disease, since it is a simple, rapid and inexpensive measure that can be applied generally to adults. Likewise, CT and MRI are more accurate measures of abdominal fat, but impractical for clinical use; thus, the recommendation for measurement of waist circumference.
In contrast to the general population, higher BMI is associated with better outcomes in dialysis patients, even when overall health status is considered. The preponderance of associative evidence suggests this BMI paradox in dialysis patients confers a survival advantage.499–502
However, BMI may be an inappropriate measure of body composition in patients with renal failure, since it is complicated by excess fluid weight and muscle wasting, and may be related to malnutrition. A recent study measured lean body mass and thus was able to evaluate the association of body composition (i.e., muscle mass as indicated by 24-hour urinary creatinine excretion) in addition to BMI, and cardiovascular and overall outcomes.503 This study showed that, as in other studies, patients with high BMI (>27 Kg/m2) had lower all-cause and cardiovascular death rates than those with normal BMI. However, the survival advantage of a high BMI was only confined to those with low body fat; even in the low BMI group, high body fat and low muscle mass were associated with increased risk of death.
Thus, in terms of body composition, it appears that maintenance of muscle mass and lowering of body fat are important in reducing cardiovascular risk. Evidence suggests that exercise training (aerobic exercise and resistance training) increases muscle mass, as does nandrolone decanoate in dialysis patients.504 There are no randomized clinical trials to determine the effects of either of these interventions, or caloric restriction to lower body fat, on cardiovascular or all-cause mortality in dialysis patients.
The following considerations are based on the NIH Clinical Practice Guidelines.498 Clearly special attention related to nutritional status is necessary for patients with renal failure. The BMI data that have established the theory of the “BMI paradox” in dialysis patients have resulted in few, if any, interventions for weight management in dialysis patients. Certainly, no randomized clinical trials have been conducted to test standardized approaches to weight management in dialysis patients. Likewise, the confounding factors of nutritional deficiency and those of determining lean body mass, fat mass, and fluid weight complicate goal setting and monitoring of any programs. Nonetheless, reduction in fat mass and maintenance of muscle mass may be important in dialysis patients.
Weight loss
While the recommended weight loss goal for the general population is to reduce body weight by approximately 10% from baseline, the safety and efficacy of weight loss in the overweight dialysis patient is unknown, as is the potential benefit to CVD outcomes. Therefore, weight loss in the dialysis patient should be approached with close monitoring by a registered dietitian and physician. Further weight loss can be attempted, if indicated, through further assessment to ensure fat loss and not muscle loss. Until weight loss studies are completed in dialysis patients, rates of weight loss should be individually determined.
Dietary therapy
For the general population, lowering caloric intake and increasing exercise are recommended for weight loss in overweight and obese persons. Reducing fat as part of a low-calorie diet is a practical way to reduce calories. Weight loss for the dialysis patient requires an individualized meal plan that is determined by a registered dietitian working with the patient. Such a diet plan would need to meet the nutritional recommendations for dialysis patients in regards to micro- and macro-nutrients (see the NKF-KDOQI Nutrition Guidelines169) while decreasing total calories appropriately. Monitoring of laboratory values and food intake during a weight loss diet is critical due to the paucity of information regarding weight loss in dialysis patients. It is important to avoid the popular diets that could induce adverse metabolic complications. Examples include high protein types, food-combining diets, and diets that encourage unusually large portion sizes of fruits and vegetables.
Physical activity
Exercise is recommended as part of a comprehensive weight loss therapy and weight control program because it 1) modestly contributes to weight loss in overweight and obese adults; 2) may decrease abdominal fat; 3) increases cardiorespiratory fitness; and 4) may help with maintenance of weight loss. Physical activity should be an integral part of weight-loss therapy and weight maintenance, and should be undertaken in combination with behavioral therapy that assesses the patient’s motivation levels and other factors that contribute to the success of an exercise program. For additional information, see Guideline 12.
Special treatment groups
Smokers
All smokers, regardless of their weight status, are likely to benefit from smoking cessation while minimizing weight gain. If weight gain does occur, it may be treated through dietary therapy, physical activity, and behavioral therapy, maintaining the primary emphasis on the importance of abstinence from smoking.
Older adults
A clinical decision to forego obesity treatment in older adults should be guided by an evaluation of the potential benefits of weight reduction for day-to-day functioning and reduction of the risk of future cardiovascular events, as well as the patient’s motivation for weight reduction. Care must be taken to ensure that any weight reduction program minimizes the likelihood of adverse effects on bone health or other aspects of nutritional status.
Strong evidence in the general population has shown that overweight and obesity are associated with increasing risks of a variety of cardiovascular complications, and with higher all-cause mortality. However, no studies have examined standardized approaches to weight management in dialysis patients. Overweight or obese patients are likely to benefit from weight reduction, but plans will need to be carefully individualized and monitored for each patient.