Weight Management in Patients on Peritoneal Dialysis

Sharon Stall

Obesity is epidemic in the United States and is associated with increased risk of morbidity and mortality in the general population (Stein & Colditz, 2004). In patients on hemodialysis (HD), there is a reverse epidemiology – that is, patients who are obese seem to have a survival advantage (Kalantar-Zadeh et al., 2005). Most, but not all, studies show this survival benefit does not exist for patients on peritoneal dialysis (PD) (Kalantar-Zadeh et al., 2005; Ikizler, 2005). Although this research places obesity in the dialysis population in a new light, it seems that for the individual patient on PD, obesity may still be considered a health risk that needs to be managed.

The primary cause of weight gain in the patient on PD is the use of dextrose-based solutions for dialysis (Jolly et al., 2001). Unwanted weight gain is a consequence of PD therapy in some patients. This article discusses weight management strategies for persons on PD.

The Peritoneal Dialysis Prescription

In peritoneal dialysis, a hyperosmolar glucose solution is infused into the peritoneal cavity and the peritoneal membrane acts as a dialyzer. Dialysis occurs by diffusion, absorption, and ultrafiltration (UF). These transport mechanisms are helpful in understanding issues with weight gain in the PD population. The amount of calories absorbed in a given dialysis patient will depend upon the glucose concentration used, the dialysate dwell volume, the dwell time, and the membrane characteristics of the patient (see Table 1).

Dextrose is a relatively safe and inexpensive osmotic agent, and as stated earlier it is also a source of calories. Dialysis solutions are available as 1.5%, 2.5% and 4.25% dextrose. In any given patient, the amount of ultrafiltration, that is water removed, may be improved by increasing the tonicity of the solution. A 4.25% solution has a higher osmolarity and is more effective at fluid removal than a 1.5% solution (Sorkin & Blake, 2001). This basic tenet of PD – the greater the glucose load, the greater the UF – is a useful tool in the clinical setting for treating volume overload. However, avoiding the use of hypertonic solutions and preventing situations that require the maximal ultrafiltration effect of hypertonic solutions, is one step in limiting unwanted weight gain in the PD patient (Blake & Diaz-Buxo, 2001). In addition, exposing the peritoneal membrane to high glucose loads over time may damage the membrane and is best to be avoided (Davies, Phillips, Naish, & Russell, 2001).

Icodextran is an alternative to dextrose containing solutions. It uses polyglucose as the osmotic agent, is effective at ultrafiltration, and is particularly useful for the long dwell, where there is the greatest likelihood of glucose absorption. It is a proprietary formula and it is expensive (Blake & Daugirdas, 2001; McCann, 2004). There are important issues in blood sugar monitoring for persons with diabetes who use icodextran (Blake & Diaz-Buxo, 2001).

Peritoneal dialysis fluid is infused into the peritoneal cavity. These fill volumes are typically 2.0-2.5 L, but may be as high 3.0 L, as tolerated by the patient. Larger volumes are increasingly used because they optimize clearance and help achieve adequacy targets. It follows, the larger the volumes, the greater the calories absorbed.
The membrane characteristics of the patients may be determined by the peritoneal equilibration test (PET). A more thorough discussion of this is elsewhere. (Blake & Daugirdas, 2001). High transporters are at greatest risk for weight gain from the infused dextrose solutions because they absorb the glucose and lose the osmotic gradient for effective ultrafiltration (Oreopoulos & Rao, 2001).

There is less dextrose absorption in automated peritoneal dialysis with shorter dwell times than continuous ambulatory peritoneal dialysis with longer dwell times. Hybrid dialysis prescriptions combining short and long dwells are becoming commonplace.

Patient Assessment: From PD Prescription to Nutrition

The nutrition component of a weight management program for patients on PD includes targeting a realistic weight, establishing a calorie level to maintain weight, determining calories absorbed from the dialysate, and reviewing diet and physical activity.

Weight (minus dwell volume) is compared to the Standard Body Weight (SBW) as outlined by the KDOQI Clinical Practice Guidelines for Nutrition in Chronic Renal Failure (National Kidney Foundation [NKF], 2000). This SBW is then used to calculate energy requirements. Recommendations for calorie intake are 35 kcal/kg/ SBW/day for persons younger than 60 years of age and 30 to 35 kcal/kg SBW/day for persons 60 years of age or older (NKF, 2000). This calorie level is thought to maintain optimal nutritional status in maintenance dialysis patients. Adjusted body weight may be used to standardize weight for nutrient calculations (NKF, 2000).

The calories from dialysate are considered as part of the energy intake. Approximately 45%-60% of glucose may be absorbed from dialysis. This may account for 10%-30% of daily calories (Blake & Diaz-Buxo, 2001; Ikizler, 2005; Kalantar-Zadeh et al., 2005). The actual calories absorbed may be measured by subtracting the grams of glucose in the effluent from the grams of glucose that were infused (Blake & Diaz-Buxo, 2001). Formulas that estimate absorption are routinely used in practice to calculate the energy input form the PD prescription (McCann, 2004).

Health care practitioners need to be familiar with body mass index (BMI,) defined as the weight in kilograms divided by height in meters squared to classify overweight and obesity. This index of fatness has become a standard to describe obesity and health risk (Hill, Catenacci, & Wyatt, 2006) (see Table 2). Nomograms and tables for BMI exist for ease of use (National Institute of Health [NIH], 2000). Weight may be compared to the National Health and Nutrition Examination Survey (NHANES) II SBW, other reference tables, the patient’s own weight history and classified by BMI; however, a realistic weight for the patient is determined by the clinical judgment of the team (McCann, 2004). The goal for patients who are overweight and obese is to prevent weight gain and to keep body weight stable (Bray, 2006).

The nutritionist uses various tools of dietary assessment such as a 24-hour food recall and food frequency to determine the patient’s food preferences and eating pattern (NKF, 2000). Diet recommendations are given, not losing sight that malnutrition is a cause of morbidity and mortality in the patient on dialysis, and that patients on PD often experience low albumin. The diet plan must encompass the protein needs of the patient, the nutritional status, and other diet restriction as indicated.

Salt intake should be kept at 2-3 gm/day in most patients despite excellent sodium clearances (McCann, 2004). An increased salt load may lead to volume overload, which may cause the need for ultrafiltration and the use of high concentrated glucose solutions. The importance of sodium modification in the diet cannot be overstated.

It is important to remember that overweight patients are not immune from the lure of diet gimmicks and quick weight loss plans. It is imperative that the nurse and RD work together as a team to make sure the patient understands the causes of weight gain and the importance of a healthy eating plan. In addition, long-term benefits of weight reduction have not been adequately studied in the CKD population (NKF, 2003).

The benefits of physical activity, one of which is an increase in energy expenditure, may be extrapolated from the general population, though few studies exist in patients with CKD (NKF, 2003). Patients who are on dialysis often have physical limitations that affect mobility. In addition, fatigue may contribute to inactivity. The dialysis team may try to accommodate more active patients by adjusting the volume of the infused dialysate or allowing a patient to go “dry” to participate in strenuous exercise such as running or jogging. This adjustment needs to be considered in the overall dialysis prescription while maintaining adequacy standards. The goal is to increase energy expenditure while accommodating the ability of the patient and the constraints of PD.
Hollis, Corden, and Williams (2005) describe a 1-year program in which they were able to demonstrate weight reduction in 7 out of 8 patients on PD. The study used dietary intervention, exercise, and manipulation of dialysis prescription (including use of alternative osmotic agent dialysate) to reduce glucose-based dialysis exposure. This work shows that with a team approach the patient on PD may achieve weight loss, although the long-term benefits of this weight loss were not studied. In addition, weight management programs with weight maintenance as the goal are similar to weight reduction in that physical activity, manipulation of dialysis, and reduced calorie intake (allowing for the calories from peritoneal dialysis) are the cornerstones of treatment.

Summary

In summary, patients on PD, along with their health care providers, can be taught tools to manage weight. These techniques include, but are not limited to, judicious use of dialysis solution to provide adequate dialysis and ultrafiltration with the least exposure to glucose, careful attention to diet including salt and calories consumed, and physical activity.

References
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