Low Serum Potassium Levels and Clinical Outcomes in Peritoneal Dialysis-International Results from PDOPPS

Introduction

Hypokalemia, including normal range values <4 mEq/l, has been associated with increased peritonitis and mortality in patients with peritoneal dialysis. This study sought to describe international variation in hypokalemia, potential modifiable hypokalemia risk factors, and the covariate-adjusted relationship of hypokalemia with peritonitis and mortality.

Methods

Baseline serum potassium was determined in 7421 patients from 7 countries in the Peritoneal Dialysis Outcomes and Practice Patterns Study (2014-2017). Association of baseline patient and treatment factors with subsequent serum potassium <4 mEq/l was evaluated by logistic regression, whereas baseline serum potassium levels (4-month average and fraction of 4 months having hypokalemia) on clinical outcomes was assessed by Cox regression.

Results

Hypokalemia was more prevalent in Thailand and among black patients in the United States. Characteristics/treatments associated with potassium <4 mEq/l included protein-energy wasting indicators, lower urine volume, lower blood pressure, higher dialysis dose, greater diuretic use, and not being prescribed a renin-angiotensin system inhibitor. Persistent hypokalemia (all 4 months vs. 0 months over the 4-month exposure period) was associated with 80% higher subsequent peritonitis rates (at K <3.5 mEq/l) and 40% higher mortality (at K <4.0 mEq/l) after extensive case mix/potential confounding adjustments. Furthermore, adjusted peritonitis rates were higher if having mean serum K over 4 months <3.5 mEq/l versus 4.0-4.4 mEq/l (hazard ratio, 1.15 [95% confidence interval, 0.96-1.37]), largely because of Gram-positive/culture-negative infections.

Conclusions

Persistent hypokalemia is associated with higher mortality and peritonitis even after extensive adjustment for patient factors. Further studies are needed to elucidate mechanisms of these poorer outcomes and modifiable risk factors for persistent hypokalemia.

Body Composition Analysis Techniques in Adult and Pediatric Patients: How Reliable are They? How Useful are they Clinically?

Complex abnormalities of body composition occur in peritoneal dialysis (PD). These abnormalities reflect changes in hydration, nutrition, and body fat, and they are of major clinical significance. Clinical assessment of these body compartments is insensitive and inaccurate. Frequently, simultaneous changes of hydration, wasting, and body fat content can occur, confounding clinical assessment of each component. Body composition can be described by models of varying complexity that use one or more measurement techniques. “Gold standard” methods provide accurate and precise data, but are not practical for routine clinical use. Dual energy X-ray absorptiometry allows for measurement of regional as well as whole-body composition, which can provide further information of clinical relevance. Simpler techniques such as anthropometry and bioelectrical impedance analysis are suited to routine use in clinic or at the bedside, but may be less accurate. Body composition methodology sometimes makes assumptions regarding relationships between components, particularly in regard to hydration, which may be invalid in pathologic states. Uncritical application of these methods to the PD patient may result in erroneous interpretation of results. Understanding the foundations and limitations of body composition techniques allows for optimal application in clinical practice.

Relationship of Demographic, Dietary, and Clinical Factors to the Hydration Status of Patients on Peritoneal Dialysis

Objectives

To establish which clinical factors are associated with an increased proportion of extracellular fluid (ECF) in peritoneal dialysis (PD) patients.

Design

A single-center, cross-sectional analysis of 68 stable PD patients.

Method

Bioelectrical impedance measurements (RJL, single frequency; RJL Systems, Clinton, Michigan, USA) of resistance and reactance were used to determine the proportion of ECF comprising total body water (TBW) in 68 stable PD patients attending for routine clearance and membrane studies. All patients underwent detailed dietetic, adequacy, and membrane function tests. Blood pressure and antihypertensive requirements were also documented.

Results

Significant gender differences in body composition were observed, such that women had lower absolute TBW and fat-free mass per kilogram body weight, but proportionately more ECF for a given TBW, mean ECF:TBW 0.5 ± 0.03 versus 0.44 ± 0.05, p < 0.005. In view of this, patients were split into two groups, defined as “over-” or “normally” hydrated, either by using the single discriminator (median ECF:TBW = 0.47) for the whole population, which resulted in groups distorted by gender, or by using different discriminators according to gender (women: 0.49, men 0.45). In both analyses, overhydrated patients were older, had significantly lower plasma albumin, less total fluid removal per kilogram body weight, and higher peritoneal solute transport. When split by a single discriminator, the overhydrated patients had lower sodium removal and significantly less intracellular fluid volume due to an excess of women in this group who also had less residual function and had been on dialysis longer. Using gender-specific discrimination, overhydrated patients were heavier due to expansion of the ECF volume: 20 ± 4.1 L versus 16 ± 3.3 L, p < 0.001. Stepwise multivariate analysis found age ( p = 0.001), albumin ( p = 0.009), and fluid losses per kilogram body weight ( p = 0.025) to be independent predictors of gender-adjusted hydration status. Sodium intake did not vary according to hydration status.

Conclusion

Gender influences the assessment of hydration status of PD patients when employing bioimpedance, such that women tend to have more ECF. Taking this into account, age, albumin, and achieved fluid removal appear to be independently associated with hydration status, whereas peritoneal solute transport is not. Advice on dietary sodium should take account of hydration status and achievable losses.

Abnormalities of Body Composition in Peritoneal Dialysis Patients

Objectives

Body composition changes occur in peritoneal dialysis (PD) due to abnormalities in nutrition and hydration. We investigated abnormalities of nutrition and hydration in PD patients compared with healthy controls by measurement of total body potassium (TBK) and body water compartments.

Design

Cross-sectional comparison study.

Methods

We measured TBK — an indicator of body cell mass — by whole body counting, total body water (TBW) by deuterium oxide dilution, and extracellular water (ECW) by bromide dilution in 29 PD patients and 32 controls.

Results

The absolute mean value of TBK for PD patients was not significantly lower than in controls. The ratios of observed TBK to predicted TBK from prediction formulas were compared. Equations used were those of Boddy, Bruce, Burkinshaw, and Ellis and our own equation derived from a local control database (Leeds). Observed/predicted ratios of TBK were significantly less in PD than in control subjects for all equations. Water volumes did not differ between PD and control groups. Observed/predicted ratios for TBK in PD patients correlated with serum potassium (Boddy r = 0.355, p = 0.06; Bruce r = 0.411, p < 0.05; Burkinshaw r = 0.457, p < 0.01; Leeds r = 0.412, p ≤ 0.05; Ellis r = 0.356, p = 0.06) and tended to correlate with serum albumin (Bruce r = 0.343, p = 0.07; Burkinshaw r = 0.421, p < 0.05; Leeds r = 0.357, p = 0.06; Ellis r = 0.310, p = NS). There was no relationship with serum potassium in controls. Serum albumin in PD correlated with TBK ( r = 0.445, p < 0.02), TBK/height ( r = 0.419, p < 0.05), TBK/weight ( r = 0.554, p = 0.002), and TBK/TBW ( r = 0.586, p = 0.0001). Extracellular water/intracellular water (ECW/ICW) was inversely related to TBK ( r = –0.455, p < 0.02 in PD; r = –0.387, p < 0.05 in controls) and to TBK/height ( r = –0.446, p < 0.02 in PD; r = –0.411, p = 0.02 in controls). TBK/weight reduced with age in PD ( r = –0.445, p < 0.02), as did TBK/TBW in PD ( r = –0.463, p < 0.02). ECW/ICW tended to increase with age in PD ( r = 0.351, p = 0.06).

Conclusions

Observed/predicted ratio of TBK is reduced in PD patients relative to healthy controls, indicating reduced body cell mass. Serum albumin and potassium reflect TBK indices in PD. Body water volumes did not differ between PD and controls, implying no overall abnormality in hydration in the PD group. However, ECW is relatively increased compared to ICW with decreasing TBK indices, suggesting relative ECW expansion with reduction in body cell mass.

Evaluation of Nutritional Status in Children during Predialysis, or Treated By Peritoneal Dialysis or Hemodialysis

OBJECTIVE

Malnutrition is one of the major causes of morbidity and mortality in children with chronic kidney disease (CKD). The objective of this study was to evaluate nutritional status of children with stage 3-4 CKD and treated by peritoneal dialysis or hemodialysis using anthropometric measurements, biochemical parameters and bioelectrical impedance analysis.

PATIENTS AND METHODS

The study included a total of 52 patients and 46 healthy children.

RESULTS

In anthropometric evaluation, the children with CKD had lower values for standard deviation score for weight, height, body mass index, skinfold thickness and mid-arm circumference than those of healthy children (p < 0.05). The fat mass (%) and the body cell mass (%) measurements performed by bioelectrical impedance analysis were lower compared with the control group (p < 0.05).

CONCLUSION

It is considered that bioelectrical impedance analysis measurement should be used with anthropometric measurements, which are easy to perform, to achieve more accurate nutritional evaluation in children.

Randomized controlled trial of nutritional counseling on body composition and dietary intake in severe CKD

BACKGROUND

Progressive loss of kidney function results in an increased risk of malnutrition. Despite this, there is little evidence informing the impact of nutrition intervention on predialysis patients with chronic kidney disease (CKD; stages 4 and 5).

STUDY DESIGN

Randomized controlled trial.

SETTING & PARTICIPANTS

56 outpatients (men, 62%; mean age, 70.7 +/- 14.0 [SD] years) with CKD were randomly allocated to intervention (n = 29) or control (n = 27) by using a concealed computer-generated sequence.

INTERVENTION

The intervention group, provided with individualized dietary counseling with regular follow-up aimed at achieving an intake of 0.8 to 1.0 g/kg of protein and greater than 125 kJ/kg of energy, or control, receiving written material only.

OUTCOMES & MEASURES

Change in body composition (body cell mass, measured by means of total-body potassium, in 40 of 56 participants), nutritional status (Subjective Global Assessment), and energy and protein intake (3-day food record).

RESULTS

During the 12 weeks, the intervention group had 3.5% (95% confidence interval, -2.1 to 9.1) less decrease in body cell mass, 17.7-kJ/kg/d (95% confidence interval, 8.2 to 27.2) greater increase in energy intake, greater improvement in Subjective Global Assessment (P < 0.01), and no significant difference in protein intake compared with the control group (-0.04 g/kg/d; 95% confidence interval, -0.73 to 0.16). The intervention was associated with greater increases in energy and protein intake in women than men (interaction P < 0.001 for both).

LIMITATIONS

Power to detect change in body cell mass, potential bias in ascertainment of Subjective Global Assessment.

CONCLUSIONS

In predialysis patients with CKD, structured nutrition intervention had a greater effect on energy and protein intake in women than men. Additional investigations are warranted to determine the impact on body composition.

Accuracy of eight-polar bioelectrical impedance analysis for the assessment of total and appendicular body composition in peritoneal dialysis patients

OBJECTIVE

To establish the accuracy of bioelectrical impedance analysis (BIA) for the assessment of total and appendicular body composition in peritoneal dialysis (PD) patients.

DESIGN

Cross-sectional study.

SETTING

University Nephrology Clinic.

SUBJECTS

In all, 20 PD patients and 77 healthy controls matched for gender, age and body mass index.

METHODS

Whole-body fat-free mass (FFM) and appendicular lean tissue mass (LTM) were measured by dual-energy X-ray absorptiometry. Resistance (R) of arms, trunk and legs was measured by eight-polar BIA at frequencies of 5, 50, 250 and 500 kHz. Whole-body resistance was calculated as the sum of R of arms, trunk and legs. The resistance index (RI) was calculated as the ratio between squared height and whole-body or segmental R.

RESULTS

RI at 500 kHz was the best predictor of FFM, LTM(arm) and LTM(leg) in both PD patients and controls. Equations developed on controls overestimated FFM and LTM(arm) and underestimated LTM(leg) when applied to PD patients. Specific equations were thus developed for PD patients. Using these equations, the percent root mean-squared errors of the estimate for PD patients vs controls were 5 vs 6% for FFM, 8 vs 8% for LTM(arm) and 7 vs 8% for LTM(leg).

CONCLUSION

Eight-polar BIA offers accurate estimates of total and appendicular body composition in PD patients, provided that population-specific equations are used.