Carlos G. Musso

Prevalence and pathogenesis of hypokalemia in patients on chronic peritoneal dialysis: One center's experience and review of the literature

In patients on chronic dialysis, serum potassium (K+) concentration is influenced by factors affecting external and internal potassium balance. The former includes diminished or absent renal excretion, diminished intake and increased fractional excretion of potassium in the feces, while the latter includes reduced K+ uptake by cells because of uremia, acidosis, drugs and alterations of the profile of hormones influencing potassium. Furthermore, mode and frequency of dialysis also affect both internal and external K+ balance [1]. The amount of K+ removed by all dialytic methods is related to the potassium concentration gradient between the dialysate and the blood, and to the passive refilling fluxes of potassium from the intracellular space (ICW) to the extracellular space (ECW) [2]. The determinants of potassium removal by CAPD are the instillation and ultrafiltration volumes, the number of daily exchanges and the average serum potassium [1]. None of the peritoneal dialysis solutions contain potassium and CAPD patients dialyzed with such solutions lose 25–30 mmol of K+ per day [3]. Potassium has not traditionally been added to peritoneal dialysis solution because such solutions do not provide sufficient K+ clearance to result in hypokalemia. Usual K+ losses via dialysis are estimated at between 1.5 mmol/h (at equilibration) and 8 mmol per hour (during rapid cycles) [4]. Even though this amount is relatively small when compared to the normal daily intake (80–90 mmol), still most of these patients have normal serum postassium [3]. While patients on CAPD are in a steady state for serum potassium, they are prone to hypokalemia if dietary intake is decreased or if they develop excessive gastrointestinal losses of potassium [1]. The prevalence of hypokalemia among the CAPD patients has been found to vary from 10% to even 36%, in some studies [3, 5]. This present study was performed to investigate the prevalence and possible mechanism(s) of hypokalemia among the PD patients and to review the literature on the various causes and pathogenetic mechanisms of hypokalemia in these patients.

Improvement in uremic symptoms after increasing daily dialysate volume in patients on chronic peritoneal dialysis with declining renal function.

Objective: Patients on peritoneal dialysis (PD) can develop uremic symptoms as their residual renal function declines. In this retrospective study, we assessed the effect of increasing the dose of dialysis in patients who developed uremic symptoms. Methods: Patients on PD who had an increase in their dialysis dose due to either the appearance of uremic symptoms or to worsening biochemical parameters were included in this study. These patients had to have been on PD for at least 6 months before and after the increase in their dialysis dose. Patients whose dialysis dose was increased after the initial Adequest (done within 2–3 months of starting PD) findings or for reasons other than underdialysis were excluded from this study. The symptoms studied in 104 patients included fatigue, anorexia, insomnia, pruritus and nausea. The presence or absence of theses symptoms was evaluated before and after the increase in the dialysis volume. Several clinical and laboratory data including the adequacy results were compared before and after the increase in dialysis dose. Results: Patients were on PD for 24.6 ± 16 months when dialysis dose was increased. Eighty-five (82%) of them were on continuous ambulatory peritoneal dialysis (CAPD) while the remaining were on continuous cycler peritoneal dialysis (CCPD). Fatigue was the most common symptom that led to an increase in the dialysis dose (64%). The prevalence of all the symptoms studied decreased significantly after the increase in dose of dialysis. The weekly peritoneal creatinine clearance increased from 47.35 ± 0.88 to 57.34 ± 1.40 l (P < 0.0001) and the weekly Kt/V increased from 1.8 ± 0.03 to 2.27 ± 0.05 (P < 0.0001). The daily urine volume and the residual GFR decreased from 318.7 ± 36.4 to 151.9 ± 22.8 ml/day (P < 0.0001) and 2.05 ± 0.2 to 0.82 ± 0.12 ml/min (P < 0.0001) respectively during the study period. Conclusion: The prevalence of all uremic symptoms decreased significantly after the daily dialysate volume was increased. The improvement in symptoms despite the decline in residual function emphasizes the beneficial effect of increased dialysate volume, which produced a significantly higher peritoneal creatinine clearance and Kt/V after the change in the PD prescription.

Renal cell carcinoma in peritoneal dialysis patients

Renal cell carcinoma is a rare but seriouscomplication in ESRD patients. In thesepatients the incidence of renal cell carcinoma(RCC) is 20–40 times higher than in thegeneral population. We performed aretrospective study to measure the incidencerate, prevalence, characteristics and survivalamong our peritoneal dialysis (PD) patientsdiagnosed with renal cell carcinoma.The study was carried out among 607 patientswho were on the PD program from January 1997 toJune 2002. RCC was detected in eight patients(four males and four females) with mean age of52.1 ± 10.6 years. Among these eight patientsfour were new cases that were diagnosed beforethe patients were started on dialysis (three innative kidneys and one in a transplantedkidney). In the other four patients the RCC wasdiagnosed after they had been on dialysis for33–204 months (mean 60.75 ± 50.48). Wefound an incidence rate of 1.3 per 1000patients per year and a prevalence of 1.3%.Six of the eight patients had renal cysts.Tumor size was less than 7 cm in seven patientsand in the other patient it was 8.5 cm. Sevenof eight patients were alive at the time ofstudy with a survival time ranging from 3–138months (mean 122.25 ± 88.2) months. In onepatient, the RCC metastasised to the scalp,and, in two other patients, the tumorssubsequently involved the second kidney. Acardiovascular complication was the cause ofone death. Two patients received a renaltransplant 36 and 66 months after diagnosis.We conclude that despite the low rate ofmetastases and mortality in our study, regularultrasonography should be added to the followup of PD patients. Renal transplantation can beconsidered in these ESRD patients with RCC;however, close follow up for metastases isrecommended.

Age and underdialysis as predictors of sleep disorders in peritoneal dialysis patients.

recently published in your journal. The authors studied the quality of sleep among patients on maintenance hemodialysis as well as among predialysis chronic kidney patients. They assessed quality of sleep using the Kidney Disease Quality of Life (KDQOL) sleep scale, where higher scores represent a better self-assessed quality of sleep. The most important findings of the study can be summarized as follows: sleep disorders were prevalent in 34% of hemodialysis patients and ranged from 14% to 27% in pre-dialysis patients with moderate or advanced renal impairment respectively. KDQOL results directly correlated with age and the difference between sleep disorders among dialysis and pre-dialysis patients was prominent among younger subjects and attenuated among older subjects. In a retrospective analysis published by our team in 2004 in your journal [2] we found a prevalence of some degree of insomnia in 36% of 104 peritoneal dialysis (PD) patients who had some evidence (clinical or laboratory indices) of underdialysis. After increasing dialysis dose (peritoneal Kt/V rose from 1.8–0.1 to 2.27–0.1) the prevalence of insomnia decreased significantly from 36% to 18% (P=0.0002, Mc Nemar’s test). In a reanalysis of our data we found that there was no difference in the age of patients with or without insomnia before the increase in dialysis dose (P=ns, unpaired t-test). On the contrary, 6 months after dialysis dose was increased, the patients with insomnia had a higher mean age than those without sleep problems (61.7–9 vs. 52.2–15, P=0.01). In a logistic regression model which included age, duration on dialysis therapy, serum creatinine and phosphorous (parameters that Kurella et al. [1] reported to correlate with sleep quality) as independent variables, only age was a significant predictor of poor quality of sleep and only after the increase in dialysis dose (P=0.01). Therefore, it can be speculated (with all the drawbacks of retrospective studies and self assessment of quality of sleep) that a sufficient increase in the dose of dialysis could compensate for a degree of renal failure and decrease the prevalence of sleep disorders, at least in PD patients. After the increase in dialysis dose the pattern of sleep disorders seems to resemble that of the general population where older people complain of poorer quality of sleep [3]. Other studies in peritoneal dialysis patients found no correlation of Kt/V and quality of sleep and were not able to detect an effect of age either [4–6]. V. Liakopoulos Æ C. G. Musso Æ D. G. Oreopoulos Division of Nephrology and the Peritoneal Dialysis Program, University Health Network and University of Toronto, Canada