Routine Monitoring of Sodium and Phosphorus Removal in Peritoneal Dialysis (PD) Patients Treated with Continuous Ambulatory PD (CAPD), Automated PD (APD) or Combined CAPD+APD.

BACKGROUND: Adequate removal of sodium (Na) and phosphorus (P) is of paramount importance for patients with dialysis-dependent kidney disease can easily quantified in peritoneal dialysis (PD) patients. Some studies suggest that automated PD (APD) results in lower Na and P removal. METHODS: In this study we retrospectively analysed our data on Na and P removal in PD patients after implementation of a routine monitoring in 2011. Patients were stratified in those treated with continuous ambulatory PD (CAPD, n=24), automated PD (APD, n=23) and APD with one bag change (CAPD+APD, n=10). Until 2015 we collected time-varying data on Na and P removal from each patient (median 5 [interquartile range 4-8] values). RESULTS: Peritoneal Na and P removal (mmol per 24h ± standard deviation) was 102 ± 48 and 8 ± 2 in the CAPD, 90 ± 46 and 9 ± 3 in the APD and 126 ± 39 and 13 ± 2 in the CAPD+APD group (ANOVA P=0.141 and <0.001). Taking renal excretion into account total Na and P removal (mmol per 24h) was 221 ± 65 and 16 ± 5 in the CAPD, 189 ± 58 and 17 ± 6 in the APD and 183 ± 38 and 16 ± 6 in the CAPD+APD group (P=0.107 and 0.764). Over time, peritoneal removal of Na but not that of P increased in all groups. In patients with modifications of PD treatment, Na but not P removal was significantly increased over-time. CONCLUSIONS: Overall Na and P removal were similar with different PD modalities. Individualized adjustments of PD prescription including icodextrin use or higher glucose concentration can improve Na removal while P removal is mainly determined by the dialysate volume.

The use of a tablet computer platform to optimize the care of patients receiving peritoneal dialysis: a pilot study.

BACKGROUND: Peritoneal dialysis (PD) affords patients increased independence and improved quality of life. However, the lack of more frequent monitoring may compromise outcomes and decrease wider uptake of this modality. This study uses a novel tablet computer-based interface to allow real-time monitoring and two-way communication to better link PD patients with a dialysis center and care providers. METHODS: A tablet computer with an application that allows enhanced monitoring of all aspects of PD was given to patients to assess their usage in a pilot trial. The interface allows patients to review sterility techniques, enter vital signs and exchange data, upload media such as photos and video clips, synchronize data to be viewed by medical staff, and allow real-time adjustments to the PD prescription. Satisfaction with the interface and comments for enhancement were analyzed using a simple self-administered questionnaire. RESULTS: Six continuous ambulatory PD patients were enrolled in this pilot study. A total number of 1,172 exchanges were recorded over a period of 251 days. Compliance with the applications ranged from 51 to 92%. No major adverse events were recorded. The overall impression of the interface was 5.2 out of 10. The major criticism was that the application needs to be adjusted depending upon the experience level of the patient and that data entry needs to be simplified and automated. CONCLUSION: A tablet computer platform is a feasible concept for continuous ambulatory PD. The major components include flexibility, advanced infrastructure, two-way communication, and real-time interaction. This may encourage more patients to take up PD as their preferred modality of therapy for end-stage renal disease. Modifications to enhance use will be incorporated in subsequent versions.

A reference equation for objectively adjusting dwell volume to obtain more ultrafiltration in daily practice of peritoneal dialysis.

OBJECTIVES: Few studies mention how to objectively adjust peritoneal dialysis (PD) dwell volume for adult continuous ambulatory peritoneal dialysis (CAPD) patients. We proposed a reference equation composed of parameters from the peritoneal equilibrium test (PET) for adjusting daily dialysate dwell volume to obtain more ultrafiltration volume. Better fluid control could reduce more fluid overload-related complications. DESIGN: We used body mass index, waist circumference, intraperitoneal pressure, and other parameters from peritoneal equilibrium test to compose a reference equation for fine-tuning daily dwell volume. PATIENTS AND SETTING: Eighty-eight PD patients in one center with laboratory data collected during half-yearly PET evaluations were enrolled. Instilled dialysate was composed of 2.57% glucose PD fluid, either 1500 ml or 2000 ml in volume. In addition to other demographic data, intraperitoneal pressure (IPP) was also measured twice in the supine position four hours apart. We applied statistical multivariate techniques of discrimination analysis and logistic regression to verify the most feasible and optimal formula to determine infill volumes for patients. RESULTS: We determined a novel formula for calculating daily dialysate dwell volume, Z: Z = (0.523 x waist circumference) + (0.852 x body mass index), derived from rotating axes to obtain an accurate prediction rate of 80.68% using the multivariate approach. CONCLUSION: The novel formula used objective, real-time parameters for determining appropriate dwell volumes for PD patients to optimize maximal ultrafiltration volumes and reduce subjective abdominal discomfort. The novel formula makes frequent adjustment of daily dwell volume by physicians or patients easy to calculate.

Kidney Disease-Specific Scores and Health Utility of Continuous Ambulatory Peritoneal Dialysis and Automated Peritoneal Dialysis Patients and Their Caregivers.

OBJECTIVES: This study aimed to compare the EuroQol 5-dimension 5-level questionnaire (EQ-5D-5L), the visual analogue scale (VAS), and the Kidney Disease Quality of Life 36-Item Short-Form Survey (KDQOL-36) scores of Thai continuous ambulatory peritoneal dialysis (CAPD) and automated peritoneal dialysis (APD) patients and to compare the utility scores with the EQ-5D-5L and VAS scores of caregivers. METHODS: This was a cross-sectional study completed between April 2016 and May 2017. In total, 34 CAPD patients, 30 APD patients, and their caregivers were recruited from a large university hospital in Thailand. A trained interviewer conducted face-to-face interviews. We collected demographic data and used the KDQOL-36 and EuroQol questionnaires (EQ-5D-5L and VAS) to assess the health-related quality of life. Caregivers were asked to assess their own health status using the EQ-5D-5L and VAS. RESULTS: The EQ-5D-5L and VAS responses of the CAPD and APD patients and their caregivers were not significantly different (P > .05). More than 50% of both patient groups had mobility problems, whereas most patients had no problems with self-care, doing usual activities, pain or discomfort, and anxiety or depression. As for the KDQOL-36, the physical and mental component summaries were not significantly different, and neither were the scores for all of the kidney disease-specific dimensions, including symptoms or problems, effects of kidney disease, and burden of kidney disease (all were P > .05). CONCLUSIONS: The results indicated that the quality of life of CAPD and APD patients and their caregivers were mostly equivalent. A further longitudinal study of utility score assessments of the differences in modality would be advantageous.

Learning about the practice of peritoneal dialysis.

Observational studies are valuable and provocative. We are learning about how we practice peritoneal dialysis (PD) and how we might improve on that practice. For example, outcomes of PD therapy are not worse in large patients. Perhaps this will encourage physicians and patients to utilize PD in large patients. In addition, better descriptions of how we practice will help to identify systematic barriers to the advancement of home dialysis.

The status of, and obstacles to, continuous ambulatory peritoneal dialysis in Thailand.

The prevalence of dialysis in Thailand is 282 per million population, and utilization of peritoneal dialysis (PD) is only 4.6% of the utilization of hemodialysis (HD). The causes of low PD utilization include a relatively higher cost of PD care, especially from the patient's perspective; less incentive for PD care on the part of health care providers and hospitals; fewer continuing medical and nursing education programs in PD; unavailability of certified PD nurses; lack of confidence in the quality of PD care; fewer offers of PD as a renal replacement therapy option during pre-dialysis counseling; fear of peritonitis on the part of the patient, and also fear of burdening family members; a less stringent government policy regarding the "PD first" strategy. To increase PD utilization. mandatory strategies are lower PD cost, make all PD equipment reimbursable, launch a stringent "PD first" policy, provide incentives to health care providers and hospitals, and improve the quality of PD care.

Impact of Volume Management on Volume Overload and Rehospitalization in CAPD Patients.

Heart failure due to volume overload is a major reason for rehospitalization in continuous ambulatory peritoneal dialysis patients. Strict volume control provides better cardiac functions and blood pressure in this population. Volume management, which is a volume control strategy, may decrease volume overload and related complications. Using a quasi-experimental design, 66 continuous ambulatory peritoneal dialysis patients were randomly assigned to the intervention group ( n = 34) and control group ( n = 32). The patients were followed up for 6 months with scheduled clinic and/or telephone visits; the intervention group adopted volume management strategy, while the control group adopted conventional care. Volume overload and cardiac function were compared between the two groups at the baseline and at 6 months. At Month 6, the intervention group resulted in significant improvement in volume overloaded status, cardiac function, and volume-overload-related rehospitalization. Volume management strategy allows for better control of volume overload and is associated with fewer volume-related readmissions.

Improving outcome of CAPD: twenty-five years' experience in a single Korean center.

BACKGROUND: Continuous ambulatory peritoneal dialysis (CAPD) is an established treatment for end-stage renal disease (ESRD). We investigated the outcome of CAPD over a period of 25 years at our institution. METHODS: CAPD has been performed in 2301 patients in 25 years. After excluding patients with less than 3 months of follow-up and missing data, we evaluated 1656 patients who started peritoneal dialysis between November 1981 and December 2005. Data for sex, age, primary disease, comorbidities, follow-up duration, cause of death, and cause of technique failure were collected. We also examined data for urea kinetic modeling (UKM), beginning in 1990, and peritonitis episodes, including causative organisms, starting in 1992. RESULTS: Compared to incident patients from 1981-1992, mean age and incidence of ESRD caused by diabetic nephropathy increased in patients from 1993 to 2005. Technique survival after 5 and 10 years was 71.9% and 48.1% respectively. Technique survival was significantly higher in patients who started CAPD after 1992 than in those who started before 1992. Peritonitis was the main reason for technique failure. Overall peritonitis rate was 0.38 episodes per patient-year, with a significant downward trend to 0.29 per patient-year over 10 years, corresponding to a decrease in gram-positive peritonitis. Patient survival after 5 and 10 years was 69.8% and 51.8% respectively. Patient survival improved significantly during 1992-2005 compared to 1981-1992 after adjustment for age, gender, diabetes, and cardiovascular comorbidities [hazard ratio (HR) 0.68, p < 0.01]. Subgroup analysis based on UKM revealed that dialysis adequacy did not affect patient survival. However, diabetes (HR 2.78, p < 0.001), older age (per 1 year: HR 1.06; p < 0.001), serum albumin level (per 1 g/dL: increase, HR 0.52; p < 0.05), and cardiovascular comorbidities (HR 2.32, p < 0.01) were identified as significant risk factors. CONCLUSION: Technique survival has improved due partly to a decrease in peritonitis, which was attributed to a decrease in gram-positive peritonitis. Patient survival has also improved considering increases in aged patients and ESRD caused by diabetes. The mortality rate of CAPD is still high in older, diabetic, malnourished, and cardiovascular diseased patients. A more careful management of higher risk groups will be needed to improve the outcome of CAPD patients in the future.

Dialysis adequacy indices for peritoneal dialysis and hemodialysis.

Dialysis adequacy indices that may be used to evaluate the efficiency of small-solute removal include Kt/V, fractional solute removal (FSR), and equivalent urea clearance (EKR). To analyze possible relationships between those indices, we used the two-compartment variable-volume urea kinetic model to simulate several dialysis modalities: hemodialysis (HD) performed three times or six times weekly, automatic nightly peritoneal dialysis (PD), and continuous ambulatory PD. Instead of targeting a chosen Kt/V value, we selected a weekly FSR of 1.81 as the target adequacy index. We determined hemodialyzer clearances and diffusive mass transport parameters for the peritoneal membrane that yielded the desired value of FSR for a typical patient and dialysis schedule. By theoretic analysis, EKR and FSR are proportional: EKR/FSR = V/Tc, where V = urea distribution volume in the body and Tc = time of the dialysis cycle, usually 1 week. Thus, FSR and EKR have the same meaning and scaling in PD and HD, and may be equivalently applied for assessment of dialysis efficacy.

Adequacy of peritoneal dialysis: Kt/V revisited.

OBJECTIVE: Kt/V urea has been used to assess adequacy of peritoneal dialysis. However, Kt/V urea only reflects the clearance of solute without taking into consideration the effects of dietary protein intake (DPI). The objective of this study is to evaluate the value of Kt/V based on nitrogen balance and to observe if it is the best adequacy index. METHODS: On the premise that nitrogen balance is obtained, we calculated the minimal adequate dialysate volume and dialysis index (DI), Kt/V and solute removal index (SRI). We compared the values of DI, Kt/V and SRI to evaluate the adequacy of peritoneal dialysis. RESULTS: Kt/V was changed with DPI and body weight of continuous ambulatory peritoneal dialysis (CAPD) patients. We cannot define adequate dialysis with a single value while DPI and body weight are different since CAPD, SRI and Kt/V are numerically equal. However, dialysis index (DI) can reflect the minimal adequate dialysate volume when DPI and body weight are different and, thus, reflects the adequacy of dialysis. CONCLUSIONS: DI reflects the balance between DPI and solute clearance; thus, it is more useful to evaluate dialysis adequacy than Kt/V and SRI in clinically stable peritoneal dialysis patients.

Developing a health-related quality-of-life measure for end-stage renal disease: The CHOICE Health Experience Questionnaire.

The Choices for Healthy Outcomes in Caring for End-Stage Renal Disease ([ESRD] CHOICE) Study was designed to evaluate the effectiveness of alternative dialysis prescriptions. As part of CHOICE, we developed an instrument for measuring health-related quality of life (HRQOL) for patients with ESRD that would complement the Medical Outcomes Study 36-Item Short-Form Survey (SF-36) and be sensitive to differences in dialysis modality (hemodialysis [HD] and peritoneal dialysis [PD]) and dialysis dose. The selection of HRQOL domains to be included was based on: (1) a structured literature review of 47 articles describing 53 different instruments; (2) content analysis of five focus groups with HD and PD patients, nephrologists, and other providers; (3) a survey of 110 dialysis providers about features of different modalities that affect patient HRQOL; and (4) a semistructured survey of 25 patients with ESRD on the effects of dialysis on functioning and HRQOL. To help prioritize domains and items identified by these methods, a representative sample of 136 dialysis patients rated each item for frequency and bother. A panel of nephrologists provided advice about the salience of items to modality or dose. Items and scales were selected with a preference for existing measures tested in patients with ESRD and were tested for reliability and validity. The first four steps yielded 22 HRQOL domains that included 96 items: 8 generic domains in the SF-36 (health perceptions, physical, social, physical and emotional role function, pain, mental health, and energy); 8 additional generic domains (cognitive functioning, sexual functioning, sleep, work, recreation, travel, finances, and general quality of life); and 6 ESRD-specific domains (diet, freedom, time, body image, dialysis access [catheters and/or vascular], and symptoms). New items were developed or adapted to assess ESRD-specific domains. Scales for these items showed adequate internal consistency (Cronbach's alpha > 0.70, except for time [alpha = 0.57] and quality of life [alpha = 0.68]), as well as convergent and discriminant construct validity in a sample of 928 patients. The final questionnaire included 21 domains (time was deleted) and 83 items. We have designed a patient-centered instrument, the CHOICE Health Experience Questionnaire, that addresses domains that may be sensitive to differences in dialysis modality and dose and shows evidence for reliability and validity as a measure of HRQOL in ESRD.

Timely initiation of dialysis: a urea kinetic approach.

The traditional approach of initiating dialysis when the patient begins to manifest uremic symptoms may result in the development of significant malnutrition with detrimental effects on subsequent morbidity and mortality. The recently issued Dialysis Outcome Quality Initiative guidelines suggest that dialysis be initiated when the Kt/V from residual renal function decreases to less than 2.0. We have used the urea kinetic model to show how dialytic dose can be titrated to compensate for declining renal function while maintaining a constant total dose of delivered therapy (Kt/V = 2.0). For hemodialysis (HD), we show that initiating dialysis with once-weekly therapy may be a viable option only for a few months, being replaced by twice-weekly and subsequently with the more typical regimen of thrice-weekly HD. We recommend that the patient be directly initiated with twice-weekly HD to minimize wide swings in the serum concentrations of small-molecular-weight solutes. With continuous ambulatory peritoneal dialysis (CAPD), a hypothetical average-sized patient with high-average transport can be maintained for approximately 8 months with a single 2.5-L nocturnal exchange and from 8 to 17 months with two nocturnal exchanges of 2.5 L each. The use of nocturnal exchanges allows more normal daytime activities and is less intrusive on patient lifestyle. We have shown that both HD and CAPD regimens can be successfully adjusted to achieve a constant total Kt/V of 2.0 for 5 or more years, although CAPD may provide a smoother transition from no dialysis to a complete 10-L regimen.

Review of combination of peritoneal dialysis and hemodialysis as a modality of treatment for end-stage renal disease.

Because the contribution of residual renal function (RRF) to total solute clearance is often significant in continuous ambulatory peritoneal dialysis (CAPD), loss of RRF over time can lead to inadequate dialysis if appropriate prescription management strategies are not pursued. Additionally, declines in ultrafiltration caused by increases in peritoneal permeability may limit continuation of CAPD therapy. Peritoneal dialysis and hemodialysis (PD + HD) combination therapy (complementary dialysis therapy) is an alternative method. This therapy allows the patient to maintain daily activities, as with CAPD, while undergoing once-a-week HD supplements for the insufficient removal of solutes and water. This therapy allows for the continuation of PD without shifting to total HD in PD patients who continue to have uremic symptoms even after individualization of the PD prescription. This treatment option is psychologically more acceptable to patients and may be expected to provide such accompanying beneficial effects as peritoneal resting, improvement of QOL and reduction in medical cost.

Clinical validation of PD Adequest software: modeling error assessment.

OBJECTIVE: PD ADEQUEST software (Baxter Healthcare, Deerfield, IL, U.S.A.) is used in peritoneal dialysis for calculating the indices of dialysis efficiency and for the mathematical simulation of the results of various dialysis regimens. The aim of our study was to quantify the modeling errors and find the methods which give best results. DESIGN: Nonrandomized, repeated measurement, clinical validation study. PATIENTS: The study included 78 patients on continuous ambulatory peritoneal dialysis (PD), daytime ambulatory PD, and automated PD. MEASUREMENTS: We used 207 collections of dialysate and urine associated with peritoneal equilibration tests (PETs) performed with different glucose concentrations (1.36%, 2.27%, 3.86%). The measured urea Kt/V, creatinine clearance (CRCL) and ultrafiltration (UF) were compared with the same data simulated mathematically using the PD ADEQUEST software version 1.4. RESULTS: The Kt/V, CRCL, and UF measured values were significantly correlated and in agreement with modeled data [concordance correlation (rc) was 0.849, 0.839, 0.625 respectively]. The errors (modeled - measured) were: Kt/V = -0.04 +/- 0.27 (p = ns), CRCL = 2.1 +/- 7.7 L (p < 0.001), UF = -121 +/- 711 mL (p = 0.016). Applying ANOVA to both the peritoneal transport data calculated by PD ADEQUEST (mass transfer area coefficient of the solutes, fluid reabsorption, and hydraulic permeability) and the modeling errors, significant differences were found in relation to the PET glucose concentrations. CONCLUSION: PD ADEQUEST proves to be a useful instrument in peritoneal dialysis, although there is undoubtedly still room for improvement in its prediction efficacy, which is influenced by the glucose concentration used in the PET.

The use of the PD Adequest mathematical model in pediatric patients on chronic peritoneal dialysis.

OBJECTIVE: To test the accuracy of the PD ADEQUEST kinetic model in calculating peritoneal transport parameters and to quantify the differences between the results of software simulations and direct measurements in order to assess the reliability of this tool in chronic peritoneal dialysis (PD) pediatric patients. PATIENTS: Twenty-nine patients (mean age: 10 +/- 4 years; range: 4-17), 5 on continuous ambulatory PD, 4 on continuous cycling PD, 19 on nocturnal intermittent PD and 1 in nocturnal tidal PD, all free from peritonitis in the previous 2 months. Fourteen patients were anuric and 15 had a mean glomerular filtration rate of 1.79 +/- 1.23 mL/min, range 0.25-4.82. METHODS: In all patients, 24-hour dialysate and urine collections associated to standard peritoneal equilibration test (PET) were performed using their usual dialytic regimen and fill volume (1023 +/- 159 mL/m2 BSA, range 614-1361). PD ADEQUEST kinetic parameters were compared with pediatric and adult data from literature. The measured weekly normalized total creatinine clearance (CRCL), weekly total Kt/V, and daily net ultrafiltration (UF) were compared with corresponding mathematically modeled values. RESULTS: Kinetic parameters calculated by the PD ADEQUEST program were comparable to adult and pediatric values from previous studies after normalization for BSA. Measured and modeled CRCL and Kt/V showed a good agreement [concordance correlation (rc) 0.937 and 0.768, respectively] with limited median percentage absolute errors (11.6% and 10.2%, respectively). Ultrafiltration showed less favorable results (rc = 0.600 and median percentage absolute error 45%) probably owing to the wide variability of this parameter. When the analysis was restricted to the peritoneal component, the rc coefficients results were 0.745 for CRCL and 0.512 for Kt/V (median absolute error: 11.6% and 15.2%, respectively). CONCLUSIONS: The overall findings of our study show that the PD ADEQUEST kinetic model can be used in pediatric patients for the calculation of kinetic indexes and for mathematical simulation of the various regimens. We also feel that the results yielded by the PD ADEQUEST program are reliable enough for this computerized mathematical model to be used in the prescription management of pediatric patients. Only UF prediction needs to be used with a certain caution on account of the marked variability of this parameter.

Patient and technique survival on CAPD in Turkey.

OBJECTIVE: To analyze the status of continuous ambulatory peritoneal dialysis (CAPD) in 12 centers in Turkey. DESIGN: Retrospective study of CAPD technique and patient outcome. SETTING: University hospital renal units. PATIENTS: 334 patients [205 males (61%),129 (39%) females; mean age 42.2 +/- 13.8 years; mean follow-up time 23.5 +/- 18.3 months] beginning CAPD between March 1992 and December 1999, and having a minimum follow-up of 3 months. OUTCOME MEASURE: Patient survival, technique survival, and duration of hospitalization. RESULTS: Mean weekly Kt/V urea was 1.9 +/- 0.8, weekly creatinine clearance was 62.9 +/- 8.5 L/1.73 m2, and mean serum albumin level was 3.7 +/- 0.6 g/dL. 93 patients (28%) were withdrawn from peritoneal dialysis due to death (12.6%), transplantation (3.9%), transfer to hemodialysis (8.7%), patient failure to adapt (1.5%), and other reasons (1.2%). The major causes of death were cardiovascular disease (60%), infection (19%), malignancy (2%), and others (19%). Cox proportional hazard model analysis indicated age, serum albumin levels, comorbidity, and functional status affected survival and hospitalization (p < 0.05), whereas gender and Kt/V did not (p > 0.05). Estimation of patient survival by Kaplan-Meier analysis showed 94.2%, 88.6%, 84.5%, and 68.9% at 1, 2, 3, and 5 years respectively. Technique survival estimate by Kaplan-Meier analysis was 96.6%, 91.1%, 90.4%, and 77.4% at 1, 2, 3, and 5 years respectively. CONCLUSION: Peritoneal dialysis is an acceptable method of renal replacement therapy in Turkey. There is controversy regarding the usefulness of Kt/V in predicting mortality and morbidity.

Taking peritoneal dialysis beyond the year 2000.

Over the past 25 years, peritoneal dialysis (PD) has steadily improved so that now its outcomes, in the form of patient survival, are equivalent to, and at times better than, those for hemodialysis. We now have a better understanding of the pathophysiology of peritoneal membrane function and damage and the importance of appropriate prescription to meet agreed-upon targets of solute and fluid removal. In the next millennium, greater emphasis will be put on prescription setting and subsequent monitoring. This will entail an increase in automated PD, especially for lifestyle reasons as well as for patients with a hyperpermeable peritoneal membrane. To improve outcomes, dialysis should be started earlier than is currently the case. It is easy to do this with PD, where an incremental approach is made easier by the introduction of icodextrin for long-dwell PD. In the future, solutions will be tailored to be more biocompatible and to provide improved nutrition and better cardiovascular outcomes. Finally, economic considerations favor PD, which is cheaper than in-centre hemodialysis. Thus, for many, PD has become a first-choice therapy, and with further improvements this trend will continue.

Calculation of 6-hour D/P creatinine ratio from the 4-hour peritoneal equilibration test. The effect of dwell duration on the results.

OBJECTIVES: Since the introduction of the peritoneal equilibration test (PET), the 4-hour dialysate/plasma creatinine (D/P Cr) has been used by several authors for determining continuous ambulatory peritoneal dialysis (CAPD) prescriptions. However, the results have been unsatisfactory because the 4-hr D/P Cr does not accurately reflect the D/P Cr in 24-hr collections. The PET and the 24-hr dialysate collections differ in the duration of dwell and the tonicity and volume of dialysate, all of which influence the equilibrated D/P Cr. It can be assumed that the D/P Cr in 24-hr collections in these patients is closer to a 6-hr D/P Cr. Because a 6-hr PET is inconvenient, we developed a mathematical model to calculate the 5- and 6-hr D/P using the results of a standard PET. DESIGN: In a retrospective analysis, D/P Cr ratios in 24-hr collections and D/P Cr ratios calculated from a mathematical formula were correlated. Using a mathematical model, the data collected fit an exponential relation of the type D/P = a(1-e-t/tau). The values of a and tau are unique for a given patient and were determined using a nonlinear regression technique. The formula performed well on our published data-the true and predicted 6-hr D/P Cr being 0.696 and 0.71, respectively. SETTING: The University Hospital and Clinics, Dalton Cardiovascular Research Center and Dialysis Clinic, Inc., Columbia, Missouri. PATIENTS: All CAPD patients on four 2-L exchanges/day at the time of the 24-hr collections were included. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Closeness of 4-hr and 6-hr D/P Cr values to those of 24-hr ratios. RESULTS: The study group comprised 74 patients (age, mean +/- SEM: 56.4 +/- 1.8 yr) with 80 PETs and 145 (24-hr) collections. The interval between the two tests was 8.3 +/- 0.9 months (0-48.7 months). The median 24-hr D/P Cr of 0.760 did not differ significantly from the predicted median 6-hr D/P Cr of 0.755. A subgroup analysis, based on transport type, showed that this relationship was most precise in the high-average transporters. The predicted 6-hr D/P Cr was within 10% of the 24-hr D/P Cr in 48% of patients and within 20% in 77% of patients. The margin of error was greatest in the low transporters. CONCLUSIONS: To conclude, the 4-hr D/P Cr from a PET cannot be used interchangeably with the D/P Cr in the 24-hr dialysate collections, hence, the clearances calculated thereof will be inaccurate. Using the proposed model, it is feasible to use the 4-hr PET results to obtain 5- and 6-hr D/P Cr values. In our study, using this model, the extrapolated 6-hr D/P Cr is similar to the D/P Cr in 24-hr dialysate collections only in the high-average transporters. Hence, the best way to determine clearances in peritoneal dialysis patients is still by collecting 24-hr dialysates.