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Timing, causes, predictors and prognosis of switching from peritoneal dialysis to hemodialysis: a prospective study

Timing, causes, predictors and prognosis of switching from peritoneal dialysis to hemodialysis: a... Background: The use of peritoneal dialysis (PD) has declined in the United States over the past decade and technique failure is also reportedly higher in PD compared to hemodialysis (HD), but there are little data in the United States addressing the factors and outcomes associated with switching modalities from PD to HD. Methods: In a prospective cohort study of 262 PD patients enrolled from 28 peritoneal dialysis clinics in 13 U.S. states, we examined potential predictors of switching from PD to HD (including demographics, clinical factors, and laboratory values) and the association of switching with mortality. Cox proportional hazards regression was used to assess relative hazards (RH) of switching and of mortality in PD patients who switched to HD. Results: Among 262 PD patients, 24.8% switched to HD; with more than 70% switching within the first 2 years. Infectious peritonitis was the leading cause of switching. Patients of black race and with higher body mass index were significantly more likely to switch from PD to HD, RH (95% CI) of 5.01 (1.15–21.8) for black versus white and 1.09 (1.03–1.16) per 1 kg/m increase in BMI, respectively. There was no difference in survival between switchers and non-switchers, RH (95% CI) of 0.89 (0.41–1.93). Conclusion: Switching from PD to HD occurs early and the rate is high, threatening long-term viability of PD programs. Several patient characteristics were associated with the risk of switching. However, there was no survival difference between switchers and non-switchers, reassuring providers and patients that PD technique failure is not necessarily associated with poor prognosis. apy. PD is typically considered a home dialysis program, Background Hemodialysis (HD) and peritoneal dialysis (PD) repre- as the patients have the autonomy to perform the treat- sent the two main modalities for renal replacement ther- ment in their home environment, whereas most HD Page 1 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 patients must travel to a dialysis center, usually three weeks after starting dialysis). This information was times a week, to receive their treatment. Despite the obtained from clinic records. The initial dialysis modality potential benefit of PD compared to HD in quality of life information was abstracted from the Centers for Medicare [1] and associated patient satisfaction [2], prevalent use of and Medicaid Services (CMS) ESRD Medical Evidence PD has declined in the United States since 1994–1995, by Report (Form 2728). All forms of PD (continuous ambu- as much as 67% in some regions of the country [3]. The latory PD, continuous cycling PD and intermittent cycling number of incident end-stage renal disease (ESRD) PD) were combined as a single category. Patients were patients initiating PD has also declined over the same considered to have switched to hemodialysis (HD) when time period [3]. This decline in PD utilization has been they changed from PD to HD and remained on the latter observed not only in the United States but also in Europe modality for at least 30 days. Causes of switch from PD to and elsewhere [3,4]. Technique failure is known to be HD were ascertained from comprehensive chart review. much higher in PD than HD patients [5-7] and this likely Patients were censored for time to switch at transplanta- plays a significant role in the declining prevalence of PD tion, loss to follow-up, death, or last date of follow-up utilization. Peritonitis has been described as one of the (December 31, 2004). leading causes of transfer from PD to HD [7-9] and only a small group of patients can return to PD after severe peri- Demographic and clinical data tonitis and Tenckhoff catheter removal [10]. All patients completed a baseline self-report question- naire and provided information on demographics, health Over the past decade, very few studies in the United Sates behaviors, work history, medical history, and distance to have analyzed both the cause of switching from PD to HD dialysis unit. Late referral was defined as <4 months and the timing of this switching process after initiation of between first nephrologist evaluation and start of dialysis, PD. Further, there is a paucity of studies, particularly in as described previously [12]. Residual urine output, the United States, aimed at identifying risk factors associ- obtained from the patient baseline self-report question- ated with switching from PD to HD in ESRD patients and naire, was defined as the ability to make at least 250 cc (1 subsequent patient outcomes. The purpose of this study cup) of urine per day. Body mass index (BMI) was calcu- was to determine patient characteristics associated with lated using the standard formula weight (in kg)/[height , based on the height and weight reported on the risk of switching from PD to HD and to assess patient (in meters)] survival following dialysis modality switches in a cohort the 2728 form. Comorbidity, referring to medical condi- of incident peritoneal dialysis patients. tions other than the primary disease itself and the severity of those conditions, was assessed using the ICED, a med- Methods ical record-derived index that has been demonstrated to Study design and research population predict death in dialysis populations [13,14]. ICED scores The Choices for Healthy Outcomes in Caring for ESRD range from 0 to 3, with 3 as the highest severity level. It is (CHOICE) is a national prospective cohort study of inci- a measure of both the presence and severity of comorbid dent dialysis patients [11]. For the purposes of this study, conditions, as described previously. Baseline data for rou- we limited our sample to 262 white and black peritoneal tine patient care were available for the following labora- dialysis patients from the CHOICE cohort. From October tory values: serum albumin, hemoglobin, total 1995 to June 1998, participants from 13 states were cholesterol, and serum creatinine. High-sensitivity C-reac- enrolled at 28 clinics offering peritoneal dialysis and asso- tive protein (CRP) level was assessed at a median of 5.0 ciated with Dialysis Clinic, Inc. (Nashville, TN; n = 178), months from dialysis initiation, using a colorimetric com- New Haven CAPD (New Haven, CT; n = 82) or St. Rap- petitive enzyme-linked immunosorbent assay (coefficient hael's Hospital (New Haven, CT; n = 2). Eligibility criteria of variation, 8.9%). Glomerular filtration rate (GFR) for enrollment included ability to provide informed con- before dialysis initiation was estimated by the six-variable sent for participation, age older than 17 years, and ability Modification of Diet in Renal Disease (MDRD) equation to speak English or Spanish. Median time from start of using serum creatinine obtained from the CMS Form peritoneal dialysis to enrollment was 29 days, with 99% 2728 [15]. enrolling within 4 months of initiating dialysis. All partic- ipants gave written informed consent after Institutional Mortality ascertainment Review Boards for Johns Hopkins University and clinical Mortality information was ascertained from clinic report, centers approved the study protocol. medical records, National Death Index and CMS (death notification forms and Social Security records). Follow-up Data collection for mortality continued until death (n = 88), transplanta- Dialysis modality and switching tion (n = 69), loss to follow-up [when patients left the Dialysis modality was defined as the modality in use at 4 study or study clinic (n = 97)], or the last follow-up date weeks after enrollment in the study (an average of 10 of December 31, 2004 (n = 8). Patients were followed for Page 2 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 mortality for up to 8.9 years (average follow-up, 2 years). Results In sensitivity analyses, we also assessed mortality without Patient characteristics Among the 262 peritoneal dialysis patients, 24.8% loss to follow-up, by including deaths tracked by passive follow-up through death certificates of patients who left switched to hemodialysis during the study period. PD the study or the study clinic. patients who switched to HD had higher BMI and serum creatinine at baseline and were less likely to be white and Statistical analysis to have residual urine output at both baseline and 1 year We compared characteristics of patients who switched of follow-up. There were no other demographic, clinical (switchers) to hemodialysis with those patients who or laboratory differences between PD switchers and non- remained on PD (non-switchers) by using t tests for con- switchers at baseline (Table 1). tinuous variables and Pearson's χ tests for categorical var- iables. CRP was log-transformed to reduce skewness of Causes of switching and time to switch from peritoneal distribution. dialysis to hemodialysis More than 40% of the PD patients who switched to HD We used time-dependent Cox proportional hazards mod- did so within the first year after starting PD and more than els to assess the risk factors for switching by analyzing the 70% within the first two years (Figure 1). Infections (peri- time to first switch from peritoneal dialysis to hemodialy- tonitis and catheter-related) (36.9%) were the leading sis. Time-dependent analyses were performed to reduce cause of switching from PD to HD, followed by cardiovas- lead-time bias, since, by definition, those who switched cular (fluid overload) causes (18.5%). Less common modality had to survive at least until the switch. In these causes of switching from PD to HD included abdominal analyses, all patients started as non-switchers, and if the surgery, pancreatitis/malnutrition, decreased mental patient switched the patient then became a switcher in the capacity and abdominal wall defect (Table 2). Infectious analyses. In multivariable models, we adjusted for poten- peritonitis was a leading cause of switch from PD to HD tial confounders, including variables associated with both during most of the follow-up period, whereas cardiovas- baseline modality and switching. We also used Cox pro- cular/fluid overload as a cause of switch became more portional hazards models to assess the mortality risk of dominant after the first year on peritoneal dialysis (Figure patients on peritoneal dialysis who switched to hemodial- 2). Patients who switched due to infectious peritonitis ver- ysis versus patients who remained on peritoneal dialysis, sus any other cause were younger (47.1 versus 54.7 years, independent of differences in demographics (e.g., age, P = 0.02) and less likely to be white (52.2% versus 83.3%, race, and employment status), clinical factors (e.g., ICED P = 0.007); otherwise there were no other significant dif- comorbidity score, diabetes mellitus status, history of car- ferences between these patients. diovascular disease, body mass index, and baseline resid- ual urine output), and laboratory values (e.g., serum Risk factors associated with switching from peritoneal albumin and creatinine). dialysis to hemodialysis In the unadjusted model, PD patients of black race were We also examined whether the mortality risk was similar nearly 3 times more likely than white PD patients to by year of follow-up and among persons with different switch from PD to HD; this risk became stronger after clinical characteristics by performing Cox proportional adjustment (Table 3). Patients who were less educated hazards analyses in subpopulations based on survival were 2.5 times more likely to switch from PD to HD, com- time, diabetes mellitus status, history of cardiovascular pared to patients who had at least a high school educa- disease, baseline residual urine output and baseline serum tion; however, this association was not statistically albumin (< 3.5 g/dl versus ≥ 3.5 g/dl). We formally tested significant. Patients living 30 miles or more from the dial- for interactions that had been found to be significant in ysis clinic were 58% less likely to switch from PD to HD previous studies by including interaction terms and test- compared to patients living fewer than 30 miles from the ing their statistical significance in the full population dialysis clinic; but this association was marginally statisti- models. Furthermore, we tested for and found no devia- cally significant. In both unadjusted and adjusted analy- tions from the proportional hazards assumption by exam- ses, the risk of switching from PD to HD significantly ining the global test of Schoenfeld residuals, both overall increased by about 10% for each 1 kg/m higher BMI. In and within each follow-up year. Finally, we accounted for the unadjusted analysis, for each 1 mg/dl higher serum possible dependence of observations within clinics [16] baseline creatinine, there was a 13% increased risk of by performing fixed-effects modeling clustered on the switching from PD to HD; however, this relationship was dialysis clinic. Statistical analyses were performed using no longer statistically significant after adjustment. We Stata version 8.2 (StataCorp, College Station, TX). found no significant risk of switching from PD to HD by age, employment status, or diabetes mellitus status (Table 3). Similarly, in sensitivity analyses, Index of Coexistent Page 3 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Table 1: Patient characteristics by peritoneal dialysis switching status Characteristic N Non-switchers Switchers P Total 262 197 (75.2%) 65 (24.8%) -- Demographic Mean age at enrollment, years 262 54.7 ± 15.4 52.0 ± 13.0 0.202 Sex (% female) 262 42.1 47.7 0.433 Race (% white) 262 83.8 72.3 0.042 Education (% high school graduate) 225 84.2 75.4 0.131 Employment (% working) 262 28.4 20.0 0.181 Marital Status (% married) 238 68.9 62.3 0.341 Distance from clinic (% >30 miles) 216 28.3 28.1 0.973 Clinical Smoking status (% ever smoker) 227 61.5 60.7 0.914 Modality at start, from 2728 (% HD) 256 7.8 9.4 0.693 ICED score (%) 262 0.848 ≤ 1 50.3 46.2 2 25.4 27.7 3 24.4 26.2 Diabetes (% diabetic) 262 49.2 58.5 0.197 History of CVD (% positive) 262 52.3 41.5 0.133 History of CHD (% positive) 262 41.1 32.3 0.207 History of CHF (% positive) 262 40.6 29.2 0.101 Primary cause of renal failure (%) 259 0.341 Diabetes mellitus 44.8 53.9 Hypertension 10.8 6.2 Glomerulonephritis 44.3 40.0 Late referral (% <4 months) 198 21.7 16.4 0.404 BMI, kg/m 245 25.9 ± 5.6 28.2 ± 6.0 0.006 Residual urine output (%) 186 0.018 Not at baseline or follow-up at 1 year 14.6 19.6 Page 4 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Table 1: Patient characteristics by peritoneal dialysis switching status (Continued) At baseline but not at follow-up at 1 year 17.7 33.9 At baseline and at follow-up at 1 year 67.7 46.4 Laboratory Mean baseline albumin, g/dl 248 3.57 ± 0.44 3.64 ± 0.38 0.316 Mean baseline hemoglobin, g/dl 246 11.3 ± 1.5 11.3 ± 1.5 0.766 Median CRP (IQR), μg/dl 162 2.6 (1.1–6.2) 3.5 (1.6–5.7) 0.638 Baseline creatinine, g/dl 252 7.08 ± 2.66 7.94 ± 2.63 0.029 Baseline cholesterol, mg/dl 220 207 ± 53 210 ± 57 0.746 Baseline GFR, cc/minute/1.73 m 254 10.5 ± 0.26 10.3 ± 0.45 0.721 *By t-test (continuous variables) or χ test (categorical variables) Disease (ICED) and residual urine output were not asso- In our sensitivity analyses, we found no significant ciated with the risk of switching from PD to HD (data not decreased risk of death for PD switchers versus non- st nd shown). switchers by year of follow-up (1 and 2 years) or after stratification by diabetes mellitus status, history of cardio- Mortality risk associated with switching from peritoneal vascular disease, baseline residual urine output, and base- dialysis to hemodialysis line serum albumin (< 3.5 g/dl versus ≥ 3.5 g/dl) (data not The mortality rate per 100 patient-years was 18.5 for PD shown). Additionally, when we examined the effects of non-switchers versus 13.5 for PD patients who switched including passive follow-up in our mortality data, results to HD (Table 4). The cumulative mortality did not differ were similar and non-statistically significant (data not between switchers and non-switchers (Figure 3). In the shown). unadjusted analyses, switchers had a 6% decreased risk of death but the association was not statistically significant. Discussion After adjustment for demographics, clinical factors, and This prospective cohort study of incident PD patients laboratory values, there was an 11% decreased risk of showed that about 25% of patients switched to HD over death in PD switchers compared to non-switchers but the time, with more than 70% of the switching occurring results were not statistically significant (Table 4). within the first 2 years of treatment. Peritonitis was the leading cause of this modality change. In this U.S. pro- Table 2: Causes of switching from peritoneal dialysis to spective cohort study, the leading independent predictors hemodialysis of dialysis modality switching from PD to HD were black race and higher BMI. Importantly, there was no statisti- Causes of Switching Number (%) cally significant survival difference between PD patients N = 65 who switched to HD compared to those who remained on Infection (peritonitis and catheter-related) 24 (36.9%) PD. Cardiovascular (fluid overload) 12 (18.5%) At the end of 2005, only about 7.6% of U.S. dialysis patients were treated with PD, and this prevalence has Abdominal surgery 8 (12.3%) been declining since the mid-1990s [3]. One of the factors certainly contributing to this low PD prevalence remains Pancreatitis/malnutrition 7 (10.8%) the unacceptable high transfer rate from PD to HD described in several cohorts [7,17-22]. In an older Italian Decreased mental capacity 2 (3.1%) study with long follow-up, 18% of PD patients switched modality, as compared to 2.8% of the HD patients [7]. In Abdominal wall defect 1 (1.6%) our U.S. incident cohort, this switching rate was 25% for PD patients switching to HD, compared to 5% for HD Unknown 11 (16.9%) patients switching to PD [18]. In the Netherlands Cooper- Page 5 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Cum Figure 1 ulative percentage of peritoneal dialysis patients by time from first dialysis to first switch to hemodialysis (switchers only) Cumulative percentage of peritoneal dialysis patients by time from first dialysis to first switch to hemodialysis (switchers only). ative Study on the Adequacy of Dialysis, 3-year technique in the early 1990s, this cause of dialysis modality transfer survival was only 53% [21]. In a more recent U.S. cohort, from PD to HD was reported to be as high as 49% [25]. Guo et al. [17] showed a significant trend towards decreas- Over the past few years, the use of the twin-bag and Y-set ing transfer rates to HD during the first year on PD, from systems has certainly helped to decrease the peritonitis 19.6% in 1999 to 17.2% in 2001. rate [26]. Ultrafiltration failure, leading to fluid overload, which was the next most important cause of transfer from In agreement with previous studies, we found that infec- PD to HD in our study, has been shown to increase with tions remain the leading cause of switching from PD to time on PD [23,27]; however, in our cohort, this trend HD, followed by cardiovascular causes, mainly fluid over- was observed only during the first 18 months. We did not load [9,17,23]. Infectious causes, which are generally pre- find an increasing number of ultrafiltration failures in our ventable, were responsible for 28% of the transfers from PD patients, possibly because a much smaller number of PD to HD in a recent study by Mujais et al. [24]. However, patients switched from PD to HD after 2 years. This ultra- Page 6 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Percentage of switching peri dialysis switch Figure 2 toneal dialysis patients by main causes of switch and by time from first peritoneal dialysis to hemo- Percentage of switching peritoneal dialysis patients by main causes of switch and by time from first peritoneal dialysis to hemodialysis switch. filtration failure is a consequence of morphological and significant association between diabetes mellitus and functional changes of the peritoneal membrane, includ- modality transfer from PD to HD, although, in our ing increased small solute transport and lymphatic cohort, more patients with diabetes mellitus switched to absorption, over time [28,29]. Loss of residual renal func- HD (28.2%) compared to nondiabetics (21.3%). This tion with decreasing urine output observed over time in lack of statistical significance could be due to our smaller this cohort is also another likely mechanism leading to sample size. Parallel to previous studies, we found no more fluid overload as a cause of transfer from PD to HD. effect of age on transfer rate from PD to HD [17], suggest- ing that PD can be performed in any age group with We identified several patient characteristics associated appropriate support. with a higher risk of switching from PD to HD over time. Patients of black race were 5 times more likely than white There are little data looking at the association of BMI with patients to switch from PD to HD. This finding is in technique survival among PD patients. In our study, accordance with an older single-center study, which higher BMI was independently associated with increasing reported a significantly higher technique failure rate in risk of switching from PD to HD. This is in concordance black patients (39%) compared to white patients (8%) with a recent retrospective cohort study [33] and another [30]. Patients with diabetes mellitus have also been study from Australia and New Zealand, in which PD tech- reported to have a higher transfer rate from PD to HD in nique failure was 17% higher in obese patients compared some cohorts [17,24] but certainly not all [31,32]. Similar to patients with normal BMI [34]. Peritoneal dialysis to Huisman et al. [31] and Viglino et al. [32], we found no patients with higher BMI may be at increased risk for not Page 7 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Table 3: Predictors of dialysis modality switching: relative hazards for switching versus non-switching (time to first switch) from peritoneal dialysis to hemodialysis Relative Hazards (95% CI) Predictors Unadjusted Adjusted* Age (per 1-year increase) 1.00 (0.98–1.01) 0.98 (0.95–1.01) Race White 1.00 (ref.) 1.00 (ref.) Black 2.79 (1.25–6.23) 5.01 (1.15–21.8) Education High school graduate or higher 1.00 (ref.) 1.00 (ref.) Less than high school graduate 1.64 (0.83–3.23) 2.53 (0.98–6.55) Employment Employed 1.00 (ref.) 1.00 (ref.) Not employed 1.51 (0.76–3.01) 1.81 (0.66–4.94) Distance to dialysis clinic Living less than 30 miles from clinic 1.00 (ref.) 1.00 (ref.) Living 30 miles or more from clinic 0.65 (0.32–1.30) 0.42 (0.17–1.02) Diabetes Nondiabetic 1.00 (ref.) 1.00 (ref.) Diabetic 1.22 (0.71–2.12) 1.79 (0.74–4.33) BMI (per 1 kg/m increase) 1.10 (1.04–1.15) 1.09 (1.03–1.16) Baseline creatinine (per 1 mg/dl increase) 1.13 (1.02–1.26) 1.13 (0.97–1.33) Number (%) of patients switching/total number of patients by subpopulation: white, 47/212 (22.2%); black, 18/50 (36.0%); employed, 13/69 (18.8%); not employed, 52/193 (26.9%); high school graduate, 46/184 (25.0%); not high school graduate, 15/41 (36.6%); nondiabetic, 27/127 (21.3%); diabetic, 38/135 (28.2%); living at least 30 miles from dialysis clinic 41/155 (26.5%); living less than 30 miles from dialysis clinic 16/61 (26.2%). * Adjusted model (n = 195) included age, race, education, employment, distance to dialysis clinic, diabetes mellitus status, BMI, baseline serum creatinine. only infectious complications and inadequate dialysis but The impact of dialysis modality switching from PD to HD also peritoneal leaks because of raised intra-abdominal on patient survival remains controversial. We found no pressure [35,36]. Although in our study there was a clear significant difference in survival over time between PD trend towards a lower risk of transfer from PD to HD for patients who switched to HD compared to those who patients living 30 miles or more from their dialysis clinic, remained on PD. Similar results have been reported in this association was not statistically significant. However, black patients in the United States [38] and in European a recent report from Canada clearly showed a significant cohorts [7]. However, other studies have shown higher trend toward decreasing PD technique failure with mortality for PD patients who switched to HD compared increasing distance from their nephrologist [37]. to those who remained on PD [9,19]. In contrast to these Page 8 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Table 4: Risk of mortality associated with switching from peritoneal dialysis to hemodialysis: relative hazards for mortality for switchers vs. non-switchers Relative Hazard (95% CI) Model Non-switchers Switchers No. of deaths/total no. of patients 62/197 26/65 Incidence rate, per 100 patient-years 18.5 13.5 Unadjusted 1.00 (ref.) 0.94 (0.51–1.73) Adjusted Model 1 (Demographics) 1.00 (ref.) 0.87 (0.46–1.66) Model 2 (Model 1 + Clinical) 1.00 (ref.) 0.68 (0.33–1.40) Model 3 (Model 2 + Laboratory) 1.00 (ref.) 0.89 (0.41–1.93) In these analyses, all patients start as non-switchers; if the patient switched modality the patient then became a switcher on the date of switch. *Demographics: age, race, employment; clinical: ICED, diabetes, CVD, BMI, residual urine output; laboratory: baseline albumin and creatinine. Fully adjusted models included all these variables. reports, Van Biesen et al. [39], found a much better prog- tions, our study represents, to our knowledge, one of the nosis for PD patients who switched to HD compared to few prospective incident cohort studies specifically in the those remaining on PD. These differences in outcomes United States analyzing in detail switching of incident PD may be explained by differences in case-mix and reasons patients to HD, in terms of rate, timing, predictors and for technique failure. Several of these studies, including prognosis. our own, showed that PD technique failure does not nec- essarily indicate worse prognosis after switching to HD; Conclusion rather, more importantly, a timely transfer is vital when This prospective study of incident PD patients in the severe PD-related complications occur [40]. United States confirmed that the observed early switching rate from PD to HD remains too high and certainly repre- There are some limitations associated with our study. We sents a significant impediment to the long-term viability had some, but not detailed, data on residual urine output. of any PD program. Additional efforts are urgently needed Furthermore, we had no data on peritoneal membrane to continue to prevent PD-related infections, the leading characteristics; high peritoneal solute transport has been cause of PD technique failure; also, when antibiotic associated with PD technique failure and mortality in response for peritonitis remains inadequate, early Tenck- observational studies [23,41] but not in a more recent hoff catheter removal may help preserve the peritoneal prospective, randomized, controlled trial [42]. Also, membrane for future return to PD [43]. Moreover, we because of the relatively smaller sample size, we com- were able to identify important independent risk factors bined automated PD and continuous ambulatory PD. But for switching from PD to HD (BMI and black race). In this recently, Mujais et al. [24], using data from the Baxter context, more studies are definitely needed to better Healthcare Corporation On-Call system reported that understand why black PD patients were more likely to transfer to HD was lower in patients on automated PD switch to HD over time. Finally, our findings of no sur- than in patients on continuous ambulatory PD. However, vival difference between PD switchers and non-switchers compared to administrative data, our study provided the should be reassuring to providers and patients that PD advantage of a prospective incident cohort with detailed technique failure is not necessarily associated with poor data on comorbidities, laboratory values, and access to prognosis, but a timely transfer in setting of complications patient charts to determine specific causes of switching. remains important. There was a notable rate of lost to follow-up; however, mortality results including passive follow-up were similar Competing interests to those without passive follow-up. Despite these limita- The authors declare that they have no competing interests. Page 9 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Kaplan-Meier Figure 3 curve for mortality, peritoneal dialysis switchers versus non-switchers (P = 0.528 by log-rank) Kaplan-Meier curve for mortality, peritoneal dialysis switchers versus non-switchers (P = 0.528 by log-rank). Authors' contributions Acknowledgements We thank the patients, staff, and medical directors of the participating clin- BGJ analyzed and interpreted the data, reviewed medical ics at Dialysis Clinic, Inc., New Haven CAPD and St. Raphael's Hospital who records for causes of switching from peritoneal dialysis to contributed to the study. hemodialysis, drafted and revised the manuscript for important intellectual content. LCP performed the statis- This work was supported by grant no. RO1 DK 59616 from the National tical analysis, analyzed and interpreted the data, and Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, revised the manuscript for important intellectual content. grant no. R01-HS-08365 from the Agency for Health Care Research and DCC reviewed medical records for causes of switching Quality, Rockville, Maryland, and grant no. R01 HL 62985 from the National from peritoneal dialysis to hemodialysis and revised the Heart Lung and Blood Institute, Bethesda, MD. Dr. Crews is supported by Grant Number 1KL2RR025006-01 from the National Center for Research manuscript for important intellectual content. NEF con- Resources (NCRR), a component of the National Institutes of Health ceived and designed the study, obtained the data and (NIH), and NIH Roadmap for Medical Research. Dr. Powe is supported by revised the manuscript for important intellectual content. grant K24DK02643. NH was involved in the provision of study patients and revised the manuscript for important intellectual content. References JC conceived and designed the study, obtained the data, 1. Wu AW, Fink NE, Marsh-Manzi JV, Meyer KB, Finkelstein FO, Chap- obtained funding, supervised the study, and revised the man MM, Powe NR: Changes in Quality of Life during Hemodi- alysis and Peritoneal Dialysis Treatment: Generic and manuscript for important intellectual content. ASK was Disease Specific Measures. J Am Soc Nephrol 2004, 15:743-753. involved in the provision of study patients and revised the 2. Rubin HR, Fink NE, Plantinga LC, Sadler JH, Kliger AS, Powe NR: Patient Ratings of Dialysis Care With Peritoneal Dialysis vs manuscript for important intellectual content. NRP con- Hemodialysis. JAMA 2004, 291:697-703. ceived and designed the study, obtained the data, ana- 3. U.S. Renal Data System, USRDS 2007 Annual Data Report: Atlas of lyzed and interpreted the data, obtained funding, End-Stage Renal Disease in the United States, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, supervised the study, and revised the manuscript for MD 2007. important intellectual content. All authors read and 4. Biesen Wv, Veys N, Lameire N, Vanholder R: Why less success of approved the final manuscript. the peritoneal dialysis programmes in Europe? Nephrol Dial Transplant 2008, 23:1478-1481. Page 10 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 5. Gokal R, King J, Bogle S, Marsh F, Oliver D, Jakubowski C, Hunt L, 25. 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Maiorca R, Cancarini GC, Zubani R, Camerini C, Manili L, Brunori G, 27. Kawaguchi Y, Hasegawa T, Nakayama M, Kubo H, Shigematu T: Movilli E: CAPD viability: a long-term comparison with hemo- Issues affecting the longevity of the continuous peritoneal dialysis. Perit Dial Int 1996, 16:276-287. dialysis therapy. Kidney Int Suppl 1997, 62:S105-S107. 8. Churchill DN, Thorpe KE, Vonesh EF, Keshaviah PR: Lower proba- 28. Fusshoeller A: Histomorphological and functional changes of bility of patient survival with continuous peritoneal dialysis in the peritoneal membrane during long-term peritoneal dial- the United States compared with Canada. Canada-USA ysis. Pediatric Nephrology 2008, 23:19-25. (CANUSA) Peritoneal Dialysis Study Group. J Am Soc Nephrol 29. Fusshöller A, zur Nieden S, Grabensee B, Plum J: Peritoneal Fluid 1997, 8:965-971. and Solute Transport: Influence of Treatment Time, Perito- 9. Woodrow G, Turney JH, Brownjohn AM: Technique failure in neal Dialysis Modality, and Peritonitis Incidence. J Am Soc peritoneal dialysis and its impact on patient survival. Perit Dial Nephrol 2002, 13:1055-1060. Int 1997, 17:360-364. 30. Korbet SM, Shih D, Cline KM, Vonesh EF: Racial differences in sur- 10. Szeto CC, Chow KM, Wong TY-H, Leung CB, Wang AY-M, Lui SF, Li vival in an urban peritoneal dialysis program. Am J Kidney Dis PK: Feasibility of Resuming Peritoneal Dialysis after Severe 1999, 34:713-720. Peritonitis and Tenckhoff Catheter Removal. J Am Soc Nephrol 31. Huisman RM, Nieuwenhuizen MGM, de Charro FT: Patient-related 2002, 13:1040-1045. and centre-related factors influencing technique survival of 11. Powe NR, Klag MJ, Sadler JH, Anderson GF, Bass EB, Briggs WA, Fink peritoneal dialysis in The Netherlands. Nephrol Dial Transplant NE, Levey AS, Levin NW, Meyer KB, Rubin HR, Wu AW: Choices 2002, 17:1655-1660. for healthy outcomes in caring for end stage renal disease. 32. Viglino G, Cancarini GC, Catizone L, Cocchi R, De Vecchi A, Lupo A, Semin Dial 1996, 9:9-11. Salomone M, Segoloni GP, Giangrande A: Ten years experience of 12. Kinchen KS, Sadler J, Fink N, Brookmeyer R, Klag MJ, Levey AS, Powe CAPD in diabetics: comparison of results with non-diabetics. NR: The Timing of Specialist Evaluation in Chronic Kidney Nephrol Dial Transplant 1994, 9:1443-1448. Disease and Mortality. Ann Intern Med 2002, 137:479-486. 33. Snyder JJ, Foley RN, Gilbertson DT, Vonesh EF, Collins AJ: Body size 13. Miskulin DC, Meyer KB, Athienites NV, Martin AA, Terrin N, Marsh and outcomes on peritoneal dialysis in the United States. JV, Fink NE, Coresh J, Powe NR, Klag MJ, Levey AS: Comorbidity Kidney Int 2003, 64:1838-1844. and other factors associated with modality selection in inci- 34. McDonald SP, Collins JF, Johnson DW: Obesity Is Associated with dent dialysis patients: The CHOICE study. Am J Kidney Dis Worse Peritoneal Dialysis Outcomes in the Australia and 2002, 39:324-336. New Zealand Patient Populations. J Am Soc Nephrol 2003, 14. Athienites NV, Miskulin DC, Fernandez G, Bunnapradist S, Simon G, 14:2894-2901. Landa M, Schmid CH, Greenfield S, Levey AS, Meyer KB: Comorbid- 35. Schmekal B: Peritoneal dialysis in patients with high body- ity assessment in hemodialysis and peritoneal dialysis using mass index. Wiener Klinische Wochenschrift 2005, 117:40-45. the index of coexistent disease. Semin Dial 2000, 13:320-326. 36. McDonald SP, Collins JF, Rumpsfeld M, Johnson DW: Obesity is a 15. Levey AS, Bosch JP, Lewis JB, Greene T, Rogers N, Roth D: A More risk factor for peritonitis in the Australian and New Zealand Accurate Method To Estimate Glomerular Filtration Rate peritoneal dialysis patient populations. Perit Dial Int 2004, from Serum Creatinine: A New Prediction Equation. Ann 24:340-346. Intern Med 1999, 130:461-470. 37. Tonelli M, Hemmelgarn B, Culleton B, Klarenbach S, Gill JS, Wiebe N, 16. Localio AR, Berlin JA, Ten Have TR, Kimmel SE: Adjustments for Manns B, Alberta Kidney Disease Network: Mortality of Canadi- center in multicenter studies: an overview. Ann Intern Med ans treated by peritoneal dialysis in remote locations. Kidney 2001, 135:112-123. Int 2007, 72:1023-1028. 17. Guo A, Mujais S: Patient and technique survival on peritoneal 38. Kim GC, Vonesh EF, Korbet SM: The effect of technique failure dialysis in the United States: Evaluation in large incident on outcome in black patients on continuous ambulatory cohorts. Kidney Int 2003, 64:S3-S12. peritoneal dialysis. Perit Dial Int 2002, 22:53-59. 18. Jaar BG, Coresh J, Plantinga LC, Fink NE, Klag MJ, Levey AS, Levin 39. Van Biesen W, Dequidt C, Vijt D, Vanholder R, Lameire N: Analysis NW, Sadler JH, Kliger A, Powe NR: Comparing the Risk for of the reasons for transfers between hemodialysis and peri- Death with Peritoneal Dialysis and Hemodialysis in a toneal dialysis and their effect on survivals. Adv Perit Dial 1998, National Cohort of Patients with Chronic Kidney Disease. 14:90-94. Ann Intern Med 2005, 143:174-183. 40. Van Biesen W, Vanholder RC, Veys N, Dhondt A, Lameire NH: An 19. Schaubel DE, Blake PG, Fenton SS: Trends in CAPD technique evaluation of an integrative care approach for end-stage failure: Canada, 1981–1997. Perit Dial Int 2001, 21:365-371. renal disease patients. J Am Soc Nephrol 2000, 11:116-125. 20. Foley RN, Parfrey PS, Harnett JD, Kent GM, O'Dea R, Murray DC, 41. Churchill DN, Thorpe KE, Nolph KD, Keshaviah PR, Oreopoulos Barre PE: Mode of dialysis therapy and mortality in end-stage DG, Page D: Increased peritoneal membrane transport is renal disease. J Am Soc Nephrol 1998, 9:267-276. associated with decreased patient and technique survival for 21. Jager KJ, Merkus MP, Dekker FW, Boeschoten EW, Tijssen JGP, Ste- continuous peritoneal dialysis patients. The Canada-USA vens P, Bos WJ, Krediet RT: Mortality and technique failure in (CANUSA) Peritoneal Dialysis Study Group. J Am Soc Nephrol patients starting chronic peritoneal dialysis: Results of the 1998, 9:1285-1292. Netherlands Cooperative Study on the Adequacy of Dialysis. 42. Paniagua R, Amato D, Vonesh E, Correa-Rotter R, Ramos A, Moran Kidney Int 1999, 55:1476-1485. J, Mujais S, Mexican Nephrology Collaborative Study Group: Effects 22. Abbott KC, Glanton CW, Trespalacios FC, Oliver DK, Ortiz MI, Ago- of Increased Peritoneal Clearances on Mortality Rates in doa LY, Cruess DF, Kimmel PL: Body mass index, dialysis modal- Peritoneal Dialysis: ADEMEX, a Prospective, Randomized, ity, and survival: Analysis of the United States Renal Data Controlled Trial. 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Timing, causes, predictors and prognosis of switching from peritoneal dialysis to hemodialysis: a prospective study

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Copyright © 2009 by Jaar et al; licensee BioMed Central Ltd.
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Medicine & Public Health; Nephrology; Internal Medicine
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Abstract

Background: The use of peritoneal dialysis (PD) has declined in the United States over the past decade and technique failure is also reportedly higher in PD compared to hemodialysis (HD), but there are little data in the United States addressing the factors and outcomes associated with switching modalities from PD to HD. Methods: In a prospective cohort study of 262 PD patients enrolled from 28 peritoneal dialysis clinics in 13 U.S. states, we examined potential predictors of switching from PD to HD (including demographics, clinical factors, and laboratory values) and the association of switching with mortality. Cox proportional hazards regression was used to assess relative hazards (RH) of switching and of mortality in PD patients who switched to HD. Results: Among 262 PD patients, 24.8% switched to HD; with more than 70% switching within the first 2 years. Infectious peritonitis was the leading cause of switching. Patients of black race and with higher body mass index were significantly more likely to switch from PD to HD, RH (95% CI) of 5.01 (1.15–21.8) for black versus white and 1.09 (1.03–1.16) per 1 kg/m increase in BMI, respectively. There was no difference in survival between switchers and non-switchers, RH (95% CI) of 0.89 (0.41–1.93). Conclusion: Switching from PD to HD occurs early and the rate is high, threatening long-term viability of PD programs. Several patient characteristics were associated with the risk of switching. However, there was no survival difference between switchers and non-switchers, reassuring providers and patients that PD technique failure is not necessarily associated with poor prognosis. apy. PD is typically considered a home dialysis program, Background Hemodialysis (HD) and peritoneal dialysis (PD) repre- as the patients have the autonomy to perform the treat- sent the two main modalities for renal replacement ther- ment in their home environment, whereas most HD Page 1 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 patients must travel to a dialysis center, usually three weeks after starting dialysis). This information was times a week, to receive their treatment. Despite the obtained from clinic records. The initial dialysis modality potential benefit of PD compared to HD in quality of life information was abstracted from the Centers for Medicare [1] and associated patient satisfaction [2], prevalent use of and Medicaid Services (CMS) ESRD Medical Evidence PD has declined in the United States since 1994–1995, by Report (Form 2728). All forms of PD (continuous ambu- as much as 67% in some regions of the country [3]. The latory PD, continuous cycling PD and intermittent cycling number of incident end-stage renal disease (ESRD) PD) were combined as a single category. Patients were patients initiating PD has also declined over the same considered to have switched to hemodialysis (HD) when time period [3]. This decline in PD utilization has been they changed from PD to HD and remained on the latter observed not only in the United States but also in Europe modality for at least 30 days. Causes of switch from PD to and elsewhere [3,4]. Technique failure is known to be HD were ascertained from comprehensive chart review. much higher in PD than HD patients [5-7] and this likely Patients were censored for time to switch at transplanta- plays a significant role in the declining prevalence of PD tion, loss to follow-up, death, or last date of follow-up utilization. Peritonitis has been described as one of the (December 31, 2004). leading causes of transfer from PD to HD [7-9] and only a small group of patients can return to PD after severe peri- Demographic and clinical data tonitis and Tenckhoff catheter removal [10]. All patients completed a baseline self-report question- naire and provided information on demographics, health Over the past decade, very few studies in the United Sates behaviors, work history, medical history, and distance to have analyzed both the cause of switching from PD to HD dialysis unit. Late referral was defined as <4 months and the timing of this switching process after initiation of between first nephrologist evaluation and start of dialysis, PD. Further, there is a paucity of studies, particularly in as described previously [12]. Residual urine output, the United States, aimed at identifying risk factors associ- obtained from the patient baseline self-report question- ated with switching from PD to HD in ESRD patients and naire, was defined as the ability to make at least 250 cc (1 subsequent patient outcomes. The purpose of this study cup) of urine per day. Body mass index (BMI) was calcu- was to determine patient characteristics associated with lated using the standard formula weight (in kg)/[height , based on the height and weight reported on the risk of switching from PD to HD and to assess patient (in meters)] survival following dialysis modality switches in a cohort the 2728 form. Comorbidity, referring to medical condi- of incident peritoneal dialysis patients. tions other than the primary disease itself and the severity of those conditions, was assessed using the ICED, a med- Methods ical record-derived index that has been demonstrated to Study design and research population predict death in dialysis populations [13,14]. ICED scores The Choices for Healthy Outcomes in Caring for ESRD range from 0 to 3, with 3 as the highest severity level. It is (CHOICE) is a national prospective cohort study of inci- a measure of both the presence and severity of comorbid dent dialysis patients [11]. For the purposes of this study, conditions, as described previously. Baseline data for rou- we limited our sample to 262 white and black peritoneal tine patient care were available for the following labora- dialysis patients from the CHOICE cohort. From October tory values: serum albumin, hemoglobin, total 1995 to June 1998, participants from 13 states were cholesterol, and serum creatinine. High-sensitivity C-reac- enrolled at 28 clinics offering peritoneal dialysis and asso- tive protein (CRP) level was assessed at a median of 5.0 ciated with Dialysis Clinic, Inc. (Nashville, TN; n = 178), months from dialysis initiation, using a colorimetric com- New Haven CAPD (New Haven, CT; n = 82) or St. Rap- petitive enzyme-linked immunosorbent assay (coefficient hael's Hospital (New Haven, CT; n = 2). Eligibility criteria of variation, 8.9%). Glomerular filtration rate (GFR) for enrollment included ability to provide informed con- before dialysis initiation was estimated by the six-variable sent for participation, age older than 17 years, and ability Modification of Diet in Renal Disease (MDRD) equation to speak English or Spanish. Median time from start of using serum creatinine obtained from the CMS Form peritoneal dialysis to enrollment was 29 days, with 99% 2728 [15]. enrolling within 4 months of initiating dialysis. All partic- ipants gave written informed consent after Institutional Mortality ascertainment Review Boards for Johns Hopkins University and clinical Mortality information was ascertained from clinic report, centers approved the study protocol. medical records, National Death Index and CMS (death notification forms and Social Security records). Follow-up Data collection for mortality continued until death (n = 88), transplanta- Dialysis modality and switching tion (n = 69), loss to follow-up [when patients left the Dialysis modality was defined as the modality in use at 4 study or study clinic (n = 97)], or the last follow-up date weeks after enrollment in the study (an average of 10 of December 31, 2004 (n = 8). Patients were followed for Page 2 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 mortality for up to 8.9 years (average follow-up, 2 years). Results In sensitivity analyses, we also assessed mortality without Patient characteristics Among the 262 peritoneal dialysis patients, 24.8% loss to follow-up, by including deaths tracked by passive follow-up through death certificates of patients who left switched to hemodialysis during the study period. PD the study or the study clinic. patients who switched to HD had higher BMI and serum creatinine at baseline and were less likely to be white and Statistical analysis to have residual urine output at both baseline and 1 year We compared characteristics of patients who switched of follow-up. There were no other demographic, clinical (switchers) to hemodialysis with those patients who or laboratory differences between PD switchers and non- remained on PD (non-switchers) by using t tests for con- switchers at baseline (Table 1). tinuous variables and Pearson's χ tests for categorical var- iables. CRP was log-transformed to reduce skewness of Causes of switching and time to switch from peritoneal distribution. dialysis to hemodialysis More than 40% of the PD patients who switched to HD We used time-dependent Cox proportional hazards mod- did so within the first year after starting PD and more than els to assess the risk factors for switching by analyzing the 70% within the first two years (Figure 1). Infections (peri- time to first switch from peritoneal dialysis to hemodialy- tonitis and catheter-related) (36.9%) were the leading sis. Time-dependent analyses were performed to reduce cause of switching from PD to HD, followed by cardiovas- lead-time bias, since, by definition, those who switched cular (fluid overload) causes (18.5%). Less common modality had to survive at least until the switch. In these causes of switching from PD to HD included abdominal analyses, all patients started as non-switchers, and if the surgery, pancreatitis/malnutrition, decreased mental patient switched the patient then became a switcher in the capacity and abdominal wall defect (Table 2). Infectious analyses. In multivariable models, we adjusted for poten- peritonitis was a leading cause of switch from PD to HD tial confounders, including variables associated with both during most of the follow-up period, whereas cardiovas- baseline modality and switching. We also used Cox pro- cular/fluid overload as a cause of switch became more portional hazards models to assess the mortality risk of dominant after the first year on peritoneal dialysis (Figure patients on peritoneal dialysis who switched to hemodial- 2). Patients who switched due to infectious peritonitis ver- ysis versus patients who remained on peritoneal dialysis, sus any other cause were younger (47.1 versus 54.7 years, independent of differences in demographics (e.g., age, P = 0.02) and less likely to be white (52.2% versus 83.3%, race, and employment status), clinical factors (e.g., ICED P = 0.007); otherwise there were no other significant dif- comorbidity score, diabetes mellitus status, history of car- ferences between these patients. diovascular disease, body mass index, and baseline resid- ual urine output), and laboratory values (e.g., serum Risk factors associated with switching from peritoneal albumin and creatinine). dialysis to hemodialysis In the unadjusted model, PD patients of black race were We also examined whether the mortality risk was similar nearly 3 times more likely than white PD patients to by year of follow-up and among persons with different switch from PD to HD; this risk became stronger after clinical characteristics by performing Cox proportional adjustment (Table 3). Patients who were less educated hazards analyses in subpopulations based on survival were 2.5 times more likely to switch from PD to HD, com- time, diabetes mellitus status, history of cardiovascular pared to patients who had at least a high school educa- disease, baseline residual urine output and baseline serum tion; however, this association was not statistically albumin (< 3.5 g/dl versus ≥ 3.5 g/dl). We formally tested significant. Patients living 30 miles or more from the dial- for interactions that had been found to be significant in ysis clinic were 58% less likely to switch from PD to HD previous studies by including interaction terms and test- compared to patients living fewer than 30 miles from the ing their statistical significance in the full population dialysis clinic; but this association was marginally statisti- models. Furthermore, we tested for and found no devia- cally significant. In both unadjusted and adjusted analy- tions from the proportional hazards assumption by exam- ses, the risk of switching from PD to HD significantly ining the global test of Schoenfeld residuals, both overall increased by about 10% for each 1 kg/m higher BMI. In and within each follow-up year. Finally, we accounted for the unadjusted analysis, for each 1 mg/dl higher serum possible dependence of observations within clinics [16] baseline creatinine, there was a 13% increased risk of by performing fixed-effects modeling clustered on the switching from PD to HD; however, this relationship was dialysis clinic. Statistical analyses were performed using no longer statistically significant after adjustment. We Stata version 8.2 (StataCorp, College Station, TX). found no significant risk of switching from PD to HD by age, employment status, or diabetes mellitus status (Table 3). Similarly, in sensitivity analyses, Index of Coexistent Page 3 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Table 1: Patient characteristics by peritoneal dialysis switching status Characteristic N Non-switchers Switchers P Total 262 197 (75.2%) 65 (24.8%) -- Demographic Mean age at enrollment, years 262 54.7 ± 15.4 52.0 ± 13.0 0.202 Sex (% female) 262 42.1 47.7 0.433 Race (% white) 262 83.8 72.3 0.042 Education (% high school graduate) 225 84.2 75.4 0.131 Employment (% working) 262 28.4 20.0 0.181 Marital Status (% married) 238 68.9 62.3 0.341 Distance from clinic (% >30 miles) 216 28.3 28.1 0.973 Clinical Smoking status (% ever smoker) 227 61.5 60.7 0.914 Modality at start, from 2728 (% HD) 256 7.8 9.4 0.693 ICED score (%) 262 0.848 ≤ 1 50.3 46.2 2 25.4 27.7 3 24.4 26.2 Diabetes (% diabetic) 262 49.2 58.5 0.197 History of CVD (% positive) 262 52.3 41.5 0.133 History of CHD (% positive) 262 41.1 32.3 0.207 History of CHF (% positive) 262 40.6 29.2 0.101 Primary cause of renal failure (%) 259 0.341 Diabetes mellitus 44.8 53.9 Hypertension 10.8 6.2 Glomerulonephritis 44.3 40.0 Late referral (% <4 months) 198 21.7 16.4 0.404 BMI, kg/m 245 25.9 ± 5.6 28.2 ± 6.0 0.006 Residual urine output (%) 186 0.018 Not at baseline or follow-up at 1 year 14.6 19.6 Page 4 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Table 1: Patient characteristics by peritoneal dialysis switching status (Continued) At baseline but not at follow-up at 1 year 17.7 33.9 At baseline and at follow-up at 1 year 67.7 46.4 Laboratory Mean baseline albumin, g/dl 248 3.57 ± 0.44 3.64 ± 0.38 0.316 Mean baseline hemoglobin, g/dl 246 11.3 ± 1.5 11.3 ± 1.5 0.766 Median CRP (IQR), μg/dl 162 2.6 (1.1–6.2) 3.5 (1.6–5.7) 0.638 Baseline creatinine, g/dl 252 7.08 ± 2.66 7.94 ± 2.63 0.029 Baseline cholesterol, mg/dl 220 207 ± 53 210 ± 57 0.746 Baseline GFR, cc/minute/1.73 m 254 10.5 ± 0.26 10.3 ± 0.45 0.721 *By t-test (continuous variables) or χ test (categorical variables) Disease (ICED) and residual urine output were not asso- In our sensitivity analyses, we found no significant ciated with the risk of switching from PD to HD (data not decreased risk of death for PD switchers versus non- st nd shown). switchers by year of follow-up (1 and 2 years) or after stratification by diabetes mellitus status, history of cardio- Mortality risk associated with switching from peritoneal vascular disease, baseline residual urine output, and base- dialysis to hemodialysis line serum albumin (< 3.5 g/dl versus ≥ 3.5 g/dl) (data not The mortality rate per 100 patient-years was 18.5 for PD shown). Additionally, when we examined the effects of non-switchers versus 13.5 for PD patients who switched including passive follow-up in our mortality data, results to HD (Table 4). The cumulative mortality did not differ were similar and non-statistically significant (data not between switchers and non-switchers (Figure 3). In the shown). unadjusted analyses, switchers had a 6% decreased risk of death but the association was not statistically significant. Discussion After adjustment for demographics, clinical factors, and This prospective cohort study of incident PD patients laboratory values, there was an 11% decreased risk of showed that about 25% of patients switched to HD over death in PD switchers compared to non-switchers but the time, with more than 70% of the switching occurring results were not statistically significant (Table 4). within the first 2 years of treatment. Peritonitis was the leading cause of this modality change. In this U.S. pro- Table 2: Causes of switching from peritoneal dialysis to spective cohort study, the leading independent predictors hemodialysis of dialysis modality switching from PD to HD were black race and higher BMI. Importantly, there was no statisti- Causes of Switching Number (%) cally significant survival difference between PD patients N = 65 who switched to HD compared to those who remained on Infection (peritonitis and catheter-related) 24 (36.9%) PD. Cardiovascular (fluid overload) 12 (18.5%) At the end of 2005, only about 7.6% of U.S. dialysis patients were treated with PD, and this prevalence has Abdominal surgery 8 (12.3%) been declining since the mid-1990s [3]. One of the factors certainly contributing to this low PD prevalence remains Pancreatitis/malnutrition 7 (10.8%) the unacceptable high transfer rate from PD to HD described in several cohorts [7,17-22]. In an older Italian Decreased mental capacity 2 (3.1%) study with long follow-up, 18% of PD patients switched modality, as compared to 2.8% of the HD patients [7]. In Abdominal wall defect 1 (1.6%) our U.S. incident cohort, this switching rate was 25% for PD patients switching to HD, compared to 5% for HD Unknown 11 (16.9%) patients switching to PD [18]. In the Netherlands Cooper- Page 5 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Cum Figure 1 ulative percentage of peritoneal dialysis patients by time from first dialysis to first switch to hemodialysis (switchers only) Cumulative percentage of peritoneal dialysis patients by time from first dialysis to first switch to hemodialysis (switchers only). ative Study on the Adequacy of Dialysis, 3-year technique in the early 1990s, this cause of dialysis modality transfer survival was only 53% [21]. In a more recent U.S. cohort, from PD to HD was reported to be as high as 49% [25]. Guo et al. [17] showed a significant trend towards decreas- Over the past few years, the use of the twin-bag and Y-set ing transfer rates to HD during the first year on PD, from systems has certainly helped to decrease the peritonitis 19.6% in 1999 to 17.2% in 2001. rate [26]. Ultrafiltration failure, leading to fluid overload, which was the next most important cause of transfer from In agreement with previous studies, we found that infec- PD to HD in our study, has been shown to increase with tions remain the leading cause of switching from PD to time on PD [23,27]; however, in our cohort, this trend HD, followed by cardiovascular causes, mainly fluid over- was observed only during the first 18 months. We did not load [9,17,23]. Infectious causes, which are generally pre- find an increasing number of ultrafiltration failures in our ventable, were responsible for 28% of the transfers from PD patients, possibly because a much smaller number of PD to HD in a recent study by Mujais et al. [24]. However, patients switched from PD to HD after 2 years. This ultra- Page 6 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Percentage of switching peri dialysis switch Figure 2 toneal dialysis patients by main causes of switch and by time from first peritoneal dialysis to hemo- Percentage of switching peritoneal dialysis patients by main causes of switch and by time from first peritoneal dialysis to hemodialysis switch. filtration failure is a consequence of morphological and significant association between diabetes mellitus and functional changes of the peritoneal membrane, includ- modality transfer from PD to HD, although, in our ing increased small solute transport and lymphatic cohort, more patients with diabetes mellitus switched to absorption, over time [28,29]. Loss of residual renal func- HD (28.2%) compared to nondiabetics (21.3%). This tion with decreasing urine output observed over time in lack of statistical significance could be due to our smaller this cohort is also another likely mechanism leading to sample size. Parallel to previous studies, we found no more fluid overload as a cause of transfer from PD to HD. effect of age on transfer rate from PD to HD [17], suggest- ing that PD can be performed in any age group with We identified several patient characteristics associated appropriate support. with a higher risk of switching from PD to HD over time. Patients of black race were 5 times more likely than white There are little data looking at the association of BMI with patients to switch from PD to HD. This finding is in technique survival among PD patients. In our study, accordance with an older single-center study, which higher BMI was independently associated with increasing reported a significantly higher technique failure rate in risk of switching from PD to HD. This is in concordance black patients (39%) compared to white patients (8%) with a recent retrospective cohort study [33] and another [30]. Patients with diabetes mellitus have also been study from Australia and New Zealand, in which PD tech- reported to have a higher transfer rate from PD to HD in nique failure was 17% higher in obese patients compared some cohorts [17,24] but certainly not all [31,32]. Similar to patients with normal BMI [34]. Peritoneal dialysis to Huisman et al. [31] and Viglino et al. [32], we found no patients with higher BMI may be at increased risk for not Page 7 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Table 3: Predictors of dialysis modality switching: relative hazards for switching versus non-switching (time to first switch) from peritoneal dialysis to hemodialysis Relative Hazards (95% CI) Predictors Unadjusted Adjusted* Age (per 1-year increase) 1.00 (0.98–1.01) 0.98 (0.95–1.01) Race White 1.00 (ref.) 1.00 (ref.) Black 2.79 (1.25–6.23) 5.01 (1.15–21.8) Education High school graduate or higher 1.00 (ref.) 1.00 (ref.) Less than high school graduate 1.64 (0.83–3.23) 2.53 (0.98–6.55) Employment Employed 1.00 (ref.) 1.00 (ref.) Not employed 1.51 (0.76–3.01) 1.81 (0.66–4.94) Distance to dialysis clinic Living less than 30 miles from clinic 1.00 (ref.) 1.00 (ref.) Living 30 miles or more from clinic 0.65 (0.32–1.30) 0.42 (0.17–1.02) Diabetes Nondiabetic 1.00 (ref.) 1.00 (ref.) Diabetic 1.22 (0.71–2.12) 1.79 (0.74–4.33) BMI (per 1 kg/m increase) 1.10 (1.04–1.15) 1.09 (1.03–1.16) Baseline creatinine (per 1 mg/dl increase) 1.13 (1.02–1.26) 1.13 (0.97–1.33) Number (%) of patients switching/total number of patients by subpopulation: white, 47/212 (22.2%); black, 18/50 (36.0%); employed, 13/69 (18.8%); not employed, 52/193 (26.9%); high school graduate, 46/184 (25.0%); not high school graduate, 15/41 (36.6%); nondiabetic, 27/127 (21.3%); diabetic, 38/135 (28.2%); living at least 30 miles from dialysis clinic 41/155 (26.5%); living less than 30 miles from dialysis clinic 16/61 (26.2%). * Adjusted model (n = 195) included age, race, education, employment, distance to dialysis clinic, diabetes mellitus status, BMI, baseline serum creatinine. only infectious complications and inadequate dialysis but The impact of dialysis modality switching from PD to HD also peritoneal leaks because of raised intra-abdominal on patient survival remains controversial. We found no pressure [35,36]. Although in our study there was a clear significant difference in survival over time between PD trend towards a lower risk of transfer from PD to HD for patients who switched to HD compared to those who patients living 30 miles or more from their dialysis clinic, remained on PD. Similar results have been reported in this association was not statistically significant. However, black patients in the United States [38] and in European a recent report from Canada clearly showed a significant cohorts [7]. However, other studies have shown higher trend toward decreasing PD technique failure with mortality for PD patients who switched to HD compared increasing distance from their nephrologist [37]. to those who remained on PD [9,19]. In contrast to these Page 8 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Table 4: Risk of mortality associated with switching from peritoneal dialysis to hemodialysis: relative hazards for mortality for switchers vs. non-switchers Relative Hazard (95% CI) Model Non-switchers Switchers No. of deaths/total no. of patients 62/197 26/65 Incidence rate, per 100 patient-years 18.5 13.5 Unadjusted 1.00 (ref.) 0.94 (0.51–1.73) Adjusted Model 1 (Demographics) 1.00 (ref.) 0.87 (0.46–1.66) Model 2 (Model 1 + Clinical) 1.00 (ref.) 0.68 (0.33–1.40) Model 3 (Model 2 + Laboratory) 1.00 (ref.) 0.89 (0.41–1.93) In these analyses, all patients start as non-switchers; if the patient switched modality the patient then became a switcher on the date of switch. *Demographics: age, race, employment; clinical: ICED, diabetes, CVD, BMI, residual urine output; laboratory: baseline albumin and creatinine. Fully adjusted models included all these variables. reports, Van Biesen et al. [39], found a much better prog- tions, our study represents, to our knowledge, one of the nosis for PD patients who switched to HD compared to few prospective incident cohort studies specifically in the those remaining on PD. These differences in outcomes United States analyzing in detail switching of incident PD may be explained by differences in case-mix and reasons patients to HD, in terms of rate, timing, predictors and for technique failure. Several of these studies, including prognosis. our own, showed that PD technique failure does not nec- essarily indicate worse prognosis after switching to HD; Conclusion rather, more importantly, a timely transfer is vital when This prospective study of incident PD patients in the severe PD-related complications occur [40]. United States confirmed that the observed early switching rate from PD to HD remains too high and certainly repre- There are some limitations associated with our study. We sents a significant impediment to the long-term viability had some, but not detailed, data on residual urine output. of any PD program. Additional efforts are urgently needed Furthermore, we had no data on peritoneal membrane to continue to prevent PD-related infections, the leading characteristics; high peritoneal solute transport has been cause of PD technique failure; also, when antibiotic associated with PD technique failure and mortality in response for peritonitis remains inadequate, early Tenck- observational studies [23,41] but not in a more recent hoff catheter removal may help preserve the peritoneal prospective, randomized, controlled trial [42]. Also, membrane for future return to PD [43]. Moreover, we because of the relatively smaller sample size, we com- were able to identify important independent risk factors bined automated PD and continuous ambulatory PD. But for switching from PD to HD (BMI and black race). In this recently, Mujais et al. [24], using data from the Baxter context, more studies are definitely needed to better Healthcare Corporation On-Call system reported that understand why black PD patients were more likely to transfer to HD was lower in patients on automated PD switch to HD over time. Finally, our findings of no sur- than in patients on continuous ambulatory PD. However, vival difference between PD switchers and non-switchers compared to administrative data, our study provided the should be reassuring to providers and patients that PD advantage of a prospective incident cohort with detailed technique failure is not necessarily associated with poor data on comorbidities, laboratory values, and access to prognosis, but a timely transfer in setting of complications patient charts to determine specific causes of switching. remains important. There was a notable rate of lost to follow-up; however, mortality results including passive follow-up were similar Competing interests to those without passive follow-up. Despite these limita- The authors declare that they have no competing interests. Page 9 of 12 (page number not for citation purposes) BMC Nephrology 2009, 10:3 http://www.biomedcentral.com/1471-2369/10/3 Kaplan-Meier Figure 3 curve for mortality, peritoneal dialysis switchers versus non-switchers (P = 0.528 by log-rank) Kaplan-Meier curve for mortality, peritoneal dialysis switchers versus non-switchers (P = 0.528 by log-rank). Authors' contributions Acknowledgements We thank the patients, staff, and medical directors of the participating clin- BGJ analyzed and interpreted the data, reviewed medical ics at Dialysis Clinic, Inc., New Haven CAPD and St. Raphael's Hospital who records for causes of switching from peritoneal dialysis to contributed to the study. hemodialysis, drafted and revised the manuscript for important intellectual content. LCP performed the statis- This work was supported by grant no. RO1 DK 59616 from the National tical analysis, analyzed and interpreted the data, and Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, revised the manuscript for important intellectual content. grant no. R01-HS-08365 from the Agency for Health Care Research and DCC reviewed medical records for causes of switching Quality, Rockville, Maryland, and grant no. R01 HL 62985 from the National from peritoneal dialysis to hemodialysis and revised the Heart Lung and Blood Institute, Bethesda, MD. Dr. Crews is supported by Grant Number 1KL2RR025006-01 from the National Center for Research manuscript for important intellectual content. NEF con- Resources (NCRR), a component of the National Institutes of Health ceived and designed the study, obtained the data and (NIH), and NIH Roadmap for Medical Research. Dr. Powe is supported by revised the manuscript for important intellectual content. grant K24DK02643. NH was involved in the provision of study patients and revised the manuscript for important intellectual content. References JC conceived and designed the study, obtained the data, 1. Wu AW, Fink NE, Marsh-Manzi JV, Meyer KB, Finkelstein FO, Chap- obtained funding, supervised the study, and revised the man MM, Powe NR: Changes in Quality of Life during Hemodi- alysis and Peritoneal Dialysis Treatment: Generic and manuscript for important intellectual content. ASK was Disease Specific Measures. J Am Soc Nephrol 2004, 15:743-753. involved in the provision of study patients and revised the 2. Rubin HR, Fink NE, Plantinga LC, Sadler JH, Kliger AS, Powe NR: Patient Ratings of Dialysis Care With Peritoneal Dialysis vs manuscript for important intellectual content. NRP con- Hemodialysis. JAMA 2004, 291:697-703. ceived and designed the study, obtained the data, ana- 3. 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