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Clinical |
Department of Epidemiology,1 Johns Hopkins Bloomberg School of Public Health; Department of Medicine,2 Johns Hopkins University School of Medicine, Baltimore, Maryland; Yale University,3 New Haven, Connecticut; Department of Health Policy and Management,4 Johns Hopkins Bloomberg School of Public Health; Nephrology Center of Maryland,5 Baltimore, Maryland, USA
Correspondence to: B.G. Jaar, Welch Center for Prevention, Epidemiology and Clinical Research, Johns Hopkins Medical Institutions, 2024 E. Monument St., Suite 2-500, Baltimore, Maryland 21287 USA. bjaar{at}jhmi.edu
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ABSTRACT |
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Objective: Very few studies have addressed the
relationship between number of peritoneal dialysis (PD) patients treated at a
clinic (PD clinic size) and clinical outcomes. In a national prospective
cohort study of incident PD patients (n = 236, from 26 clinics), we
examined whether being treated at a larger PD clinic [>50 PD patients
(n = 3 clinics) vs 
50 PD patients (n = 23 clinics)] was
associated with better patient outcomes, including fewer switches to
hemodialysis, fewer cardiovascular events, lower cardiovascular mortality, and
lower all-cause mortality. Methods: Multivariable Cox models were used to assess
relative hazards (RHs) for modality switches, cardiovascular events,
cardiovascular deaths, and all-cause deaths by PD clinic size. All models were
adjusted for demographics, comorbidities, laboratory values, and clinic years
in operation. Results: Being treated at a clinic with >50 patients
was associated with fewer switches to hemodialysis (RH = 0.13, 95% CI 0.06
– 0.31) and fewer cardiovascular events (RH = 0.62, 95% CI 0.06 –
0.98). No associations of PD clinic size with cardiovascular or all-cause
mortality were seen. Conclusion: PD patients treated at clinics with greater
numbers of PD patients may have better outcomes in terms of technique failure
and cardiovascular morbidity. PD clinic size may act as a proxy of greater PD
experience, more focus on the modality, and better PD practices at the clinic,
resulting in better outcomes.
KEY WORDS: Clinic size; technique failure; cardiovascular morbidity; mortality.
Dialysis clinics that offer peritoneal dialysis (PD) vary widely in the number of PD patients they treat: some clinics may have only a few patients at a time, while others may be entirely devoted to PD and have dozens of PD patients. The number of PD patients treated, or PD clinic size, may act as a proxy for the clinic's PD experience and investment in the modality. Clinics with larger PD clinic size may devote more time and staff to establishment and maintenance of good PD practices; conversely, staff may be overwhelmed by a large patient load and be less able to give patients individual attention. Whether PD patients treated at clinics with a larger PD clinic size have better or worse outcomes has not been well studied.
One possible adverse outcome for PD patients is technique failure, in which the patient starts on PD and must switch to hemodialysis (HD). Although some patients may switch due to personal choice, often the reasons are related to infection, catheter issues, inadequate dialysis, or psychosocial issues (1). Approximately 20% – 25% of PD patients switch modality to HD during the first year and, by 4 years, the rate is approximately 50% (1,2). A recent study of administrative data on four large cohorts of USA adult PD patients showed that a greater number of PD patients treated at a center was a powerful predictor of greater technique survival (1); a study in The Netherlands also showed that larger clinics had fewer technique failures (3).
Other patient outcomes may also be affected by PD clinic size, including morbidity and mortality. A Canadian study showed that a greater cumulative number of PD patients treated at a clinic was associated with decreased mortality among the patients treated at such clinics (4). The authors postulated that this association was due to the clinics with more experience (reflected by the cumulative number of patients) adopting better PD practices, or choosing more appropriate patients for PD, or both. For these same reasons, cardiovascular (CV) events and mortality could also be decreased among patients at clinics with large PD clinic size.
Few studies have examined the relationship between PD clinic size and outcomes in incident patients well-characterized with respect not only to demographics but also to comorbid disease status and other clinical and laboratory characteristics. In a national prospective cohort study of incident PD patients, we examined whether being treated at a larger PD clinic was associated with better patient outcomes, including fewer switches to HD, fewer CV events, lower CV mortality, and lower all-cause mortality.
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MATERIALS AND METHODS |
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DATA COLLECTION
Independent Variable: As part of the EQUAL Study, a questionnaire
was administered to medical directors or head nurses at the 81 participating
clinics in October 1998. The questionnaire collected information regarding
customary practice for several processes of care
(6–8).
For this study, our independent variable was derived from questionnaire items
related to PD processes of care, and only those responses from clinics with PD
patients enrolled in CHOICE (n = 30) were examined. Peritoneal
dialysis clinic size was derived from the item "How many peritoneal
dialysis patients were dialyzed at your clinic in October 1998?," with
possible responses being "None," "Less than 25
patients," "25 – 50 patients," "51 – 100
patients," "101 – 200 patients," and "More than
200 patients." Of the 30 clinics that enrolled PD patients, 26 (87%)
responded to this item, representing 236 of the 274 total PD patients. The
distribution of patients according to clinic response was as follows: none,
1%; <25, 17%; 25 – 50, 26%; 51 – 100, 9%; 101 – 200, 48%;
and >200, 0%. Due to small numbers of patients in the individual
categories, we collapsed responses into two categories (50 or fewer patients
vs more than 50 patients) for all analyses. We chose the 50-patient size
cutoff because this gave a fairly even distribution of patients and we planned
to do patient-level outcomes analyses.
Outcome Ascertainment: Our outcome variables included modality switch (to HD), CV events, CV mortality, and all-cause mortality. Modality switches were defined as switches to HD that lasted more than 30 days, as described previously (2).
Nonfatal CV events were assigned by the following algorithm: (1) adjudicated records (from medical chart review) were considered the primary source of information for a nonfatal CV event, regardless of whether it was a procedure or a non-procedure event; (2) in the absence of an adjudicated record, any USRDS billing data record or report from DCI confirmed a procedure event; (3) for non-procedure events without an adjudicated record, the algorithm for assigning CV events was as follows: (a) any USRDS or HCFA billing data record allowed assignment of the CV event; (b) a clinic record when supported by a corresponding comorbidity record allowed assignment of the event; and (c) subsequent CV events in the same broad category within 30 days of discharge from a prior hospitalization for an assigned CV event were not assigned as separate events. Cardiovascular events included myocardial infarction, cerebrovascular accident, and the following atherosclerotic CV disease-related procedures: abdominal aortic aneurysm, percutaneous transluminal coronary angioplasty, coronary artery bypass graft, carotid endarterectomy, peripheral bypass of the lower extremity, and amputations (excluding digit amputations).
For fatal CV events, CV cause of death was assigned according to the following hierarchy: (1) the immediate cause of death from the adjudicated record, if CV related; (2) the underlying cause of death from the adjudicated record, if CV related; and (3) the first listed CV-related cause in the National Death Index (NDI) record, excluding contributing causes; otherwise death was considered non-CV. The first CV event (fatal or nonfatal) during the study period was considered an incident CV event; fatal CV causes of death were considered CV mortality. All-cause mortality information was ascertained from NDI records, clinic reports, medical records, and Centers for Medicare & Medicaid Services (CMS; death notification forms and Social Security records). Follow-up for CV events and mortality continued until death, transplantation, or the last follow-up date of 31 December 2004.
Other Variables: Data on patients' demographics (age, sex, and race) and socioeconomic status (education, employment, and marital status) were collected from a baseline self-report questionnaire. Presence and severity of comorbid conditions were assessed at baseline using the Index of Coexistent Disease (ICED), the composite integer score of which ranges from 0 to 3 (with 3 as the highest severity level) (9,10). Presence of individual conditions, including diabetes, was determined from the same medical record review process through which ICED was determined. Late referral was defined as a time between first nephrologist evaluation and start of dialysis of less than 4 months, as described previously (11). Laboratory values and height and weight (used to calculate body mass index) were obtained from patients' records and from the CMS Medical Evidence reports (CMS Form 2728). Clinic years in operation were obtained along with the independent variable from the facility questionnaire, as described above.
STATISTICAL METHODS
We first compared patient characteristics by dichotomized measures of
processes of care, using Pearson's chisquare tests for categorical variables
and two-sided t-tests for continuous variables. Kaplan–Meier estimates
were calculated for time to modality switch, first CV event, CV mortality, and
all-cause mortality; multivariable Cox models were used to obtain relative
hazards of the outcomes by PD clinic size. Due to concerns about possible bias
in the >50 patient group (representing only 3 clinics), we also performed
sensitivity analyses in which outcomes were examined using a 25-patient
cutoff. This cutoff gave an even distribution of clinics rather than
patients.
Variables were chosen as covariates for the adjusted models if they were confounders (i.e., significantly associated with both the PD clinic size and patient outcomes) or had been previously shown to be associated with patient outcomes. All analyses were performed using STATA v. 9.1 (College Station, TX, USA).
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RESULTS |
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ASSOCIATION OF PD CLINIC SIZE WITH MODALITY SWITCH TO HD
Figure 1 shows that the
cumulative incidence of modality switches from PD to HD was much lower in the
clinics with more than 50 PD patients. This association held up to adjustment
for demographics, clinical characteristics, laboratory values, and clinic
years in operation (Table 3),
with the risk of switching to HD being 74% – 86% less in those patients
treated at clinics with more than 50 patients overall.
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ASSOCIATION OF PD CLINIC SIZE WITH CV EVENTS, CV MORTALITY, AND ALL-CAUSE MORTALITY
Cumulative CV event incidence was lower in the larger clinics
(Figure 2). This 38% –
55% lower risk of CV event incidence in patients treated at larger clinics was
independent of adjustments for demographics, clinical characteristics,
laboratory values, and clinic years in operation
(Table 3). Although the
relative hazard for CV mortality indicated that incidence was lower in the
larger clinics, these associations were not statistically significant and
disappeared after adjustment for comorbidity
(Table 3). Finally, no
associations of PD clinic size and all-cause mortality were seen in this study
(Table 3).
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SENSITIVITY ANALYSES
Using a clinic size cutoff of 25 rather than 50 patients (giving an equal
number of clinics in each group), we found that the results were generally
similar to those using the original cutoff. Patients in the larger (
25
patients) PD clinics were less likely to switch modality [adjusted relative
hazard (RH) = 0.23, 95% confidence interval (CI) 0.12 – 0.43; p
< 0.001] and less likely to have a CV disease event (adjusted RH = 0.55,
95% CI 0.33 – 0.92; p = 0.023). As with the 50-patient cutoff,
clinic size using a 25-patient cutoff was not associated with either CV or
all-cause mortality.
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DISCUSSION |
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TOPABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONDISCLOSUREREFERENCES |
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Our results showing that patients treated at clinics with greater numbers of PD patients were far less likely to switch to HD over the course of the study are consistent with previous reports showing decreased technique failure with large PD clinic size (3,4). Greater numbers of PD patients at a clinic reflect a greater investment in the PD modality, in terms of both staff and time dedicated to training and patient care. Such an investment could result in better overall PD practices, more individual time spent with PD patients, and more efficient training of PD patients, in turn resulting in fewer complications (or better management of complications) that lead to modality switching. The staff at these large clinics may also have strong incentive to encourage patients to stay with PD for as long as possible. Additionally, clinic staff caring for a larger number of PD patients have probably logged more PD experience than those caring for fewer PD patients and may be more adept at recruiting the best candidates for this modality, and such candidates would have fewer reasons to switch to HD.
The occurrence of CV events was also decreased in patients treated at clinics with greater numbers of PD patients. More staff and better training at clinics that have more PD patients may lead to more opportunities for CV disease prevention through dietary or medication compliance. Such clinics could also have better, more established, referral systems — including pretransplant evaluation and comprehensive CV workups — and better management, including improved fluid volume management (12); these improvements could prevent some CV events. Another possibility is that these larger, more established clinics recruit fewer patients with severe CV disease; although, since we adjusted for presence and severity of comorbid conditions, this would likely not completely explain the association we found.
Finally, we saw no association of PD clinic size with CV mortality after adjustment for comorbidity, although there was a nonsignificant trend toward decreased risk without this adjustment. The leading cause of mortality in dialysis patients is CV disease and it may be that the inflammatory processes and hypertension that go along with dialysis cannot be sufficiently controlled to prevent CV death, even if intermediate events can be reduced. We also found that all-cause mortality was not decreased in patients treated at clinics with greater numbers of PD patients, although one Canadian study did find such an association with cumulative numbers of PD patients treated (4). It may be that differences between Canada and the United States account for this difference (13), or it may be that cumulative number of patients treated is a better marker of PD experience than a cross-sectional determination of number of patients treated in PD clinics.
Some limitations of this study deserve mention. First, measure of PD clinic size was taken cross-sectionally at the start of the study and PD practice may have changed over time. Additionally, clinic size does not necessarily completely reflect clinic experience, since we did not have information on staff experience, which may be greater in some of the smaller clinics. Second, we had no information on the characteristics of the PD trainers, and it has been recommended that trained experienced nurses provide PD training whenever possible to improve outcomes (14). Third, the number of clinics being examined was small and imbalanced in terms of size (3 larger clinics vs 23 smaller clinics); although we performed sensitivity analyses with balanced numbers of clinics and showed similar results, the possibility of bias cannot be discounted. Finally, the observational design of the study does not allow for causal inference and, despite measurement of and adjustment for many patient and clinic characteristics, there is always the possibility of residual confounding due to unmeasured patient or clinic factors.
In summary, patients treated at clinics that have more experience in caring for PD patients, which may be reflected by having greater numbers of PD patients, may have better outcomes in terms of switching to HD and CV morbidity. Peritoneal dialysis clinic size may act as a proxy of not only more PD experience but also more focus on the modality and more incentives to improve PD practices at the clinic.
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DISCLOSURE |
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ACKNOWLEDGMENTS |
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We thank B. Piraino for her expert advice in preparing this manuscript. We also thank the patients, staff, and medical directors of the participating clinics at DCI and New Haven CAPD who contributed to the study.
Received 28 March 2008; accepted 8 September 2008.
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This article has been cited by other articles:
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  B. Piraino, E. Minev, J. Bernardini, and F. H. Bender DOES EXPERIENCE WITH PD MATTER? Perit. Dial. Int., May 1, 2009; 29(3): 256 - 261. [Full Text] [PDF]
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
