In this national prospective cohort study, we found that PD patients who were treated at clinics with greater numbers of PD patients were at lower risk of switching to hemodialysis and cardiovascular events. The associations of decreased switching to hemodialysis and cardiovascular events with larger PD clinic size were consistent, regardless of adjustments for demographics, comorbidities, body size, albumin, creatinine, and clinic years in operation; the results were also robust to a change in clinic size cutoff. No association of PD clinic size with cardiovascular mortality or all-cause mortality was seen.
Our results showing that patients treated at clinics with greater numbers of PD patients were far less likely to switch to hemodialysis over the course of the study are consistent with previous reports showing decreased technique failure with large PD clinic size (3
). 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, clinical 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 hemodialysis.
The occurrence of cardiovascular events was also decreased in patients treated at clinics with greater numbers of PD patients. Greater staffing and better training at clinics that have more PD patients may lead to more opportunities for cardiovascular disease prevention through dietary or medication adherence. Such clinics could also have better, more established, referral systems—including pre-transplant evaluation and comprehensive cardiovascular workups—and better management, including improved fluid volume management (12
); these improvements could prevent some cardiovascular events. Another possibility is that these larger, more established clinics recruit fewer patients with severe cardiovascular 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 cardiovascular mortality after adjustment for comorbidity, although there was a non-significant trend toward decreased risk without this adjustment. The leading cause of mortality in dialysis patients is cardiovascular disease, and it may be that the inflammatory processes and hypertension that go along with dialysis cannot be sufficiently controlled to prevent cardiovascular 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. 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 is small and imbalanced in terms of size (3 larger clinics versus 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 hemodialysis and cardiovascular morbidity. PD clinic size may act as a proxy of not only greater PD experience but also more focus on the modality and more incentives to improve PD practices at the clinic.