Comparison of infectious complications in peritoneal dialysis patients using either a twin-bag system or automated peritoneal dialysis
Jenq-Wen Huang1,
Kuan-Yu Hung2,
Chung-Jen Yen2,
Kwan-Dun Wu2 and
Tun-Jun Tsai2,
1 Department of Internal Medicine, Far Eastern Memorial Hospital
2 National Taiwan University Hospital, Taipei, Taiwan, ROC
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Abstract
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Background. Automated peritoneal dialysis (APD) and twin-bag (TB) systems are two major peritoneal dialysis (PD) modalities. Published data comparing the infectious complications of these modalities is limited.
Subjects and methods. Ninety-five patients using APD (the APD group) and 117 patients using TB system (the TB group) were recruited. Among them, 35 patients used both modalities. The two groups clinical characteristics, incidences of infectious complications, and the time intervals to first PD-related infection were compared.
Results. Clinical characteristics, incidence of exit-site infection (ESI), and time intervals to first ESI were similar in the TB and APD groups. The incidence of peritonitis in the APD group (1.22 episodes/100 patient-months) was significantly (P<0.001) lower than that of the TB group (2.28 episodes/100 patient-months). Using the Cox proportional hazard model, APD was found to have a lower risk of peritonitis relative to TB systems, with marginal significance (RR 0.58, P=0.051).
Conclusion. APD was found to have a lower peritonitis rate than the TB system. Since reducing the peritonitis rate helps to maintain technical survival during PD, from this viewpoint, APD may be preferred for patients undergoing PD, unless contraindicated.
Keywords: automated peritoneal dialysis; exit-site infection; peritoneal dialysis; peritonitis; twin-bag system
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Introduction
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Infectious complications, including peritonitis and exit-site infections (ESI), remain important causes of technique failure, hospitalization, and death among patients undergoing peritoneal dialysis (PD) [1,2]. Automated peritoneal dialysis (APD) and twin-bag (TB) systems have become the most popular PD modalities, in large part because of their unique advantages [3,4]. With improvements in the design of exchange systems, the peritonitis rate has declined markedly. It has been previously reported that TB systems and APD enjoy a lower peritonitis rate than other Y-set systems [35]. With regards to ESI, it is still controversial whether TB systems and APD cause a lower incidence that other exchange systems [38]. However, comparisons between TB systems and APD of infectious complication rates are limited [9,10]. This motivated the present study in order to compare the incidence of peritonitis and ESI in PD patients treated with either APD or with the TB system.
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Subjects and methods
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Patients
Between February 1993 and March 2000, a total of 177 patients who underwent PD using either the TB system or APD for more than 3 months were included in the study. Of these patients, 95 used APD with a cycler (13 with PacXtraTM, Baxter®, USA; 78 with HomeChoiceTM, Baxter®, USA; four used both), and another 117 patients used the TB system (UltrabagTM, Baxter®, USA). There were 35 patients who used both modalities during their chronic PD treatment. All patients had a double-cuffed silastic Tenckhoff catheter positioned with the standard surgical procedure. The daily exchange procedure was once or twice for APD depending on the necessity of supplementary daytime manual exchange, and four or five times for the TB system, depending on clinical assessment.
Clinical characteristics for all patients including age, sex, serum albumin level prior to dialysis, the underlying cause of uraemia, duration of PD, episodes and incidence of peritonitis and ESI, time interval to first infection, and dropout of PD were reviewed for statistical analysis and comparison between APD and the TB treatment system.
In order to exclude bias in patient selection, the incidences of infectious complications were also studied among the 35 patients who had experienced both APD and the TB system.
Infectious complications
Peritonitis was diagnosed using the same criteria from previous studies [11], namely, if two of the following three criteria were present: (i) abdominal pain or tenderness; (ii) turbid effluent with WBC>100/µl with more than 50% being PMN; and (iii) an identified pathogen from effluent culture or smear. ESI was diagnosed in the presence of local tenderness, redness, and discharge at the exit-site of the Tenckhoff catheter, and negative culture did not exclude the diagnosis of ESI [12]. The incidence of infectious complication was calculated with the total number of infectious episodes divided by the total PD follow-up duration and presented as episodes per 100 patient-months.
Statistic analysis
All values are presented as mean±SEM unless specified otherwise. Univariate analysis was carried out using the chi-square, paired and unpaired t-test methods. Since PD duration was not normally distributed, the MannWhitney test was used to analyse PD duration. The incidences of infectious complications were compared using the Poisson test. The time intervals to first infection and the risk factors for infection were analysed by using KaplanMeier survival analysis and the Cox proportional hazard model respectively. A P-value <0.05 was considered to be significant.
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Results
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The clinical characteristics of patients using the APD and TB systems are shown in Table 1
. Mean age, sex, predialysis serum albumin, underlying renal disease, and mean duration were not significantly different between the two groups. The incidence of ESI did not differ between the two groups but patients undergoing APD had a significantly lower incidence of peritonitis than patients using the TB system. The mean survival interval to first episode of peritonitis for APD (50.9±3.9 months) was longer than that for the TB system (35.9±2.7 months), but the difference was not conclusive (P=0.079, Figure 1
). The mean survival interval to first ESI in APD (55.8±7.7 months) was not significantly different from that for the TB system (40.2±2.7 months, P=0.805, Figure 2
).
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Table 1. Patients treated with automated peritoneal dialysis (APD) and with the twin-bag system (TB); clinical characteristics compared
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Fig. 2. KaplanMeier survival analysis of time to first exit-site infection for APD and TB system patients.
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Of the 35 patients (M, 20; F, 15) who used both modalities, 30 patients switched from the TB system to APD and the other five patients changed from APD to TB. The ESI incidence was not significantly different for the two modalities (1.14/100 patient-months during APD vs 1.44/100 patient-months during TB, P=0.32). While using APD, patients had a significantly lower peritonitis incidence than when using the TB system (0.9/100 patient-months during APD vs 2.2/100 patient-months during TB, P<0.01).
By using the Cox proportional hazard model, we found that lupus patients had a significantly higher risk of both peritonitis and ESI than non-lupus patients (Table 2
). Patients undergoing APD had a lower risk of peritonitis than patients using the TB system, with marginal significance (P=0.051).
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Table 2. Risk factors for ESI and peritonitis for all patients (n=177) using Cox proportional hazard regression analysis
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Discussion
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Peritoneal dialysis is an effective modality for end-stage renal disease patients; however, it can be complicated by infections, in particular peritonitis and ESI [13]. APD using a cycler is as effective as other PD modalities [4,5,14]. In this study, there was no statistically significant difference in demographic characteristics of the patients using APD and or the TB system. The patient selection bias should therefore have been minimal. The study showed that APD enjoys a significantly lower peritonitis incidence than the TB system. By using KaplanMeier survival analysis and the Cox proportional hazard model, APD was shown to have a longer interval of time to the first instance of peritonitis (Figure 1
) and a relatively lower risk for peritonitis (Table 2
) than the TB system. Interpretation of these results leads to the conclusion that TB systems may be associated with a higher peritonitis incidence than APD, although the results from this study indicating this effect are not conclusive.
Lupus patients had a higher risk of infectious complications in our centre [12], which may be related to steroid use and lupus per se in these patients. The percentage of lupus was similar in patients using either APD or the TB system. Although diabetes and serum albumin levels can affect technical survival of PD patients [1,15], neither factor influenced the infectious complications in our study.
Random assignment of treatment modality in patients undergoing chronic PD is difficult [5], therefore the study of patients undergoing both modalities may eliminate the patient selection bias. The results of the study in these patients provided further confirmation that APD is associated with a lower incidence of peritonitis than the TB system.
The peritonitis rates for TB systems and APD have been reported as being similar in previous studies [9,10]. The reports pointed out that patients operate APD with manual spiking of the solution bags, whereas the TB system eliminates the spiking procedure and avoids touch contamination [9]. Convincing explanations for the lower peritonitis rate seen with APD in this study include fewer exchange procedures and the fact that it is done at home in a familiar environment with good hygiene [16]. In addition, the impairment of peritoneal immune function has been shown to improve with increasing dwell time [17,18]. Patients receiving APD either with a dry daytime or with a wet daytime may allow a longer period for recovery of peritoneal defence [19]. The above advantages may explain why APD is superior to the TB system in lowering the peritonitis rate.
There is still debate as to whether APD reduces ESI rates [57]. ESI rates were not significantly different for either of APD or the TB system in this study. Both the TB system and APD are disconnecting systems, using a minitransfer set with a Luerlock, which may result in the similar ESI incidence for the two modalities.
The convenience of APD can improve patient compliance. Additionally, PD-related peritonitis is decreased when using APD relative to use of the TB system. Since peritonitis was the major cause of hospitalization in the CANUSA study [1], the lower rate of peritonitis enjoyed by APD patients is an important advantage of APD over other PD modalities, as previously reported [5]. In conclusion, APD is an important treatment modality for PD patients, especially when there is a particular need to minimize the risk of peritonitis.
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Acknowledgments
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The authors would like to thank the Ta-Tung Kidney Foundation and the Mrs Hsiu-Chin Lee Kidney Research Fund for grant support of this study.
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Notes
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Correspondence and offprint requests to: Tun-Jun Tsai, MD, PhD, Division of Nephrology, Department of Internal Medicine, National Taiwan University Hospital, No.7, Chung-Shan South Road, Taipei 100, Taiwan, ROC. 
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Received for publication: 28. 7.00
Revision received 19.10.00.