Peritoneal Dialysis International, Vol. 8, pp. 253 -263,1988 0896-8608/88 $3.00 + .00 Printed in the USA. All rights reserved. Copyright 1988 Peritoneal Dialysis Bulletin, Inc.

Peritonitis During Continuous Ambulatory Peritoneal Dialysis (CAPD): Risk Factors, Clinical Severity, and

Pathogenetic Aspects

Anders Tranus, Olof Heimbrger, and Bengt Lindholm

Department of Renal Medicine, Karolinska Institute, Huddinge University Hospital, Stockholm, Sweden This study of 228 episodes of peritonitis occurring during a

total observation time of 2365 treatment months over a six-year period in a uniformly selected, trained, and treated continuous ambulatory peritoneal dialysis (CAPD) population (N = 124) showed the following major findings: 1) the risk of developing peritonitis was 55% within the first year and 89% within the first three years on CAPD; 2) high age (60 years) and year of CAPD start were risk factors for peritonitis; 3) neither sex, diabetes, or hypoalbuminemia were found to be risk factors for peritonitis; 4) the year of start, but neither the degree of severity, nor the time of the first episode affected the risk of developing a second episode of peritonitis; 5) no specific characteristics were identified in patients with the highest mean peritonitis incidence or in the patients without peritonitis; 6) in 27% of all episodes, turbidity of the dialysate was the only clinical finding; 7) the proportion of asymptomatic episodes was lower in patients 60 years; 8) the degree of clinical severity of peritonitis was not statistically influenced by the number of previous episodes; 9) the cause of peritonitis was established in only 26% of all cases; and 10) no statistical association was found between the cause of peritonitis and p atient characteristics.

KEY WORDS: Risk factors; pathogenesis; peritonitis.

D espite more than ten years of accumulated knowledge and experience, peritonitis is still the dominating complication of continuous ambulatory peritoneal dialysis (CAPD) (1, 2). The number of large, long-term, one-center studies on peritonitis are so far limited (3-6), and data regarding risk factors of peritonitis and possible relationships between peritonitis, pathogenesis, and clinical characteristics of patients are sparse.

In order to find methods for specific preventive and therapeutic measures, data regarding all episodes of peritonitis occurring during a six-year period were evaluated retrospectively in the present study. This analysis of peritonitis constitutes a continuation of a

Correspondence to: Anders Tranus, Karolinska Institute, Department of Nephrology, K 56, Huddinge University Hospital, S-141 86 Sweden.

Manuscript received April 12, 1988; accepted May 25, 1988.

survey of the overall results and experiences of CAPD at one center regarding the same patients and the same period of time as previously reported (7). The present study was facilitated by a uniform performance of CAPD with patients using mainly one type of bag-tubing connection (spike system). A total number of 228 episodes of peritonitis was studied to evaluate possible risk factors, pathogenesis, and the clinical severity of peritonitis. Risk factor analysis was carried out with Cox stepwise proportional hazards model (8).

METHODS

PATIENTS

The study includes all 124 patients who completed training for CAPD (including 2 patients trained for continuous cyclic peritoneal dialysis, CCPD) in our center from December 1978 to December 1984. Patients with early discontinuation were not excluded. Three of the patients were small children (males, 1 to 5 years of age). There were 77 males with a mean age of 55 years (range 1-76 years), and 47 females with a mean age of 52 years (range 29-76 years). The mean age of all patients at the start of CAPD was 54 years. The total observation time was 2365 patient months.

To evaluate the influence of age and diabetes the patients were classified into three groups: a) younger (

tent peritoneal dialysis (IPD) with 500 to 1000 mL i.p. volumes before CAPD was started. During 1978 through 1981, isoxapenicillin was given i.p. for 7 to 10 days after catheter implantation.

A standard spike system (Travenol System I, Tra venol Laboratories, Inc.) was used exclusively or temporarily by 93% of all patients. The spike system was used during 89% of the total observation time; in 198 months it was used together with an inline bacterio logical filter (Peridex, Millipore Corp.). During the study period, filters were also used (14 months) in patients dialyzing with the Swedish ACO-System (7). In all, the number of months with CAPD performed with systems (including filters) other than the standard spike system represented 19% of the total obser-vation time. Nonstandard systems were not excluded in this report as the aim of the study was to present all (unselected) data regarding peritonitis.

Most of the patients (86%, n = 107) were dialyzed mainly with 2000 mL bags exchanged four times a day. Only dialysis fluids containing lactate were used. The performance of CAPD was in accordance with internationally recommended guidelines (9-11). However, no disinfection of the spike-bag area was used until 1983 or 1984 (except for a short period of ethylalcohol disinfection of the spike in 1979) when routine use of a poviodine clamp (Baxter-Travenol) was begun. The avoidance of poviodine disinfection of the spike-bag area followed local recommendations and was based on the reported doubtful disinfectant capacity of this substance (12). No exit-site covering was used in 1981 through 1983. Since 1981, a daily shower was recommended, and swimming was allowed since 1983.

Procedures at bag exchange comprised the use of mask and either repeated hand disinfection with glycerol-alcohol solution after soap washing (after 1982) or the use of gloves (before 1982).

Suspected or certain spike contamination was followed by exchange of the tubing, as a rule performed by the patient. Thus, spike disinfection was not practiced in cases of touch contamination. One patient only was prescribed antibiotics prophylactically, and then merely periodically. Other details regarding training, and the performance of CAPD have been presented previously (7).

DEFINITION OF

PERITONITIS

The following definition of peritonitis was used for the whole study period: turbid dialysate, where etiology other than peritonitis (blood, fibrin) was not obvious. Thus, abdominal pain, fever, or positive dialysate analyses (Gram stain, elevation of the leucocyte count, or positive culture) were not required for the diagnosis of peritonitis (7). Elevation of the leucocyte count was not used as a criterion as this test was not performed routinely in 1978 or 1979, and also because leucocyte counts mild, < severe); and severe (severe abdominal pain, febrility, prominent turbidity). In cases of changing degree of severity during a single episode of peritonitis, the episode was classified according to its most severe phase.

DIAGNOSTIC AND THERAPEUTIC

PROCEDURES

In 1981, pre-culture membrane filtration (0.45 pore size) of all dialysate samples replaced the standard culture technique. After 1980 dialysate leucocytes were counted routinely (counting chamber) in cases of suspected peritonitis.

Whenever possible, peritonitis therapy was carried out at home. We used antibiotics with a narrow antibacterial spectrum. In the majority of all episodes a cephalosporin, cephradine was given. Antibiotics were administered for10 to 14 days and with few exceptions given i.p. Although controversial, lavage using a cycler was used in the initial phase of clinically severe episodes, as this measure frequently diminished pain.

STATISTICAL

METHODS

Probability of peritonitis was calculated using life table analysis, and differences between patient groups were analyzed by log rank test (18-19). Multivariate risk factor analysis was performed according to Cox stepwise proportional hazards model (8, 20).

Statistical comparisons and analyses of possible relationships as regards degree of severity and pathogenetic factors were evaluated with chi-square analysis, Fisher's exact test, calculations of Pearsson's correlation coefficient, and Student's unpaired t test.

Statistical analyses comprised (unless otherwise noted) only conditions of the first epis ode of peritoni tis, as two or more episodes in one patient can not universally be regarded as from each other independent observations. Statistical significance was accepted as p < 0.05.

RESULTS

OVERALL

OUTCOME

A total of228 episodes of peritonitis (149 in men, 79 in women) in 71 of all 124 patients were registered during the study period, corresponding to an average incidence of one episode per 10.4 patient months. Ex

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pressed as probability, the risk of developing peritoni tis was 55% during the first year of CAPD and 75% within two years (Figure 1). The risk of developing one, three, and six episodes within the first three years of CAPD were 89%, 51 %, and 23%, respectively (Figure 1).

RISK FACTORS

Age, sex, diabetes, year of starting CAPD

The probability of peritonitis did not differ significantly between the three patient groups (Figure 2), nor was there any statistically significant difference between men and women in the probability of the first episode of peritonitis. The average interperitonitis interval in the three patient groups was 10.2 to 10.6 months; this was similar in younger (all

(p = 0.028) (Table 1, Figure 4). Thus, the use of Cox analysis exposed a risk factor otherwise masked by other risk factors. In a further analysis using the Cox proportional hazards model, no additional risk factor was identified, but the significance of the year of start increased (p = 0.006, Table 1).

A comparison, using log rank test, between patients trained early and late during the observation period showed that the risk of peritonitis was significantly higher in patients commencing CAPD before July 1981 (n = 49) than in patients starting later (n = 75; p = 0.027; Figure 5). July 1981 was chosen as breakpoint as many of the changes of routines and the performance of CAPD were introduced at this approximate midpoint of the study period. Patients trained before this midpoint had an overall average peritonitis incidence of 1/9.3 months and patients trained later 1/12.9 months.

CAPD system, number of daily bag exchanges

The mean overall incidence of peritonitis was 1/10.8 patient months while using the standard spike system and 1/9.0 patient months during the use of other systems including spike system plus filter. Due

to the small number of observation months for the different nonstandard spike systems used during the study period (7), statistical comparisons between the different systems are not meaningful. Peritonitis that occurred while non-spike systems or spike system with filter were being used did not seem to differ from peritonitis developing during the usage of the standard spike system as regards etiological organisms, complications, or the need of hospital care.

The average interperitonitis interval in patients being dialyzed with three, four, and five exchanges per day appeared to be similar, although the number of patients regularly practicing three or five exchanges were too small to allow a statistical comparison.

Serum albumin

No statistically significant difference was found in the serum albumin level after three months of CAPD treatment between (adult) patients developing the

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first episode of peritonitis between 3 and 12 months of CAPD (n = 20, albumin 37.0 4.8 g/L; mean SD) and (adult) patients without peritonitis within their first year of CAPD (n = 27, albumin 39.1 5.3 g/L). No significant correlation was found in the former patient group between the three-month serum albumin value and the time of occurrence of the first epi-sode of peritonitis.

High risk patients

In a further attempt to trace potential risk factors, the patients with the highest incidence of peritonitis were studied separately. Thus, the 20 patients with the shortest interperitonitis interval at time of drop out or at the end of the study period had an incidence of 1 episode in 4.8 treatment months at that time. These patients did not differ from the other patients as regards sex, age, diabetes, visual acuity, year of CAPD start, etiological organisms, pathogenesis, or degree of severity of peritonitis. Nor was there any major differences in manual skill, motivation, or compliance when these factors were evaluated retrospec-tively. Furthermore, only 2 of the 13 patients who discontinued CAPD due to peritonitis {7) were considered to have an inadequate technique.

Patient characteristics did not differ between the 20 patients who developed their first episode ofperitonitis earlier than the others and the rest of the population. Nine of these 20 patients {all of whom had experienced their first episode of peritonitis within two months after CAPD start) were identified also among the above mentioned 20 patients with the shortest mean interperitonitis interval.

Peritonitis free patients

Fifty-three patients did not experience peritonitis during the study period. When evaluating this group

separately no statistically significant (chi-square analysis) difference in sex, age, or presence of dia betes was demonstrable in comparison with peritonitis patients. No patient remained free of peritonitis at four years of treatment {Figure 6). Among patients continuing CAPD for at least 2 years, only 18% were without experience of peritonitis at this time, and only 40% of patients observed at least one year were peritonitis -free during their first year of treatment {Figure 6).

Only 14 (21% ) out of the 67 patients treated with CAPD 1 year were free from peritonitis at the time of drop out or at the end of the observation period. Thirteen of the 67 patients were diabetics. This small peritonitis -free subpopulation of 14 patients did not differ from other patients as regards to sex or age. However, only one of these 14 peritonitis -free patients was diabetic.

Time and degree of severity of first episode

Risk factor analysis showed that the risk of developing a second episode of peritonitis was not influenced by the degree of severity of the first episode or by the duration of CAPD before the occurrence of the first episode (Table 2). However, the year of CAPD start seemed to affect also the risk of developing a second episode (p = 0.047, Table 2).

CLINICAL SEVERITY OF

PERITONITIS

Total autcome and outcome in different patient groups

Twenty-seven percent of all episodes of peritonitis were asymptomatic {Table 3). When all episodes were studied, the severity of peritonitis did not seem to change during the study period and showed a similar distribution in men and women. However, the sub

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clinical form seemed to be less frequent in non-diabetics 60 years than in the other two patient groups (Table 3). Statistical analysis of the first episode of peritonitis showed that subclinical infections were more uncommon in older (60 years) non-diabetics than in a) younger non-diabetics (p = 0.04) and b) in diabetics and younger non-diabetics categorized together (p = 0.006). Other comparisons between the three patient groups, between the sexes, or between diabetics and (all) non-diabetics did not show any statistically significant differences. In a comparison of all patients

Of all episodes, 12 (5%) occurred during in-hospital care. In 8 of these, bag exchanges were performed by staff.

Relation to year of treatment and patient groups

The proportion of peritonitis associated with tunnel and/or exit-site infection (with the same organism(s) around the exit site as in the dialysate) increased from 19% (of episodes with established etiology) in 1979 through 1982 to 43% in 1983 through 1984. Contemporaneously, the percentage ofperitonitis caused by touch contamination seemed to decrease. The proportion of episodes with unknown cause did not appear to change during the study period.

In the analysis of a possible relationship between the cause of peritonitis, including all episodes, and patient characteristics, no difference was found between males and females or between the three patient groups except that diabetics tended to have a lower proportion of touch contamination as a cause of peritonitis than younger and older non-diabetic patients: 3%, 15%, and 15% of all episodes, respectively. However, this tendency could not be confirmed statistically when data regarding only the first episode were analyzed. In this analysis all causes were categorized into three groups: a) contamination plus defective equipment; b) tunnel infections; and c) unknown causes, including exit-site infections.

Relatian to cause in subsequent episodes

No statistical association (chi-square analysis) was proved between the cause of the first episode of peritonitis and the cause of the second, third, and fourth episode. However, the result of these analyses are influenced by the high proportion of episodes with unknown origin.

DISCUSSION

The high mean age of the patients and the high proportion of diabetics in this study exceed those of

most other studies covering the same period of time (2, 21-23). Patient selection was influenced by the high transplantation activity in Sweden, by the liberal policy employed to accept patients for CAPD, and by the influence of patients' own preferences in the choice of dialysis modality, though, except during the first year of the study, most diabetics were recommended CAPD prior to hemodialysis.

PERITONITIS

INCIDENCE

The mean incidence of peritonitis in this study (1/10.4 patient months) equals that of most other studies regarding standard devices and covering the same period of time (3,22,24,25). However, the inaccuracy of estimating complications such as peritonitis by this mean incidence method has been pointed out in several reports. Instead, the use of the life table technique has been proposed (1, 7, 19, 26-28). Thus, expressed as probability, the risk of developing the first episode of peritonitis was 55% in this study (Figure 1), a figure comparable to that of many other units using standard devices (25,29). However, others have found a probability of 60 to 75% (2, 13, 30-32) within twelve months of treatment. Data as regards the probability of contracting >2 episodes (Figure 1) have been reported only occasionally (26).

RISK

FACTORS

The importance of a proper statistical evaluation in the analysis of peritonitis data is underlined by some seemingly conflicting findings in the present study. For example, a difference in the mean incidence between males and females in two of the three patient groups but not in the probability of developing the first or the second episode of peritonitis (Tables 1,2). Furthermore, no influence of sex or age was established in the univariate analysis of probability of the first episode of peritonitis (Table 1, Figure 2), but after adjustment for differences in the year of start, high age was found to be a risk factor (Table 1, Figure 4). In other studies, low (33, 34) as well as high (35) age have been identified as a risk factor. An increased

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incidence of infections in general in elderly patients has also been pointed out (36).

The identification of the year of start as a major risk factor (Tables 1,2; Figure 5) agrees with the gradual decrease in mean incidence of peritonitis over time (Figure 3). This might be due to changes in the performance of CAPD as well as to changes in staff experience (37,38). A similar decline in the peritonitis rate over time has also been observed at other centers (3, 4, 13, 21, 22, 25, 27, 34, 39-42). However, in some previous reports such a decline has coincided with the introduction of new connector systems (43). In other studies it has not been possible to confirm a decreased incidence of peritonitis with increasing center experience (26, 44) or size (41).

Our finding of diabetes not being a risk factor for peritonitis is in accordance with most other reports (4, 29-31, 45-47). Thus, the puncture of the bag for adding of insulin seems not to be a significant risk factor for peritonitis.

Hypoalbuminemia might be a contributing cause to peritonitis (48, 49) as well as an effect of peritonitis. However, in this study no correlation was found between the serum albumin level and the first episode of peritonitis. This negative finding is in keeping with the observation that a more severe first episode of peritonitis (with a subsequent decrease in serum albumin) were not accompanied by an increased risk of a second episode of peritonitis (Table 2).

Probability calculations for the first to the sixth episode of peritonitis (Figure 1, Table 2) might indicate a random distribution of peritonitis, as suggested in other reports (27,40,47). That the time from one episode to another does not seem to decrease has also been noted by others (34,50). Such observations are, however, influenced by the policy as regards transfer from CAPD after peritonitis and diverging findings have been reported (30). Furthermore, if observed long enough, all patients seem to, eventually, experience peritonitis (Figure 6) (32). On the other hand, there are considerable differences in the occurrence rate of peritonitis between patients. The occurrence of multiple episodes in some patients and none in others can, however, well be consistent with the law of random distribution of peritonitis (51). Thus, the difficulties in identifying individual high risk factorsother than age and motivation (33)-in this and other studies (4,47,52,53) can be explained by a random distribution of risk factors among the patients (40).

CLINICAL SEVERITY OF

PERITONITIS

Asymptomatic peritonitis is reported in non-uremic patients (54). The existence of peritonitis episodes without clinical findings or symptoms other than a cloudy dialysate in CAPD patients is, however, only occasionally reported (55-59). The high proportion of subclinical episodes (27%) in this study might be explained by our definition of peritonitis being wider than that used in most other studies. In only 4 (all with a positive culture) of the 15 subclinical episodes

where leucocytes were counted the initial leucocyte count of the dialysate was below lOO. 106/L, which is the recommended limit for the diagnosis of peritonitis (14). Thus, it is likely that episodes classified as subclinical in this study do represent true infections.

As most patients were able to reach the dialysis unit within one hour after the debut of signs of infection, and all but a few were trained in adding antibiotics to the bags, early institution of antibiotic treatment was possible in most cases. Thus, the high proportion of asymptomatic forms of peritonitis in this study could probably be explained by early diagnosis and early start of treatment. Furthermore, the severity of peritonitis has been reported to be proportional to the interval between presentation of cloudy fluid and the start of treatment (53).

Most authors agree that statistical comparisons as regards peritonitis should preferably be restricted to the first episode only (26,27). However, comparisons including all episodes (calculations of the mean incidence of peritonitis) are still used (45, 60) and can provide useful information (51). A random distribution of peritonitis (vide supra) , the lack of association between different episodes as regards the clinical severity as well as the cause of peritonitis, and that patients do not tend to contract peritonitis more often with time (34, 50) (Figure 1), might indicate that different peritonitis episodes may in fact be regarded as from each other independent events.

CAUSE OF

PERITONITIS

The finding of a high proportion of peritonitis episodes developing without any obvious or even suspected cause (Table 4) is in accordance with observations by others (3, 61) and underlines the need of further studies as regards the pathogenetic mechanisms of peritonitis. In agreement with others, touch contamination can be suspected in a large number of episodes classified as occurring without any known cause (3,60). Thus, in the present study the frequency of touch contamination (14%) as cause of peritonitis most likely underestimates the true frequency of "poor technique" as the underlying cause.

The observation that 7% of all episodes in this study, as well as 4 to 22% in other studies (3,5,47) occurred as a result of defective equipment emphasizes the need of further product improvements.

In one episode of peritonitis, the fallopian tubes were strongly suspected to be the portal of entrance (Table 4). Such cases, described occasionally in the literature (62-64), have been suggested to represent approximately 2% of all peritonitis episodes in CAPD (65). The existence of peritonitis associated with retrograde menstruation (66) and the finding of bacteria (67) and spermatozoa (68) in the female abdominal cavity emphasizes the possibility of this route of infection. That Staphylococcus epidermidis is a common finding in bacteriological vaginal samples (67, 69) indicates that this organism might reach the peritoneal cavity via a route other than along the in or outside of the peritoneal dialysis catheter .

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In the present study, 4% of all episodes were considered to be causally associated with a coexisting exitsite infection (Table 4) whereas in other studies 10 to 29% of all episodes of peritonitis have been reported to be secondary to or associated with an exit site infection (70-72). This difference might be explained by a dissimilarity in the incidence or in the efficacy in the treatment of exit-site infections.

ACKNOWLEDGMENTS

This study was supported by grants from Frenade Liv Mutual Group Life Insurance Company, Travenol Laboratories, The Swedish Association for Renal Diseased, ACO Lkemedel AB, and the National Institutes of Health, USA, Grant No. AM 27519.

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