short reports

Peritoneal Dialysis International, Vol. 27, pp. 203–213 Printed in Canada. All rights reserved.

0896-8608/07 $3.00 + .00 Copyright © 2007 International Society for Peritoneal Dialysis

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Peritoneal Transport Function and Endothelium-Dependent Vasodilation

PATIENTS AND METHODS

A cross-sectional study enrolled 31 clinically stable adult PD patients who were free of peritonitis for at least 1 month. Each participant was presented and signed an informed consent; the study protocol was approved by the hospital Research Ethics Committee. A standard PET following an overnight fasting period was used to evaluate SSMT (7,8). In order to allocate a comparable number of individuals to each SSMT category, quartiles of the 4-hour dialysate-to-plasma ratios of creatinine (D4 /P creat) were used to classify transport as low (0.39 – 0.50), low-average (0.52 – 0.60), high-average (0.62 – 0.71), and high (0.73 – 0.95). Additionally, the initial and final dialysate sample glucose concentrations were measured to calculate a timed glucose ratio (D4 /D0 glucose). Dialysis adequacy was estimated by a normalized weekly urea clearance (Kt/V). Urea (urease method), creatinine (Jaffé reaction, undeproteinized), and glucose (glucose oxidase) determinations were performed by automated methods (Advia 1650; Bayer HealthCare, Tarrytown, New York, USA). Nitric oxide metabolites [nitrate and nitrite

RESULTS

The study population characteristics are presented in Table 1. Brachial artery FMD and categories of SSMT are depicted in Table 2. No significant differences in pre-flowocclusion vessel diameter or FMD among categories were found, albeit FMD in the low transport category seemed to be of greater magnitude. Linear tendency evaluation (p = 0.052 and p = 0.062 for untransformed and log-transformed data respectively) was also unable to demonstrate differences. Flow-mediated vasodilation was negatively correlated with the initial vessel diameter (r = –0.443, p = 0.013) and 4-hour (r = –0.358, p = 0.048) and 24-hour (r = –0.393, p = 0.029) peritoneal NOx, and positively correlated with D4/D0 glucose (r = 0.358, p = 0.048). DISCUSSION

Flow-mediated vasodilation was evaluated along different SSMT categories. No significant differences were found, although FMD was higher in the low transport 203

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Peritoneal dialysis (PD) patients display significant differences in peritoneal small solute membrane transport (SSMT) (1,2). It has been thought that transport magnitude is dependent upon the ratio of the perfusing vessels and peritoneal membrane surface areas. Local vessels’ surface area and permeability may be submitted to endothelial control. Flow-mediated vasodilation (FMD), a surrogate indicator of endothelial-dependent vasodilation, may be estimated by high-resolution ultrasound of peripheral arteries. Reduced nitric oxide (NO) activity, altered endothelial-dependent vasodilation, and endothelial dysfunction have been reported in end-stage renal disease (ESRD) patients (3–6). Small solute membrane transport characteristics and abnormal peritoneal endothelial function may be related. The current study evaluated FMD in stable PD patients allocated to different categories of SSMT based on a peritoneal equilibration test (PET).

(jointly referred to as NOx)] were measured by chemiluminescence (Nitric Oxide Analyzer, model 280; Sievers Ionics Instrument, Boulder, Colorado, USA) in deproteinized samples of serum obtained for Kt/V and PET estimates (serum, 4-hour and 24-hour dialysate). Duplicate calibration curves (1 – 100 µmol/L; r = 0.9993) were used, as previously described (9). Flow-mediated vasodilation was evaluated according to recommendations of the International Brachial Artery Reactivity Task Force, using a 7.0 MHz transducer (Model 128XP/10; Acuson, Mountain View, California, USA) (10,11). Results are expressed as mean ± standard deviation, median and interquartile range, or percentage. Chisquare (or Fisher exact) test was used in comparisons. ANOVA with Duncan post hoc test was employed to localize differences. Associations were explored by Pearson’s correlation coefficient and tendencies by linear regression analysis of untransformed and logarithm-transformed data. The software Statistical Package for Social Sciences (SPSS version 11.5; SPSS Inc., Chicago, Illinois, USA) for Windows operating system (Microsoft Corp., Redmond Washington, USA) was used overall.

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TABLE 1 Study Population Characteristics (n=31) Variable

Value

49±18 years 52% 87% 136±22 mmHg 85±16 mmHg 84% 23 (9–50) months 300 (200–400) mL 200 (0–500) mL 1.86±0.33 0.63±0.14 0.54±0.11 47 (31–84) µmol/L 33 (20–46) µmol/L 40 (23–59) µmol/L

SD = standard deviation; BP = blood pressure; CAPD = continuous ambulatory peritoneal dialysis; IQR = interquartile range; Kt/V = normalized weekly urea clearance; D4/P creat = dialysateto-plasma ratios of creatinine; D/D0 glucose = timed glucose ratio; NOx = serum nitric oxide metabolites; D4hr = 4-hour dialysate NO metabolites; D24hr = 24-hour dialysate NO metabolites.

category. Also, linear regression analysis was unable to unravel significant differences, suggesting that peritoneal membrane transport function and FMD may be unrelated in peritonitis-free patients on PD. Alternatively, the results could be the effect of other factors upon endothelial or peritoneal function, such as diet, levels of Larginine and its analogs, blood pressure control and drugs, fluid status, presence of atherosclerosis, and the cause of renal failure. Reduced total NO production and impaired endothelial function were detected in ESRD and

continuous ambulatory PD patients respectively (3,4,12), yet were apparently not linked to SSMT. Flow-mediated vasodilation was negatively correlated with 4-hour and 24-hour peritoneal NOx, albeit not with serum NOx. Lack of correlation between FMD and plasma NO has been reported in healthy individuals and in patients with systemic sclerosis (13,14). Apparently, correlation between brachial artery FMD and peritoneal NO levels has not been previously explored: no study in ESRD or dialysis patients could be found. The weak positive correlation between D4 /D0 glucose and FMD may reflect a tendency to higher FMD in the low transport group. Negative correlation between FMD and resting artery diameter has been previously found in individuals with cardiovascular risk (11,15), yet a positive correlation has been observed in hemodialysis and PD patients, suggesting that other factors, dependent on dialysis or ESRD, may be contributory, but no such factors could be identified in the current study (5,11,16). In addition to vascular reactivity, other factors may affect SSMT. Nitric oxide-mediated peritoneal vascular changes may be local events, thus far undetectable from a distance (the brachial artery). Results of the current study suggest that a relationship between peritoneal membrane transport function and endothelial-mediated vasodilation was not apparent in peritonitis-free patients on PD. ACKNOWLEDGMENTS The Nephrology Laboratory received support from Conselho Nacional de Pesquisa (CNPq), Secretaria de Ciência e Tecnologia do Estado do Rio Grande do Sul (SCT), Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul (FAPERGS), and Pontifícia Universidade Católica do Rio Grande do Sul (PUCRS).

Ana Elizabeth Figueiredo* Bartira E. Pinheiro da Costa Adriana Conti André A. Poitevin Breno José Acauan Filho

TABLE 2 Brachial Artery Diameter Changes and Transport Categories (n=31)

High (n=8) IAD (mm) FMD (%)

3.7±0.6 12.3 (1.6–14.2)

PET categories High-average (n=9) Low-average (n=8) 4.3±0.8 13.5 (3.7–19.0)

3.9±0.6 9.6 (4.5–14.2)

Low (n=6)

Total

p Valuea

3.6±0.5 19.8 (10.9–28.4)

3.9±0.7 12.8 (5.1–17.8)

0.119 0.070

PET = peritoneal equilibration test, classified by quartiles of small solute membrane transport; IAD = initial artery diameter; FMD = flow-mediated dilation. a ANOVA, with post hoc Duncan. Data are presented as mean±SD, or median (interquartile range 25–75). 204


Demographic Age (mean±SD) Female Caucasian Clinical Systolic BP (mean±SD) Diastolic BP (mean±SD) Treatment CAPD Duration on dialysis [median (IQR)] Daily ultrafiltration [median (IQR)] Residual diuresis [median (IQR)] Kt/V (mean±SD) D4/P creat (mean±SD) D/D0 glucose (mean±SD) Biological NOx [median (IQR)] D4hr [median (IQR)] D24hr [median (IQR)]

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Elton Torres Domingos O. d’Avila Carlos E. Poli de Figueiredo Programa de Pós-Graduação em Medicina e Ciências da Saúde (Nefrologia) Pontifícia Universidade Católica do Rio Grande do Sul/IPB/HSL/FAMED/FAENFI Porto Alegre, Brazil *e-mail: [email protected] REFERENCES

Nephrol Dial Transplant 2000; 15:1194–2000. 13. Li R, Lyn D, Lapu-Bula R, Oduwole A, Igho-Pemu P, Lankford B, et al. Relation of endothelial nitric oxide synthase gene to plasma nitric oxide level, endothelial function, and blood pressure in African Americans. Am J Hypertens 2004; 17:560–7. 14. Andersen GN, Mincheva-Nilsson L, Kazzam E, Nyberg G, Klintland N, Petersson AS, et al. Assessment of vascular function in systemic sclerosis: indications of the development of nitrate tolerance as a result of enhanced endothelial nitric oxide production. Arthritis Rheum 2002; 46:1324–32. 15. Celermajer DS, Sorensen KE, Gooch VM, Spiegelhalter DJ, Miller OI, Sullivan ID, et al. Non-invasive detection of endothelial dysfunction in children and adults at risk of atherosclerosis. Lancet 1992; 340:1111–15. 16. van Guldener C, Lambert J, Janssen MJFM, Donker AJM, Stenhouwer CDA. Endothelium-dependent vasodilatation and distensibility of large arteries in chronic haemodialysis patients. Nephrol Dial Transplant 1997; 12(Suppl 2):14–18.

Spectrum and Sensitivity Pattern of GramNegative Organisms Causing CAPD Peritonitis in India Peritonitis remains the most important cause of morbidity and mortality in patients on continuous ambulatory peritoneal dialysis (CAPD), despite reductions in the rates in recent years (1). With improved quality of exitsite care, gram-negative bacteria have emerged as major organisms causing peritonitis. Antimicrobial use for gram-negative cover in the initial empirical treatment varies according to the spectrum of organisms causing peritonitis, as well as their sensitivity patterns. Hospitals worldwide are facing rapid emergence and spread of antimicrobial-resistant bacteria. For patients with end-stage renal disease (ESRD), this not only translates into prohibitive costs of hospitalization, but also increases morbidity and mortality (2). There is a general consensus in the medical community that antimicrobial resistance has emerged as an important variable influencing patient outcomes and overall resource utilization (3). We studied the spectrum and sensitivity patterns of gram-negative organisms causing peritonitis in ESRD patients on CAPD at a large tertiary-care public-sector hospital in India. MATERIALS AND METHODS

Patients symptomatic with features suggestive of peritonitis between January 2000 and July 2004 were 205


1. Haraldsson B. Assessing the peritoneal dialysis capacities of individual patients. Kidney Int 1995; 47:1187–98. 2. Davies SJ. Monitoring of long-term peritoneal membrane function. Perit Dial Int 2000; 21:225–30. 3. Schmidt RJ, Yokota S, Tracy T, Sorkin MI, Baylis C. Nitric oxide production is low in end-stage renal disease patients on peritoneal dialysis. Am J Physiol 1999; 276:F794–F797. 4. Schmidt RJ, Baylis C. Total nitric oxide production is low in patients with chronic renal disease. Kidney Int 2000; 58:1261–6. 5. van Guldener C, Janssen MJFM, Lambert J, Steyn M, Donker AJ, Stehouwer CD. Endothelium-dependent vasodilatation is impaired in peritoneal dialysis patients. Nephrol Dial Transplant 1998; 13:1782–6. 6. Cross JM, Donald A, Vallance PJ, Deanfield JE, Woolfson RG, MacAllister J. Dialysis improves endothelial function in humans. Nephrol Dial Transplant 2001; 16:1823–9. 7. Twardowski ZJ, Nolph KD, Khanna R, Prowant BF, Ryan LP, Moore HL, et al. Peritoneal equilibration test. Perit Dial Bull 1987; 7:138–47. 8. Figueiredo AE, Conti A, Poli de Figueiredo CE. Influence of the preceding exchange on peritoneal equilibration test. Adv Perit Dial 2002; 18:75–7. 9. Lessio C, de Assunção Silva F, Gloria MA, Di Tommaso AB, Gori Mouro M, Di Marco GS, et al. Cyclosporine A and NAC on the inducible nitric oxide synthase expression and nitric oxide synthesis in rat renal artery cultured cells. Kidney Int 2005; 68:2508–16. 10. Corretti MC, Anderson TJ, Benjamin EJ, Celermajer D, Charbonneau F, Creager MA, et al. Guidelines for the ultrasound assessment of endothelial-dependent flowmediated vasodilation of the brachial artery. A report of the International Brachial Artery Reactivity Task Force. J Am Coll Cardiol 2002; 39:257–65. 11. Celermajer DS, Sorensen KE, Bull C, Robinson J, Deanfield JE. Endothelium-dependent dilation in the systemic arteries of asymptomatic subjects relates to coronary risk factors and their interaction. J Am Coll Cardiol 1994; 24: 1468–74. 12. Morris STW, McMurray JJV, Rodger SC, Jardine AG. Impaired endothelium-dependent vasodilatation in uraemia.

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RESULTS

Over a span of 54 months, 97 episodes of peritonitis were prospectively and retrospectively evaluated in 89 patients (72 males, 69 diabetics, mean age 56.2 ± 12.8 years) on CAPD. The peritonitis rate was 0.62 episodes/patient–year. Twenty-seven (27.8%) episodes of peritonitis were culture negative and 70 (72.2%) episodes were culture positive; 43 (44.3%) of these episodes were caused by gram-negative organisms and 22 (22.6%) by gram-positive organisms. There were 3 (3.1%) episodes of fungal peritonitis and 2 episodes (2%) of peritonitis were due to mixed infections. Escherichia coli was the most common gram-negative organism; it was recovered in 14 episodes (32.6%). Other organisms grown include Klebsiella pneumoniae in 206

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8 (18.6%), Acinetobacter calcoaceticus in 7 (16.3%), Pseudomonas aeruginosa in 6 (13.9%), and Enterobacter species in 5 episodes (11.6%). The relatively uncommon organisms (in the context of CAPD peritonitis) Morganella morganii and Alcaligenes faecalis were recovered from peritoneal fluid cultures in 2 (4.7%) episodes and 1 (2.3%) episode respectively (Table 1). When susceptibility patterns of antimicrobials that provide gram-negative coverage were compared, amikacin showed resistance in only 6 cases (13.9%) but resistance to ciprofloxacin was seen in 27 cases (62.8%) (p < 0.05) and to third-generation cephalosporins (cefotaxime and ceftazidime) in 29 cases (67.4%) (p < 0.05) (Table 2). When individual antimicrobial strain sensitivity to amikacin was evaluated, only 28.6% of isolates of E. coli, 12.5% of isolates of Klebsiella pneumonia, and none of the Pseudomonas, Enterobacter, or Acinetobacter strains showed resistance to amikacin. However, the uncommon organism Alcaligenes faecalis showed resistance to amikacin. DISCUSSION

The microbial cause of CAPD-related peritonitis is an important determinant of clinical outcome, with greater rates of catheter loss, hospitalization, and death in patients with gram-negative compared with gram-positive infections (1). Our study revealed E. coli as the most common gram-negative organism causing peritonitis, which is similar to the pattern observed in other parts of the world. However, in contrast to other recently published studies, we found higher proportions of episodes due to Klebsiella pneumoniae and Acinetobacter calcoaceticus than Pseudomonas aeruginosa (6). We also found uncommon organisms, such as Morganella morganii and Alcaligenes faecalis. Another important observation in our study was the antimicrobial resistance to quinolones. Even more draTABLE 1 Etiology of Gram-Negative Organisms Causing Peritonitis Organism Escherichia coli Klebsiella pneumoniae Acinetobacter calcoaceticus Pseudomonas aeruginosa Enterobacter species Morganella morganii Alcaligenes faecalis

Frequency (n=43) 14 (32.6%) 8 (18.6%) 7 (16.3%) 6 (13.9%) 5 (11.6%) 2 (4.7%) 1 (2.3%)


analyzed retrospectively and prospectively in the present study. Peritonitis was diagnosed when two of the following three criteria were present: (1) signs and symptoms of peritonitis (rebound tenderness, abdominal pain, fever, chills, nausea, vomiting, diarrhea); (2) leukocyte count ≥100 cells/µL, with more than 50% polymorphs; and (3) positive culture (and/or positive Gram stain). Peritoneal effluents from suspected cases of peritonitis were cultured by inoculating in bile broth and trypticase soy broth. The bottles were inspected at varying time intervals and growth was detected by the appearance of turbidity. At that time, subcultures were made on blood agar and MacConkey plates. Decisions were made about nature and number of culture media to be seeded from each sample, the method of incubation, and frequency of examination of cultures in the laboratory. Culture-negative peritonitis was considered if no growth was seen despite 48 hours of incubation. Strains recovered were tested for antimicrobial susceptibility against various antimicrobial agents by disc diffusion (standard Kirby–Bauer technique). Zone size was approximately correlated with minimum inhibitory concentration considered for various antimicrobial agents based on the criteria of the National Committee for Clinical Laboratory Standards (4). Infection rates were calculated as the number of infections during the study period, divided by the number of patient–years on CAPD. Patients hospitalized for more than 48 hours prior to the onset of peritonitis, patients who had an episode of peritonitis with in 4 weeks of the present episode, and patients diagnosed to have refractor y or resistant peritonitis (as defined by the expert committee on peritoneal dialysis-related infections) were excluded from the study (5). Independent sample t-test was used to assess differences in antimicrobial susceptibility.

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TABLE 2 Antimicrobial Susceptibility Patterns of Gram-Negative Organisms

Amikacin Ciprofloxacin Third-generation cephalosporins Piperacillin with tazobactama Cotrimoxazole Gentamicin Netilmicin a b

Resistant

Intermediate

p Valueb

6 (13.9%) 27 (62.8%) 29 (67.4%) 2 (16%) 21 (48.8%) 20 (46.5%) 23 (53.4%)

2 (4.6%) 4 (9.3%) 2 (4.6%) — — 3 (6.9) 4 (9.3%)

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