NDT Advance Access originally published online on June 14, 2008
Nephrology Dialysis Transplantation 2008 23(11):3585-3591; doi:10.1093/ndt/gfn317
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Factors influencing the prevalence of central venous catheter use in a Canadian haemodialysis centre
Division of Nephrology, Department of Medicine, The Ottawa Hospital and the Kidney Research Centre, Ottawa Health Research Institute, University of Ottawa, Ottawa, Ontario, Canada
Correspondence and offprint requests to: Kevin D. Burns, Professor of Medicine, Division of Nephrology, Department of Medicine, The Ottawa Hospital, Director, Kidney Research Centre, Ottawa Health Research Institute, University of Ottawa, 1967 Riverside Drive, Room 535, Ottawa, Ontario, K1H 7W9, Canada. Tel: +1-613-738-8400-82580; Fax: +1-613-738-8337; E-mail: kburns{at}ottawahospital.on.ca
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Abstract |
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Background. The arteriovenous (AV) fistula is the optimal vascular access for chronic haemodialysis (HD) patients. The Dialysis Outcomes and Practice Patterns Study (DOPPS II) reported a high use of central venous (CV) catheters for HD in Canadian centres. We studied factors influencing the choice of access in a prevalent HD population at a Canadian centre.
Methods. This was a cross-sectional study of all HD patients at the Ottawa Hospital (Ottawa, Canada). Demographic information, the type of HD vascular access used and the factors influencing access choice were obtained from medical records. Nephrologists at the Ottawa Hospital were surveyed to identify attitudes that might influence the choice of HD access.
Results. In the survey of nephrologists (n = 17), there was 100% agreement that the AV fistula is the optimal HD access. In 599 prevalent chronic HD patients, AV fistulae were used in 58.0% (n = 347), CV catheters in 39.7% (n = 238) and only 2.3% had AV grafts (n = 14). By multivariate logistic regression, female gender, peripheral vascular disease and shorter duration of HD were independent predictors of CV catheter use. Of the patients with CV catheters, 68.9% had vascular factors or medical contraindications that precluded AV fistula creation. System/resource limitations influenced choice of access in only 19.3% of patients with CV catheters, although these factors were more important in patients within the first 6 months of HD initiation.
Conclusions. The relatively high prevalence of CV catheter use at our HD centre is due mainly to patient-specific factors (e.g. unsuitable vessels or medical co-morbidities), rather than resource limitations or physician attitudes. Target setting for AV fistula use requires consideration of these factors as well as the effect of HD duration.
Keywords: arteriovenous fistula; central venous catheters; haemodialysis; vascular access
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Introduction |
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Maintenance of a well-functioning vascular access represents a major challenge in the care of patients requiring haemodialysis (HD). It is generally agreed that the preferred type of vascular access for HD is the native arteriovenous (AV) fistula, followed by AV grafts and then central venous (CV) catheters [1–5]. The use of AV grafts and CV catheters is associated with an increased incidence of several HD-related complications, including infections, inadequate flow, access failure and increased costs [1–6]. In the HEMO trial, for example, HD patients with CV catheters had higher rates of hospitalization due to access-related infections, compared to HD patients with AV fistulae or even AV grafts [7]. AV fistula use has also been associated with improved long-term survival in HD patients, compared to use of AV grafts or CV catheters [5,8,9]. Accordingly, clinical practice guidelines have recommended early creation of AV fistula whenever possible to avoid use of CV catheters in HD [10,11]. The Canadian Society of Nephrology has also recommended that at least 60% of prevalent patients on HD should have a native AV fistula [11].
Recently, Mendelssohn and colleagues reported on data related to HD vascular access use, derived from the Dialysis Outcomes and Practice Patterns Study (DOPPS II) [12]. The prevalence of AV fistula use in Europe was relatively high (74%), compared to Canada (53%). In the USA, AV fistula use was relatively low (32%), although 42% of patients had AV grafts. In Canadian HD centres, there was a particularly high rate of CV catheter use (33% of prevalent patients, 70% of incident patients). This study identified a number of resource limitations that might contribute to the relatively high use of CV catheters for HD in Canada, including a relative lack of vascular access surgeons (associated with increased waiting times) and a deficiency in surgical time devoted to vascular access, compared to Europe or the USA [12].
The HD program at the Ottawa Hospital in Ottawa, Canada, has a dedicated HD vascular access surgical team, with five surgeons and 7 h per week of operating room time devoted to access creation. A vascular access clinic is held one full day per week, with involvement of the access coordinator and vascular surgeon. Patients in the clinic undergo a formal physical assessment of arteries and veins, Doppler studies and venography if needed, education about access and planning for AV fistula or graft surgery, as indicated. The clinic operates on a triage basis with respect to patient acuity, with waiting times <1 week for patients with failed or failing accesses and typically <2 weeks for all patients on HD therapy or expected to start HD within 6 weeks. Furthermore, waiting times for surgical creation of simple AV fistulae or grafts are generally <4 weeks from the time of assessment in vascular access clinic. We therefore postulated that surgical resource limitations did not solely account for the relatively high prevalence of CV catheter use at our centre. In this regard, it is clear that the rising incidence of end-stage renal disease (ESRD) in recent years has been associated with a significant increase in the average age of patients on chronic HD, accompanied by increased medical complexity and costs [13]. Thus, we hypothesized that patient-specific factors, including vascular disease and other co-morbidities, might contribute to the use of CV catheters for vascular access. To address this issue, we conducted a cross-sectional study to identify factors that influence the choice of vascular access in prevalent HD patients, and we surveyed nephrologists at our centre for attitudes regarding access.
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Subjects and methods |
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Survey of nephrologists
To determine the attitudes regarding choice of vascular access for HD, nephrologists at the Ottawa Hospital were asked to complete an anonymous questionnaire, comprising 34 questions using the Likert scales format (see Supplementary material).
Cross-sectional study
A cross-sectional study was performed on all patients who were receiving regular maintenance HD treatments in the nine dialysis units in the Ottawa Hospital HD program on 1 November 2006. Patients who were receiving HD for acute kidney injury or acute intoxications were excluded from the analysis, but other hospitalized patients were included.
In the Ottawa Hospital HD program, all nephrologic care is provided in a group practice model whereby each patient's care is shared by at least two nephrologists. Vascular access care is provided by a multi-disciplinary team consisting of a vascular access coordinator (Ms J.G., a lead author of the current study), vascular surgeons, interventional radiologists, the attending nephrologists and HD unit nurse leaders. In addition to a weekly vascular access clinic, team rounds are held weekly to review radiologic procedures and planned surgical access cases. As part of the continuous quality improvement (CQI) program, the records of all HD patients are surveyed on a monthly basis by the access coordinator, and with input from the HD unit nurse leaders, to identify patients with problems related to AV fistula or graft use. In addition, all patients with CV catheters are surveyed monthly by the access coordinator to determine suitability for creation of AV fistulae or grafts. In cases where a patient with a CV catheter has not visited the access clinic for a formal assessment or no appointment has been arranged, the access coordinator communicates with the nephrologist to determine the reason for continued CV catheter use. For this cross-sectional study, the vascular access coordinator (J.G.) surveyed all patient records on the designated date. Data were collected from the patients’ electronic dialysis records (NephroCare, CyberREN, Fresenius Medical Care Canada, Richmond Hill, ON, Canada) as well as the hospital records, and included (i) the type of vascular access being used for HD at the time of the study, (ii) demographic information, including significant co-morbidities, as well as time on HD and vascular access history, and (iii) the factors responsible for selection of a CV catheter as vascular access for HD. Because of the nature of our CQI program, this information was readily available for all patients. For each patient, the predominant factor was assigned to one of four separate categories: system/resource limitations, vascular factors, medical contraindications and other factors.
Statistical analysis
The collected data regarding HD vascular access are presented in percentages, and the data characteristics were examined by univariate analysis using frequency histograms, scatter plots and descriptive statistics. Normality was tested for continuous variables using the Kolmogorov–Smirnov test. The patient characteristics are presented as mean ± SD for normally distributed continuous variables, as median (range) for the other continuous variables and as percentages for categorical variables. For some analyses, patients with AV fistulae and AV grafts were grouped together. Differences between two groups were analysed by the student t-test. The chi-square statistic was used for categorical variables. A two-tailed P < 0.05 was considered statistically significant. A binary logistic regression analysis was performed to determine which variables were independent predictors of CV catheter use. Clinically relevant variables (age, gender, diabetes, peripheral vascular disease, cancer, dementia and duration on HD) were forced into the model. Only variables with a P-value < 0.05 were retained in the model. Statistical analysis was conducted using SPSS for Windows, version 13.0 (Lead Technologies, Inc., Charlotte, NC, USA).
Ethics
This study was approved in its entirety by the Ottawa Hospital Research Ethics Board.
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Results |
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Survey of nephrologists
The complete results of the 34-question survey of nephrologists regarding vascular access for HD are provided in Supplementary material. The answers to selected questions of interest are depicted in Table 1. The survey was completed by 100% of nephrologists at the Ottawa Hospital (n = 17). Of importance, there was unanimous agreement by nephrologists that the optimal access for HD is the AV fistula (100% strongly agreed).
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Cross-sectional study
There were 613 patients receiving HD treatments in the Ottawa Hospital program on the study date chosen. Of these, 14 (2.3%) were receiving HD treatments for acute kidney injury and were excluded from further study. Of the remaining 599 patients, 361 patients (60.3%) were being dialyzed with either an AV fistula (n = 347, 58.0%) or an AV graft (n = 14, 2.3%) (Table 2). The remaining 238 patients (39.7%) had CV catheters as HD vascular access, with most using tunelled catheters (n = 229, 38.2%).
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On univariate analysis, patients with CV catheters were older and significantly more likely to be female, diabetic and to have peripheral vascular disease compared to those using AV fistulae or grafts (Table 2). CV catheter use was associated with a significantly shorter duration on HD treatment, compared to use of AV fistulae or grafts (3.0 ± 3.5 versus 5.0 ± 4.6 years, respectively, P < 0.05). In contrast, co-morbid diagnoses such as cancer or dementia were not associated with CV catheter use for HD. The multivariate logistic regression showed that female gender, presence of peripheral vascular disease and shorter duration of HD were independent predictors of CV catheter use (Table 3).
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Table 4 shows the impact of dialysis duration on the choice of HD access. CV catheter use was highly prevalent in patients on HD for <6 months (75.0%). As dialysis duration increased, there was a higher likelihood of AV fistula or graft use. Thus, the majority of patients on chronic HD beyond 5 years were using either an AV fistula or graft (78.6%).
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The factors influencing the choice of CV catheter as HD access were identified from the patients’ medical records. A total of 16 factors were identified, and assigned to one of four categories, as described in the Subjects and methods section. Of the 238 patients with CV catheters for HD, system/resource limitations were identified as influencing factors in only 46 patients (19.3%) (Table 5). The majority of these patients were either awaiting assessment for peritoneal dialysis as a modality option, or awaiting AV fistula creation, revision or maturation. Vascular factors were the most commonly identified reasons influencing the choice of CV catheter for HD (n = 112, 47.1%). The majority of these patients (n = 58) experienced failure of previous AV access(es). These 58 patients had undergone a total of 99 previous surgeries for AV fistulae or grafts (median = 2, range 1–4), with 17 radiocephalic, 26 basilic vein transpositions, 32 brachiocephalic fistulae and 24 AV grafts. The vascular access team was involved in the reassessments for access surgery in all cases, and the majority was evaluated by the vascular surgeon. These patients were determined to have unsuitable vessels for further surgery, or had arterial steal syndromes. A minority of patients (n = 7) did not require a surgical assessment because they were deemed unsuitable for further surgery, due to documented CV occlusion, for example.
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Medical contraindications to AV access were identified in 52 patients (21.8%), with the majority of these due to poor cardiac status or poor overall prognosis, as assessed by the nephrologist. Finally, ‘other factors’ affecting the choice of CV catheters were identified in 28 patients (11.8%). All of these patients refused AV fistulae or graft creation, despite education by the nephrology team.
The patient characteristics associated with each of the four factors influencing the choice of CV catheter as HD access are depicted in Table 6. There was a significantly higher prevalence of females and patients with a longer duration on HD when vascular factors dictated the use of CV catheters for HD access. There was a preponderance of males when system/resource limitations, medical contraindications and other factors dictated the use of CV catheters.
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As shown in Figure 1, system/resource limitations and other factors were important determinants of CV catheter use in the first 6 months of HD treatment, whereas vascular factors and medical contraindications were more influential after 1 year of HD.
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Discussion |
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TopAbstractIntroductionSubjects and methodsResultsDiscussionSupplementary dataReferences |
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The major finding of this study is that the relatively high prevalence of CV catheter use for HD at our centre (39.7%) is due primarily to patient-specific factors (e.g. vascular disease and medical contraindications) that preclude the creation of AV fistulae or grafts, rather than resource limitations (e.g. lack of surgeons or operating room time). The survey of nephrologists revealed unanimous support (100%) for the AV fistula as the preferred vascular access for HD, and indicated that age, female gender, presence of diabetes and listing on the deceased donor waiting list for transplant were not barriers to referral for AV fistula or graft creation.
In the DOPPS II study on vascular access patterns, Canada had an AVF utilization of 53%, which approximates the 58.0% of patients with AVF in our prevalent HD population [12]. AVF use in Canada exceeds that in the USA (32%), but is lower than that in Europe (74%). In our patients, we observed a relatively low use of AV grafts (2.3%), compared to DOPPS II data from Canadian (14%), European (8%) or US centres (42%) [12]. At our centre, the creation of AV grafts is avoided because of the overall lower patency rates and increased risk of infection compared to AV fistulae [4,14]. AV graft surgery is recommended only if the patient has inadequate veins for fistula creation, and has a suitable artery and patent central veins. If these conditions are not met, then the insertion of a CV catheter is recommended.
The high use of CV catheters for HD at our centre (39.7%) indeed exceeds the 33% rate reported for Canadian centres in DOPPS II, and may be partly explained by our relatively low use of AV grafts. However, it is important to emphasize that Canadian CV catheter use is higher than that in either Europe (18%) or the USA (25%) [12], and far exceeds the Kidney Disease Outcomes Quality Initiative (KDOQI) guideline that <10% of prevalent chronic HD patients should have CV catheters [10]. The increased prevalence of CV catheter use in Canada is at least partly due to a high use rate in incident HD patients. Indeed, in our study, there was a significant influence of duration of HD on the type of access. Our study included patients who had recently started on HD. In patients within 6 months of HD initiation, there was a very high prevalence of CV catheter use (75%), consistent with the 70% prevalence reported for Canadian centres [12]. As dialysis duration increased in our patients, the prevalence of CV catheter use decreased progressively, reaching a low of 21.3% in patients after 5 years of HD.
We found that system/resource limitations accounted for the highest percentage of factors influencing the choice of CV catheter as HD access within the first 6 months of HD (54.8%), compared to only 8.6% of factors influencing access choice in patients on HD beyond 5 years. Mendelssohn et al. reported data on a number of factors that might influence vascular access choice in incident HD patients [12]. In Canada, high CV catheter use exists in incident HD patients, despite 79% of patients reporting having seen a nephrologist >4 months before ESRD, and despite unanimous agreement by medical directors that new incident HD patients should have AV fistulae as the preferred access [12]. However, average waiting times for access evaluation and surgery are higher in Canada compared to Europe and the USA, and in Europe, the majority of medical directors indicate that AV fistulae should be cannulated within 2 months of creation, while most Canadian medical directors recommend waiting at least 2 months [12]. Moreover, Canada has fewer access surgeons per 100 HD patients, compared to either Europe or the USA, associated with fewer weekly hours devoted to vascular access surgery per patient [12]. These factors, as well as the contribution of late referral at our centre, might have contributed to the high prevalence of CV catheter use in patients within 6 months of HD in our study. Although our centre has a dedicated HD vascular access team and allocated operating room time for access creation, and waiting times were not perceived to be prolonged by nephrologists, the average number of access surgeons per 100 HD patients (0.82 surgeons/100 patients) is much lower than that reported for other Canadian centres (2.9), Europe (4.6) or the USA (8.1) [12]. Nonetheless, of the 238 patients with CV catheters at our centre, only 25 (10.5%) were awaiting AV fistula creation, revision or maturation, while a number of patients with system/resource limitations influencing CV catheter choice (21/46 patients) were either awaiting assessment for peritoneal dialysis, undecided about modality choice or awaiting transplant (Table 5). Thus, a lack of vascular access surgical support is only one of several factors contributing to the high prevalence of CV catheter use in incident HD patients.
Our study indicates that patient-specific factors (vascular factors and medical contraindications) are the predominant influences on CV catheter use in our prevalent HD patients. The contribution of these factors increases with HD duration, such that after 5 years on HD, they account for 77.1% of all factors (27/35 patients). Patients with CV catheters were more likely to be female, and had a higher prevalence of peripheral vascular disease (Table 3). In this regard, prior studies have reported an association between female gender and diabetes with lower rates of AV fistulae use [15–17]. Advanced age is also a risk factor for the maintenance of AV access [18]. In a retrospective cohort study of 11 290 patients approaching ESRD, O’Hare et al. found that older patients were less likely to undergo surgery to create a permanent vascular access, compared to younger patients, and were less likely to start dialysis [19]. Although we observed a small but significant increase in the average age of patients with CV catheters, nephrologists did not consider age as a barrier to referral for AV fistula creation in our survey. However, we did note that a minority of patients receiving HD treatments by CV catheters were not referred for AV fistulae or grafts because of advanced age as the determining factor (8/238 patients, 3.4%). Ageing may be a surrogate marker for other co-morbidities that influence choice of access, such as peripheral vascular disease or cardiac failure. Indeed, vascular factors accounted for the majority of factors influencing CV catheter use (112/248 patients, 47.1%), while poor cardiac status influenced decision making in 21 patients (8.8%).
The strength of this study is the complete capture of information related to choice of access for all prevalent HD patients in our centre on the study date. Although there are limitations associated with abstraction of data solely from chart review, our cross-sectional study was performed with lead involvement of our vascular access coordinator (J.G.), who had detailed knowledge regarding the patients with continued CV catheter use at our centre, through our CQI program. Patients with CV catheters uniformly underwent a vascular access assessment prior to being deemed unsuitable for AV fistula or graft creation, unless they refused access creation, or if the nephrologist determined that medical co-morbidities posed contraindications for access surgery. Our data, therefore, are based on a uniform practice model for vascular access at our centre. Nonetheless, we recognize that the results of our study may not apply to all HD centres, since patient demographics, surgical practice and referral patterns may vary.
Although our survey of nephrologists revealed strong support for AV fistula creation, the weaknesses associated with survey instruments are acknowledged, including the possibility that responses may not accurately reflect clinical practice or that the questions may not address all the factors involved in decision making. There are also limitations associated with cross-sectional studies, including the inability to follow patients prospectively to determine outcomes, and selection bias. For example, access outcomes of patients awaiting peritoneal dialysis could not be determined from this analysis. In addition, since this was a prevalence study, it cannot address the impact of factors that might change with time. Although vascular factors may have precluded creation of an AV fistula or graft in some patients at the time of our study, it is possible that with ongoing survey of access as part of our CQI program, a few of these patients might eventually be considered suitable surgical candidates. This represents a limitation of our analysis. Furthermore, the finding that AV fistula prevalence increases with HD duration might initially seem unexpected, considering that medical co-morbidities and vascular disease increase with time on HD. However, patients with CV catheters might have a higher mortality rate than patients with AV fistulae or grafts, and might undergo transplant at a higher rate. This survival bias could at least partly account for the decreased prevalence of catheter use with dialysis duration.
In summary, this study indicates that patient-specific factors (related to vascular disease and medical co-morbidities) are major determinants influencing the high prevalence of CV catheter use for HD, rather than limitations in surgical resources or nephrologists’ attitudes. With increasing duration on HD, patient-specific factors play a predominant role in access decision making. Individual HD centres should conduct CQI initiatives to determine factors that impede the creation of AV fistulae, particularly in patients within 6 months of starting HD, where resource limitations may contribute significantly. We suggest that target setting for AV fistula use in chronic HD patients requires consideration of these factors as well as the influence of HD duration.
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Supplementary data |
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Supplementary data is available online at http://ndt.oxfordjournals.org.
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Acknowledgments |
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This study was supported by unrestricted funds from the Kidney Research Centre, Ottawa Health Research Institute, University of Ottawa.
Conflict of interest statement. The authors declare that the results presented in this paper have not been published previously in whole or in part, except in abstract form. The study represented a component of the requirement for completion of a Masters of health science and nursing thesis at Charles Sturt University (to J.G.), and parts of this work were presented in abstract form at the annual meeting of the American Society of Nephrology, San Francisco, CA, November 2007 (J Am Soc Nephrol 2007; 18: 138A).
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Notes |
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* Should be considered as co-first authors of this manuscript.
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References |
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Accepted in revised form: 16. 5.08
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