NEPHROLOGY 2002; 7, 72-76

Original Article

Factors affecting haemodialysiscaccess survival in a single centre retrospective cohort study

CHRISTOPHER LAWRENCE,’ JOSEPHINE CHOW’ AND MICHAEL SURANYI’

‘Imperial College School of Medicine, Norfolk Place, London, UK and ’Renal Unit, Liverpool Health Service, Liverpool BC, New South Waks, Australia

SUMMARY: A retrospective review was undertaken in the prevalent haemodialysis population of an Australian Tertiary Renal Unit of patients who started haemodialysis between April 1994 and Sep- tember 2000. The study aimed to assess the factors affecting the choice of long-term arteriovenous haemodialysis access, and the factors influencing access survival. Data were obtained from clinical charts and Australia and New Zealand Dialysis and Transplant (ANZDATA) Registry data. The minimum follow up was 3 months. There were 71 patients studied (66.2% male, 22.5% diabetic, mean age 56.9 years). Late referral (<3 months) patients constituted 35.2%. Only 39% of patients were Australian born. Seventy-one patients had a total of 96 new vascular access operations, and 57 revision operations. Of the 71 first-access procedures, 56 were native fistulae and nine were syn- thetic grafts. Only 31 % of long-term vascular access was in place 6 weeks or longer prior to the start of dialysis. Of 25 subsequent (new) access placements, only eight were fistulae and 17 were grafts. Diabetes, peripheral vascular disease and coronary artery disease all significantly predisposed to the placement of synthetic grafts. First native fistulae had superior survival to subsequent native fistu- lae. Subsequent fistulae had a significant rate of early loss, but were then stable. Survival of native fistulae was always superior to synthetic grafts (P= 0.0072). First synthetic graft survival was similar to the survival of subsequent grafts. Although native fistulae are already favoured for first access, these results suggest that native fistulae should more often be considered for subsequent (secondary) access.

KEY WORDS: haemodialysis, fistula, vascular access.

INTRODUCTION

The primary arteriovascular (A-V) fistula was described by Brescia et al. in 1966,’ and has been the gold standard of haemodialysis access since. The advantages of primary ‘arteriovenous fistulas’ over ‘synthetic arteriovenous grafts’ have been widely recognized, both in terms of longevity and relative freedom from complications,’ while at the same time, there has been an increasing tendency towards the placement of synthetic grafts.’

Loss of vascular access for haemodialysis patients is now a major cause of hospitalization, morbidity (espe-

Correspondence: Dr Michael Suranyi, Renal Unit, Liverpool Health Service, Locked Bag 7103, Liverpool BC, NSW 1871, Australia. Email: michaelmrany i@swsahs.nsw.gov.au

Accepted for publication 6 August 2001.

cially resulting from the prolonged use of temporary central venous catheters), and rn~rtality.~ The Caring for Australians with Renal Impairment (CARI) Guide- l i n e ~ , ~ published in March 2000, support the creation of native arteriovenous fistulae as paramount, and promote data collection and benchmarking, along with previously published guidelines such as the DoQI Clinical Practice Guidelines for Vascular Access5

This review of haemodialysis vascular access was undertaken to assess current practice in the Renal Unit at The Liverpool Hospital in south-west Sydney, a fast growing dialysis unit that opened in 1994, providing dialysis services to a catchment population of approxi- mately 800 000 with diverse ethnic and social make-up, and a high incidence of renal failure. These vascular access survival data will have value as a benchmark for the subsequent implementation of CAR1 guideline recommendations.

Factors affecting access survival NEPHROLOGY 73

METHODS

The prevalent haemodialysis population at Liverpool Hospital was taken to be that as of the end of September 2000, the time of the most recent ‘Australia and New Zealand Dialysis and Transplant Registry (ANZDATA) data survey’. Patient demographics were taken from the survey sheets. The end-point of the study was taken as the first of January 2001, ensuring a minimum of 3 months follow up.

Those patients who commenced haemodialysis at a site other than Liverpool Hospital were excluded from the study to avoid the inclu- sion of data on management decisions and vascular access surgery taken at other hospitals.

Data collected included patient age, sex, race, cause of renal failure, and presence of comorbidities (peripheral vascular disease, coronary artery disease, hypertension and diabetes mellitus) at the start of di- alysis. The patients’ case notes were searched for data on ‘permanent’ vascular access formation. The operation notes and diagrams, in-patient and haemodialysis notes, as well as clinic letters, yielded information on the identity of the surgeon, the type of access created and the date of operation. Where available, the date of first use of the vascular access was recorded. Similar data were collected from any surgical revision of an existing vascular access or creation of a new access. The distinction between a new access and a revision of an old vascular access is not always clear cut. We were guided by the operation definition, but in addition, any operation that involved a new site for access or the intro- duction of a different material was classed as a new access.

RESULTS

Seventy-one of 129 prevalent haemodialysis patients met the inclusion criteria for the study. Of these, 47 (66.2%) were male and 16 (22.5%) had diabetes melli- tus (15 of 16 Type 2). The average age at the start of dialysis was 56.9k1.71 years, and 25 patients (35.2%) commenced dialysis in an unplanned fashion (late referral, defined as not having been referred to a nephrol- ogist at least 3 months before commencing dialysis). Only 28 patients (39.4%) were born in Australasia. In addition to the 71 first access procedures, there were a further 25 new access procedures and 57 revisions of access.

The 96 (total) native fistulae and synthetic grafts required 57 revisions to maintain patency, 28 on fistulae, and 28 on grafts (unknown in one case). Ninety-two per cent of these operations were carried out by three vascular access surgeons. The main findings at revision surgery were: thrombosis (42.1%); stenosis (31.6%), infection (14%), and others (12.3%). The revision treatment consisted of interposition/bypass (28.1 %); thrombectomy (1 7.5%); re-anastamosis (15.7%); sur- gical drainage and antibiotics ( 14.0%), angiopiasty (10.5%), and others (14.2%).

FIRST VASCULAR ACCESS

Of 71 first permanent vascular access procedures, 56 (78.9%) were primary native fistulae, nine (12.7%) used synthetic graft materials, and information was unavail- able on the type of A-V access in six (8.5%) cases.

Of all first access operations, only 11 (15.5%) were conducted between 6 and 26 weeks prior to commenc- ing haemodialysis. A further 11 were in place more than 26 weeks before the start of haemodialysis. Thus, only a total of 22 (31%) were placed in a timely fashion. Eight (1 1.9%) were placed during the 6 weeks before starting. Twenty-five (37.3%) first access operations were undertaken up to 12 weeks after starting haemodialysis, and in 12 cases (16.9%), the first permanent vascular access was created more than 12 weeks after starting haemodialysis.

The mean age at the start of dialysis of the group that received primary native fistula (n=56, mean age 55.49f2.00 years), and the group that received syn- thetic grafts (n=9, mean age 64.88It3.21 years) was not significantly different (Student’s t-test, P= 0.062, CI: 0.480-19.26).

Chi-squared tests were used to determine those factors predisposing to the formation of grafts rather than fistulae. The significant factors were diabetes (x* = 8.436, P= 0.004.); peripheral vascular disease (xZ = 8.436, P = 0.004); and coronary artery disease ( x 2 = 6.568, P=O.Ol). Hypertension, late referral, age group and sex could not be shown to play a role.

Kaplan-Meier survival curves were used to assess group survival of permanent access, and this was divided into ‘primary patency’ (failure is judged to have occurred at any intervention) and ‘assisted patency’ (where A-V access revisions are included to extend the access survival).

The primary patency for all types of first vascular access showed a 1-year survival of 64.5%, and a 2-year survival of 58.6% with a median survival of 39.33 zk 14.24 months (CI: 11.42-67.24). Assisted patency for all types of first vascular access was 88.37% at 1 year, and 84.2% at 2 years. Separating the access into the two groups, that is, ‘fistulae’ and ‘grafts’, revealed that primary patency was 66.1% at 1 year and at 2years in the fistulae group, but only 44.4 and 29.6%, respectively, in the grafts (Fig. 1). The median survival was 53.87 months in the fistulae, but only 11.3 months in the grafts. This difference in primary patency did not reach statistical significance because of small numbers.

Surgical revisions improved the patency (assisted patency) to 94.2% at 1 year, and 91.7% at 2 years in the fistulae, but only to 66.7 and 50.0%, respectively, in the grafts (Fig. 2). Median assisted patency survival was unavailable at the time of follow up, as more than 50% of the fistulae were still in use at the study end- point. There was a significant difference in assisted patency between the fistulae and the grafts (log rank, P=0.0072).

No significant difference in survival of vascular access could be demonstrated when grouped by: surgeon; sex; age group; late referral; timing of fistula formation; dia- betes; and peripheral vascular disease or coronary artery disease. There was, however, a clear trend for less good

74 NEPHROLOGY C Lawrence et al.

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vascular access patency in those over 65 years of age and in those with coronary artery disease.

ALL NEW VASCULAR ACCESS CREATIONS

The 71 patients had a total of 96 de novo access creations (i.e. excluding revisions). Primary patency in this group at 1 year was 79.1%, and 73.6% at 2 years. Including revisions (assisted patency ), these figures rose to 82.3% at 1 year, and 77.7% at 2 years. Ofthe 96 opera-

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tions, 64 (71.1%) were native fistulae and 26 (28.9%) were synthetic grafts (insufficient data was available in the same six cases). Primary patency (Fig. 3) for fistulae was 87.0% at 1 year and the same at 2 years compared with 63.1 and 49.7% for grafts (Log rank, P=0.0015). The graph for assisted patency (Fig.4) shows the expected improved patency rates. The much higher relative increase in the number of grafts in this group suggests that in this Renal Unit, the operation of choice

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Fig. 2 Assisted patency: First grafts versus fistulae. Access: ( A ) fistula; (0) graft.

Fig. 4 Assisted patency: All access: Grafts versus fistulae. (A) fistula; (0) graft.

Factors affecting access survival NEPHROLOGY 75

for second, or subsequent ‘permanent’ haemodialysis access has been the creation of a graft rather than a fistula.

The patency rate of first ever access was compared with the patency of ‘second or subsequent’ (secondary) vascular access. There was a significant difference in assisted patency (Fig. 5) with first ever access having 1- and 2-year patency rates of 86.9 and 82.9%, respectively, while the second and subsequent access had 1- and 2- year patency rates of only 69.5 and 63.2%, respectively (log rank, P= 0.026). While the second and subsequent fistulae had a higher early failure rate than the first fis- tulae (Fig. 6), they were still substantially superior to grafts (second grafts n= 15). Synthetic grafts showed equally poor patency, irrespective of the order of whether they were first or subsequent synthetic grafts (Fig. 7).

A Cox multivariate regression analysis was used to assess the major factors affecting arteriovenous access patency. The Cox multivariate analysis, using a wide range of predictors (surgeon, age, sex, late referral, peripheral vascular disease (PVD), coronary artery disease (CAD), diabetes, synthetic graft vs native fistula), showed that only the type of access, whether an arteriovenous fistula or a synthetic arteriovenous graft significantly affected patency (Wald value 5.703, P=0.017).

DISCUSSION

The results of this retrospective review show that Australian access survival data is comparable with other

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published data.6s Native fistulae have a significantly better primary and assisted patency rate than synthetic grafts, supporting previous findings and adding evidence to the CAR1 guidelines. Our data on A-V access revi- sions shows an equal number of revisions between

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Fig. 7 Assisted patency grafts: First versus subsequent. (A) First; (0) subsequent.

76 NEPHROLOGY C Lawrence et al.

fistulae and grafts, but as fistulae outnumbered grafts by almost 2.5: 1, this indicates that fewer grafts needed more revisions. Synthetic grafts are more prone to complica- tions such as thrombosis, stenosis and infection than are fistulae, which largely accounts for the poorer synthetic graft access survival that was demonstrated.

Native fistulae placed as a second or subsequent access have a higher failure rate than those placed as first access. However, the 1- and 2-year patency rate is still superior to that of grafts. In contrast, prosthetic graft patency rate is similar, whether placed as primary or secondary access (Fig.7). These data support the use of fistulae as sec- ondary access, leading to the conclusion that fistulae should more often be considered as the second access, and not just the first access procedure of choice, perhaps at a more proximal site or on the other limb. The increased early failure rate in the fistulae placed second may be due to the fact that they may be allowed less time to mature. Prolonged exposure to central venous catheters has been associated with increased morbidity and mortality and is generally a ~ o i d e d , ~ but may have a role in allowing subsequent fistulae to mature longer before first use, and thus enhancing fistula survival. This would require more investigation.

While any retrospective study has limitations, such studies fulfil a useful role as a launching pad for prospec- tive studies. This retrospective study has benchmarked contemporary haemodialysis access survival data in a typical Australian renal unit. All dialysis units should

monitor and audit vascular access survival prospectively to benchmark, review and improve the performance of this integral part of renal replacement care.

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