Factors responsible for fistula failure in hemodialysis patients

Factors  responsible for fistula failure in hemodialysis patients

Ahmed Saif Al-Islam Abd Elfattah,MD

Department of Vascular Surgery, Sohag University, Sohag, Egypt.

Abstract

Background: Autogenous arteriovenous fistula (AVF) is regarded as the first and perhaps the best choice of vascular access in hemodialysis patients. Vascular  access procedures  and their subsequent complications represent major causes of morbidity, hospitalization, and cost for chronic hemodialysis patients.

Aim of the study: The main objective of this study is to identify  risk factors for failure of

autogenous arteriovenous  fzstulae which had successfully  matured and were used for dialysis in hemodialysis patients.

Patients and methods: Sixty selected cases of chronic renal failure patients who were referred for AVF during March 2006 to April 2008 were operated on to create AVF and followed up for two years.

Results: There were a total of76 autogenous  AVF performed for 60 patients. 32  (53.3%) of the procedures were distal fistulae, followed by 25 (41.7%)  cubital fossa fistulae (proximal fistulae) and other sites fistulae were only 3 (5%). Hypertension was present in 24 (40%) of the patients, and diabetes was present in 11 (18.3%). 12 (20%) of the studied cases were overweight. HCV was found in 28 (46.7%)  of the patients. 21 (35%) of patients had past history of fistula failure during their course of renal dialysis. Patients who developed AVF failure had significantly lower hemoglobin levels  and   were more likely  to  have previous fistula failure.

Conclusion: Predictors of AV-fistula malfunction in our dialysis  population were lower hemoglobin levels and previous fistula failure.

Key words: Arteriovenous fistula, hemodialysis, vascular  access,  fistula  failure,  fistula thrombosis.

Introduction:

End-stage renal disease (ESRD) is a major public health problem, the incidence of which is increasing every year.It is associated with significant morbidity and mortality, and incurs a huge financial cost, of which a significant portion is directly related to vascular access, not only  related to complications of the procedures themselves, but  also for management of thrombotic events or infections of different blood accesses.l

The most frequently used fistula and the standard one, by which all other fistulae are compared  is the Brescia- Cimino  fistula.2,3

Fistula procedure requires well experienced surgeons and ensuring of adequate collateral flow from the ulnar artery by performing Allen test before surgery, in order to minimize the

problem of  hand  ischemia. In  addition, evaluating superficial veins and distal arteries must be achieved for selecting the best site for fistula.4

Autogenous arteriovenous fistula (AVF) is regarded as the first and perhaps the best choice of vascular  access in hemodialysis patients. Among the various sites, fistula placed at the wrist is the first choice of access because of its  simplicity and  fewer  complications.5,6

Arteriovenous fistula transforms a vein into a high-flow vessel. It is obvious that obstacles to flow must be avoided, e.g., kinking, acute angles, torque etc. They create turbulence, damage endothelial cells, and increase the risk of stenosis formation. Transverse cutaneous incisions should be avoided, and  we recommend longitudinal incisions if possible.

It has been recommended that veins should be mobilized so that they  can be more  easily adapted to the artery.7

Most AVFs require a maturation period of

4 to  6 weeks  before they  can  be used  for hemodialysis; however, some do not mature in this period. These AVFs, which experience nonmaturation, are left to mature longer but often  without success and  are  frequently eventually   abandoned  altogether.s Anemia is a characteristic and an important clinical manifestation of progressive  kidney diseases. It usually  worsens  with   the development of kidney failure. Severe anemia (Hb level lower than 10 gldL), age (older than

60 years), diabetes mellitus, and smoking were risk factors for access failure.9

Aim of the work:

The main objective of this study is to identify risk factors for  failure of autogenous arteriovenous fistulae which had successfully

matured and  were used  for  dialysis in hemodialysis patients.

Patients and methods:

A prospective clinical study of selected 60 patients  (50 men and 10 women) on regular renal hemodialysis were included in our study to whom 76 autologous fistulae were created.

Data of all AVFs  created between March

2006  and  April  2008  in Vascular Surgery Department Sohag University Hospital were prospectively collected Data collected included gender, age at the creation of AVF, history of renal disease, presence of diabetes, hypertension, obesity, haemoglobin level, and characteristics  of AVF (date of creation, site of creation;  distal radiocephalic or proximal brachio-cephalic or  brachiobasilic). Study included all chronic hemodialysis patients who met   the   following inclusion criteria: (1) On renal hemodialysis at the time of the

frrst access cannulation.

(2) Had a mature AVF.

(3) Had a successful  first cannulation  of the access  with  adequate dialysis achieved.

Statistical analysis:

The statistical analysis was performed using the SPSS software version 10. Demographic, clinical variables  and initial laboratory  data

were  compared between patients with  and without  fistula failure  using a two-sample t test for continuous variables and Pearson's Chi-square test  for discrete variables. The survival functions of the AVF were studied using the Kaplan-Meier method.  The AVF creation  date was considered as the starting point, while the first AVF failure as the event. Covariates for fistula survival were analyzed using the Cox regression model.

Results:

There were a total of 76 autogenous AVF performed for 60 patients. There were 50 males (83.3%)  and 10 females (16.7%).  The mean

± SD  for  age  and  dialysis duration were

46±18.5 years  and  25.24±21.04 months, respectively. Hypertension  was present in 24 (40%) of the patients, and diabetes was present in 11 (18.3%). 12 (20%) of the studied cases were  overweight. HCV  was  found in  28 (46.7%) of the patients. 21 (35%) of patients had past history of fistula failure during their course of renal dialysis.

Baseline clinical, comorbidity variables and initial laboratory data inpatients who developed AVF failure were compared to those without AVF failure Table(l):Patients who developed AVF failure were significantly more likely to have lower hemoglobin levels and history of previous fistula failure. While hypertension was significantly reported more in patients without fistula failure, this may pay the attention to the role of hypotension  as a risk factor for fistula failure.

Sites of AV fistulae created in hemodialysis patients Figure(!): More  than  half  of  the procedures were by distal fistulae 32 (53.3%), followed by 25 (41.7%) cubital fossa fistulae (proximal fistulae) and other sites fistulae were only 3 (5%).

Frequency of different causes of AVF failure Figure(2): Showed that thrombosis was the commonest complication in fistulae  failure (55%), followed  by bleeding and infection (25%, 20% respectively).

The  Kaplan-Meier analysis for  fistula survival Figure(3): The Kaplan-Meier analysis revealed the 12 and 24 months cumulative fistula survivals were 83%  and  73% respectively.

Effect  of hemoglobin on fistula  survival Figure(4):In patients with haemoglobin level less than 9 gm/dl, cumulative fistula survivals were 77% and 61% after 12 and 24 months respectively.Whileinpatients withhemoglobin level more than 9 gm/dl was 86% both after

12 and 24 months. AVF smvived significantly

longer among patients with hemoglobin greater

than   9 g/dL than in   those with lower

hemoglobin levels (P = 0.030).

Cox regression multivariate analysis for

risk factors in fistula  failure  Table(l): The only factors that significantly influenced fistula patency, were previous fistula  failure (P  =

0.023, RR = 5.140, CI = 1.265 - 25.443) and

hemoglobin level (P = 0.030, RR = 4.705, CI

= 0.076 - 0.878).

Table(1): Baseline clinkal, comorbidity variables,and initilll lllboratory data in patients who developed AVF failure werecompared to those without AVF failure.

other site  5.00%

Fistula site

D cubital fossa

• distal forearm

•.... ther srte

cubitalfossa  41.67%

distal forearm

Figure (1): Sites of AV fistulae created in hemodialysis patients.                                                                                                                               -

D Infection

•Thrombosis

IW1 Bleeding

55%

Figure (2): Frequency of different causes of AV fiStulae failure.

1 .0

.9

.8

::J

(/)

E

0 .7 ---------------- --------4

0                           10                           20           30

0  SurvivalFtlndlon

+ Censored

months

Figure(3):The Kaplan-Meieranalysis for fistula survival.

1 .0

.9

.8                                                                                      Hemoglobin level

ro

->    .7

:::l

(/)

E

0    .6-------------- -------4

0                        10                        20          '30

i( Hb >9 g/dl

* Hb >9 g/dl-censored

Hb

* Hb

months

Figure (4): The Kaplan-Meier analysis of the effect of hemoglobin level on.fistula survival

(P = 0.030).

Table (2): Cox regression multivariate analysis for risk factors in fistula failure.

RR = relative risk.

Discussion:

The autogenous arteriovenous fistula is the access  of choice  in hemodialysis patients. It produces the  highest survival compared to grafts and  catheters, is less  thrombotic and results in  fewer infectious complications.7

In  our  study, fistula failure occurred in

26.7% of  the  created AV  fistulae and  this incidence of fistula failure is similar to the 23-

53%  observed by  previous  studies.l0-13,5

Our results showed no significant difference in the age between patients with and without fistula failure. This is in agreement with many studies.14-16 But in contrast to Lok, 2007 and Gheith and Kamal, 2008, who  reported that old age was a risk factor for the vascular access failure.17, 9

In our  study we  found no significant difference in  gender distribution between patients with and without fistulae failure (P =

0.593). This is in agreement with Gheith  and Kamal., 2008, who found insignificant impact of sex on the mean duration of fistula surviva1.9

However, in other research, being female has been associated with a higher incidence ofloss of primary functional patency, hypothesized to be  due  to smaller vascular structures in women.13  Also, Sajgure et al.,  2007  found fistula  patency was affected by gender, with longer patency  noted in males.18

Gheith and  Kamal., 2008  found  diabetes mellitus associated with a higher frequency  of fistula failure.9 This is in contrast to our results

as we found insignificant difference in the frequency of diabetes mellitus between patients with and without fistulae failure also we noticed hypertension was significantly more in patients without fistula failure, this may pay the attention to the role of hypotension as a risk factor for fistula  failure  in this field, further studies are needed. But our results were in agreement with Gheith and Kamal., 2008 as regards the higher frequency of fistula failure in severely anemic patients than  among less  anemic patients.9

In our study, we found  hypertension and

diabetes mellitus in 40% and 18.3% in patients on renal dialysis respectively. While Qasaimeh et al., 2008 reported that diabetes mellitus was the most  common etiology of renal  failure, followed by hypertension.19

In our study, we  found significant differences in fistula survival in patients with Hb levels  below  9 gldL and above  9 gldL (P

= 0.028). This is in agreement with Gheith and

Kamal, 2008 who reported that vascular access survived longer in less anemic patients than among severely anemic patients.9

Thrombosis of arteriovenous fistula  used for chronic hemodialysis remains a major cause of morbidity in hemodialysis patients.20 Intimal fibromuscular hyperplasia at the  venous anastomosis may be  an  important factor associated with thrombosis.21

Inour study, we found that thrombosis was the commonest complication in fistulae failure where it was present in 55% of patients with

fistula  failure. Also,  Hodges et  al.,  1997 reported that  the most  common  reason  for access  failure in  AVF  was  thrombosis.l5

We found no significant  difference in the frequency of fistula failure between patients with distal forearm and cubital fossa AVF (P

= 0.480). On the contrary Dixon et al, 2002,

and Roozbeh et al., 2006 found forearm fistulae were at greater risk ofloss of patency compared with  those  located in the  upper  arm  (P  =

0.014).5,20

Hayakawa  and colleagues 2008 reported that the older age, female sex, and diabetes mellitus were risk factors for fistula failure. In our  study,  predictors of AVF  failure  were previous fistula failure and low hemoglobin level, while the  other clinical and demographical factors did not influence AV­ fistula patency.22

Conclusion:

Predictors  of AVF failure  in our dialysis population were lower hemoglobin levels and previous fistula failure. These risk factors can be used as a guide for intensive management protocol after fistula operation to maintain its patency. We recommend  further multicenter studies on other risk factors which may have a role in fistula failure like hypotension  and hypercoagulability.

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