| Abstract|| |
Arteriovenous fistula (AVF) is the most appropriate vascular access for all chronic kidney disease patients for hemodialysis. However, patients with diabetic nephropathy are at increased risk for primary failure after AVF creation, mainly due to atherosclerosis and calcification of blood vessels. We conducted this study to find out the risk factors for primary failure of radiocephalic AVF in end-stage renal disease (ESRD) patients due to diabetic nephropathy and develop a risk predicting model. This study was conducted at a tertiary care teaching hospital of South India. Patients with ESRD due to diabetic nephropathy whom underwent left radiocephalic AVF at wrist were enrolled. Risk factors for primary failure were analyzed by univariate and multivariate logistic regression models. Sixty-six patients were included in the study. Thirty-one patients had a primary failure. Independent risk factors for primary failure were palpable vessel wall of the radial artery (P = 0.003, odds ratio [OR] = 15.317), smaller radial artery diameter (P = 0.001, OR = 16.526), radial artery peak systolic velocity (PSV) <45 cm/s (P = 0.005, OR = 8.494), and linear radial artery calcification (P = 0.006, OR = 7.942). The risk predicting model obtained by adding the score given for each risk factors (vessel wall not palpable = 0, palpable = 1, no linear calcification in digital X-ray = 0, linear calcification = 1, PSV ≥45 cm/s = 0, <45 cm/s = 1 and 2.5 - radial artery diameter in mm) had an area under receiver-operating characteristic curve of 0.886. Cutoff score of 1.5 had sensitivity of 83.9% and specificity of 80.0% for primary failure. Risk predicting model for primary failure based on condition of the vessel wall on palpation, radial artery diameter, flow velocity, and calcification may be helpful for suitable patient selection.
|How to cite this article:|
Kumar J S, Sajeev Kumar K S, Arun Thomas E T, Hareesh K G, George J. Prediction model for successful radiocephalic arteriovenous fistula creation in patients with diabetic nephropathy. Saudi J Kidney Dis Transpl 2019;30:1058-64
|How to cite this URL:|
Kumar J S, Sajeev Kumar K S, Arun Thomas E T, Hareesh K G, George J. Prediction model for successful radiocephalic arteriovenous fistula creation in patients with diabetic nephropathy. Saudi J Kidney Dis Transpl [serial online] 2019 [cited 2019 Nov 21];30:1058-64. Available from: http://www.sjkdt.org/text.asp?2019/30/5/1058/270261
| Introduction|| |
Arteriovenous fistula (AVF) is the most appropriate vascular access for all chronic kidney disease (CKD) patients for hemodialysis (HD) initiation and continuation.,,,, Patients with diabetes are considered as “difficult patients” for AVF creation due to increased failure rates, as atherosclerotic changes and calcification of blood vessels are more common.,,,, Although the most favored site for AVF is distal forearm, failure rates are more when compared to proximal sites due to smaller caliber of the blood vessels. Primary failure of new fistulas remains a major obstacle for increasing the proportion of dialysis patients with fistulas. Prior studies conducted to develop algorithms using combination of risk factors have failed to accurately identify individuals in whom AVF placement is futile., This may be because these models were made to encompass CKD of all etiologies and all types of AVF. We designed this study to develop a prediction model, specifically to predict the success of radiocephalic AVF creation in patients with end-stage renal disease (ESRD) due to diabetic nephropathy. This type of specific risk predicting model can become relevant as diabetic nephropathy is the most common cause of ESRD., A successful model if developed can be used for suitable patient selection. Those with a reduced chance for success can be considered for brachial AVF or other types of vascular accesses.
| Aims of the Study|| |
We aimed to find the risk factors for primary failure of radiocephalic AVF creation in patients with ESRD due to diabetic nephropathy and to develop a risk equation to predict primary failure of radiocephalic AVF in patients with ESRD due to diabetic nephropathy.
| Methods|| |
This was a single-center prospective observational study conducted at a tertiary care teaching hospital of South India (Government Medical College Hospital) from July 1 to December 31, 2017. All consecutive patients with ESRD due to diabetic nephropathy aged between 30 and 80 years who were posted for AVF creation and gave informed written consent for the study were enrolled. ESRD was defined as estimated glomerular filtration rate less than 15 mL/min/l.73 m2. For this study, ESRD due to diabetic nephropathy was defined as albuminuric CKD with more than 10-year diabetes duration or renal biopsy showing evidence of diabetic nephropathy. For all patients, left radiocephalic AVF creation at the wrist was considered first. Other types of AVF were considered only when any one of the following was present: (1) palmar arch not patent on performing Allen’s test, (2) evidence of cephalic vein thrombosis in left distal forearm clinically or in Doppler ultrasound (DUS), (3) non-augmented calibre of cephalic vein in left distal forearm less than 2 mm in DUS, (4) absent flow or peak systolic velocity (PSV) less than 25 cm/s in radial artery, and (5) radial artery diameter less than 1.3 mm in DUS.
Patients with previous attempts of AVF creation were excluded. Patients who underwent left radiocephalic AVF were followed up for three months or till, patient death, transplant or transfer another center whichever was earlier. Primary failure was defined as no appearance of or a loss of bruit or thrill within 72 h of creation (immediate vascular access failure) or an access that cannot be used successfully for dialysis by three months despite radiological or surgical intervention (early dialysis suitability failure). All AVF creations were done by cardiothoracic and vascular surgery department of the study center. All surgeons who created the AVF had more than five years’ experience in dialysis access creation. Anastomosis done was end to side. All patients received 2500 units of unfractionated heparin intravenously every 6 h in the first postoperative day unless there was a contraindication for the same. All patients also received Clopidogrel 75 mg for 14 days if not already on any antiplatelets, and there were no contraindications. Preoperative DUS vascular mapping was done using a linear 7.0–12.0 MHz Doppler probe of Mindray DC-T6 machine. Patients were in supine position without angling of the elbow joint to avoid compression of the vessels during DUS imaging. Vessel diameter was measured from inner edge to inner edge by B-mode scan and average of three measurements was determined. PSV in distal radial artery was also determined by averaging three successive measurements. All DUS were done by two nephrologists trained in DUS for vascular mapping. Radial artery diameter risk score was calculated for each patient. This score was obtained by subtracting patients radial artery diameter from the maximum diameter of the radial artery observed in this study population. Digital X-ray of the forearm was taken in both antero-posterior and lateral view to look for calcification. Calcification will be reported as linear if there is ≥6 cm of linear radial artery calcification at distal forearm.
| Statistical Analysis|| |
Categorical variables were compared by Chi-square test. Fisher’s exact test was used when the expected count was less than five. Continuous data were expressed as means ± SD. Continuous variables with non-normal distribution were compared by Mann–Whitney U-test between groups. Possible risk factors for primary failure of AVF were first analyzed using univariate logistic regression models. The multivariate model included all covariates with P <0.10 in the univariate analysis. The odds ratio (ORs) and corresponding 95% confidence intervals (CIs) for each variable were calculated. Risk prediction equation was made using the risk factors obtained in multivariate model. Receiver-operating characterristic (ROC) curve was drawn for this equation. The area under the curve (AUC) was calculated. The determination of optimal cutoff score was done using Youden’s index. Sensitivity, specificity, and predictive values for the cutoff were measured. All tests were two-tailed, and a P <0.05 was considered statistically significant.
| Results|| |
Sixty-six patients who underwent left radio-cephalic AVF satisfied the inclusion criteria. Thirty-seven patients were males and 29 were females. The mean age was 54.0 ± 8.2 years. The youngest patient was 31-year-old and the oldest was 69 years old. Of the total 66 study individuals, 34 patients were already started on HD with internal jugular catheter as vascular access. The mean duration of dialysis of these 34 patients was 3.3 ± 2.2 months. On preoperative clinical assessment, the vessel wall of radial artery was palpable in 26 patients. On DUS assessment, the mean caliber of radial artery was 2.0 ± 0.3 mm (maximum: 2.5, minimum: 1.3) and mean peak systolic velocity was 50.63 ± 12.28 cm/s (maximum: 73.0, minimum: 24.10). On pre-operative digital X-ray of the forearm, radial artery was calcified in 24 patients of whom nine had linear calcification. On three months’ follow-up, 31 patients (47%) had primary failure of the AVF.
Age, sex, HD, dialysis vintage, palpable vessel wall, radial artery diameter risk score, PSV in radial artery, linear and nonlinear radial artery calcification and hemoglobin concentration were analyzed as risk factors for primary failure using univariate [Table 1]. Age, palpable vessel wall, radial artery diameter risk score, PSV, and linear radial artery calcification were found to be significant risk factors in univariate analysis [Table 2]. Multivariate analysis showed only palpable vessel wall, radial artery diameter risk score, PSV and linear radial artery calcification as independent risk factors - age (P = 0.131, OR 1.116, 95% CI 0.968−1.287), palpable radial artery (P= 0.003, OR 15.317, 95 % CI 2.533–62.629), radial artery diameter risk score (P = 0.001, OR 16.526, 95% CI 3.442–123.722), PSV <45 cm/s in the radial artery (P = 0.005, OR 8.494, 95% CI 3.042–87.112), linear radial artery calcification (P= 0.006, OR 7.942, 95% CI 1.476–42.710).
|Table 1: Risk factors for primary failure of radiocephalic arteriovenous fistula in univariate analysis.|
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|Table 2: Risk factors for primary failure of radiocephalic arteriovenous fistula in multivariate analysis.|
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Of the 31 patients with primary failure, 17 patients had palpable radial artery, whereas palpable artery was present in only in nine patents out of 35 patients with successful AVF (P = 0.016). The mean radial artery diameter in DUS was 2.13 ± 0.26 mm in the group with successful AVF creation whereas only 1.78 ± 0.35 mm in the primary failure group (P <0.001). The mean radial artery PSV in DUS imaging was 55.61 ± 10.38 cm/s in the group with successful AVF creation whereas only 45.0 ± 11.94 cm/s in the primary failure group (P <0.001). Linear radial artery calcification was observed more frequently in primary failure group, (P = 0.046). Seven of the 9 (77.8%) patients with linear calcification had primary failure whereas only 24 out of 57 (42.9%) patients without linear calcification had a primary failure.
Based on the risk factors obtained for primary failure in multivariate analysis, risk equation was constructed [Table 3]. This risk equation adds the score given for each risk factors (vessel wall not palpable = 0, palpable = 1, no linear calcification in digital X-ray = 0, linear calcification = 1, PSV ≥45 cm/s = 0, <45 cm/s = 1 and 2.5- radial artery diameter in mm). ROC curves for this equation has AUC of 0.886 with 95% CI 0.807–0.964 [Figure 1]. The cutoff score of 1.5 had a sensitivity of 83.9%, specificity of 80.0%, positive predictive value of 78.8%, and negative predictive value of 84.8% for primary failure [Table 4]. The internal validity check of the risk equation was done using 1000 bootstrap samples, which showed AUC of 0.884 with 95% CI 0.779–0.984.
|Table 3: Risk scoring for primary failure of radio-cephalic arteriovenous fistula.|
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| Discussion|| |
Although diabetes mellitus is generally thought to be a risk factor for AVF failure, it is not the diabetic state per se, but the poor quality of the vessels seen more frequently in diabetic nephropathy is the main cause. Preprocedure vascular evaluation can make a marked difference in achieving success with AVF creation. The most important determinant in the success of an AVF is the quality of the available vessels and hemodynamic factors, i.e., vein size, feeding artery size, quality of feeding artery and blood flow. Consistent with these facts, our study also showed that thickened vessel wall of radial artery due to atherosclerosis, reduced radial artery diameter, reduced radial artery PSV and linear radial artery calcification were independent risk factors for primary failure of distal forearm AVF. Many authors have already postulated that an arterial diameter ≥2.0 mm and a PSV of at least 50 cm/s were predictive of successful AVF placement.,,, The risk of AVF failure increases significantly when the internal diameter of the radial artery is ≤1.6mm.. In our study, the mean radial artery diameter of the group with successful AVF creation was 2.13 ± 0.26 mm. Furthermore, in our study, primary failure was significantly more when PSV in distal radial artery was <45 cm/s. The prevalence of vascular calcification is more in CKD due to diabetic nephropathy when compared to other etiologies. Calcification of radial artery leads to increased pulse pressure and abnormal endothelial and vasomotor function resulting in increased chance of primary failure of AVF. Arterial calcifications can also create difficulty in performing vascular anastomosis., We observed that patients with linear calcification of radial artery had more risk for primary failure. Nonlinear calcification was not found to be a risk factor in our study.
Older age has been cited as a risk factor for failure of AVF fistula maturation and long-term functional survival. We found advanced age as a risk factor in univariate logistic regression, but not in multivariate analysis, suggesting that this observed risk can be due to poor quality of blood vessels in the elderly. Sex did not affect the AVF outcome in our study, but most investigations have found significant differences in outcomes when comparing males and females, although there are reports to the contrary., There is an increased risk of AVF failure when created in patients on HD, as intradialytic hypotension can result in AVF thrombosis, but our study did not find any significant difference. Hemoconcentration can lead to vascular access thrombosis. We analyzed hemoglobin concentration as a risk for primary failure, but no significance was noted.
Although risk stratification schemes based on demographic and clinical parameters to identify individuals with poor success of AVF are already available, none are exclusively meant for diabetic nephropathy patients., We tried to create a simple risk equation, using the risk factors identified for primary failure. The risk score was obtained by adding scores given for thickened vessel wall of radial artery on palpation, radial artery diameter, flow velocity, and calcification. The equation had a fairly good sensitivity, specificity, and predictive values. This equation can only be used if the cephalic vein at distal forearm is patent with a good caliber.
The major limitation of this study was small sample size. Due to the small sample size, internal validation of the risk equation was done using bootstrap samples. The training and experience of the surgeon available to create AV access may vary and may have affected the success of AVF creation making external validation of the equation important.,,,, External validation is yet to be conducted.
| Conclusion|| |
Distal AVF in diabetic nephropathy patients has a relatively high primary failure rate. Risk predicting model for primary failure based on condition of the vessel wall on palpation, radial artery diameter, flow velocity, and calcification may be helpful for suitable patient selection. Patients with a higher risk score for primary failure can be given a choice for more proximal sites, especially in the elderly and in those with additional co-morbidities.
Conflict of interest: None declared.
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K S Sajeev Kumar
Department of Nephrology, Government Medical College, Thiruvananthapuram - 695 011, Kerala
[Table 1], [Table 2], [Table 3], [Table 4]