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Sex, race, and hemodialysis vascular access processes

Sex, race, and hemodialysis vascular access processes

J Vasc Access 2017; 18(2): 132 - 138

Article Type: ORIGINAL RESEARCH ARTICLE

DOI:10.5301/jva.5000657

Authors

Rita L. McGill, Eduardo Jr. Lacson

Abstract

Purpose

Hemodialysis (HD) patients who are female or black receive fewer arteriovenous fistulas (AVF) and more grafts (AVG). We evaluated race- and sex-based differences for three process exposures: access surgery, peripherally-inserted central catheters (PICCs), and vascular imaging.

Methods

US Renal Data System with linked Medicare claims for patients initiating HD between April 2010 – December 2011 were used to identify PICC placement, imaging, AVF and AVG surgeries, and the vascular accesses in use at individual HD treatments. Poisson, logistic, and Cox regression models adjusted for clinical and demographic variables were used to evaluate relationships between process exposures, vascular access outcomes, and sex.

Results

Among 18,883 individuals initiating HD with catheters with at least one surgical claim for AVF or AVG, women had 16% more PICC and 5% more imaging (p = 0.002), were 43% less likely to have AVF surgery and 68% more likely to have AVG surgery (p<0.001). The odds of AVF surgery producing a working AVF were 18% lower and of AVG surgery producing a working AVG 38% higher (p<0.001). Black patients had 24% more PICCs and 12% more imaging, were 48% less likely to have AVF surgery and 84% more likely to have AVG surgery (p<0.001). The odds of achieving a working AVF were 8% lower and of a working AVG were 38% higher. The hazard of future catheter use after AVF creation was 25% higher for women (p<0.001), but did not differ by race.

Conclusions

Divergences in vascular access by race and sex were partly related to differential process exposures. Black and female patients had more AVG and less AVF surgery, and more PICC and imaging. Success rates were lower for AVF surgery and higher for AVG surgery. Further work is needed to determine whether choices of process exposures arise from differential ability to detect veins on physical examination.

Article History

Disclosures

The data reported here have been supplied by the United States Renal Data System (USRDS). The interpretation and reporting of these data are the responsibility of the author(s) and should in no way be seen as an official policy or interpretation of the US Government.
Financial support: The project described was supported by the National Center for Advancing Translational Sciences, National Institutes of Health (NIH), Award Number UL1TR001064. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.
Conflict of interest: Dr. Lacson receives salary support from Dialysis Clinic, Inc. paid to his institution.

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Introduction

Vascular access is crucial for people who depend upon hemodialysis (HD) for survival. In the USA, ~ 60% of patients start HD with a central venous catheter (CVC) as their sole vascular access (1). After the first year, 2/3 of those who survive will have transitioned to an arteriovenous fistula (AVF) or graft (AVG) – but the types of vascular access in prevalent HD patients differ sharply by race and sex. US Renal Data System (USRDS) data from 2013 show that men have 68.7% AVF and 14.2% AVG (1). By contrast, women have 54.5% AVF and 23.7% AVG, and black patients have 56.9% AVF and 25.5% AVG. These differences have persisted despite considerable progress in reducing CVC use in prevalent HD patients over the past 15 years (2).

The mechanisms by which vascular access selection diverges by race and sex are unknown. Two studies in which veins were measured by Doppler ultrasound failed to reveal significant sex-related discrepancies in vessel caliber, but a single-center study of male patients indicated decreased vein diameter in black patients (3-4-5). Primary and secondary patency of fistulas were both reduced in men receiving HD in a recent systematic review (6).

In women and black patients, veins may be less apparent upon physical examination, even in patients who are not obese (3). When superficial blood vessels are not evident, the choice between exploratory surgery, contrast venography, and Doppler vein mapping might alter or delay the surgical plan. Venography poses the risk of intravenous contrast; on the other hand, the utility of Doppler vein mapping remains subject to debate, with questions raised as to whether increased surgical attempts result in more working vascular access (7-8-9). Finally, patients with kidney disease have frequent hospitalizations. Less obvious peripheral veins in women and black patients may result in more peripherally-inserted central catheters (PICC), which may damage peripheral and central veins needed to construct and drain future AVFs (10, 11).

This study was performed to examine the process exposures of patients who initiated HD with CVC as their sole vascular access and the outcomes of access surgery when performed, by race and sex. We hypothesized that because women and black patients have less obvious vessels on examination, that they would have excess exposure to the harmful effects of PICC, and fewer attempts at fistula creation. We further sought to determine the effects of sex and race on the success of AVF and AVG surgeries, and define the use and impact of vascular imaging nationally.

Materials and methods

Patient population

USRDS standard analytical files were linked with Medicare claims for the years 2008-2012. This study was approved by the Institutional Review Board of Tufts Medical Center, and deemed exempt from requirement for informed consent for the use of de-identified data.

The study population included patients who initiated HD between April 1, 2010 and December 31, 2011, in whom CVC was the sole vascular access at the first outpatient HD treatment, if there were subsequently one or more claims for surgery to create an AVF or an AVG (Fig. 1). We restricted our analysis to adult Medicare beneficiaries with Medicare coverage two years prior to the first HD according to the USRDS payer history file, and had at least two existing pre-dialysis Medicare claims, at least six months apart, with one or more ≥365 days before first HD. The requirement for past Medicare coverage allowed for recovery of claims for PICC and vascular imaging, and for making direct determinations of comorbid conditions. Medicare benefits usually begin at age 65, except in cases of chronic disability, so the requirement for Medicare claims necessarily identified a patient cohort that was older than the overall US hemodialysis cohort because most, though not all, patients with Medicare benefits 2 years prior to dialysis initiation would be at least 67 years of age. The vascular access at HD initiation was obtained from the USRDS medical evidence form (CMS Form 2728) and verified by examination of HD treatment claims for the first 6 weeks. USRDS treatment history files were used to ascertain dates of death, transplant, and changes in treatment modality. Patients were followed until either death, transplant, transfer to another dialysis modality or December 31, 2012, whichever came first.

Derivation of the study population.

Exposures to access surgery, vascular imaging, and PICC

Vascular access surgeries were ascertained from claims for AVF (Common Procedural Terminology (CPT) codes 36818, 36819, 36820, and 36821) and AVG (CPT 36825 and 36830) creation. Exposures to AVF surgeries and AVG surgeries were counted for each patient. Vascular imaging was determined for the two years prior to HD initiation and up until achievement of a working AVF or AVG, using CPT codes for venography of the upper extremity or central veins (CPT 36005, 75820, 75822, and 75827) and Doppler vein mapping for dialysis access planning (CPT G0365). Imaging of the lower extremities was not included. PICC placements were ascertained in institutional details, physician/supplier, and revenue center details files as CPT codes 36569 and 36571, which are specific for peripherally inserted catheters.

Primary outcomes

Vascular access was determined from the vascular access modifier codes on individual HD treatment claims. Conversion to fistula or graft access was defined by the first day of the earliest 30-day period in which all available vascular access modifiers on all HD treatment claims were for AVF-only (modifier V7) or AVG-only (modifier V6) with no intervening codes for catheter use (modifier V5), based on established definitions for a working AVF (12, 13). The first subsequent claim, if any, for HD with a CVC after conversion to a working AVF or AVG was also collected.

Covariates

Comorbid conditions were determined directly from pre-dialysis Medicare claims, by a previously validated method (14). Diabetes was ascertained either by Medicare claims or by a primary diagnosis of diabetic nephropathy on CMS Form 2728, which was also used to determine age, sex, race, body mass index (BMI), primary causes of kidney failure, pre-HD nephrology care, pre-HD erythropoietin (EPO) use, inability to ambulate, and laboratory values (hemoglobin, albumin, and creatinine) at the time of HD initiation.

Statistical analyses

Means and medians were used to summarize distributions of normally and non-normally distributed continuous variables, respectively, Wwith t-tests, Wilcoxon rank sum tests and chi-squared tests used as appropriate. Poisson regression was used to evaluate incidence rate ratios (IRR) for exposures to PICC and imaging. Logistic regression models were used to derive odds ratios (OR) for receiving AVF or AVG surgery, and for achievement of working AVF after one or more fistula surgeries and working AVG after one or more graft surgeries, as well as a model for persistent catheter use in patients who had received any surgery. Cox models were used to generate the hazard ratios (HR) for catheter use after successful AVF and AVG. All models included: age, sex, race, BMI, primary causes of kidney failure, pre-HD nephrology care, ability to ambulate, and hemoglobin, albumin, and creatinine at HD initiation, as well as comorbid conditions. All IRR, OR, and HR were expressed as: ratio (95% confidence interval [CI]).

Results

Participant characteristics

Over the study period, 178,878 patients initiated HD in USRDS, of whom 69% were excluded for insufficient Medicare coverage, 12% for non-CVC vascular access, and 9% for absence of vascular access surgery claims. Our study population consisted of 18,883 patients (Fig. 1), of whom 48.2% were women and 25.0% were black. The average age of the population was 71.9 years. Median follow-up after HD initiation was 19.8 months (interquartile range [IQR], 12.0-25.4 months), during which 6780 patients (35.9%) died. Table I compared the baseline characteristics grouped by race and sex. Compared to men, women were older, had higher BMI, and were more likely to have congestive heart failure, pulmonary disease, stroke, inability to ambulate, and primary diabetic nephropathy, but less likely to have atherosclerotic heart disease, arrhythmia, peripheral vascular disease and cancer. Compared to all others, black patients were younger, less likely to have pre-ESRD EPO/nephrology care, and had more stroke and heart failure, but less atherosclerotic heart disease, peripheral vascular disease, and arrhythmia. Imaging prior to surgery was significantly more common in both women and blacks (Tab. I).

Baseline patient characteristics, by sex and race

All Men Women p Values
Black Non-black Black Non-black By race By sex
Conversion factors to SI units: serum albumin in g/dL to g/L, ×10; hemoglobin in g/dL to g/L, ×10; serum creatinine in mg/dL to µmol/L, ×88.4.
ESRD = end-stage renal disease; GI = gastrointestinal; SD = standard deviation.
N 18,883 2197 7593 2530 6563
Age, mean (SD) 71.9 (11.4) 66.9 (12.5) 73.1 (11.1) 69.0 (12.1) 73.4 (1.04) <0.001 0.004
Body mass index, mean (SD) 29.1 (7.9) 28.3 (7.1) 28.2 (7.0) 30.7 (8.6) 29.9 (8.6) <0.001 <0.001
Pre-ESRD nephrology care (%) 52.2 45.1 54.2 49.0 53.4 <0.001 0.01
Pre-ESRD erythropoietin use (%) 16.7 12.3 16.6 16.7 18.2 <0.001 <0.001
Imaging prior to surgery (%) 49.8 52.7 47.8 54.3 49.4 <0.001 0.008
Primary ESRD diagnosis (%) <0.001 <0.001
 Diabetes 45.6 45.6 42.8 49.8 47.4
 Hypertension 33.6 39.4 32.7 37.7 31.2
 Primary glomerulonephritis 3.4 2.5 3.8 2.5 3.4
 Other 17.4 12.5 20.7 10.0 18.0
Comorbid conditions (%)
 Atherosclerotic heart disease 49.7 41.9 55.2 41.9 49.0 <0.001 <0.001
 Congestive heart failure 46.0 45.0 45.2 49.2 46.1 0.05 0.01
 Other cardiac conditions 31.0 27.4 29.9 33.2 32.5 0.4 <0.001
 Arrhythmia 27.8 23.0 32.8 19.8 26.8 <0.001 <0.001
 Peripheral vascular disease 28.9 26.5 31.8 26.1 27.5 <0.001 <0.001
 Pulmonary disease 26.4 22.2 26.1 25.3 28.4 <0.001 <0.001
 Diabetes, not cause of ESRD 22.8 25.1 22.3 25.3 21.8 <0.001 0.8
 Stroke 14.7 15.5 13.3 18.5 14.5 <0.001 0.004
 Cancer 10.7 10.6 14.1 7.9 7.8 <0.001 <0.001
 Inability to ambulate 9.6 9.8 8.1 10.9 10.6 0.02 <0.001
 GI bleeding 5.0 5.3 4.8 4.8 5.2 0.8 0.5
 Liver disease 3.5 3.8 3.9 2.9 3.3 0.4 0.01
Pre-ESRD labwork, mean (SD)
 Serum albumin (mg/dL) 3.1 (0.7) 3.03 (0.66) 3.08 (0.64) 3.03 (0.64) 3.07 (0.64) <0.001 0.2
 Serum creatinine (mg/dL) 5.5 (2.7) 6.8 (3.5) 5.5 (2.5) 5.6 (2.9) 4.8 (2.3) <0.001 <0.001
 Hemoglobin (g/dL) 9.8 (1.5) 9.5 (1.6) 9.9 (1.5) 9.4 (1.5) 9.8 (1.4) <0.001 <0.001

Surgical procedures and vascular access outcomes

There were 32,341 vascular surgeries performed on 18,883 patients. The distribution of vascular surgeries is summarized in Supplementary Table I, available online as Supplementary material at www.vascular-access.info. There were 85.5% of patients who had either one or two operations. The odds ratios for receiving a fistula surgery was 0.57 (0.53, 0.62) for female sex and 0.52 (0.48, 0.57) for black race. The ORs for having graft surgery was 1.68 (1.58, 1.79) for female sex and 1.84 (1.71, 1.97) for black race (Tab. II). Interaction terms between sex and race were not significant for either type of surgery, indicating two separate main effects.

Odds ratios for performance of access surgery (n = 18,883)

Variable Fistula surgery Graft surgery
OR (95% CI) p value OR (95% CI) p value
*ORs shown for the most significant variables. Models adjusted for: body mass index, primary kidney diagnosis, pre-dialysis nephrology care, inability to ambulate, atherosclerotic heart disease, congestive heart failure, arrhythmia, other cardiac diagnoses, stroke, peripheral vascular disease, lung disease, GI bleeding, liver disease, cancer, and pre-dialysis creatinine, albumin, and hemoglobin.
OR = odds ratio; CI = confidence interval; PICC = peripherally-inserted central catheters; GI = gastrointestinal; ESRD = end-stage renal disease.
Female sex 0.57 (0.53, 0.62) <0.001 1.68 (1.58, 1.79) <0.001
Black race 0.52 (0.48, 0.57) <0.001 1.84 (1.71, 1.97) <0.001
Age (per 10 years) 0.86 (0.83, 0.89) <0.001 1.09 (1.06, 1.12) <0.001
Pre-ESRD nephrology care 1.19 (1.10, 1.29) <0.001
PICC exposure 0.83 (0.75, 0.93) 0.001 1.27 (1.16, 1.39) <0.001
Vascular imaging 1.13 (1.06, 1.20) <0.001

Among the 18,883 patients, 51.9% achieved working fistulas, 18.6% achieved working grafts, and 29.5% had persistent catheter access. Median time to a working fistula was 209 days (IQR 150-294 days), and median time to a graft was 165 (IQR 110-264) days.

Among 15,206 patients who had one or more fistula surgeries, the ORs for transition to working AVF were 0.82 (0.76, 0.88, p<0.001) for female sex and 0.92 (0.85, 1.00, p = 0.06) for black race. Among 7044 who had any graft surgery, the odds of achieving a working graft were 1.38 (1.26, 1.53) for female sex and 1.38 (1.25, 1.54) for black race (p<0.001 for both). Persistence of catheter access did not differ between women and men, but was 20% lower (p<0.001) in blacks (Tab. III).

Odds ratios for outcomes of vascular access surgery

N Working fistula 15,206 Working graft 7044 Persistent catheter use 18,883
Variable OR (95% CI) p value OR (95% CI) p value OR (95% CI) p value
N for fistula outcome is all patients who had ≥1 fistula surgery; n for graft outcome is all patients who had ≥1 graft surgery; n for catheter outcome is all patients who had any access surgery.
Models adjusted for: body mass index, primary kidney diagnosis, pre-dialysis nephrology care, inability to ambulate, atherosclerotic heart disease, congestive heart failure, arrhythmia, other cardiac diagnoses, stroke, peripheral vascular disease, lung disease, GI bleeding, liver disease, cancer, and pre-dialysis creatinine, albumin, and hemoglobin.
OR = odds ratio; CI = confidence interval; PICC = peripherally-inserted central catheters; GI = gastrointestinal.
Female sex 0.82 (0.76, 0.88) <0.001 1.38 (1.26, 1.53) <0.001 0.98 (0.92, 1.05) 0.6
Black race 0.92 (0.85, 1.00) 0.06 1.38 (1.25, 1.54) <0.001 0.80 (0.74, 0.87) <0.001
Age (per 10 years) 0.96 (0.94, 0.99) 0.02 1.06 (1.01, 1.10) 0.01 1.02 (0.99, 1.05) 0.2
Pre-dialysis nephrology care 1.09 (1.02, 1.16) 0.02 1.06 (0.97, 1.17) 0.2 0.88 (0.83, 0.94) <0.001
PICC exposure 0.80 (0.73, 0.89) <0.001 0.90 (0.79, 1.04) 0.2 1.21 (1.10, 1.33) <0.001
Vascular imaging 0.96 (0.90, 1.03) 0.3 1.22 (1.11, 1.34) <0.001 0.92 (0.87, 0.98) 0.01

Adjusted hazard ratios for subsequent catheter use after establishment of a working AV fistula or graft

N After fistula creation 9804 After graft creation 3505
Variable OR (95% CI) p value OR (95% CI) p value
Models adjusted for: body mass index, primary kidney diagnosis, pre-dialysis nephrology care, inability to ambulate, atherosclerotic heart disease, congestive heart failure, arrhythmia, other cardiac diagnoses, stroke, peripheral vascular disease, lung disease, GI bleeding, liver disease, cancer, and pre-dialysis creatinine, albumin, and hemoglobin.
AV = arteriovenous; OR = odds ratio; CI = confidence interval; PICC = peripherally-inserted central catheters; GI = gastrointestinal.
Female sex 1.24 (1.14, 1.35) <0.001 1.08 (0.94, 1.23) 0.3
Black race 0.98 (0.89, 1.04) 0.7 1.02 (0.89, 1.17) 0.8
Age (per 10 years) 1.00 (0.96, 1.04) 0.9 0.95 (0.89, 1.00) 0.06
PICC exposure 1.19 (1.05, 1.35) 0.006 1.13(0.95, 1.35) 0.2
Vascular imaging 1.07 (0.99, 1.16) 0.08 1.13 (1.00, 1.30) 0.2

Subsequent CVC use was detected more often in patients who received grafts than in those who received fistulas (28.0% vs. 24.8%, p<0.001). The HR for CVC use after achieving a working AVF was 1.25 (1.14, 1.37, p<0.001) for female sex, but did not differ significantly by race. Neither sex nor race had any significant associations with CVC use after AVG (Tab. IV).

Exposures to PICC and imaging

Compared to men, women had more exposure to PICCs (12.9% vs. 11.5%, p = 0.003). Compared to all others, black patients had more exposure to PICCs (13.4% vs. 11.8%, p = 0.004). In Poisson models adjusted for time at risk and all clinical and demographic factors, the IRR for PICC placement was 1.16 (1.12, 1.28) for female sex and 1.24 (1.15, 1.34) for black race, (p<0.001 for both). Adjusted IRRs for vascular imaging were 1.05 (1.01, 1.09, p = 0.002) for female sex and 1.12 (1.08, 1.16, p<0.001) for black race.

Discussion

In a large national cohort of Medicare patients initiating HD with catheters who underwent at least one vascular access surgical procedure, exposures to PICC, imaging, and AVG were all more frequent in women and blacks. Transition from catheter to any AVF or AVG did not differ significantly by sex, but was significantly higher in black patients.

Compared to men, women were less likely to undergo fistula surgery and more likely to undergo graft surgery. The success of fistula attempts was lower and that of graft attempts was higher in women. The rate of catheter use after successful fistula was higher in women. Compared to all others, black patients were also less likely to undergo fistula surgery and more likely to undergo graft surgery. The success of fistula attempts was lower and that of graft attempts was higher in black patients. However, catheter use after either fistula or graft did not differ by race.

Our findings are in agreement with other studies that have noted decreased fistula achievement in women and blacks and decreased success of fistula surgeries (5, 15-16-17); however, the finding that graft surgeries were significantly more successful in women and black patients was unexpected, as there is no obvious biological mechanism for graft insertion to be more successful in patients who are black or female. In the absence of data outlining the motivation for selection of surgical procedure, one hypothesis is that women and blacks may arrive at AVG surgeries with better veins. This could arise from increased difficulty in detecting candidate veins in these groups: due to less superficial veins in women and decreased visualization of veins in the setting of darker skin, in which case an unfavorable physical examination might indicate true venous depletion much more accurately in men and non-black patients than in women and blacks. This hypothesis would also explain the increased placement of PICC in women and blacks, a negative interaction in which failure to detect vessels would promote PICC placement, in turn damaging veins that might otherwise have been adequate for AVF construction. Vessel damage from PICC could then result in less successful outcomes of AVF surgery and greater need to resort to imaging and AVG creation, all of which were more likely in women and blacks. Alternative explanations might include differential intervals between presentation and need for dialysis, or unequal access to care.

Our findings are consistent with those of Caplin et al (3), who noted comparable vein diameters in women and men, and considerable equalization of vascular access outcomes in a population in which all individuals were imaged. Closer examination of this study reveals that they too observed higher proportions of working AVG in women and working AVF in men, although their findings were not significant due to lack of statistical power. Our findings are also in agreement with the DOPPS Practice Monitor, which reported a positive association of AVG with both female sex and black race (18).

Our data suggest that once the commitment to perform surgery had been made, transition from CVC was minimally more likely when imaging was performed. Imaging was performed more often in women and blacks; however, the overall use of imaging was approximately 50%. We demonstrated that imaging was associated with more AVG surgery and more working AVGs, and fewer AVF attempts and working AVFs, with no difference in the likelihood of subsequent catheter use. One interpretation is that use of vessels detected by imaging may be as successful as use of vessels that are evident on visual inspection, provided that an increased proportion of AVG is acceptable. Although attempting AVF may be the optimal choice for the majority of patients (19), the survival advantage associated with any transition from CVC is considerable (20), and imaging followed by AVG creation may therefore represent an alternative pathway by which patients with marginal vasculature may avoid the risks of CVC. This aligns our findings with other reports in which the benefits of AVGs are reported to be similar to those of AVFs. Another possibility is that the vessels identified on imaging alone may be smaller in caliber than those found upon direct examination, influencing choice of surgical approach in favor of graft placement. We could not estimate the potential impact of imaging, were it to be more frequently applied, so further work is needed to determine whether greater exposure to vascular imaging might improve the vascular access prospects of blacks and women.

The strength of this study was the large population in which vascular access surgeries and their outcomes could be ascertained, and adjusted for many potential confounders. These data reflected national practice rather than local trends. Certain limitations merit discussion. Our study was limited to individuals with Medicare coverage, selecting an older group than the overall HD population; our findings may not be generalizable to non-Medicare patients or children. In this relatively modern cohort, the follow-up times were limited to one or two years, which nonetheless represented the full lifespan of more than one-third of subjects. This administrative data set lacks information about the motivations for imaging and for choice of surgical procedures. Finally, residual confounding by unmeasured covariates may remain.

Conclusions

The process exposures of patients who initiate hemodialysis with CVC as sole vascular access differed by sex and race, which may in part explain the observed differences in vascular access outcomes. Uniformly applied processes that can relate imaging findings to surgical choices and access outcomes may further delineate whether the race and gender gaps in vascular access can be narrowed. The use of PICC lines should be avoided in all patients with chronic kidney disease, irrespective of sex or race. Further work is needed to determine whether there is untapped potential to increase vascular access achievement for black and female dialysis patients.

Disclosures

The data reported here have been supplied by the United States Renal Data System (USRDS). The interpretation and reporting of these data are the responsibility of the author(s) and should in no way be seen as an official policy or interpretation of the US Government.
Financial support: The project described was supported by the National Center for Advancing Translational Sciences, National Institutes of Health (NIH), Award Number UL1TR001064. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.
Conflict of interest: Dr. Lacson receives salary support from Dialysis Clinic, Inc. paid to his institution.
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Authors

Affiliations

  • Division of Nephrology, Tufts Medical Center, Boston, MA - USA

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