Resource utilization in the treatment of critical limb ischemia: the effect of tissue loss, comorbidities, and graft-related events

Article Outline

• Abstract
• Methods
  • Trial design
  • Statistical analysis
• Results
• Discussion
• Conclusions
• Author contributions
• References
• Copyright

Objective

Resource utilization (RU) in the care of patients with critical limb ischemia (CLI) is not well quantified. We present a cohort study to quantify in-hospital RU and analyze the role of tissue loss (TL), comorbidities, and vascular graft-related events (GREs) in patients undergoing peripheral bypass for CLI.

Methods

A retrospective analysis of 1404 patients enrolled in a multicenter clinical trial (PREVENT III) of vein bypass grafting for CLI was performed with analysis of RU during the 1-year follow-up period. Univariate and multivariable linear regressions were performed to determine RU predictors and outcomes.

Results

Compared with patients with rest pain, patients presenting with TL as the indication for bypass surgery had a longer index length of stay (mean, 9.8 vs 6.2 days), more rehospitalizations (mean, 1.6 vs 1.2), and a longer cumulative length of stay (mean, 27.7 vs 17.3 days; P < .0001 for all comparisons). Rehospitalizations over the ensuing year were for additional procedures (37.5%), wound infection (14.6%), graft failure (10.7%), and other cardiovascular (10%) and noncardiovascular (26%) reasons. Early GRE (stenosis ≥70%, thrombosis, revision, or major amputation within 30 days) occurred in 162 (11.5%) patients, resulting in a longer index length of stay (mean, 11.8 vs 8.6 days; P = .0002) and cumulative length of stay (mean, 25.9 vs 24.6 days; P = .0043), but no difference in the number of rehospitalizations (mean, 1.6 vs 1.5 days; P = .3272). During the 1-year follow-up, 554 (39.5%) patients had GREs, and this resulted in more rehospitalizations (mean, 2.1 vs 1.1; P < .0001) and a longer cumulative length of stay (mean, 28.2 vs 21.9 days; P < .0001) compared with patients without GRE. Multivariable analysis demonstrated the highly positive association of TL (hazard ratio [HR], 1.75) and early GRE (HR, 1.77) with the index length of stay, whereas comorbidities—namely, dialysis dependency (HR, 1.31), nonsmoking status (HR, 1.29), hypertension (HR, 1.26), and increasing age (HR, 1.01)—also had strong effects. The effect of TL and GRE on later RU (number of rehospitalizations and cumulative length of stay) was present but less pronounced than patient comorbidities (namely, dialysis).

Conclusions

The stage of disease at presentation (TL vs rest pain) and the patency of the bypass graft (freedom from GRE) are critical determinants of RU over the first year after limb-salvage surgery. These effects predominate early (index length of stay) and persist through 1 year. Patient-specific factors, particularly dialysis-dependent renal failure, are also critical comorbidities affecting RU in these patients.

Considerable resources are required to diagnose, treat, and follow up patients with chronic progressive critical limb ischemia (CLI). These patients need limb salvage, arterial intervention, and management of multiple medical comorbidities. Patient evaluation involves (1) diagnostic testing to determine suitability for arterial revascularization and (2) assessment of frequent comorbidities, such as coronary artery disease and renal dysfunction. To achieve limb salvage, especially in patients presenting with tissue loss (TL) or foot infection, multiple procedures may be required, and postoperative readmission for wound care is common. Despite best efforts, some patients may still experience limb loss or develop procedure-related complications. Although there are established general practice patterns in the treatment of CLI, diagnostic, therapeutic, and follow-up decisions vary among clinicians and institutions. Accordingly, resource utilization (RU) will depend on the clinical decisions and their outcomes.

Prior work on RU in vascular surgery has been descriptive of one institution¹, ² or has focused on the effect of policy or protocol implementation.³ Several studies have also examined utilization in specific vascular-related cohorts limited to single institutions: dialysis patients⁴ and diabetic foot ulcers.⁵ Studies using large databases such as Medicare recipients have wider application, but they lack depth in outcome analysis.⁶

This report details RU in a cohort study of 1404 patients who received infrainguinal lower extremity bypasses for CLI in the PREVENT III trial. Measures of RU included the index length of stay (iLOS), number of rehospitalizations (NOR), and cumulative length of stay (cLOS) over the 1-year follow-up period. Our analysis examined the influence of patient presentation, comorbidities, technical success, and mid-term graft patency on RU.

Back to Article Outline

Methods 

Trial design 

PREVENT III was a multicenter, double-blinded, randomized, placebo-controlled trial of edifoligide for the prevention of vein graft failure in patients undergoing lower extremity bypass for the treatment of CLI (gangrene, ischemic ulcer, or rest pain). Details of the trial design have been previously reported.⁷ The trial was sponsored by Corgentech Incorporated (South San Francisco, Calif) and Bristol-Myers Squibb (Princeton, NJ). Eighty-three sites in the United States and Canada randomized 1404 patients aged more than 18 years with CLI to receive either edifoligide or placebo during intraoperative preparation of the vein graft. Exclusion criteria included claudication as the indication for bypass, a nonautogenous component of the infrainguinal graft, or an in situ vein graft configuration (treatment with edifoligide required ex vivo delivery to the vein graft). The primary trial end point was reintervention for nontechnical index graft failure or major amputation as a result of index graft failure at 1 year.

Postoperative assessments included adverse event monitoring during the first 30 days after bypass, intensive ultrasound-based graft surveillance (1, 3, 6, and 12 months), and clinical follow-up with vascular examinations. Rehospitalizations, additional procedures on the index limb, and concomitant medications were recorded during the 1-year study period. The primary reason for rehospitalization was determined by the treating surgeons according to study-defined categories. Wound infections were defined as having infection, necrosis, hematoma/hemorrhage, or seroma/lymphocele at the surgical incision or harvest site. Although the PREVENT III protocol recommended graft revision for >70% stenosis, final decisions about graft revision, rehospitalizations, and other uses of resources were left to the discretion of the treating surgeon.

Statistical analysis 

Graft-related events (GREs) were defined as thrombosis, stenosis of 70% or more (ultrasonography or angiography), revision, or major amputation. Early GREs were defined as those that occurred within the first 30 days of the index bypass. Any GRE was defined as GREs occurring within any time of the study, including within the first 30 days. The iLOS was defined as the number of postoperative days the patient was hospitalized after the index operation; it was calculated by subtracting the discharge date from the date of operation. The NOR was defined as the number of inpatient readmissions incurred by the patient during the 1-year follow-up period. The cLOS was defined as the total number of inpatient days incurred during the 1-year follow-up and includes the iLOS.

Univariate comparisons of factors influencing RU outcomes were performed with a Wilcoxon rank-sum or Kruskal-Wallis test for categorical variables and a log-transformed linear regression for continuous variables. The following variables were tested: age, sex, race, diabetes, dialysis dependency, hyperlipidemia, hypertension, baseline aspirin use, β-blocker use, lipid-lowering agent use, smoking status, treatment assignment (study drug), TL vs rest pain, and occurrence of a GRE. Variables that demonstrated a potential association (P ≤ .20) were included in the multivariable models. Multivariable analysis on iLOS and cLOS was performed by using Cox proportional hazard models with study termination (death or withdrawal) as the censoring variable. NOR modeling was performed by using a Poisson regression model to better fit the discrete NOR outcomes. An α value of .05, corresponding to P = .05 and 95% confidence intervals (CIs), was used as a criterion for statistical significance. Analysis was performed by using SAS version 9.1 (SAS Institute, Cary, NC).

Back to Article Outline

Results 

The details of the demographics and comorbidities of patients enrolled in the PREVENT III trial have been previously reported.⁸, ⁹ Pertinent demographic and surgical data are summarized here. There were 1404 patients who had lower extremity vein bypass as part of the PREVENT III trial (897 men and 507 women; mean age, 69 ± 12 years). The primary indication for surgery was ischemic rest pain in 25%, nonhealing ulceration in 39%, and gangrene in 36%. The mean preoperative ankle-brachial index was 0.5 ± 0.4. Sixty-four percent had diabetes, 73% were smokers, 12% were on dialysis, and 28% had undergone a previous infrainguinal bypass. During the 1-year follow-up period, 222 patients (15.8%) died, 18 were lost to follow-up, and 26 withdrew from the study. The most common site of proximal anastomosis was the common femoral artery (n = 687; 49%), followed by the superficial femoral artery (n = 348; 25%), deep femoral artery (n = 80; 5.7%), and popliteal artery (n = 247; 17.6%). The most common site of distal anastomosis was the below-knee popliteal artery (n = 312; 22%), followed by the posterior tibial artery (n = 290; 21%), peroneal artery (n = 239; 17%), anterior tibial artery (n = 219; 15.6%), pedal/plantar artery (n = 166; 11.8%), and above-knee popliteal artery (n = 145; 10%).

The results of PREVENT III have been reported⁹ and are briefly summarized here only to provide context for the RU analysis. Perioperative (30-day) mortality for the entire cohort occurred in 38 patients (2.7%). Major perioperative complications included myocardial infarction in 66 patients (4.7%) and cerebrovascular events in 20 (1.4%). A total of 162 patients (11.5%) experienced an early GRE, including occlusion of the index graft in 73 (5.2%) patients during the first 30 days. At 1 year, primary graft patency was 61%, secondary patency 80%, and limb salvage was 88% by Kaplan-Meier estimates.

The mean iLOS was 8.8 days (median, 6 days; range, 1-117 days; Fig 1; Table I). Patients who initially presented with TL (n = 1046) had a longer iLOS (mean, 9.8 days; median, 7 days; range, 1-117 days) than patients with rest pain (n = 353; mean, 6.2 days; median, 5 days; range, 1-43 days; P < .0001). Patients who experienced an early GRE (n = 162) had a longer iLOS (mean, 11.1 days; median, 7days; range, 2-92 days) than those who had no early GRE (n = 1242; mean, 8.6 days; median, 6 days; range, 1-117 days; P = .0002). Patients who experienced any GRE during the study had an iLOS (mean, 8.8 days; median, 6days; range, 1-100 days) similar to the iLOS of those free from GRE (mean, 8.9 days; median, 6 days; range, 1-117 days; P = .4573).

• 
  • View Large Image
  • Download to PowerPoint

• Fig 1. 

  Frequency distribution of the index length of stay.

Table I. Resource utilization comparisons for TL and GRE

Variable	iLOS (d)	NOR	cLOS (d)
Total (N = 1404)	8.8(6)	1.5(1)	24.8(17)
Tissue loss (n = 1046)	9.8(7)⁎	1.6(1)⁎	27.7(21)⁎
Rest pain (n = 353)	6.2(5)⁎	1.2(1)⁎	17.3(9)⁎
Early GRE (n = 162)	11.1(8)⁎	1.6(1)	25.9(20)†
No early GRE (n = 1242)	8.6(6)⁎	1.5(1)	24.6(15)†
GRE during study (n = 554)	8.8(6)	2.1(2)⁎	28.2(20)⁎
No GRE during study (n = 867)	8.9(6)	1.1(1)⁎	21.9(13)⁎

TL, Tissue loss; GRE, graft-related event; iLOS, index length of stay; NOR, number of rehospitalizations; cLOS, cumulative length of stay.

Data are expressed as mean (median).

Overall, the mean NOR over the 1-year study period was 1.5 (median, 1; range, 0-17); 436 patients had no rehospitalizations, 426 had 1, 253 had 2, 121 had 3, and 168 had ≥4 (Fig 2). Patients who had TL at presentation had a greater NOR (mean, 1.6; median, 1, range, 0-17) than those with rest pain (mean, 1.2; median, 1; range, 0-7; P < .0001). The occurrence of an early GRE had no measurable effect on NOR (P = .3272). However, patients who experienced any GRE during the study had greater NOR (mean, 2.1; median, 2.0; range, 0-11) than those without GRE (mean, 1.1; median, 1.0; range, 0-16; P < .0001). The most common primary reasons for rehospitalizations included additional non–graft-related procedures on the index leg (25.6%), nonvascular issues (25.8%), wound infections in the index leg (14.6%), and graft failure (10.6%) (Table II).

• 
  • View Large Image
  • Download to PowerPoint

• Fig 2. 

  Frequency distribution of number of rehospitalizations in 1 year.

Table II. Reasons for hospital admission over a 1-year follow-up period (N = 2149)

The mean cLOS for the 1-year follow-up was 24.8 days (median, 15.5 days; range, 1-365 days). Increased cLOS was positively associated with TL (mean, 27.7 vs 17.3 days; P < .0001), the occurrence of an early GRE (mean, 25.9 vs 24.6 days; P = .0043), and GRE during the 1-year follow-up period (mean, 28.2 vs 21.9 days; P < .0001).

Multivariable regression analysis showed that early GRE (hazard ratio [HR], 1.77; 95% CI, 1.412-2.169; P < .0001) and TL (HR, 1.75; 95% CI, 1.412-2.169; P < .0001) had the greatest effect on increasing iLOS, whereas dialysis (HR, 1.31; 95% CI, 1.042-1.639; P = .0209), nonsmoking status (HR, 1.291; 95% CI, 1.090-1.530; P = .0032), hypertension (HR, 1.26; 95% CI, 1.018-1.567; P = .0336), and increasing age (HR, 1.01; 95% CI, 1.000-1.014; P = .0489) had less pronounced but significant effects (Table III). Dialysis (relative risk, 1.64; 95% CI, 1.432-1.868; P < .0001), TL (relative risk, 1.30; 95% CI, 1.100-1.546; P = .0022), any GRE during the study (relative risk, 1.30; 95% CI, 1.166-1.450; P < .0001), and hypertension (relative risk, 1.21; 95% CI, 1.021-1.425; P = .0273) were associated with increasing NOR. Dialysis (HR, 1.96; 95% CI, 1.527-2.571; P < .0001), TL (HR, 1.61; 95% CI, 1.297-2.020), any GRE during the study (HR, 1.56; 95% CI, 1.326-1.838; P = .0147), and nonwhite race (HR, 1.12; 95% CI, 1.036-1.838; P = .0049) were associated with greater cLOS. Treatment assignment to edifoligide or placebo was not associated with increased RU in univariate or multivariable analysis.

Table III. Significant factors in multivariable analysis for RU outcomes

RU, Resource utilization; HR, hazard ratio; CI, confidence interval; iLOS, index length of stay; GRE, graft-related event; NOR, number of rehospitalizations; cLOS, cumulative length of stay; RR, risk ratio.

Back to Article Outline

Discussion 

The course of patients who undergo lower extremity bypass can be affected by many factors. Accordingly, the resources used in caring for these patients can vary greatly. This study examined the resources used for CLI patients who received lower extremity bypass at 83 institutions. Our findings of a mean iLOS of 8.8 days for lower extremity bypass are consistent with prior findings from other authors.¹⁰, ¹¹ To our knowledge, only one study from the Veterans Administration has looked at RU and clinical outcomes in peripheral vascular surgery across many institutions in great detail. Those authors found that age, presence of complications, patient complexity, illness severity, and acute arterial thromboembolism were increasingly and independently associated with greater in-hospital mortality.¹² However, outcomes were limited to in-hospital findings and did not include any long-term follow-up. Although most prior published studies focus on length of stay after the index bypass, no prior study has examined the resources used in the subsequent care of patients after limb-salvage surgery.

For patients with CLI, TL is one easily identifiable measure of disease severity. In our study, patients who presented with TL experienced a greater iLOS, NOR, and cLOS compared with patients with rest pain. TL patients were rehospitalized for additional non–graft-related procedures in the leg. Early GRE also was highly associated with greater iLOS, although an effect on subsequent NOR was not seen. The association of early GRE with cLOS is due in large part to the differences in iLOS. We also found that patients who had early GRE but were successfully treated and maintained patency during the study period tended to have lower cLOS than patients whose grafts were not successfully salvaged, although this was not statistically significant. Not surprisingly, patients who experienced a GRE at any time during the study had a greater NOR and longer cLOS than patients who were free from any GRE.

Multivariable analysis also demonstrated the highly positive association of TL and GRE with iLOS, although comorbidities (namely, increasing age, hypertension, dialysis dependency, and nonsmoking status) also had positive effects. The effect of TL and GRE on later RU (beyond the index hospitalization) was less pronounced than patient factors and comorbidities, particularly dialysis-dependent renal failure. In essence, vascular disease presentation (as represented by TL) and GRE have early RU effects that persist but taper in later periods, whereas patient comorbidities have smaller early effects that become more prominent in the long-term.

One limitation in this study is patient selection bias. All patients in the study cohort were participants in a clinical trial. However, the entry criteria for PREVENT III were broadly inclusive⁷ and, hence, are largely reflective of the general population of CLI patients undergoing surgical revascularization. The measures of RU in this study were chosen because they reflected utilization not required by the trial protocol. The iLOS, NOR, and cLOS were left to the discretion of the patient’s surgeon or other relevant medical health care providers in the case of nonsurgical admissions. Arguably, patients in trials may be subjected to closer scrutiny and follow-up than other patients, thus resulting in higher RU. Although this is a potential source of bias, concomitant financial and clinical factors may still play a large role in negating that bias. Furthermore, the bias is likely to be less for nonvascular readmissions because those admitting physicians are presumably more removed from the study. The study surgeons and their institutions were also selected to participate in the trial because of their prior interest and experience in caring for CLI patients. Thus, the conclusions from this study may not be directly applicable to institutions that differ in practice characteristics or case volumes.

Although most of the positive factors in the multivariable analysis associated with increased RU are clinically intuitive, we do not have a definitive explanation for the isolated association of nonsmoking status with increased iLOS and nonwhite race with cLOS. We speculate that nonsmokers (while controlling for diabetes and other related variables) who develop CLI have an increased burden of cardiovascular disease that is not yet well quantified. Likewise, nonwhite race may be associated with socioeconomic factors that result in increased cLOS.

Another critical limitation of this study is that the PREVENT III study was not designed to capture all the resources that patients incur in the care of their CLI. Length of stay and NOR are proxies for RU that are easy to understand and generalize. We have not performed cost accounting for actual materials, equipment, and professional time used during these hospitalizations. Those data are not available from the PREVENT III study. We have also not accounted for rehabilitation resources, visiting nurses, family contributions, loss of labor by the patient, and many other direct and indirect resources in preparation for revascularization and during the year afterward. Such precise accounting is beyond the scope of this study, although it is the authors’ future intent to explore these areas by using financial and economic tools.

In summary, this study found that TL was highly associated with increased RU in early and later time periods. The effect of early GRE was significant in early RU but diminished in later time periods. GRE in later periods incurred greater RU in subsequent time periods. Several patient demographics and comorbidities were also associated with RU, including dialysis-dependent renal failure, older age, hypertension, and nonwhite race. Our findings may have implications for patient care and health care policy. Prevention of TL through patient and physician education, better foot care, or earlier detection of peripheral arterial disease may decrease RU. Similarly, early GREs are commonly attributed to technical problems, and thus efforts to reduce such events through training or process improvements may also reduce RU. Mid-term graft failure is common and also incurs significant RU; hence, the development of novel strategies to reduce the frequency of vein graft disease would have important benefits to the health care system. Finally, our findings further underscore the significant care needs of CLI patients beyond their revascularization procedure, and current resource allocations for this patient population may need to be re-examined.

Back to Article Outline

Conclusions 

Several patient-specific factors, including dialysis-dependent renal failure, older age, hypertension, and nonwhite race, have important effects on RU during the first postoperative year. Stage of disease at presentation (TL) and sustained patency of the bypass graft (freedom from GRE) are also critical determinants of RU in limb salvage surgery. These effects predominate early (iLOS) and persist through 1 year.

Back to Article Outline

Author contributions 

Back to Article Outline

References 

1. Maini BS, Orr RK, O’Mara P, Hendershott T. Outcomes and resource utilization in a managed care setting for lower extremity vein bypass grafts. Am J Surg. 1996;172:113–116discussion 117
   • View In Article
   • Abstract
   • Full-Text PDF (563 KB)
   • CrossRef
2. Munoz E, Cohen J, Zelnick R, et al. Hospital costs by clinical parameters for peripheral vascular surgical DRGs. J Cardiovasc Surg (Torino). 1989;30:58–63
   • View In Article
   • MEDLINE
3. Hobart DC, Nicholas GG, Reed JF, Nastasee SA. Carotid endarterectomy outcomes research: reduced resource utilization using a clinical protocol. Cardiovasc Surg. 2000;8:446–451
   • View In Article
   • MEDLINE
   • CrossRef
4. Arora P, Kausz AT, Obrador GT, et al. Hospital utilization among chronic dialysis patients. J Am Soc Nephrol. 2000;11:740–746
   • View In Article
   • MEDLINE
5. Van Acker K, Oleen-Burkey M, De Decker L, et al. Cost and resource utilization for prevention and treatment of foot lesions in a diabetic foot clinic in Belgium. Diabetes Res Clin Pract. 2000;50:87–95
   • View In Article
   • Full-Text PDF (214 KB)
   • CrossRef
6. Huber TS, Seeger JM. Dartmouth Atlas of Vascular Health Care review: impact of hospital volume, surgeon volume, and training on outcome. J Vasc Surg. 2001;34:751–756
   • View In Article
   • Full Text
   • Full-Text PDF (103 KB)
   • CrossRef
7. Conte MS, Lorenz TJ, Bandyk DF, et al. Design and rationale of the PREVENT III clinical trial: edifoligide for the prevention of infrainguinal vein graft failure. Vasc Endovasc Surg. 2005;39:15–23
   • View In Article
8. Conte MS, Bandyk DF, Clowes AW, et al. Risk factors, medical therapies and perioperative events in limb salvage surgery: observations from the PREVENT III multicenter trial. J Vasc Surg. 2005;42:456–464discussion 464-5
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (325 KB)
   • CrossRef
9. Conte MS, Bandyk DF, Clowes AW, et al. Results of PREVENT III: a multi-center, randomized trial of edifoligide for the prevention of vein graft failure in lower extremity bypass surgery. J Vasc Surg. 2006;43:742–751
   • View In Article
   • Abstract
   • Full Text
   • Full-Text PDF (205 KB)
   • CrossRef
10. Landry GJ, Moneta GL, Taylor LM, et al. Comparison of procedural outcomes after lower extremity reversed vein grafting and secondary surgical revision. J Vasc Surg. 2003;38:22–28
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (165 KB)
    • CrossRef
11. Antonello M, Frigatti P, Battocchio P, et al. Open repair versus endovascular treatment for asymptomatic popliteal artery aneurysm: results of a prospective randomized study. J Vasc Surg. 2005;42:185–193
    • View In Article
    • Abstract
    • Full Text
    • Full-Text PDF (325 KB)
    • CrossRef
12. Kazmers A, Jacobs LA, Perkins AJ. Outcomes after lower-extremity reconstruction in DRGs 478 and 479. J Surg Res. 2000;88:18–22
    • View In Article
    • Abstract
    • Full-Text PDF (88 KB)
    • CrossRef