The development of a VBHOM-based outcome model for lower limb amputation performed for critical ischaemia

Predicting Functional Outcomes Following Dysvascular Lower Limb Amputation: An Evidence Review of Personalizing Patient Outcomes

Most research on people undergoing lower limb amputations for dysvascular disease summarizes average patient outcome risks and average associations between patient factors and these outcomes. More recently, the importance of predicting patient-specific outcomes based on individual factors (ie, personalized rehabilitation) has become evident. This article reviews the evidence and discusses the importance of the following: (1) predicting outcomes to facilitate amputation-level and prosthesis prescription decisions and (2) how prediction models can be leveraged to develop decision support tools to facilitate provider/patient shared decision-making to ensure decisions considering each individual patient's priorities and preferences. Examples of these tools are discussed and referenced.

Life Expectancy and Mortality After Lower Extremity Amputation: Overview and Analysis of Literature

Lower limb amputation (LLA) is a major surgical procedure with a significant impact on quality of life and mortality rates as well. Previous studies have shown that mortality rates following LLA can range from 9-17% within 30 days in the UK. This study systematically evaluates and reviews the published literature on life expectancy, mortality, and survival rates following lower extremity amputation (LEA). We have conducted a comprehensive search on Medline, CINAHL, and Cochrane Central databases resulting in 87 full-text articles. After a thorough review, only 45 (52.9%) articles met the minimum inclusion criteria for the study. Our analysis indicated 30-day mortality rates following LEA ranged from 7.1% to 51.4%, with an average mortality rate of 16.45% (SD 14.35) per study. Furthermore, 30-day mortality rates following below-knee amputation (BKA) and above-knee amputation (AKA) were found to be between 6.2% to 51.4%, X= 17.16% ± 19.46 SD and 12.7 to 21.7%, X= 16.15% ± 4.17 SD, respectively. Our review provides a comprehensive insight into the life expectancy, mortality, and survival rates following LEA. These findings highlight the importance of considering various factors, including patient age, presence of comorbidities such as diabetes, heart failure, and renal failure, and lifestyle factors such as smoking, in determining prognosis following LLA. Further research is necessary to determine strategies for improving outcomes and reducing mortality in this patient population.

Short-term risk prediction after major lower limb amputation: PERCEIVE study

BACKGROUND

The accuracy with which healthcare professionals (HCPs) and risk prediction tools predict outcomes after major lower limb amputation (MLLA) is uncertain. The aim of this study was to evaluate the accuracy of predicting short-term (30 days after MLLA) mortality, morbidity, and revisional surgery.

METHODS

The PERCEIVE (PrEdiction of Risk and Communication of outcomE following major lower limb amputation: a collaboratIVE) study was launched on 1 October 2020. It was an international multicentre study, including adults undergoing MLLA for complications of peripheral arterial disease and/or diabetes. Preoperative predictions of 30-day mortality, morbidity, and MLLA revision by surgeons and anaesthetists were recorded. Probabilities from relevant risk prediction tools were calculated. Evaluation of accuracy included measures of discrimination, calibration, and overall performance.

RESULTS

Some 537 patients were included. HCPs had acceptable discrimination in predicting mortality (931 predictions; C-statistic 0.758) and MLLA revision (565 predictions; C-statistic 0.756), but were poor at predicting morbidity (980 predictions; C-statistic 0.616). They overpredicted the risk of all outcomes. All except three risk prediction tools had worse discrimination than HCPs for predicting mortality (C-statistics 0.789, 0.774, and 0.773); two of these significantly overestimated the risk compared with HCPs. SORT version 2 (the only tool incorporating HCP predictions) demonstrated better calibration and overall performance (Brier score 0.082) than HCPs. Tools predicting morbidity and MLLA revision had poor discrimination (C-statistics 0.520 and 0.679).

CONCLUSION

Clinicians predicted mortality and MLLA revision well, but predicted morbidity poorly. They overestimated the risk of mortality, morbidity, and MLLA revision. Most short-term risk prediction tools had poorer discrimination or calibration than HCPs. The best method of predicting mortality was a statistical tool that incorporated HCP estimation.

The PERCEIVE quantitative study: PrEdiction of Risk and Communication of outcome following major lower-limb amputation: protocol for a collaboratiVE study

BACKGROUND

Accurate prediction of outcomes following surgery with high morbidity and mortality rates is essential for informed shared decision-making between patients and clinicians. It is unknown how accurately healthcare professionals predict outcomes following major lower-limb amputation (MLLA). Several MLLA outcome-prediction tools have been developed. These could be valuable in clinical practice, but most require validation in independent cohorts before routine clinical use can be recommended. The primary aim of this study is to evaluate the accuracy of healthcare professionals' predictions of outcomes in adult patients undergoing MLLA for complications of chronic limb-threatening ischaemia (CLTI) or diabetes. Secondary aims include the validation of existing outcome-prediction tools.

METHOD

This study is an international, multicentre prospective observational study including adult patients undergoing a primary MLLA for CLTI or diabetes. Healthcare professionals' accuracy in predicting outcomes at 30-days (death, morbidity and MLLA revision) and 1-year (death, MLLA revision and ambulation) will be evaluated. Sixteen existing outcome-prediction tools specific to MLLA will be examined for validity. Data collection began on 1 October 2020; the end of follow-up will be 1 May 2022. The C-statistic, Hosmer-Lemeshow test, reclassification tables and Brier score will be used to evaluate the predictive performance of healthcare professionals and prediction tools, respectively.

STUDY REGISTRATION AND DISSEMINATION

This study will be registered locally at each centre in accordance with local policies before commencing data collection, overseen by local clinician leads. Results will be disseminated to all centres, and any subsequent presentation(s) and/or publication(s) will follow a collaborative co-authorship model.

A Systematic Review and Narrative Synthesis of Risk Prediction Tools Used to Estimate Mortality, Morbidity, and Other Outcomes Following Major Lower Limb Amputation

OBJECTIVE

The decision to undertake a major lower limb amputation can be complex. This review evaluates the performance of risk prediction tools in estimating mortality, morbidity, and other outcomes following amputation.

METHODS

A systematic review was performed following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The MEDLINE, Embase, and Cochrane databases were searched to identify studies reporting on risk prediction tools that predict outcomes following amputation. Outcome measures included the accuracy of the risk tool in predicting a range of post-operative complications, including mortality (both short and long term), peri-operative morbidity, need for re-amputation, and ambulation success. A narrative synthesis was performed in accordance with the Guidance on the Conduct of Narrative Synthesis In Systematic Reviews.

RESULTS

The search identified 518 database records. Twelve observational studies, evaluating 13 risk prediction tools in a total cohort of 61 099 amputations, were included. One study performed external validation of an existing risk prediction tool, while all other studies developed novel tools or modified pre-existing generic calculators. Two studies conducted external validation of the novel/modified tools. Nine tools provided risk estimations for mortality, two tools provided predictions for post-operative morbidity, two for likelihood of ambulation, and one for re-amputation to the same or higher level. Most mortality prediction tools demonstrated acceptable discrimination performance with C statistic values ranging from 0.65 to 0.81. Tools estimating the risk of post-operative complications (0.65 - 0.74) and necessity for re-amputation (0.72) also performed acceptably. The Blatchford Allman Russell tool demonstrated outstanding discrimination for predicting functional mobility outcomes post-amputation (0.94). Overall, most studies were at high risk of bias with poor external validity.

CONCLUSION

This review identified several risk prediction tools that demonstrate acceptable to outstanding discrimination for objectively predicting an array of important post-operative outcomes. However, the methodological quality of some studies was poor, external validation studies are generally lacking, and there are no tools predicting other important outcomes, especially quality of life.

Mortality prediction following non-traumatic amputation of the lower extremity

BACKGROUND

Patients who undergo lower extremity amputation secondary to the complications of diabetes or peripheral artery disease have poor long-term survival. Providing patients and surgeons with individual-patient, rather than population, survival estimates provides them with important information to make individualized treatment decisions.

METHODS

Patients with peripheral artery disease and/or diabetes undergoing their first unilateral transmetatarsal, transtibial or transfemoral amputation were identified in the Veterans Affairs Surgical Quality Improvement Program (VASQIP) database. Stepdown logistic regression was used to develop a 1-year mortality risk prediction model from a list of 33 candidate predictors using data from three of five Department of Veterans Affairs national geographical regions. External geographical validation was performed using data from the remaining two regions. Calibration and discrimination were assessed in the development and validation samples.

RESULTS

The development sample included 5028 patients and the validation sample 2140. The final mortality prediction model (AMPREDICT-Mortality) included amputation level, age, BMI, race, functional status, congestive heart failure, dialysis, blood urea nitrogen level, and white blood cell and platelet counts. The model fit in the validation sample was good. The area under the receiver operating characteristic (ROC) curve for the validation sample was 0·76 and Cox calibration regression indicated excellent calibration (slope 0·96, 95 per cent c.i. 0·85 to 1·06; intercept 0·02, 95 per cent c.i. -0·12 to 0·17). Given the external validation characteristics, the development and validation samples were combined, giving a total sample of 7168.

CONCLUSION

The AMPREDICT-Mortality prediction model is a validated parsimonious model that can be used to inform the 1-year mortality risk following non-traumatic lower extremity amputation of patients with peripheral artery disease or diabetes.

Limitations of Vascular Quality Initiative-derived models to predict the outcomes of intervention for infrapopliteal limb-threatening ischemia

OBJECTIVE

The purpose of this study was to validate published Society for Vascular Surgery Vascular Quality Initiative (VQI) prediction models for patients with limb-threatening ischemia (LTI) undergoing open or endovascular revascularization for infrapopliteal occlusive disease.

METHODS

We sought to validate our prior VQI LTI models for major adverse limb events (MALEs) and amputation-free survival (AFS) in a VQI new cohort undergoing open or percutaneous interventions from September 2014 through August 2016. Receiver operating characteristic curves were generated including the C statistic, and the predicted vs actual outcomes were correlated. The Hosmer-Lemeshow (HL) statistic was calculated to determine goodness of fit, and the Tjur R² statistic was derived to demonstrate the degree to which the observed outcomes were accurately predicted by the models.

RESULTS

Of 15,576 open infrainguinal and 34,679 percutaneous interventions collected in the VQI during the 24-month interval, 8852 and 17,124, respectively, were performed for LTI, among which 4410 and 5116 specifically targeted the infrapopliteal vessels. MALEs and AFS were identified for 400 of 927 (43.1%) and 576 of 982 (58.7%) open procedures and 197 of 855 (23.0%) and 658 of 1115 (59.0%) percutaneous procedures, respectively. For open operation, the predictive ability of the model was poor for MALEs (C = 0.59; HL = 107; R² = 0.03) and only marginally better for AFS (C = 0.69; HL = 130; R² = 0.10). Similarly, for endovascular intervention, the model performed poorly for MALEs (C = 0.62; HL = 183; R² = 0.06) and slightly better for AFS (C = 0.68; HL = 68; R² = 0.11). Breaking AFS into its component determinants, the predictive ability of the open operation model for patient survival (C = 0.77; HL = 70; R² = 0.15) surpassed that for limb salvage (C = 0.64; HL = 54; R² = 0.05). For endovascular interventions, the survival model (C = 0.71; HL = 94; R² = 0.11) also outperformed the limb salvage model (C = 0.67; HL = 28; R² = 0.07). For both types of intervention, the actual MALE rate was lower and AFS was higher than predicted by the models.

CONCLUSIONS

The ability of reported VQI-derived models to accurately predict major outcomes for infrapopliteal LTI is limited and cannot be advocated for clinical decision-making at this time. Further study would be necessary to determine whether this is due to intraoperative and postoperative variables not accounted for in our models, absence of pertinent data points from the registry, or incomplete follow-up.

Matrix metalloproteinases and risk stratification in patients undergoing surgical revascularisation for critical limb ischaemia

Critical limb ischaemia (CLI) is the most advanced form of peripheral artery disease (PAD) and it is often associated with foot gangrene, which may lead to major amputation of lower limbs, and also with a higher risk of death due to fatal cardiovascular events. Matrix metalloproteinases (MMPs) seem to be involved in atherosclerosis, PAD and CLI. Aim of this study was to evaluate variations in MMP serum levels in patients affected by CLI, before and after lower limb surgical revascularisation through prosthetic or venous bypass. A total of 29 patients (7 females and 22 males, mean age 73·4 years, range 65-83 years) suffering from CLI and submitted to lower extremity bypass (LEB) in our Institution were recruited. Seven patients (group I) underwent LEB using synthetic polytetrafluoroethylene (PTFE) graft material and 22 patients (group II) underwent LEB using autogenous veins. Moreover, 30 healthy age-sex-matched subjects were also enrolled as controls (group III). We documented significantly higher serum MMPs levels (P < 0·01) in patients with CLI (groups I and II) with respect to control group (group III). Finally, five patients with CLI (17·2%) showed poor outcomes (major amputations or death), and enzyme-linked immunosorbent assay (ELISA) test showed very high levels of MMP-1 and MMP-8. MMP serum levels seem to be able to predict the clinical outcomes of patients with CLI.

Association of total white cell count with mortality and major adverse events in patients with peripheral arterial disease: a systematic review

OBJECTIVES

Peripheral arterial disease (PAD) is principally caused by atherosclerosis, an established inflammatory disease. Total white cell count (TWCC) is a marker of inflammation and has been associated with outcomes for patients with inflammatory diseases. The aim of this systematic review was to assess the association of TWCC with mortality and major adverse events (MAEs) in PAD patients.

METHODS

Studies investigating the association of TWCC with outcome in patients with PAD were identified by a literature search using the Medline and Cochrane databases. To be eligible for inclusion, studies needed to investigate the association of TWCC with mortality or a composite endpoint that included mortality in patients with PAD. Studies were excluded when the primary focus was carotid artery disease, aortic aneurysmal disease, intracranial vascular disease, or rheumatoid arthritis and treatment with chemotherapy or transplantation of stem cells. Secondary searching of reference lists and relevant reviews was performed.

RESULTS

Ten studies including 8,490 patients with PAD met the inclusion criteria. All studies investigated more than 100 patients with four studies assessing more than 1,000 patients. Study quality varied with well-established risk factors of outcome such as age, smoking, diabetes, and the ankle brachial index being adjusted for inconsistently. The study populations were also disparate. Few studies reported relative risk and 95% confidence intervals for the association of TWCC with mortality or MAE. TWCC was positively and significantly associated with death alone in four of five studies investigating 3,387 patients. TWCC was positively and significantly associated with MAE in five of six studies investigating a total of 6,846 patients.

CONCLUSIONS

Current evidence suggests a positive association of TWCC with mortality and MAEs in patients with PAD. Further well-designed prospective studies are required with high-quality analysis and more complete reporting of outcomes.

Efficacy of VBHOM to Predict Outcome Following Major Lower Limb Amputation

Purpose: This study tests an existing Vascular Biochemistry and Haematology Outcome Model (VBHOM) on independent data and presents further refinements to the model. Methods: Data from 306 patients who underwent lower limb amputation over a 4-year period were collated. Urea, creatinine, sodium, potassium, hemoglobin, white cell count, albumin, age, gender, mode-of-admission, and short-term mortality events were extracted from the database. This study tests an existing model and trains a new model for predicting mortality using forward stepwise logistic regression. Results: The existing model suggests a significant lack of fit (c-index = 0.665, P = .04). For the exception of gender and mode-of-admission, all predictor variables had significant univariate associations with short-term mortality ( P < .05). The refined model included age, sodium, potassium, creatinine, and albumin and had good discriminatory power (c-index = 0.8, no evidence of lack of fit, P = .616). Conclusions: Our simplified model had good predictive ability and suggests redundancy in input variables used by the existing models.

Predicting outcome following colorectal cancer surgery using a colorectal biochemical and haematological outcome model (Colorectal BHOM)

AIM

To present a new biochemistry and haematology outcome model which uses a minimum dataset to model outcome following colorectal cancer surgery, a concept previously shown to be feasible with arterial operations.

METHOD

Predictive binary logistic regression models (a mortality and morbidity model) were developed for 704 patients who underwent colorectal cancer surgery over a 6-year period in one hospital. The variables measured included 30-day mortality and morbidity. Hosmer-Lemeshow goodness of fit statistics and frequency tables compared the predicted vs the reported number of deaths. Discrimination was quantified using the c-index.

RESULTS

There were 573 elective and 131 nonelective interventional cases. The overall mean predicted risk of death was 7.79% (50 patients). The actual number of reported deaths was also 50 patients (χ(2) = 1.331, df = 4, P-value = 0.856; no evidence of lack of fit). For the mortality model, the predictive c-index was = 0.810. The morbidity model had less discriminative power but there was no evidence of lack of fit (χ(2) = 4.198, df = 4, P-value = 0.380, c-index = 0.697).

CONCLUSIONS

The Colorectal Biochemistry and Haematology Outcome mortality model suggests good discrimination (c-index > 0.8) and uses only a minimal number of variables. However, it needs to be tested on independent datasets in different geographical locations.

Bypass versus Angioplasty in Severe Ischaemia of the Leg (BASIL) trial: A survival prediction model to facilitate clinical decision making

BACKGROUND

An intention-to-treat analysis of the Bypass versus Angioplasty in Severe Ischaemia of the Leg (BASIL) trial showed that in patients with severe lower limb ischemia (SLI) due to infrainguinal disease who survived for 2 years after intervention, initial randomization to a bypass surgery (BSX)-first vs balloon angioplasty (BAP)-first revascularization strategy was associated with improvements in subsequent overall survival (OS) and amputation-free survival (AFS) of about 7 and 6 months, respectively. This study explored the value of baseline factors to estimate the likelihood of survival to 2 years for the trial cohort (Cox model) and for individual BASIL trial patients (Weibull model) as an aid to clinical decision making.

METHODS

Of 452 patients presenting to 27 United Kingdom hospitals, 228 were randomly assigned to a BSX-first and 224 to a BAP-first revascularization strategy. Patients were monitored for at least 3 years. Baseline factors affecting the survival of the entire cohort were examined with a multivariate Cox model. The chances of survival at 1 and 2 years for patients with given baseline characteristics were estimated with a Weibull parametric model.

RESULTS

At the end of follow-up, 172 patients (38%) were alive without major limb amputation of the trial leg, and 202 (45%) were alive. Baseline factors that were significant in the Cox model were BASIL randomization stratification group, below knee Bollinger angiogram score, body mass index, age, diabetes, creatinine level, and smoking status. Using these factors to define five equally sized groups, we identified patients with 2-year survival rates of 50% to 90%. The factors that contributed to the Weibull predictive model were age, presence of tissue loss, serum creatinine, number of ankle pressure measurements detectable, maximum ankle pressure measured, a history of myocardial infarction or angina, a history of stroke or transient ischemia attack, below knee Bollinger angiogram score, body mass index, and smoking status.

CONCLUSIONS

Patients in the BASIL trial were at high risk of amputation and death regardless of revascularization strategy. However, baseline factors can be used to stratify those risks. Furthermore, within a parametric Weibull model, certain of these factors can be used to help predict outcomes for individuals. It may thus be possible to define the clinical and anatomic (angiographic) characteristics of SLI patients who are likely-and not likely-to live for >2 years after intervention. Used appropriately in the context of the BASIL trial outcomes, this may aid clinical decision making regarding a BSX- or BAP-first revascularization strategy in SLI patients like those randomized in BASIL.

Critical limb ischemia

Critical limb ischemia (CLI) continues to be a significantly morbid disease process for the aging population. Rigid guidelines for the management of patients with CLI are inappropriate due to the complexities that are involved in optimally treating these patients. A thin line exists in the decision process between medical management vs surgical management by revascularization or amputation, and the perception of "success" in this patient population is evolving. This review explores these issues and examines the challenges the treating physician will face when managing the care of patients with CLI. The epidemiology and natural history of CLI is discussed, along with the pathophysiology of the disease process. A review of the literature in regards to the different treatment modalities is presented to help the physician optimize therapy for patients with CLI. New scoring systems to help predict outcomes in patients with CLI undergoing revascularization or amputation are discussed, and an overview of the current status of patient-oriented outcomes is provided. Finally, we briefly examine emerging therapies for the treatment of CLI and provide an algorithm to help guide the practicing physician on how to approach the critically ischemic limb with regard to the complicated issues surrounding these patients.