Implicit discount rates of vascular surgeons in the management of abdominal aortic aneurysms

Prospective decision analysis for peripheral vascular disease predicts future quality of life

OBJECTIVE

Decision making for peripheral vascular disease can be quite complex as a result of pre-existing compromise of patient functional status, anatomic considerations, uncertainty of favorable outcome, medical comorbidities, and limitations in life expectancy. The ability of prospective decision-analysis models to predict individual quality of life in patients with lower extremity arterial occlusive disease was tested.

METHODS

This was a prospective cohort study. The settings were university and Veterans Administration vascular surgery practices. All 214 patients referred with symptomatic lower extremity arterial disease of any severity over a 2-year period were screened, and 206 were enrolled. A Markov model was compared with standard clinical decision-making. Utility assessment and generalized (Short Form-36; SF-36) and disease-specific (Walking Impairment Questionnaire; WIQ) quality of life were derived before treatment. Estimates of treatment outcome probabilities and intended and actual treatment plans were provided by attending vascular surgeons. The main outcome measures were generalized (SF-36) and disease-specific (WIQ) variables at study entry and at 4 and 12 months.

RESULTS

Primary intervention consisted of amputation for 9, bypass for 42, angioplasty for 8, and medical treatment for 147 patients. Considering all patients, no improvement in mean overall patient quality of life measured by the SF-36 Physical Component Score (27 +/- 8 vs 28 +/- 8; P = .87) or WIQ (39 +/- 22 vs 39 +/- 23; P = .13) was noted 12 months after counseling and treatment by the vascular surgeons. Individually considered SF-36 categories were improved only for Bodily Pain (40 +/- 23 vs 49 +/- 25; P = .03), with the most significant improvement observed among patients with the most severe pain (68 +/- 25 vs 37 +/- 23; P = .02) and among those undergoing bypass (60 +/- 29 vs 31 +/- 22; P = .02). It is noteworthy that when the treatment chosen was incongruent with the Markov model, patients were more likely to report a poorer quality of life at 1 year (Physical Component Score, 25 +/- 8 vs 29 +/- 8; P < .001). The quality of life predicted at baseline by the Markov model correlated positively with the Physical Component Score (r = 0.23), Bodily Pain (r = 0.33), and Fatigue (r = 0.44) and negatively with WIQ (r = -0.08) observed 1 year later.

CONCLUSIONS

Prospective application of an individualized decision Markov model in patients with vascular disease was predictive of patient quality of life at 1 year. The patient's outcome was worse when the treatment received did not follow the model's recommendation. This decision analysis model may be useful to identify patients at risk for poor outcomes with standard clinical decision making.

Towards a better QALY model

This paper presents a test of the predictive validity of various classes of QALY models (i.e. linear, power and exponential models). We first estimated TTO utilities for 43 EQ-5D chronic health states and next these states were embedded in nonchronic health profiles. The chronic TTO utilities were then used to predict the responses to TTO questions with nonchronic health profiles. We find that the power QALY model clearly outperforms linear and exponential QALY models. Optimal power coefficient is 0.65. Our results suggest that TTO-based QALY calculations may be biased. This bias can be corrected using a power QALY model.

Prospective decision analysis modeling indicates that clinical decisions in vascular surgery often fail to maximize patient expected utility

BACKGROUND

Applied prospectively to patients with peripheral arterial disease, individualized decision analysis has the potential to improve the surgeon's ability to optimize patient outcome.

METHODS

A prospective, randomized trial comparing Markov surgical decision analysis to standard decision-making was performed in 206 patients with symptomatic lower extremity arterial disease. Utility assessment and quality of life were determined from individual patients prior to treatment. Vascular surgeons provided estimates of probability of treatment outcome, intended and actual treatment plans, and assessment of comfort with the decision (PDPI). Treatment plans and PDPI evaluations were repeated after each surgeon was made aware of model predictions for half of the patients in a randomized manner.

RESULTS

Optimal treatments predicted by decision analysis differed significantly from the surgeon's initial plan and consisted of bypass for 30 versus 29%, respectively, angioplasty for 28 versus 11%, amputation for 31 versus 6%, and medical management for 34 versus 54% (agreement 50%, kappa 0.28). Surgeon awareness of the decision model results did not alter the verbalized final plan, but did trend toward less frequent use of bypass. Patients for whom the model agreed with the surgeon's initial plan were less likely to undergo bypass (13 versus 30%, P < 0.01). Greater surgeon comfort was present when the initial plan and model agreed (PDPI score 47.5 versus 45.6, P < 0.005).

CONCLUSIONS

Individualized application of a decision model to patients with peripheral arterial disease suggests that arterial bypass is frequently recommended even when it may not maximize patient expected utility.

Controlling Blood Pressure in 50% of All Hypertensive Patients: An Achievable Goal in the Healthy People 2010 Report?

Background

One important objective defined in the Healthy People 2010 report was to improve blood pressure (BP) control to < 140/90 mm Hg in 50% of all hypertensive patients. Because the US population is becoming older, more obese, and ethnically diverse, the health and economic benefits of reaching this goal become more valuable each year. Hypertension control rates are currently at ∼ 31% of all hypertensives and have risen slowly and erratically since 1988. In the absence of a coordinated strategic plan, achieving this critically important goal for BP control is highly unlikely.

Methods

A selected literature review was undertaken to briefly assess the cardiovascular benefits of controlling hypertension. Greater focus was placed on variables that impact hypertension awareness, treatment, and control. The impact on hypertension control rates of theoretic changes in awareness, treatment, and control individually and collectively was examined. Four categories of potential barriers to optimizing BP control are discussed: systems, provider, patient, and treatment factors.

Results

Raising awareness to 80% of all hypertensives, ensuring treatment of 90% of aware hypertensives, and controlling BP to < 140/90 mm Hg in 70% of treated patients would achieve control rates of 50%.

Conclusions

The barriers to achieving the Healthy People 2010 goal of controlling hypertension in 50% of all patients are formidable but appear to be resolvable with a coordinated strategic plan. Given projected demographic changes in the United States, the health and economic benefits of attaining the national goal for hypertension control would seem to merit a serious integrated effort.

Time-related issues with application to health gains and losses

Time-related aspects of health have attracted increasing interest, and it has become evident that many medical situations concern the exchange of present-day costs for future benefits. Traditional decision analytic paradigms weigh the probability of outcomes and the value of outcomes. Such analyses are incomplete if they do not consider the time of the outcome as well. The concept of diminishing value over time is positive discounting. Time discounting processes and effects have a potentially large impact on clinical decision making. Therefore, characteristics of discounting should be taken into consideration. Discounting processes are variable with individuals and also within different contexts such as gains and losses. No single model can be expected to describe time-related decisions within health. A more diversified use and critical appraisal of these concepts in medicine become more important as we attempt to refine decision models. A summary of valuation factors in medical decision making is presented: (a) long-term decisions are very sensitive to discount rates; (b) discount rates are greater for gains than for losses; (c) discount rates vary by domain, by outcome, by individuals over time, and by level of certainty; (d) individual preferences may reverse themselves over time; (e) the doctor uses expected value; the patient is risk aversive; (f) over a lifetime perspective, a flat or even negative discount rate will result in choices that minimize lifetime disability.

Discounting and clinical decision making: physicians, patients, the general public, and the management of asymptomatic abdominal aortic aneurysms

Clinical decisions often entail in intertemporal trade-off. Moreover, they often involve physicians of different specialities. In an experiment dealing with the management of small asymptomatic abdominal aortic aneurysms (a clinically relevant problem) we find that specialists in internal medicine exhibit higher implicit discount rates than vascular surgeons, general practitioners, and actual and prospective patients. Several personal characteristics expected to be directly related to pure time-preference and risk aversion (gender, smoking habits, age, place of employment) have the hypothesised effects. Additionally, financial incentives appear to affect the estimated implicit discount rates of physicians, but are unlikely to have caused the inter-group differences. Differences in discount rates could lead to variations in clinical practice, which may conflict with equality of treatment or equal access to health care.

Theoretical arguments for the discounting of health consequences: where do we go from here?

Despite the theoretical arguments presented in the literature regarding discounting over the last 25 years, no satisfactory reply has yet been offered to the question of whether health consequences have to be discounted at the same rate as monetary consequences in the economic evaluation of health programmes or interventions designed to improve health. Against this background, the main objective of this paper was to review and systemise these theoretical arguments, with the aim of determining whether any of the positions identified can be accepted without reservation. Having determined that this is not possible, we investigated the rationality of discounting in the literature and, on this basis, propose a potential way to resolve the problem. Thus, we argue that the relationship between the discount of monetary and health consequences has to be determined in an indirect manner, by reference to the relationship maintained by the individual time preference rates for health and money in the context of private and social choice. Although this proposal moves the debate into the empirical field, its advantages must be weighed against the difficulties associated with the estimation of the time preferences.

Early surgery versus conservative management of dissecting aneurysms of the descending thoracic aorta

BACKGROUND

Optimal management for patients who present acutely with uncomplicated type III dissections of the descending thoracic aorta remains controversial. Patients with dissecting aneurysms represent a subgroup at high risk of rupture who may benefit from early elective surgery as an alternative to standard medical therapy. METHODS. The authors constructed a Markov decision model to compare the following clinical strategies: 1) early elective surgery immediately after diagnosis (EARLY SURGERY), 2) medical therapy with periodic computed tomography and with elective surgery when aortic diameter is projected to reach 6 cm (CT FOLLOW-UP), and 3) medical therapy with urgent surgery for dissection-related complications (WATCHFUL WAITING). Data sources included Medline (1966-1995) and a case series of patients with type III dissecting aneurysms who received medical therapy with radiographic follow-up.

RESULTS

For a typical 60-year-old patient with an acute, uncomplicated 5-cm dissecting aneurysm of the descending thoracic aorta and an operative 30-day mortality rate of 14% for EARLY SURGERY, the model predicts that EARLY SURGERY improves survival compared with CT FOLLOW-UP (9.91 vs 9.44 QALYs). Conservative management may be preferred for patients who have maximum aneurysm diameters < or = 4 cm, are elderly (> or = 75 years), or have higher-than-expected risk of operative mortality.

CONCLUSIONS

The choice between early surgery and medical therapy for uncomplicated dissecting aneurysm of the descending thoracic aorta should be tailored to the individual patient's operative risk, risk of dissection-related events, and age. Early surgery may be a reasonable alternative to medical therapy for carefully selected patients at centers with favorable perioperative mortality rates.

Negative and zero time preference for health

The assumption of positive time preference is seldom challenged in analyses of intertemporal choices, despite considerable evidence of zero and negative discount rates. In this study, the majority of respondents have positive discount rates, but a substantial number have negative or zero discount rates. Using probit regression, the perception of the severity of the health-state, gender, education and perception of the questions in terms of difficulty are shown to influence whether individuals have positive discount rates.

Do people value their own future health differently from others' future health?

The purpose of this study was to investigate whether time preferences for own health are the same as time preferences for others' health. A random sample of the general public was sent a postal questionnaire containing six choices between ill health in the near future and ill health in the further future. They were asked to indicate the maximum duration of more distant ill health they would be willing to accept in return for a specified delay in the onset of the period of ill health. For half of the sample the questions were set in the context of their own health and for the other half in terms of others' health. The median implied discount rates were not statistically different, 0.061 for own health and 0.062 for others' health. A multilevel analysis of the determinants of these implied discount rates provided additional evidence of the similarity of time preferences for own health and others' health.

Should endovascular surgery lower the threshold for repair of abdominal aortic aneurysms?

PURPOSE

Because endovascular repair of abdominal aortic aneurysms (AAAs) is less invasive, some investigators have suggested that this increasingly popular technique should broaden the indications for elective AAA repair. The purpose of this study was to calculate quality-adjusted life expectancy rates after endovascular and open AAA repair and to estimate the optimal diameter for elective AAA repair in hypothetical cohorts of patients at average risk and at high risk.

METHODS

A Markov decision analysis model was used in this study. Assumptions were made on the basis of published reports and included the following: (1) the annual rupture rate is a continuous function of the AAA diameter (0% for <4 cm, 1% for 4.5 cm, 11% for 5.5 cm, and 26% for 6.5 cm); (2) the operative mortality rate is 1% for endovascular repair (excluding the risk of conversion to open repair) and 3.5% for open repair at age 70 years; and (3) immediate endovascular-to-open conversion risk is 5%, and late conversion rate is 1% per year. The main outcome measure in this study was the benefit of AAA repair in quality-adjusted life years (QALYs). The optimal threshold size (the AAA diameter at which elective repair maximizes benefit) was measured in centimeters.

RESULTS

The benefit of endovascular repair is consistently greater than that of open repair, but the additional benefit is small-0.1 to 0.4 QALYs. For men in average health with gradually enlarging AAAs with initial diameters of 4 cm, endovascular surgery reduces the optimal threshold diameter by very little: from 4.6 to 4.6 cm (no change) at age 60 years, from 4.8 to 4.7 cm at age 70 years, and from 5.1 to 4.9 cm at age 80 years. For older men in poor health, endovascular surgery reduces the optimal threshold diameter substantially (8.1 to 5.7 cm at age 80 years), but the benefit of repair in this population is small (0.2 QALYs).

CONCLUSION

For most patients, the indications for AAA repair are changed very little by the introduction of endovascular surgery. Only for older patients in poor health does endovascular surgery substantially lower the optimal threshold diameter for elective AAA repair.