Eliciting patient disutilities for the adverse outcomes of cardiopulmonary resuscitation☆
Introduction
Physicians in the United States commonly ask their patients, especially those who are seriously ill and in the hospital, to decide whether or not they want to be resuscitated if they suffer a cardiac arrest. Physicians in France ask such issues less frequently, but increasingly [1], [2]. Making a decision about cardiopulmonary resuscitation (CPR) is, however, often very difficult even for healthy patients because of the complexity, uncertainty, and emotion necessarily associated with it. The adverse outcomes of CPR range from the trivial to the catastrophic, from minor bruises from chest compressions to death or survival in a vegetative state.
Typically a physician will, for CPR as for other proposed interventions, describe the nature of the procedure and its alternatives, their possible outcomes and effects, and the general likelihood of these outcomes. The patient (or the surrogate) is required to integrate this information about outcomes and likelihoods and arrive at a decision about whether to agree to CPR. This way of informing patients implies that the patients engage, admittedly with considerable imprecision and inconsistency, in the following mental operations: that, largely unconsciously, they assign subjective relative values (or ‘utilities’) to possible outcomes and events, use likelihoods to weight these utilities (multiplying the utility by the likelihood), add the weighted utilities to arrive at an overall expected utility for each management strategy, and compare the expected utilities of the alternative strategies. These implicit assumptions about patients’ real decision making are formalized in medical decision analysis [3], namely in the theories of expected utility analysis and its variants, but, more importantly, they are the basis for practicing physicians’ efforts to help their patients deal with uncertainty as they make difficult decisions.
Validating these assumptions and clarifying patients’ individual decisions and the patterns of these decisions by elucidating what aspects of the issue are most important to them and how they integrate the different aspects of the decision are particularly important for patients, physicians, and policy makers in end-of-life issues such as whether to undergo CPR. Eliciting patients’ utilities is, however, fraught with difficulties: as shown for multiple clinical issues, patients give different responses to different methods of eliciting utilities and are only moderately reliable when tested at a later date [4]. In a study of two methods of eliciting utilities specifically for outcomes of CPR [5], what was most striking was the great differences between the results of the two methods (linear rating and the standard gamble).
Furthermore, it is not certain that most patients will use a multiplicative rule to combine the utilities and the likelihoods of the outcomes of CPR. While college students generally multiple utility by probability in situations where the information relates to material, utilitarian stimuli and to monetary values [6], [7], outcomes that are extreme and emotionally charged have not been studied. In addition, it has been found [8], [9] that the type of value judgment involved in the response influences the cognitive algebra; when a monetary response scale is used, the combination rule is multiplicative (probability×value), but it becomes additive (probability+value) when an attraction scale is used (i.e. when subjects are asked how attractive or desirable a result is for them). Since the scales by which utilities are measured for the outcomes of CPR, as well as of other medical interventions, seem a priori more like attraction than monetary scales, it is possible that patients employ an additive rather than a multiplicative rule in these cases. Finally, the effect of aging on cognitive algebra has been studied only in young children [10], [11], where it has been found that probabilistic and utilitarian information is integrated multiplicatively in a clear and consistent fashion only starting at approximately age 9. Whether the elderly continue to use a multiplicative rule even in simple monetary decisions is unknown; yet most complex decision making, especially concerning CPR and other end-of-life issues, is done with the elderly.
NH Anderson's functional theory of cognition (also called ‘Information Integration Theory’) [12] offers a hitherto little-utilized way of dealing with the difficulties of eliciting utilities in medicine and of knowing how, in practice, patients combine them with likelihoods. Anderson is interested primarily in revealing the cognitive rules used by people to integrate information when making a judgment or decision. His methodology assumes that people place subjective values on different pieces of information and that they combine these subjective values by means of a cognitive algebra dominated by addition, multiplication, and averaging. It studies how they do this functionally, i.e. it infers from people's judgments of the combined value of two (or more) stimuli (or pieces of information) the cognitive rules used to arrive at these judgments. Anderson's procedure has multiple advantages: it is simple to perform; because it is indirect and functional, it avoids the problem that people tend to be inaccurate judges of their own mental processes ([13] pp. 161–228); and it corresponds to the real decision making situation in which the patient and physician must in practice judge information in combinations (such as the combination of a particular likelihood and a particular outcome of CPR).
The purposes of the current study were, therefore, to investigate (1) whether the functional method is feasible to use with patients; (2) whether it provides for CPR a plausible and consistent set of utilities that can guide decision making and policy making about CPR; (3) what cognitive rule patients utilize in combining utilities and likelihoods; and (4) whether this rule changes with age.
Section snippets
Subjects
The subjects were 77 adults of all age groups recruited and tested by psychology students at the Université François-Rabelais in Tours, France. The sample included 16 persons of age 20–29 years (mean age 23.9 years), 19 of age 30–39 years (mean age 33.1 years), 17 of age 40–49 (mean age 44.5), 13 of age 50–59 years (mean age 52.3), and 12 persons of age 60 and over (mean age 71.8). The two sexes were approximately equally represented within each age group.
Applying the functional theory of cognition
The procedure for applying Anderson's
Results
Fig. 2 shows the mean ratings of each adverse outcome of CPR for each level of likelihood. Three features of the curves are important. First, they are regularly ascending, demonstrating that the scenario was perceived as more disagreeable as the likelihood of an adverse outcome increased. Second, the curves are distinctly separate, showing that the nature of the outcome under consideration (labeled below as ‘severity’) also affected the ratings. Chest injury had the lowest disutility, and
Discussion
The elicitation by Anderson's methods of the subjective relative values for patients of the outcomes of CPR was a success. All participants were able to perform the tasks. The ‘utilities’ (or disutilities) derived by this indirect rating were, as shown in Table 2, comparable to, though somewhat different in quantity from, those derived by Sorum [5] from his office patients by direct rating and by standard gamble. The different experimental conditions and the wide individual variations among the
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Presented in part at the 20th Annual Meeting of the Society for Medical Decision Making, Cambridge, MA, 25–28 October, 1998.