Mark R. Tonelli

While the importance of mechanisms in determining causality in medicine is currently the subject of active debate, the role of mechanistic reasoning in clinical practice has received far less attention. In this paper we look at this question in the context of the treatment of a particular individual, and argue that evidence of mechanisms is indeed key to various aspects of clinical practice, including assessing population-level research reports, diagnostic as well as therapeutic decision making, and the assessment of treatment effects. We use the pulmonary condition bronchiectasis as a source of examples of the importance of mechanistic reasoning to clinical practice.

Something important is happening in applied, interdisciplinary research, particularly in the field of applied health research. The vast array of papers in this edition are evidence of a broad change in thinking across an impressive range of practice and academic areas. The problems of complexity, the rise of chronic conditions, over-diagnosis, co- and multimorbidity are serious and challenging, but we are rising to that challenge. Key conceptions regarding science, evidence, disease, clinical judgement, health and social care, are being revised and their relationships reconsidered: boundaries are indeed being redrawn; reasoning is being made 'fit for practice'. Ideas like 'person-centred care' are no longer phrases with potential to be helpful in some yet-to-be-clarified way: theorists and practitioners are working in collaboration to give them substantive import and application.

Within the evidence-based medicine construct, clinical expertise is acknowledged to be both derived from primary experience and necessary for optimal medical practice. Primary experience in medical practice, however, remains undervalued. Clinicians’ primary experience tends to be dismissed by EBM as unsystematic or anecdotal, a source of bias rather than knowledge, never serving as the “best” evidence to support a clinical decision. The position that clinical expertise is necessary but that primary experience is untrustworthy in clinical decision-making is epistemically incoherent. Here we argue for the value and utility of knowledge gained from primary experience for the practice of medicine. Primary experience provides knowledge necessary to diagnose, treat, and assess response in individual patients. Hierarchies of evidence, when advanced as guides for clinical decisions, mistake the relationship between propositional and experiential knowledge. We argue that primary experience represents a kind of medical knowledge distinct from the propositional knowledge produced by clinical research, both of which are crucial to determining the best diagnosis and course of action for particular patients.

While the importance of mechanisms in determining causality in medicine is currently the subject of active debate, the role of mechanistic reasoning in clinical practice has received far less attention. In this paper we look at this question in the context of the treatment of a particular individual, and argue that evidence of mechanisms is indeed key to various aspects of clinical practice, including assessing population-level research reports, diagnostic as well as therapeutic decision making, and the assessment of treatment effects. We use the pulmonary condition bronchiectasis as a source of examples of the importance of mechanistic reasoning to clinical practice.

Consensus is growing among ethicists and lawyers that medical decision making for incompetent patients who were previously competent should be made in accordance with that person's prior wishes and desires. Moreover, this legal and ethical preference for the substituted judgment standard has found its way into the daily practice of medicine. However, what appears on the surface to be an agreement between jurists, bioethicists, and clinicians obscures the very real differences between disciplines regarding the actual implementation of the sub stituted judgment standard. Ethicists and judges have carefully outlined how substituted judgments ought to be made and evaluated. Although differences arise, especially at the state court level, regarding the scope of the substituted judgment standard and its relation to other standards of surrogate decision making, agreement is fairly widespread on the priority of substituted judgment and on the necessity of sufficient evidence being available in order to support a particular substituted judgment.

Evidence-based medicine (EBM) has thus far failed to adequately account for the appropriate incorporation of other potential warrants for medical decision making into clinical practice. In particular, EBM has struggled with the value and integration of other kinds of medical knowledge, such as those derived from clinical experience or based on pathophysiologic rationale. The general priority given to empirical evidence derived from clinical research in all EBM approaches is not epistemically tenable. A casuistic alternative to EBM approaches recognizes that five distinct topics, 1) empirical evidence, 2) experiential evidence, 3) pathophysiologic rationale, 4) patient goals and values, and 5) system features are potentially relevant to any clinical decision. No single topic has a general priority over any other and the relative importance of a topic will depend upon the circumstances of the particular case. The skilled clinician must weigh these potentially conflicting evidentiary and non-evidentiary warrants for action, employing both practical and theoretical reasoning, in order to arrive at the best choice for an individual patient.