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Teaching Evidence-Based Medicine

Teaching Evidence-Based Medicine. Gary S Gronseth, MD, FAAN Professor of Neurology University of Kansas. To Teach EBM…. Explicitly Reason Exclude the unreasonable Distinguish opinion from principles Rate Evidence on a Hierarchy Understand two sources of error Love the 2 x 2 table

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Teaching Evidence-Based Medicine

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  1. TeachingEvidence-Based Medicine Gary S Gronseth, MD, FAAN Professor of Neurology University of Kansas

  2. To Teach EBM… • Explicitly Reason • Exclude the unreasonable • Distinguish opinion from principles • Rate Evidence on a Hierarchy • Understand two sources of error • Love the 2 x 2 table • Emphasize Evidence never enough • Apply to your patient • Incorporate patient values

  3. A case… • A 58 year-old right-handed man suddenly developed problems speaking, right lower facial weakness and right hand clumsiness. His symptoms slowly resolved over a week. • He had a history of controlled HTN and no other risk factors. • Head MRI: small left frontal infarct. • EKG: sinus rhythm. • MRA: no cranial artery stenosis. • Echocardiogram: PFO

  4. The Physician’s Dilemma To Close or Not to Close Even if the answer is unknown, a decision must be made!

  5. Clinical Reasoning Close PFO? “Where I trained”

  6. Clinical Reasoning Close PFO? To Teach EBM… • Explicitly Reason • Exclude the unreasonable

  7. Deceitful

  8. “Closure of PFO in patients with cryptogenic ischemic stroke is the standard of care in the community.” “The consequences of a second stroke are potentially devastating. PFO closure is mandatory.”

  9. Fallacious Irrelevant Rhetoric Psychological appeal Emotion-Driven Persuasion

  10. Patient Intervention Co-intervention Outcome Determining relevance:Define the question PICO

  11. Determining relevance:Define the question For patients with cryptogenicstroke and PFOdoes PFO closurevs no PFO closurereduce the risk of the next stroke PICO

  12. Popular Appeal “Closure of PFO in patients with cryptogenic ischemic stroke is the standard of care in the community.”

  13. Begging the Question “The consequences of a second stroke are potentially devastating. PFO closure is mandatory.”

  14. I’ll be sued. I’ll be reimbursed Irrelevant Outcomes

  15. Deceitful Fallacious

  16. Close PFO? Fallacy Deceit To Teach EBM… • Explicitly Reason • Exclude the unreasonable

  17. Deceitful Fallacious Reasoned

  18. Reasoned • Relevant • Logical appeal • Data-Driven • Truth

  19. Close PFO? Principles Evidence Judgment To Teach EBM… • Explicitly Reason • Exclude the unreasonable • Distinguish opinion from principles

  20. Principles Decision

  21. Deductive InferenceFrom Principles • The left side of the brain controls the right side of the body • My patient can’t control the right side of his body • My patient has a problem with the left side of his brain

  22. Principles Use a Parachute?

  23. Principles Close PFO?

  24. PFO • Fibrous adhesions fail to seal the atrial septum after birth • Persistence of a potential shunt between the right and left atria of the heart

  25. PFO might allow paradoxical embolism • Small emboli normally filtered by lung without clinically important consequence • In patients with PFO, emboli can travel to the brain and cause ischemic stroke • Closing the PFO will prevent future strokes

  26. Principles Close PFO?

  27. Reasoned • Relevant • Reason • Logical appeal • Data-Driven • Truth Deduction (Principles)

  28. Principles Evidence Close PFO?

  29. Jane has a stroke and PFO. We should treat her with closure to prevent another stroke. Analogy and Inductive Inference • Bob had a stroke and PFO and wasn’t treated with closure, he had another stroke • John had a stroke and PFO and was treated with closure, he didn’t have another stroke. • Sue had a stroke and PFO and was treated with closure, she didn’t have another stroke.

  30. Cases Evidence What happened to patients?

  31. Principles Evidence Close PFO?

  32. Reasoned • Relevant • Reason • Logical appeal • Data-Driven • Truth Induction (Evidence) Deduction (Principles)

  33. Close PFO? Principles Evidence Judgment Best Guess Opinion Hypothesis

  34. Reasoned • Relevant • Reason • Logical appeal • Data-Driven • Truth Intuition (Judgment) Induction (Evidence) Deduction (Principles)

  35. Close PFO? Principles Evidence Judgment Distinguishing Opinion from Principles • Is there equipoise? • Do reasonable people disagree? • Would an IRB approve a trial? • Is there an ongoing trial? • Evidence separates judgment from principles

  36. Scientific Method Theory Experiment Hypothesis

  37. Close PFO? Principles Evidence Judgment To Teach EBM… • Explicitly Reason • Exclude the unreasonable • Distinguish opinion from principles

  38. Strong Weak To Teach EBM… • Explicitly Reason • Exclude the unreasonable • Distinguish opinion from principles • Rate Evidence on a Hierarchy

  39. Strong Weak • John had a stroke and PFO and was treated with closure, he didn’t have another stroke. • Sue had a stroke and PFO and was treated with closure, she didn’t have another stroke. • Bob had a stroke and PFO and wasn’t treated with closure, he had another stroke • Jane has a stroke and PFO. We should treat her with closure to prevent another stroke.

  40. Strong Weak Inferences from Evidence… Are not valid or invalid Are never certain

  41. Strong Weak Informally recalled cases • John had a stroke and PFO and was treated with closure, he didn’t have another stroke. • Sue had a stroke and PFO and was treated with closure, she didn’t have another stroke. • Bob had a stroke and PFO and wasn’t treated with closure, he had another stroke • Jane has a stroke and PFO. We should treat her with closure to prevent another stroke. Why is this a weak inference?

  42. Cases Inferences from informally recalled cases can mislead • Too few cases • Selective recall: remember those • That are more recent • With extreme results • That support our pre-conceptions Experts are not immune to these limitations

  43. To Teach EBM… • Explicitly Reason • Exclude the unreasonable • Distinguish opinion from principles • Rate Evidence on a Hierarchy • Understand two sources of error

  44. Two Sources of Error Random Chance • Often too few cases • Selective recall: remember those • That are more recent • With extreme results • That support our pre-conceptions Systematic Bias

  45. Find More Cases Retrospective Observational Sudy 2002 to 2010 Of all Stroke and PFO Cases: 319

  46. Rats… I’m going to have to start counting these cases 319 Cases

  47. To Teach EBM… • Explicitly Reason • Exclude the unreasonable • Distinguish opinion from principles • Rate Evidence on a Hierarchy • Understand two sources of error • Love the 2 x 2 table

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