Introduction to Evidence-Based Medicine


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Presentation given to second year medical students at McGill University.

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  • Q:What are the five A’s?A:Ask, Acquire, Appraise, Apply and Assess
  • Either A or B are correct.
  • Outcomeis to prevent brain damage – C
  • This is a therapy question – answer is D (even better to have a SR of an RCT)
  • Introduction to Evidence-Based Medicine

    1. 1. Evidence-Based Medicine (EBM)INDS 301, Jan. 2013Prosanto Chaudhury, MD, MSc, FRCSC, FACSRobin Featherstone, MLIS
    2. 2. ObjectivesBy the end of the lecture, you will be able to: 1. Describe objectives and expectations for the course 2. Describe the five stages of the EBM process 3. Differentiate between background and foreground questions 4. Describe the components of a PICO question 5. Categorize PICO questions and identify the best studies to answer each question type
    3. 3. EBM Course ContentsFormat ContentLecture 1 Overview of the course and an introduction to EBM, PICO question formation, and EBM resourcesWorkshop Searching EBM resourcesSmall group 1 PICO question formationLecture 2 Critical appraisal of randomized controlled trials (RCT) and systematic reviews (SR)Small group 2 Appraisal of a RCTSmall group 3 Appraisal of a SRSmall group 4 Appraisal of a diagnostic test studyCourse website:
    4. 4. EvaluationItem Description WeightSmall Groups 4 interactive sessions with clinical tutors. 40% Evaluation based on participation.Assignment 3 pages including: 30% • Clinical scenario • PICO • Search strategy • Name of chosen paper • Critical appraisal • Your conclusionOSCE 15 minute station: 30% • Develop a question based on a clinical scenario • Perform a search based on your question
    5. 5. Introduction to EBMWhy are we doing this?
    6. 6. Why is EBM important?“Evidence-based medicine is the integration of bestresearch evidence with clinical expertise and patientvalues” Patient - Dave Sackett Concerns EBM Best research Clinical evidence Expertise Slide courtesy Prof Paul Glasziou, CEBM
    7. 7. EBM in practice• Took an “evidence cart” on rounds - 1995• Looked up 2-3 questions per patient• Took 15-90 seconds to find evidence• Changed about 1/3 decisions• Rounds took longer! Dave Sackett
    8. 8. Challenges to practicing EBM RCTs published over the last 50 years 20000 18000 16000 14000 12000 RCTs 10000 8000 6000 4000 2000 0 1960 1970 1980 1990 2000 2010Source: PubMed data for "randomized controlled trial"[Publication Type]
    9. 9. How I use EBM
    10. 10. How you can use EBM• Keep a logbook of questions• Answer a few important questions• Identify important knowledge gaps• Discuss and share evidence with colleagues (journal club)
    11. 11. EBM Process Formulating Evaluating the clinicalAssess Ask the Process question Your patient for whom you are uncertain about therapy, diagnosis, or Searching Incorporating prognosis the Evidence evidence into decision-making Acquire AppraiseApply Appraising the Evidence
    12. 12. EBM Question Formation1. Background vs Foreground
    13. 13. Can a 70 year old pancytopenic patient with suspected meningitis receive platelets before undergoing a lumbar puncture? What is pancytopenia? What is the diagnostic test for meningitis? [1.]Guyatt G, Rennie D, Cook D. Users Guides to the Medical Literature : A Manual for Evidence-Based Clinical Practice (2nd Edition). NewYork, NY, USA: McGraw-Hill Professional Publishing; 2008. Ask
    14. 14. A 25 year-old female has been recently diagnosed withclassical Hodgkin’s lymphoma (nodular sclerosing subtype).Staging reveals that she is a stage IIA with a 4.5 cm nodalmass in her neck and mediastinal nodes. Her hematologistrecommends combined modality therapy(chemotherapy/radiation therapy). The patient has donesome reading about therapy and is worried about the longterm effects of radiation especially the risk of breast cancer.Background ForegroundWhat is the pathophysiology of For a 25 year old female withHodgkin’s lymphoma? stage IIA Hodgkin’s lymphoma, is combined modality therapy superior to chemotherapy alone? Ask
    15. 15. A 35 year-old patients presents to the ER with a left leg swelling x 3 days. The patient recently returned from a business trip in Malaysia and therefore you suspect a deep vein thrombosis (DVT). It is the weekend and so the patient receives a CT angiogram that does not reveal any pulmonary embolism and the venous portion of the study does not reveal any above or below knee clots. That said, you are still convinced that the patient may have a lower limb DVT and so you ask for a lower limb doppler which requires the radiologist to come into the hospital in the middle of the night to perform the study. The radiologist is reluctant to come as the venous phase of the CT angiogram was negative. Discuss with your neighbour. Record one background and one foreground question.Creative copyright image. Attribution: James Heilman, MD. Accessed from Ask
    16. 16. Background QuestionsSources for Background Questions (AKA “Filtered Information”)• Textbooks• Handbooks• Manuals• etc [1.] Acquire
    17. 17. EBM Question Formation2. P.I.C.O. Patient, Population, or Problem Intervention or exposure Comparison Outcome
    18. 18. SimpleYou have been asked to review thepractice guidelines for treating warts. Youare confident that cryotherapy is the mosteffective treatment but a colleaguesuggested some alternatives toinvestigate, including duct tape. Ask
    19. 19. SimplePatient, Population, or Patients with common wartsProblemIntervention or Duct tapeexposureComparison CryotherapyOutcome Eliminating wartsAnswerable clinical question:In patients with common warts, is duct tape as effective ascryotherapy in eliminating warts? Ask
    20. 20. IntermediateYou are following a 35 year-old pregnant female for lowplatelets thought to be due to immune thrombocytopenia asshe had thrombocytopenia prior to her pregnancy. Sheundergoes a delivery without complications. She and thebaby are medically ready to leave the hospital 48 hourslater. She asked if she should be concerned for hernewborn, knowing that her antibodies, the same that arecausing her immune thrombocytopenia, are passed alongto the baby. Ask
    21. 21. IntermediatePatient, Population, or Newborns with suspected immune thrombocytopeniaProblemIntervention or Blood test to check plateletsexposureComparison No blood testOutcome Diagnosis of immune thrombocytopeniaAnswerable clinical question 1:For newborns with suspected immune thrombocytopenia, is a blood test to determineplatelet count recommended to diagnose immune thrombocytopenia?Answerable clinical question 2:For newborns with suspected immune thrombocytopenia, when should a blood testbe given to diagnose immune thrombocytopenia? Ask
    22. 22. Best studies to answer each question type
    23. 23. Question Best Evidence Cost • Cost-effectiveness study Diagnosis • Diagnostic validation studies • Prospective studies / blind comparison to a gold standard Etiology/Harm • Cohort study • Case control study Prognosis • Cohort study • Case control study Quality of life • Qualitative studies Therapy • Systematic review of Randomized Controlled Trials (RCTs) • Single RCT12 Heneghan, Carl, and Douglas Badenoch. Evidence-Based Medicine Toolkit. 2nd ed. Malden, Mass.: BMJ Books/Blackwell Pub., 2006. Glover, Jan, and Lei Wang. Find it Fast: The Clinical Question : Acquire
    24. 24. Levels of Evidence for Therapy Question Level of Evidence Type of Study 1a Systematic reviews of randomized controlled trials (RCTs) 1b Individual RCTs with narrow confidence interval 2a Systematic reviews of cohort studies 2b Individual cohort studies and low-quality RCTs 3a Systematic reviews of case-control studies 3b Case-control studies 4 Case series and poor quality cohort and case-control studies 5 Expert opinionLevels of evidence (2001). Centre for Evidence Based Medicine. Retrieved 26 Aug 2008 from Acquire 24
    25. 25. Filtered vs Unfiltered Information Sources Less time 1a - SRs of Less work RCTs Less evidence Summaries Filtered 1b 1b 2b 2a 2b 2a UnfilteredMore time 3b 3bMore work 4 4 5 5More evidence Acquire
    26. 26. Filtered UnfilteredExpert Opinion Acquire
    27. 27. Summary
    28. 28. EBM Process Formulating Evaluating the clinical? ? the Process question Your patient for whom you are uncertain about therapy, diagnosis, or SearchingIncorporating prognosis the Evidenceevidence intodecision-making ? ?? Appraising the Evidence
    29. 29. What kind of question is this: What causes jaundice?A. BackgroundB. EtiologyC. ForegroundD. PICO
    30. 30. What is the “O” in this question:When should fibreoptic phototherapy be initiated to prevent brain damage for a jaundiced newborn?A. Fibreoptic phototherapyB. Jaundiced newbornC. Prevent brain damage
    31. 31. Which of the following is the best source of evidence to answer the question: In jaundiced infants, is single volume exchangetransfusion superior to double volume exchange?A. Case seriesB. Cohort studyC. Diagnostic validation studyD. RCT