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BÀI DẪN NHẬP Y HOC ( EBM) / Y TẾ CÔNG CỘNG ( EBPH) DỰA VÀO CHỨNG CỨ GS TS BS LÊ HỒNG NINH Nội dung cốt lõi • Tại y hoc chứng quan trọng • Y học chứng ? • Phân biệt foreground vs background questions • Đặt câu hỏi dạng PICO • Tìm nguồn tư liệu • Giá trị bào báo khoa học y học / sức khoẻ • Đánh giá dạng báo : can thiệp điều trị / dự phịng; chẩn đốn/ sàng lọc; ngun nhân… Tại EBM quan trọng? • MEDLINE – 400,000 new entries added each year • To keep up-to-date – Need to read 6,000 articles each day Tại EBM quan trọng? chậm trễ “ từ lúc biết lúc áp dụng” – 13 years for thrombolytic therapy – 10 years for corticosteroids for acceleration of fetal lung maturity (Antman EM, JAMA, 1992) Traditional Approaches Self-reported reading time per week (University setting) – Medical students – Interns – Senior residents – Fellows – Attendings graduating • Post 1975 • Pre 1975 60 none 10 45 60 30 There is simply no way we can keep up to date in medicine using traditional approaches! Nội dung cốt lõi • Why is EBM important? • What is EBM? • Understand foreground vs background questions • Formulate PICO questions • Find resources, searches • Validity of an article • Appraise “Therapy” articles • Appraise “Diagnostic” articles Research Evidence Decision Making Clinical Expertise Patient Preference Qui trình y học chứng / y tế công cộng Patients Appraise Ask Questions Searching Validity Results Applicability Disease + Disease - Test + A True + B False + Test - C False - D True - X=A+C Y=B+D At what rate are Dis + patients identified by a “- test” ? C/X At what rate are Dis – patients identified by a “- test”? D/Y What is the LR for a “negative” test result? (C/X) ÷ (D/Y) Negative Likelihood Ratio (LR-) LR - = (1 – sensitivity)/specificity = False neg rate/True neg rate Guide to Likelihood ratios LR+ LR- 1–2 V Poor – 0.5 2–5 Poor 0.5 – 0.2 – 10 Fair 0.2 – 0.1 10 – 20 Good 0.1 – 0.05 > 20 V Good < 0.05 Why Do We Care About LR? Allow us to think about pre-test and post-test probabilities so that we can personalize the test to our patients Test & Treatment Thresholds in the Diagnostic Process Test threshold Treatment threshold 0% No test needed 100% Further testing needed Testing completed; treatment starts Step 1: Pre-test Probability • Prevalence The number of events (instances of a given disease or other condition) in a given population at a designated time It is not a rate It is used as pre-test probability It is the number of “disease +” patients to the “total” Pre-test Probability sources to determine this: Clinical experience Regional or national prevalence statistics Practice databases Original report on accuracy of the test Studies that calculate pre-test probability Step 3: Calculate LR Test + Test Total Culture + Culture 65 18 10 72 75 90 Amir, 1994 Rapid Strep • Pretest probability is 30% • LR+ = ? LR + = TP rate/FP rate = (65/75) ÷ (18/90) = 4.35 LR - = FN rate/TN rate = (10/75) ÷ (72/90) = 0.16 Fagan Nomogram Pre-test probability on the left hand column LR in the middle Post-test probability on the right hand column Translation • You see a yo child who comes in c/o sorethroat, no other complaints • Your pre-test probability is that she has a 30% chance of having strep throat • You wonder how good is rapid strep • You look up an article (Amir, 1994) and find its sensitivity (86.5%) and specificity (80%) Translation • Your patient rapid strep is positive • You calculated the LR + to be 4.35 • You determined the post-test probability to be 66% • Is that enough of a threshold for you to treat or would you rather more test? Test & Treatment Thresholds in the Diagnostic Process Test threshold Treatment threshold 0% No test needed 100% Further testing needed Testing completed; treatment starts A Different Article Showed… • What if the LR+ is 12? • What is the post-test probability? “Diagnostic” Summary… • Use the x table to determine likelihood ratio (LR) • LR + = True pos rate/False pos rate • LR - = False neg rate/True neg rate • Use Fagan Nomogram ... atrovent used acutely make you feel better? Background or Foreground? • What is asthma? (B) • What are the newest medication for asthma? (B) • Does atrovent used acutely make you feel better? (F) •... stomach (C) in terms of risk of SIDS (O)? Can You Form a PICO Question? Clinical scenario: yo with moderate persistent asthma now in severe acute asthma exacerbation Intern gave albuterol and orapred... Etiology – Prognosis Limit any of the categories to sensitivity (broad) or specificity (narrow) • Or, search for Systematic Reviews OVID • Most librarians favor this search engine • Allow you
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