Evidence Based Obstetrics

Evidence Based Obstetrics: 

Evidence Based Obstetrics

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In an Ideal World The most effective care for every condition would be known Every clinician would know the most effective care for every patient Every clinician would practice the most effective care that she or he knows

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The Proof A proof is a proof. What kind of proof? It’s a proof. And when you have a good proof it is because it is proven Jean Chretien

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In the Real World Much of what should be known is not known Much that is known, is not known by most clinicians Clinicians often fail to practice what they know to be the most effective form of care

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‘It is surely a great criticism of our profession that we have not organized a critical summary, by specialty or subspecialty, adapted periodically, of all randomized controlled trials.’ Archie Cochrane Medicine for the year 2000 , 1979

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Data Sources Cochrane Library SOGC Guidelines Guidelines from other professional organizations Published clinical evidence

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Evidence ALARM uses primarily quantitative, rather than qualitative evidence Prospective trials control for variables, making them more powerful than retrospective trials Randomized trials avoid selection bias The most powerful evidence is from the Prospective Randomized Controlled Trial (RCT)

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Quality of Evidence I at least one properly randomized controlled trial II-1 well-designed controlled trials without randomization II-2 well-designed cohort or case-control analytic studies II-3 comparisons between times or places with or without the intervention III opinions of respected authorities, clinical experience, descriptive studies or expert committees Canadian Task Force on the Periodic Health Exam, 1994

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Grades of Recommendation for Specific Clinical Preventive Actions A Good evidence to recommend B Fair evidence to recommend C Evidence is conflicting and does not allow a recommendation; other factors may influence decision making D Fair evidence to recommend against E Good evidence to recommend against I Insufficient evidence to make recommendation Canadian Task Force on Preventive Health Care, 2003

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Odds Ratio Compares the odds of an outcome in the intervention group with that in the control group Relative Risk Compares the risk (probability) of an outcome in the groups both give a point estimate of true effect size the O.R. will approximate the R.R for rare outcomes Number Needed to Treat (NNT) Number of patients needed to treat to prevent one outcome

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95% Confidence Interval The confidence interval is a range (95% chance) in which the true effect size can be found If the range of the C.I. overlaps 1.0 then there is a > 5% possibility ( p > 0.05) that the observed outcome difference is due to chance

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 Confidence interval  Outcome significantly less Odds ratio  Outcome significantly more 0.01 0.1 1 10 100 Results consistent with chance  Odds Ratio (95% confidence interval) Outcome A Outcome B Outcome C Outcome D Outcome E Intervention versus Control

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How can we find and use existing information to practice more effectively? Meta-analysis can help Meta-analysis is the systematic selection and compilation of RCTs relevant to a question of interest

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Presentation of Meta-analysis Results 0.01 0.1 1 10 100 Odds Ratio (95% confidence interval) Outcome less likely Outcome more likely Trial A (n=220) Trial B (n=145) Trial C (n=550) Trial D (n=205) Trial E (n=325) Meta-analysis result

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Effect of EFM versus IA in labour Relative Risk (95% Confidence Interval) Outcome RR (95% CI) Caesarean delivery 1.41 (1.23,1.61) Assisted vaginal birth 1.20 (1.11,1.30) NICU admission 1.00 (0.92,1.09) Perinatal death 0.89 (0.60,1.33) Neonatal seizures 0.51 (0.32,0.82) Cerebral Palsy 1.66 (0.92,3.00) Thacker SB, Cochrane Library 9 trials, Issue 2,2005

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Statistical Chance of Error Significance testing (e.g. p < 0.05 ) does not eliminate the possibility that the result is due to chance Clinical Significance It is up to the practitioner to decide whether a statistically significant or non-significant result is important to clinical practice.