Validation of the Ottawa Subarachnoid Hemorrhage Rule in patients with acute headache
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- Point-of-care clinical decision tools, paired with Bayesian thinking, can help us choose wiselyAravind GaneshPosted on: 30 November 2017
- Posted on: (30 November 2017)Page navigation anchor for Point-of-care clinical decision tools, paired with Bayesian thinking, can help us choose wiselyPoint-of-care clinical decision tools, paired with Bayesian thinking, can help us choose wisely
- Aravind Ganesh, Neurology Resident, Stroke Fellow, (1) Dept of Clinical Neurosciences, University of Calgary, (2) Centre for Prevention of Stroke & Dementia, University of Oxford
I thank Dr. Perry and colleagues for their validation study of the Ottawa Subarachnoid Hemorrhage (SAH) Rule, which demonstrated 100% sensitivity and 13.6% specificity in identifying patients with SAH.[1] Application of such clinical decision tools by physicians at the point-of-care could certainly help us reduce unnecessary neuroimaging by reassuring physicians that they are unlikely to miss serious pathology if guided by these evidence-based history/examination findings. In an time where access to diagnostic imaging in urban centres is so easy that ordering tests can become reflexive, the importance of continuing to develop, validate, and curate such decision tools cannot be overstated. For instance, a study of 51 million headache-related visits to physicians in the United States between 2007 and 2010 found that approximately $1 billion was spent annually on MRI and CT scans for patients with headache who actually have migraines.[2] The growing recognition of such inappropriate resource use has given rise to the well-known Choosing Wisely campaign in Canada and the United States, but behavioural change should be driven by well-validated clinical decision tools that we can trust.
Academic initiatives such as JAMA’s Rational Clinical Examination series have curated high-yield history/examination findings in several high-quality reviews.[3] Such findings may be most useful for physicians and trainees when they are paired with Bayesian thinking i.e. when they incorpo...
Show MoreI thank Dr. Perry and colleagues for their validation study of the Ottawa Subarachnoid Hemorrhage (SAH) Rule, which demonstrated 100% sensitivity and 13.6% specificity in identifying patients with SAH.[1] Application of such clinical decision tools by physicians at the point-of-care could certainly help us reduce unnecessary neuroimaging by reassuring physicians that they are unlikely to miss serious pathology if guided by these evidence-based history/examination findings. In an time where access to diagnostic imaging in urban centres is so easy that ordering tests can become reflexive, the importance of continuing to develop, validate, and curate such decision tools cannot be overstated. For instance, a study of 51 million headache-related visits to physicians in the United States between 2007 and 2010 found that approximately $1 billion was spent annually on MRI and CT scans for patients with headache who actually have migraines.[2] The growing recognition of such inappropriate resource use has given rise to the well-known Choosing Wisely campaign in Canada and the United States, but behavioural change should be driven by well-validated clinical decision tools that we can trust.
Academic initiatives such as JAMA’s Rational Clinical Examination series have curated high-yield history/examination findings in several high-quality reviews.[3] Such findings may be most useful for physicians and trainees when they are paired with Bayesian thinking i.e. when they incorporate pre- and post-test probabilities. In this regard, Perry et al’s paper offers a valuable pre-test probability from a Canadian setting - in their sample of 1,153 patients (1,743 eligible consecutive cases) with headache peaking within 1 hour of onset, only 67 (5.8%) actually had SAH. A clinician in a similar acute care setting, seeing a patient with a headache that peaked within an hour, may then assume that there is already a roughly 6% probability of that patient having a SAH even before beginning their assessment. If none of the history/exam findings on the Ottawa SAH Rule are present on assessment, then the “post-test” probability of SAH essentially drops to zero (0.06 pretest odds x negative likelihood ratio [LR] of 0) – making neuroimaging clearly inappropriate for this indication. On the other hand, if one or more of the findings are present, then the post-test odds of SAH = 0.06 x 1.16 (positive LR) = 0.07, giving a post-test probability of around 6.5% (post-test odds divided by 1 plus post-test odds), a marginal increase that wouldn’t change one’s enthusiasm to pursue further imaging and/or lumbar puncture.
Electronic medical records and decision-support systems can mitigate inappropriate testing by incorporating these types of Bayesian algorithms into order entry. Over the past 4 years, we have been using a free point-of-care app, SnapDx Clinical, to help clinicians and trainees easily visualize how pre-test probabilities of common conditions, from best-available epidemiological studies, are modified by the positive and negative likelihood ratios from best-available clinical decision rules/findings.[4] The Ottawa SAH Rule adds yet another tool to our armamentarium, and it is my sincere hope that Canada will continue lead the way in both developing and disseminating clinical decision tools to facilitate better stewardship of our healthcare resources.
REFERENCES
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1. Perry JJ, Sivilotti MLA, Hohl CM, et al. Validation of the Ottawa Subarachnoid Hemorrhage Rule in patients with acute headache. CMAJ 2017;189(45);E1379-E1385.
2. Callaghan BC, Kerber KA, Pace RJ, Skolarus LE, Burke JF. Headaches and Neuroimaging: High Utilization and Costs Despite Guidelines. JAMA Intern Med 2014; 174(5):819-821.
3. Detsky ME, McDonald DR, Baerlocher MO, et al. Does this patient with headache have a migraine or need neuroimaging? JAMA 2006;296(10):1274-1283.
4. Fok D, Ganesh A, Mehta R, Jette N, Cooke L. Development of an interactive educational bedside assessment tool with validation in headache clinic. Neurology 2015;84(14S):P3.046.Competing Interests: Aravind Ganesh is a co-founder of SnapDx.
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