Every Peddler Praises His Own Needle: Have Clinical Rules in the Diagnosis of Subarachnoid Hemorrhage Supplanted Lumbar Punctures Yet?

Abstract

1The authors state, “Research conducted among ED [emergency department] patients with possible acute coronary syndrome suggests that patients often have much higher risk thresholds for themselves than do the treating physicians.”1 AAssuming both patients and physicians are making rational decisions, list some reasons why they may have different risk thresholds. Do you think that emergency physicians have higher or lower risk thresholds than other physicians (eg, internists, pediatricians, neurosurgeons)? Why might this be so? Should our health care system try to align patient and physician acceptable risk thresholds? If so, how might this be achieved?BAssume 1) the 97% sensitivity reported for the Mark et al decision rule is externally validated and 2) the incidence of subarachnoid hemorrhage in patients presenting to the ED with acute headache is 2% and an emergency physician treats 3,500 patients per year. On average, how many years would an emergency physician have to apply this clinical rule to miss 1 subarachnoid hemorrhage? Do these sound like reasonable numbers to you? Why or why not?CNoncontrast computed tomography (CT) of the brain and lumbar punctures have associated complications. Summarize the reported frequency of complications associated with CT and lumbar puncture. Using the same data listed in question 1B, calculate how often these complications might occur. Does it matter that lumbar puncture–associated complications typically occur acutely, whereas noncontrast CT radiation exposure is associated with late-occurring morbidity and mortality? How might patient age factor into the likelihood of complications associated with CT and lumbar puncture?DIf this clinical rule were widely adopted, in 5 years would you expect that more or fewer patients would be investigated for subarachnoid hemorrhage (the use of similar decision aids in pulmonary embolism may serve as a useful example)?2The authors performed a matched control study. AUnder what circumstances are case-control studies ideal? Consider the time course of exposure and disease, the nature of the exposure and outcomes, and the frequency of the disease.BDiscuss the importance of matching in case-control studies. Why does one match? What should one match on? What should one not match on?CWhy did the authors choose 3 controls for each case? Why not 1? Why not 6?DWhat are the biases of case-control studies in general? In this study specifically?3The authors state, “Approximately 80% of subarachnoid hemorrhage cases are due to ruptured cerebral aneurysms.”1 AWhat are other common causes of nontraumatic subarachnoid hemorrhage?BIn general terms, describe the sensitivity of a noncontrast head CT in detecting these other causes. When choosing a screening test, is it preferable to be highly sensitive or highly specific? What test characteristic (ie, sensitivity, specificity) is desired for a confirmatory study?CAfter a patient complaint about a post–lumbar puncture headache, a hospital administrator proposes that the ED replace lumbar puncture with CT angiography when attempting to exclude subarachnoid hemorrhage in patients with a negative initial head CT result. What do you think about this, assuming the combination of CT and CT angiography is 99% sensitive for diagnosing a subarachnoid hemorrhage, as recently reported?24The authors performed a sensitivity analysis to assess the rule's stability, using a 1,000-iteration bootstrap analysis. AWhat is a sensitivity analysis? Why are sensitivity analyses often performed in observational studies?BWhat is a bootstrap analysis? Why are bootstrap analyses especially important when evaluating clinical decision rule performance? What assumptions are invoked by bootstrap analyses?