In this second part of “Playing by the Rules,” we will examine validated clinical decision rules that assist emergency physicians (EPs) in the diagnosis and treatment of nontraumatic conditions. Most trauma rules seek to answer a yes or no question regarding the utility of testing for specific disease states when the diagnosis is not clinically apparent.
For example, the Canadian CT Head Rule describes a number of conditions that, if met, can predict the absence of traumatic lesions requiring neurosurgical intervention in the alert patient with head injury, and thus obviate the need for imaging in those instances. In contrast, many medical rules are actually risk stratification scales for treatment and diagnosis, categorizing patients into low- to high-risk groups based on clinical factors. While traumatic conditions are linked to a specific inciting event or “trauma,” medical diseases may have multiple causative factors or may be delayed in presentation to the emergency department (ED), which subsequently increases the complexity of these decision instruments.
Rather than an exhaustive list of all clinical decision rules or risk stratification scales relevant to emergency medicine, this installment will provide EPs with a review of common instruments and the evidence behind them.
Central Nervous System
Ottawa Subarachnoid Hemorrhage Rule
The Ottawa Subarachnoid Hemorrhage Rule offers guidance for diagnosing atraumatic subarachnoid hemorrhage (SAH) in alert, neurologically intact adult patients presenting to the ED with a headache reaching maximal intensity within 1 hour of onset. The rule states that if none of the following conditions are present, then the diagnosis of SAH can be excluded without further testing:
Symptom of neck pain or stiffness
Age greater than 40 years old
Witnessed loss of consciousness
Onset during exertion
Thunderclap headache with peak pain instantly
Limited neck flexion on exam
The validation study prospectively enrolled 1153 adults of whom 67 had a positive workup for SAH (defined as subarachnoid blood visible on noncontrast CT scan of the head, xanthochromia of cerebrospinal fluid on visual inspection, or the presence of >1 million erythrocytes in the final tube of cerebrospinal fluid with an aneurysm or arteriovenous malformation confirmed on cerebral angiography).1 Of note, patients with prior history of cerebral aneurysm or SAH were excluded, as were patients with recurrent headaches similar to the presenting complaint, patients with focal neurologic deficits or papilledema, or patients with a history of brain neoplasm, ventricular shunt, or hydrocephalus. The authors found that the rule was 100% sensitive and 13% specific for detecting SAH, with a kappa of 0.82, which suggests good interrater reliability.1
Comment: It is important to note that the authors excluded patients with a history of cerebral aneurysm or prior SAH, and therefore the rule should not be applied to these patients in clinical practice. The utility of this rule is somewhat limited secondary to the age cutoff, as the incidence of aneurysmal SAH increases considerably after the fifth decade of life.2 Ultimately, this rule—combined with the authors’ previous work showing that CT performed within 6 hours of headache onset can rule out SAH—provides a powerful diagnostic tool for EPs considering SAH in the ED.3
The ABCD2 score was developed to identify transient ischemic attack (TIA) patients at risk for early stroke, and thus inform decisions regarding admission and resource utilization in the ED and outpatient clinic setting.4 The score was created by combining elements of two previously existing rules, the California and the ABCD scales. Patients presenting with TIA symptoms are assigned points based on:
Age: 1 point if ≥ 60 years
Blood Pressure: 1 point if ≥ 140/90
Clinical Deficit: 2 points for unilateral weakness, 1 point for speech impairment without unilateral weakness
Duration: 2 points for ≥ 60 minutes, 1 point for 10 to 59 minutes
Diabetes: 1 point if diabetic