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Minor Head Injury — The CHIP Prediction Rule
Abstract & Commentary
By Scott C. Elston, MD, Eastern Regional Medical Director, NextCare Urgent Care, Cary, NC, is Associate Editor for Urgent Care Alert.
Dr. Elston reports no financial relationships relevant to this field of study.
Synopsis: Prediction rules for patients with minor head injury suggest that the use of computed tomography (CT) may be limited to certain patients at risk for intracranial complications. These rules apply only to patients with a history of loss of consciousness, which is frequently absent. These authors propose a highly sensitive CHIP (CT in Head Injury Patients) prediction rule for the selective use in patients with minor head injury with or without loss of consciousness.
Source: Smits, M et al. Predicting intracranial traumatic findings on computed tomography in patients with minor head injury: The CHIP prediction rule. Ann Intern Med. 2007;146:397-405.
Minor head injury is one of the most common injuries seen in Western emergency departments, with an estimated incidence of 100-300 per 100,000 people. Patients with minor head injury include those with blunt injury to the head who have a normal or minimally altered level of consciousness on presentation in the emergency department, that is a Glasgow Coma Scale (GCS) of 13 to 15, and a maximum loss of consciousness of 15 minutes, post-traumatic amnesia for 60 minutes, or both.
Existing prediction rules to guide selected use of CT after minor head injury were developed in patients whose injury caused loss of consciousness. In the CT in Head Injury Patients (CHIP) study, Smits and colleagues prospectively evaluated 3181 adults with minor head injury regardless of whether it was associated with loss of consciousness. A prediction rule based on such factors as age, GCS score, skull fracture, and post traumatic vomiting, amnesia, or seizure successfully identified in patients who had intracranial findings on CT or who required neurosurgical intervention.
Intracranial complications after minor head injury are infrequent but commonly require in-hospital observation, and occasionally require neurosurgical intervention. The imaging procedure of choice for reliable, rapid diagnosis of intracranial complications is computed tomography. Because most patients with minor head injury do not show traumatic abnormalities on CT, it seems inefficient to scan all patients with minor head injury to exclude intracranial complications. Of the published prediction rules for selective use of CT in patients with minor head injury, the New Orleans Criteria (NOC) and the Canadian CT Head Rule (CCHR) have been externally validated. Researchers in internal and external validations studies have shown that both rules identify 100% of patients requiring neurosurgical intervention, and most patients with traumatic intracranial findings on CT. The external validation studies, however, yielded lower specificities than the development studies. The originally reported specificities were probably too optimistic because of their partial derivation from data sets that were also used for the model development. Also, in both studies, researchers included only a subset of patients with minor head injury. Most notably, the researchers developed the NOC and the CCHR for patients with minor head injury who have a history of loss of consciousness or amnesia, which many of these patients presenting the emergency departments do not have. Generalizability of the NOC and the CCHR is therefore limited.
Smits et al aimed to develop a widely applicable and easy-to-implement prediction rule for the selective use of CT in all patients with minor head injury with or without a history of loss of consciousness. The highly sensitive CHIP prediction rule (see below) for the use of CT in patients with minor head injury may be applicable to a large proportion of patients presenting to the emergency departments.
Simple prediction model for intracranial traumatic computed tomography findings in patients with minor head injury:
A CT is indicated in the presence of one major criterion:
A CT is indicated in the presence of at least 2 minor criterion:
Increasingly, physicians use prediction rules as decision rules; that is, they now frequently use predicted probabilities of an outcome in the decision making process. A prediction rule should be used as an aid in the decision making process, but should never replace clinical judgment. If clinical suspicion is high, a CT is indicated regardless of the prediction rule.
With the use of such reliable tools, as well as solid clinical skills/judgment (as always), urgent care centers/providers can safely evaluate and treat a large percentage of patients with minor head injuries. Certainly, select patients will still require CT (and observation), and these patients may be best served by the emergency departments. However, we now can be more selective and confident in our referrals. This serves to further alleviate the burden on the over-crowded emergency departments and provide a safe and convenient alternative for much of this patient population, thus conserving the "higher end" medical resources for those patients more likely to benefit.
Also, giving the patients or guardians informed consent about the risks and benefits, from either obtaining or not obtaining a CT scan, is of paramount importance, and the documentation of the informed consent should by included in the medical record.