The Gist: Loss of consciousness (LOC) in mild traumatic brain injury (mTBI) in adults isn't easily established as we think but often marks a decision point for imaging. Use the patient's clinical status and risk factors to determine the need for neuroimaging and follow up in cases of mTBI. Dr. Chad Kessler has a great free open access (FOAM) talk on the subject.
The Cases: Initially, as a medical student confronted with a patient with mild head injuries in the emergency department, I spent a good portion of the history attempting to establish the presence and exact duration of loss of consciousness and post-traumatic amnesia. A few attendings harped on this point early on in my training, thus I felt it was crucial to establish with accuracy. Take, for example, the following cases of GCS 15, neurologically intact patients with normal vital signs and otherwise asymptomatic. Which one needs a head CT?
- 16 year old volleyball player fell at practice, certain she was out for "minutes." Pain free, doing homework in exam room.
- 20 year old restrained driver in an MVC with a tree, unable recall the accident or the few minutes following the accident. Abrasions on legs, no vomiting.
- 68 year old restrained driver on ASA 81 mg daily with facial trauma requiring sutures on the forehead, denies LOC, recalls entire accident, conversant.
- 3 year old fell from the sofa unwitnessed, hit her head with epistaxis that stopped spontaneously at home, and was "possibly" out for a moment before the baby sitter ran into the room
Major decisions in these mild head injury patients:
- Who needs a CT scan to identify clinically important injuries?
- Or, in Europe or the future in the US, we may need to ask who needs an increasingly popular sensitive but poorly specific S100-B biomarker (Study: Zongo et al, Responses: Graham et al, Taira et al)
- Who is at risk for deterioration?
- Who can be sent home after a normal CT scan? Who needs intervention? What follow up/precautions are advised?
Why do we care about LOC/retrograde amnesia when we work up these patients?
- It's scary to the patient and family/bystanders. It can be important for building rapport and shared decision making to recognize that the experience of LOC/post-traumatic amnesia can be frightening.
- Witnessed LOC or retrograde amnesia over 30 minutes before the trauma marks an entry point into clinical decision aids such as the Canadian CT Head Rule and New Orleans Criteria. Here is my post on a comparison between the two decision aids.
- LOC also serves as a high risk criterion in PECARN (for pediatric patients).
- Questionable indicator of severity of injury.
- Longer durations of LOC (> 5 minutes) associated with higher likelihood of significant injuries. These are, perhaps, more likely to be witnessed or documented.
- Some cite a study by Owings et al to demonstrate the preponderance of badness associated with patients with only a transient LOC; however, this study selected for really sick patient (Inclusion criteria in one phase was admission to OR or ICU).
How do we determine LOC after mTBI?
- Self-reporting is unreliable.
- Mayou et al conducted a study in which patients with blunt head trauma in a motor vehicle accident were asked whether they definitely had LOC, definitely did not have LOC, or were uncertain.
- n=124 patients reported definite LOC. 15% of those definitely had LOC and 23% (n=29) probably had LOC.
- Essentially, 2/3 of patient's reporting LOC did not actually have LOC.
- Confounders: alcohol, drugs, PTSD, pain, perception of time, pediatric patients.
- Pediatric patients may not be able to communicate or identify LOC.
- For neuroimaging purposes, the data suggest that we probably don't need to split hairs over whether someone had LOC for a few seconds or a minute. Estimates of time are likely inaccurate - was it many minutes or just 1-2?
- Talk to paramedics, bystanders, parents, etc to better establish whether LOC occurred.
How much does LOC matter for the things we care about?
- 15% of mild TBI patients have intracranial pathology (Jagoda et al).
- 0.5-1% have clinically significant injuries requiring neurosurgical intervention (Jagoda et al).
- Do not have to have LOC to have mild TBI or significant cognitive dysfunction.
- Normal neuroimaging may be falsely reassuring to a patient with mTBI.
- Good follow up, precautions, and discharge instructions should still be given to these patients (CDC recommendations)
- LOC alone is not predictive of need for neurosurgical intervention. Smits et al noted that LOC/PTA plus other risk factors were associated with more significant injuries (note: this cohort was a little higher risk than some other mTBI studies, including patients with GCS 13-14 or high risk criteria + GCS 15).
What do we do in practice?
- Wide variation between emergency physicians with regard to ordering head CTs in the context of head trauma (Stiell et al, Prevodello et al).
- The figure below demonstrates variations between providers in one academic ED in ordering a head CT in patients with head trauma (Limitation: may be confounded by variable injury severity level.
Prevedello LM, Raja AS, Zane RD, et al.Variation in use of head computed tomography by emergency physicians. Am J Med. 2012 Apr;125(4):356-64.
- Lowest ordering rates not necessarily associated with greater pathology or "misses" requiring further neurosurgical intervention (Stiell et al).
- Probably don't use clinical decision aids like the CCHR properly. Reductions in CT scanning in these populations have not panned out as expected, likely secondary to gaps in knowledge translation (Morton et al, Curran et al)
What can we do?
- Educate ourselves with excellent free, open access resources (FOAM): Life in the Fast Lane has a great review of Mild TBI workup and disposition and EBMedicine - evidence based review.
- Know how to use decision aids properly and use one that suits one's community and risk tolerance as providers: PECARN, CCHR, NOC
- Engage in shared decision making with patients. In patients who don't need neuroimaging, discuss the limitations of scans with regard to concussions and emphasize measures they can take (follow up, precautions, rest, etc).
- ACEP's clinical policy can also serve as a guide: Order a non-contrast head CT if the patient looks like they have badness or at high risk (following clinical features - Level A if they also have LOC, Level B without LOC):
- Focal neurologic deficit
- GCS <15
- Coagulopathy/on anticoagulants
- St. Emlyn's post on anticoagulated head trauma patients
- Headache (Severe Headache without LOC)
- >60-65 years old
Or, if the patient has LOC/PTA AND:
- Drug or alcohol intoxication
- Deficits in short-term memory
- Physical evidence of trauma above the clavicle
- Post-traumatic seizure
- Physical signs of a basilar skull fracture
- Dangerous mechanism of injury: ejection from a motor vehicle, a pedestrian struck, or fall from a height of greater than 3 feet or five stairs
Case Resolution: The 68 year old and 20 year old received CT scans although family members in the other cases wanted scans. The 20 year old didn't meet NOC or CCHR criteria and the scan was negative. The 68 year old patient without LOC had a subdural hemorrhage on CT which was expansile and required neurosurgical drainage within a few hours.