Technology: Real Time Cerebral Blood Flow Monitoring For TBI
Here’s a new toy that has recently received some funding from the US military. It allows real-time monitoring of cerebral blood flow. It may help identify flow problems from elevated intracranial pressure (ICP) or vasospasm early on, allowing prompt initiation of appropriate therapies to increase blood flow.
This device uses an array of ultrasound beams and locks onto the middle cerebral artery. It then continuously monitors blood flow and displays the result in real time. I predict that there will be a learning curve with this one, similar to near infrared monitoring of tissue perfusion. What’s a normal baseline? What kind of variation is considered “normal?” We’ll have to answer these questions before this tool is ready for prime time. Ultimately, it may allow noninvasive monitoring of ICP in the intensive care unit.
We all know that the combination of traumatic brain injury (TBI) and warfarin can be dangerous. Here at Regions, we developed a reversal protocol a few years ago. However, we found that just having a list of preferred “antidotes” to give was not enough. The time factor is very important, and we found that we needed to ensure prompt use of these medications when indicated.
So we added features that ensured timely response and reversal. You can download the protocol by clicking the image above or the link at the bottom of this post.
First, we recognized that any patient with a known or suspected TBI who was taking warfarin was at risk. If the initial GCS was <14, then a full trauma team activation is called. This gives the patient priority lab processing and immediate access to the CT scan. In addition, 2 units of thawed plasma are administered while in the resuscitation room. If the head CT is negative, plasma is stopped.
For patients with a GCS of 14 or 15, a “Code RED” is called, ensuring that an ED physician sees the patient immediately. A point of care INR is drawn and the patient is sent for stat head CT. If the head CT is negative with INR>2.5, the patient is admitted for observation and a repeat head CT is obtained 12 hours later. We have seen patients develop delayed hemorrhage when they have high INR.
We apply a restrictive set of criteria to determine if a patient may go home from the ED, which causes us to admit most for observation. And if they do have a positive CT, we use the algoritm listed below for comprehensive management and reversal.
Bottom line: Patients with any head trauma and an elevated INR are a walking time bomb. They need prompt assessment and reversal of their anticoagulation if indicated. Feel free to share your protocols here as well by posting a comment.
In May, I wrote about a new direct thrombin inhibitor named dabigatran (Pradaxa). This drug appears beneficial for patients who need ongoing anticoagulation without the hassle of blood testing to check drug levels. The danger for trauma patients is that there is no antidote or rapid reversal possible. This means that significant traumatic bleeding, particularly in and around the brain, cannot be stopped! At Regions Hospital, we have seen a few patients on this drug, but luckily they have not had bleeding from trauma.
Late last month, Bristol-Myers Squibb and Pfizer announced that a new drug has shown very favorable results in preventing strokes in patients with atrial fibrillation (apixaban, Eliquis). Indeed, it cut the relatively low risk of stroke in half, compared to warfarin. It also had about a third fewer bleeding complications. It looks like it may also give dabigatran a run for its money.
This drug is a Factor Xa inhibitor, and also has no antidote other than time. There is some evidence that activated charcoal given orally within 3 hours of apixaban dosing may be somewhat helpful in reducing blood concentrations.
Trauma professionals need to be on the lookout for patients who use this drug. Any trauma patient who admits to being on a “blood thinner” needs to be questioned carefully to determine which one it is. If it is one of the newer drugs without an antidote, they need to be monitored continuously for signs of bleeding (read: ICU), especially if they have experienced head trauma.
Bottom line: Be on the lookout for these drugs. If any patients who have fallen are taking this drug (elderly, frequently intoxicated, etc.), contact their primary physician so that the risks vs benefits of continuing it can be considered.
I previously wrote about a new review that looked at using chemical prophylaxis for deep venous thrombosis (DVT) in patients with traumatic brain injury (TBI). The authors showed that it was safe to give subcutaneous heparin products within 24 to 48 hours after a stable 24 hour followup CT.
A just-published article now helps to refine the selection of the heparin product. A retrospective review looked at 386 ICU patients with a head Abbreviated Injury Score (AIS) > 2. A total of 57 received mechanical prophylaxis, the remainder received heparin products. Chemical prophylaxis consisted of subcutaneous enoxaparin 30mg bid or unfractionated heparin 5000u tid, at the whim of the attending neurosurgeon.
The heparin group had a slightly but significantly higher Head AIS (4.1 vs 3.8). The drugs were started at the same time post-injury, about 48 hours from admission. Unfractionated heparin was found to be inferior to enoxaparin. The unfractionated heparin patients had both a higher rate of pulmonary embolism, and were more likely to have progression of any intracranial hemorrhage (12% vs 5%). The authors claim a significantly lower DVT rate, but information in their data tables do not support this. Additionally, their overall DVT rate is very low, most likely because they did not routinely screen for it.
Bottom line: The head injury / DVT prophylaxis literature is expanding rapidly. It’s time to start working with your neurosurgeons to initiate chemoprophylaxis early (within 48 to 72 hours from injury once any intracranial bleeding is stable). And it looks like the drug of choice is enoxaparin, not unfractionated heparin.
Reference: Safety and efficacy of heparin or enoxaparin prophylaxis in blunt trauma patients with a head abbriviated injury severity score >2. J Trauma 71(2):396-400, 2011.
Traumatic brain injury (TBI) is one of the leading causes of death from trauma worldwide. The assessment of TBI was revolutionized in 1976 when the GCS scale was first introduced. Shortly after its introduction, it was found to be predictive of outcome after brain injury. But it does have some drawbacks: it is somewhat complicated, and interrater reliability is low.
Interestingly, a number of studies have shown that the motor component of GCS is nearly as accurate as the full score in predicting survival. Thus, the Simplified Motor Score (SMS) was introduced as a possible substitute for the GCS in 2007. It was found to be equivalent for predicting survival when applied in the ED.
Obeys commands = 2
Localizes pain = 1
Withdraws (or less) to pain = 0
So can this scale be validated in the field when applied by prehospital providers?
Nearly 10 years of data (almost 20,000 patients) from the Denver Health trauma registry was analyzed to attempt to validate SMS when used by EMS. Although the statistics were not perfect, they found that GCS and SMS were equivalent for predicting the presence of a brain injury, need for emergency intubation, need for neurosurgical intervention, and death. Interestingly, they found that both SMS and GCS were not quite as good at predicting overall outcomes as previously thought.
Bottom line: The simplified motor score is a simple system that has now been shown to be as accurate as GCS in predicting severity and outcome from head injury. To be clear, though, neither is a perfect system. They must still be combined with clinical and radiographic assessments to achieve the best accuracy. But SMS can and should be used both in-hospital and prehospital to get a quick assessment, and may help determine early intervention and need for activating the trauma team.
Assessment of coma and impaired consciousness: a practical scale. Lancet 2:81-84, 1976.
Assessment and prognosis of coma after head injury. Acta Neurochir (Wien) 34:45-55, 1976.
Validation of the simplified motor score in the out-of-hospital setting for the prediction of outcomes after traumatic brain injury. Ann Emerg Med, in press, Aug 2011.
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