Shock Index and Head Trauma

How many of you see pets with head trauma in your practice? Okay, that’s good. There are several ways to look at prognosis following head trauma but the key feature of any of the measurements is serial evaluations. One singular measurement doesn’t seem to correlate well with prognosis in such a dynamic disease. A recent retrospective study evaluated the shock index (heart rate divided by systolic BP) to determine the correlation with mortality in a population of dogs with head trauma. A second part of the study was to determine if it was predictive of survival to discharge or improvement in signs during hospitalization.

Results

 A total of 86 cases and an unknown number of control dogs (normal dogs) were included. There was quite a list of possible ways these poor dogs were traumatized and an even longer list of breeds affected. See the study for full details on that.  The mean SI for the control group was 0.75 (range 0.62-0.92 with not normal distribution). The mean SI for dogs with head trauma was 0.91 (range 0.34-3.33, also not normally distributed). SI was significantly (0.0014) higher in the trauma group compared to the control group. However, the SI was not significantly different between dogs that diet or were euthanized compared to those that lived until discharge. There was also no significant difference in SI between dogs with a normal neurologic examination at discharge and those that were improved or static, but not normal, at discharge.

So, what does this tell us? My take away is that the SI is higher in dogs with head trauma, but it doesn’t prognosticate (using the data from this cohort of dogs) regarding survival or neurologic outcome. Why is SI higher in pets with head trauma? Following trauma, if the intracranial pressure (ICP) goes UP (hemorrhage, edema) the mean arterial BP goes up to keep blood flowing to the brain. The HR will concurrently drop due to a feedback loop. This SHOULD result in a lower SI (HR/systolic BP). The authors noted that in one case they had a dog with significant hypovolemia at the initial evaluation which resulted in a very high SI but due to a swing in pressure dynamics in the brain, the dog oscillated between hypo and hypertension over time. The authors suggest that SI may be an unreliable measurement in post-head trauma patients for this reason. So, I return to all of you smart people out there. Why is the SI higher in head trauma than in control dogs? This has also been reported in humans post head trauma so there must be a very good reason, but I can’t figure it out and would love your thoughts!

Thanks for reading this TidBit Tuesday! I hope you have a wonderful week and look forward to seeing you soon!

Reference: McConnell BM, Cortes Y, Bailey D. Retrospective evaluation of shock index and mortality in dogs with head trauma (2015-2020): 86 cases. DOI: 10.1111/vec.13411

Traumatic Brain Injury And Blood Glucose

We're approaching the month of October - known for scary costumes and sugar overload. Why not look at a recent study about glucose to kick up our adrenaline? Okay, so this is a study in dogs and cats, specifically about traumatic brain injury and relationship between glucose and prognosis but don't shame me for trying to make a link to "current events"!

Background

This was a retrospective study (Cameron S, et al. JVECCs, 2021) looking at 131 dogs and 81 cats that were presented to one of two teaching hospitals following trauma and were diagnosed with traumatic brain injury (TBI). (TBI is the new term for head trauma, in case you're wondering.) At admission, glucose and a modified Glasgow Coma Scale, among other tests, were evaluated from the record and correlated to outcome. The animals were termed "survivors" if they lived to be discharged from the hospital and they were termed "non-survivors" if they, well, didn't.

Results

Here are the key points, and the interesting bits!

Dogs:

• The MGCS was significantly lower in non-survivors compared to survivors.

• Blood glucose concentration was significantly higher in non-survivors compared to survivors.

• A cut off of 148 had a sensitivity of 73% and specificity of 76% for a poor outcome (non-survivor)

Cats:

• The MGCS was the ONLY significant predictor of outcome

• Glucose was not significantly related to outcome!

Take home message:
When presented with a post-traumatic patient, perform a serum blood glucose concentration and a neurologic examination (to get a MGCS). Both of those may be able to help you predict the outcome for a DOG (not cat) and guide the clients towards or away from referral if they are considering humane euthanasia. Naturally, we must account for co-morbidity, financial impact and prior medical conditions of the pet when faced with a post-traumatic patient but hopefully these two little points will further improve your ability to help the patient.

Thanks for reading! I hope you have a nice week and keep those consults coming!
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