The following is a list and a discussion of the factors which influence prognosis after severe brain injury. It was summarised from "Early Indicators of Prognosis in Severe Traumatic Brain Injury" by the Brain Trauma Foundation.
This issue has come up in several past paper SAQs:
- Question 3.2 from the second paper of 2010
- Question 7 from the second paper of 2007( though it was more interested in "moderate" head injury)
- Question 11 from the first paper of 2007
In brief, the major prognostic features are:
- Age > 60 (poor outcome risk increases by 20-30%)
- Pupillary abnormalities (70-90% mortality with bilaterally absent light reflex)
- Presence of hypotension (doubles mortality)
- Presence of hypoxia (doubles the likelihood of a poor neurological outcome)
- Low GCS on presentation (65% mortality if the GCS is 3)
- CT scan abnormalities (absence of abnormalities equates to a better prognosis)
Age > 60
The BTF soberly reports that "The prognosis for recovery from trauma as one ages is a function not only of the aged brain, but the type of injury that occurs frequently in each age group". The confused 80 year old who fell off the roof while cleaning his gutters might not have got up there if he were a lucid 60 year old. With this caveat, we see an age-related deterioration in prognosis of brain injury patients. There seems to be a significant increase in poor outcome for the over-60s.
In this definitive document, on page 175 there is a summary table of all Class I data for age-related poor outcome. In summary, your chances of poor outcome jump from 50-60% up to 80-90% across this 6th decade threshold.
This is all about traumatic injury to the midbrain, or of brainstem herneation. Both can cause a third nerve palsy, and both would be - lets face it - unpleasant, prognostically. Bilateral absence of light reflex has been associated with a 70-90% mortality.
The BTF guidelines recommend that:
1. Pupillary light reflex for each eye should be used as a prognostic parameter.
2. The duration of pupillary dilation and fixation should be documented.
3. A pupillary size greater than 4 mm is recommended as the measure for a dilated pupil.
4. A fixed pupil should be defined as no constrictor response to bright light.
5. Right or left distinction should be made when the pupils are asymmetric.
6. Hypotension and hypoxia should be corrected before assessing pupils for prognosis.
7. Direct orbital trauma should be excluded.
8. Pupils should be reassessed after surgical evacuation of intracranial hematomas.
Presence of hypotension
According to an analysis of the Traumatic Coma Data Bank (TCDB) data, one or more episode of hypotension during the initial resuscitation resulted in a doubling of mortality.
Hypotension in this context was considered anything below 90mmHg. A local project has demonstrated that hypotension is frequently the only major variable amentable to modification, when it comes to mortality in brain injury.
Presence of hypoxia
As a cause of secondary brain injury, hypoxia - like hypotension - seems to more than double the likelihood of a poor outcome, at least in a study which directly measured brain oxygen. A more pragmatic at-the-coalface analysis of the IMPACT study data also yielded an odds ratio of 2.1.
Low GCS on presentation:
The abovementioned local project has generated a nice table of GCS score vs. mortality in traumatic brain injury.
The motor component may be the more useful feature.
CT scan abnormalities
Without getting into details like "what kind of abnormalities", one can safely say only that the absence of abnormalities is significant (i.e. it predicts a good prognosis). Unfavourable oucomes were already around 70% in this group. In terms of prognostication, one might comment that the abnormal CT only tells you what you already know - that everything is not going to go well.
Strangely, not much is known about which comorbidities are wose than others, or what their influence is on outcome. Certainly, for some reason a history of hypertension seems to be associated with a poorer outcome in elderly trauma patients. The overall TBI population, however, seems to be reasonably healthy.