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BRAIN INJURY ASSESSMENT IS COMPLEX.21 September at 15:54 from atlas
Date: 26th January 2012Traumatic Brain Injury - assessing severity
The measurement of severity of traumatic brain injury (TBI),is important as it guides initial emergent management, is an index of progress during rehabilitaton, assists in determining prognosis and is also of medico-legal significance.There are various aspects of severity assessment of TBI, including obvious scalp/skull and brain structural damage, measure of brain function and investigations ,such as CT/MRI/EEG studies etc.It is known however that structural damage and results of investigations do not always accurately correlate with outcome,and are at times unreliable measures in the analysis of severity.Patients can be deeply unconscious with dercerebrate posturing with a relatively normal CT scan.Conversely, patients can walk in and out of A&E department with a large EDH ,hours away from death.
The most commonly used TBI severity markers in Australia are the Glasgow Coma Scale(GCS)and duration of Post Traumatic Amnesia (PTA).The GCS was devised by Professors Bryan Jennett & GordonTeasedale in 1974in Glasgow, Scotland (Lancet.Jul 13 1974;2(7872):81-4).It assesses best responses in 3 areas : Eye opening, Motor response and Verbal response-total score 3 - 15. An initial score of 3-8 indicates severe TBI, a score of 9-12 indicates moderate TBI, and a score of 13-15 indicates mild TBI.The GCS has obtained world wide acceptance as it is reliable, objective, numeric, stable irregardless of experience of observer and correlates well with outcome.It correlates very well with Glasgow Outcome Scale,(.Jennett B & Bond M.Lancet.Mar1 1975;1(7905):480-4.).It is used not only as a measure of severity of TBI, but as part of general, and ICU monitoring of patients' neurological status, or conscious level around the world and in the Neurological , Neurosurgical and General Medical scientific literature.
The other major measure in Australia relates to assessment of PTA In 1882 , Ribot proposed a combined amnesia classification including both anterograde and retrograde amnesia. Retrograde amnesia (RGA) was recognised as changing and not a reliable indicator of ongoing problems.Typically RGA involves a recency-events closer to the insult are less likely to be recalled than earlier events and with time , and recovery the duration of RGA shrinks. 1932 Russell (Russell WR in Brain.1932;55:549-603) introduced the concept of post-traumatic amnesia (PTA), and described it as duration from injury to demonstration of continuous memory.Retrograde amnesia (RGA) was also another index ,however it was obvious that RGA ( last accurate recollection before loss of consciousness) was not an accurate, or reliable measure of TBI severity. After passage of the PTA period,the retrieval of remote memories remains impaired but there no longer is sparing of the oldest memories as there was whilst still in PTA.- the gradient existing whilst in PTA ceases to protect remote memories and shrinkage of RGA is facilitated.RGA can contract from years to an hour-it is evolving and NOT an accurate measure of TBI.Usually PTA is significantly longer than RGA.
Levin (Levin HS et al.J Nerv Ment Dis.Nov 1979;167911):675-84) validated the accuracy of PTA as a predictor of severity of TBI with the Galveston Orientation and Amnesia Test (GOAT).GOAT primarily assesses temporal orientation and is recommended primarily in the acute care situation.This was again validated by Zafonte et al in 1997 (PTA :its relation to functional outcome.Arch Phys Med Rehabil.Oct 1997;78(10):1103-6).In Australia the most common PTA tool is the Westmead PTA Scale.
The Westmead PTA Scale was described in 1986 by Shores EA (Shores EA et al.The Med J Aust 1986;144:569-72).It comprises a series of 9 set questions and 3 pictures and is simple to perform, taking a few minutes. It comprises 7 orientation questions and 5 memory items e.g. how old are you,name of this place etc.It is different to the GOAT in that both orientation and re-establishment of the daily activity to recall newly learned information are required for defining of the end of PTA period.(E Arthur Shores 1988).A patient is deemed out of PTA if they can achieve a perfect westmead PTA score for 3 consecutive days- date of emergence is thus the 1st of the 3 normal score consecutive days.(There is also a modified Westmead Scale for use in mild TBI in the ED utilising 10 items each hour over 3 consecutive hours-Ponnsford et al Melbourne 2004). Shores believes that duration of PTA explained 24% more of his study variance in terms of verbal learning outcome than did duration of coma (GCS 4 weeks-extremely severe ( Jennett & Teasdale,1981), & (2) INITIAL GCS : 13-15-mild TBI; 9-12-moderate TBI; and 3-8 -severe TBI.
Other measures are published and used around the world.Greenwald BD (Greenwald BD et al.Arch Phys Med Rehabil.Mar 2003;84(3 Suppl 1):S3-S7) classify Mild TBI as mental status change or LOC 6 hours.
There are a number of TBI Outcome Measures in use.The best known is the Glasgow Outcome Scale (GOS).Others incliude the Functional Independence Measure- FIM score(RA Keith et al 1987) and the Disability Rating Scale (DRS). The FIM measures a patient's independence in self-care,sphincter control,mobility, communication and social interaction. The GOS rates 1-dead; 2-persistent vegetative-minimal responsiveness; 3-severe disability-conscious but disabled& dependent on others for daily support: 4-moderate disability-disabled but independent,can work in a sheltered setting ,and 5-good recovery-resumption of normal life despite minor deficits. (Jennett & Bond, 1975). The DRS is much more complex encompassing the GOS score, disability and return to work measures. All 3 measures of TBI Outcome are widely used and accepted as valid-FIM, GOS and DRS.
Valid predictors of outcome after TBI include: Initial GCS score, PTA Duration (Westmead scale), Age ( 40), educational status and sex.
Valid predictors and markers of severity of TBI include Initial GCS and Duration of PTA (Westmead Scale). Duration of coma and RGA are not statistically as reliable. GCS, Westmead PTA Scale and GOS are widely used in Australian Neurology, Neurosurgical and Brain Injury Rehabilitation Units. GCS, PTA Westmead Scale and GOS are taught to Nursing, Medical and Paramedical students.
GCS opening 1-4 + Motor response 1-6 + Verbal response 1-5.
Decorticate (flexor response)=lesion above mesencephalic red nuclei ("cerebral") ; Decerebrate (extensor response) = lesion between mesencephalic red nuclei and medullary lateral vestibular nuclei ("brain stem") and Flaccid below medullary lateral vestibular nuclei ("spinal" ).
Predictors and marker severe TBI : Initial GCS 3-8 AND PTA duration (Westmead Scale) 2- 7 days. ( Mild TBI : Initial GCS 13-15 and PTA duration 1-4 hours.) . N.B. drugs, alcohol, anaesthetic agents, hypoxia and hypotension may influence results.