The Numbers Game

Is anybody using anything other than the GCS for field assessment of head injuries?

Way, way back in 2003 DTs pointed out in a paper that there were only two GCS scores that were reliable:  GCS 3 and GCS 15.  And a 3 can be obtained by the CPR dummy, a chair, a rock…

The main problem is the number of ways a patient can score a GCS.  Different values for Eye, Verbal, and Motor can change and still give an overall GCS that remains the same.

A pre-hospital provider reports to medical control that his patient has a GCS  score of 9.  There are eighteen combinations of the three sub-scores which will result in a GCS of 9:

E4V4M1, E4V3M2, E4V2M3,  E4V1M4,  E3V5M1, E3V4M2, E3V3M3, E3V2M4, E3V1M5, E2V5M2, E2V4M3, E2V3M4, E2V2M5, E2V1M6, E1V5M3, E1V4M4, E1V3M5, and E1V2M6.  Each of these combinations is attainable; that is, it is not impossible for a patient to be E4V4M1.

Overall

Glasgow Coma Score

3 4 5 6 7 8 9 10 11 12 13 14 15
Number of Sub-score Combinations

To Total This Score

1 3 6 10 14 17 18 17 14 10 6 3 1

Patient’s Sub-scores

Inferred Accuracy

100% 33% 17% 10% 7% 6% 6% 6% 7% 10% 17% 33% 100%
Bell curve

Glasgow Coma Score Distributions

As the apex of the Bell curve is approached, the individual sub-scores comprising the GCS total score become less predictable.  There are, for example, seventeen (17) possible combinations each to account for a GCS total of eight (8) or ten (10); if one were to guess the individual sub-scores, one would have a 3 in 50 chance of pinning down the appropriate values.

The inherent problem with this scoring method is easily illustrated.  A patient who at the scene scores an E3V4M3 on initial examination receives a GCS of 10.  En route to the hospital, after interventions have been applied (e.g. O2, bleeding control, etc.) another GCS of 10 is derived – this time, however, from sub-scores E2V3M5.  The patient’s overall condition, according to the GCS scale, has neither degraded nor improved, as both are GCS 10.  However, the individual scores have changed significantly either because of or in spite of prehospital interventions. In this case, the Best Eye response has degraded from “Opens on command” to “Opens on pain”; the Best Verbal response has degraded from “Disoriented speech” to “Inappropriate words”, while the Best Motor response has changed from “Flexion withdrawal” to “Localizes pain.”

To the receiving ER physician or Medical Control the changes in these individual performance criteria may provide significant insights to the patient’s condition or underlying problem, but reporting only the GCS total, which remains constant (10 in the example) will impart none of this information.

A workaround might be to report “Eye, Verbal, and Motor” scores separately rather than their sum.  Care would be needed in reporting over the radio, as “E” can sound the same as “V” if one is reporting “E 2 V 3 M 5” for instance.  Or I suppose we could just say “Eye”, “Verbal”, and “Motor”, but this seems unwieldy.

But somehow I think we can come up with something just as quick but more useful.  We in EMS are used to scrapping stuff all the time when something better comes along – MAST, paper bags for hyperventilation, tourniquets, then bring back the tourniquets – we’re flexible.  The GCS itself is a replacement for a previous system.

Of course, we’d need to overhaul the Trauma Score (which uses GCS as one of its inputs), but, hey.

Anyone?

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