This has come up in Question 22 from the first paper of 2012. The college specifically wanted a discussion of the limitations of the GCS.

The Glasgow Coma Scale undergoes a thorough dissection in LITFL.

Additionally, a good editorial on this topic is available, and summarises the problems pretty well.

Eye opening Best verbal response Best motor response
Spontaneous 4 Oriented and coherent 5 Obeys commands 6
To command 3 Confused conversation 4 Localizes 5
To pain 2 Inappropriate words 3 Withdrawal 4
No response 1 Incomprehensible sounds 2 Flexor 3
  No response 1 Extensor 2
    No response 1

Advantages of the Glasgow Coma Scale

  • The most widely recognised of all conscious level scoring systems in the world.
  • Reproduceable by well-trained staff
  • Easy to perform with minimal training
  • LITFL mention that it has "face validity" (i.e. it looks like it should work)
  • It has prognostic value: the motor score particularly has a significant impact on the prognosis.
  • The motor score findings (2,3,4) have specific pathophysiological correlations
  • It is used to categorise traumatic brain injury into mild, moderate and severe.
  • It is used to determine the need for an EVD in a patient with traumatic brain injury in the absence of any CT abnormalities (at a GCS of 8, you'd want an EVD)
  • It can be used to indicated a depth of coma at which one's airway reflexes are likely to become unreliable
  • It has been incorporated into the APACHE-II scoring system

Disadvantages of the Glasgow Coma Scale

Apart from being confused by the presence of drugs, the GCS has a few important problems.

  • When first designed in 1974, it was never meant as an assessment tool for trauma. Teasdale and Jennett even said so themselves.
  • It is unreliable in patients in the middle range of 9-12
  • People dont know how to use it. Only 15% of military physicians were able to calculate it correctly.
  • Even when calculated correctly, It has high inter-observer variability: even trained emergency staff get a different score on the same patient in 38% of cases. 6-17% of scores were 2 or more points apart.
  • Its inter-observer variability means we should always report the exact findings rather than the number which the patient has scored.
  • It is inadequate to assess higher cortical functions, and there may be a lot of variability at the upper range of the score. The delirious person scoring 14 could have a massively impaired cognition, or a mild confusion.
  • It is inadequate to assess brainstem reflexes.
    • Therefore, it cannot be used as a trigger for intubation (GCS of 8)
  • The eye score is unreliable if the eyes are damaged. Alternatively, it is possible to score an E4 even if one is braindead, provided one's eyes are open. Intelligence in interpretation is called for, and perhaps because of this the GCS is not ideal as a screening tool among partially trained staff.
  • The total score is meaningless:
    • The components are more important individually
    • Depending on the individual component score, the prognosis may be very different for patients with the same total score.
  • It is affected by drugs and alcohol.
    • However, it is still used in assessing drug overdose patients.
  • It is affected by language barriers
  • Intubation makes a mockery of its verbal conponent
  • It needs to be modified for use in young children.

 

References

Oh's Intensive Care manual: Chapter 49   (pp. 549) Disorders  of  consciousness  by Balasubramanian  Venkatesh

Plum, Fred, and Jerome B. Posner. The diagnosis of stupor and coma. Vol. 19. Oxford University Press, 1982. - warning! This link takes you to a download of the whole 9.0Mb file, which represents the entire volume of the 1980 second edition.

Maramattom, Boby Varkey, and Eelco FM Wijdicks. "Uncal herniation."Archives of neurology 62.12 (2005): 1932-1935.

Skrzat, J., et al. "The clinical significance of the petroclinoid ligament." Folia morphologica 66.1 (2007): 39-43.

Conomy, John P., and Michael Swash. "Reversible decerebrate and decorticate postures in hepatic coma." New England Journal of Medicine 278.16 (1968): 876-879.

Bateman, David E. "Neurological assessment of coma." Journal of Neurology, Neurosurgery & Psychiatry 71.suppl 1 (2001): i13-i17.

Feldman, Martin H., and Shirley Sahrmann. "The Decerebrate State in the Primate: II. Studies in Man." Archives of neurology 25.6 (1971): 517-525.

Teasdale, Graham, and Bryan Jennett. "Assessment of coma and impaired consciousness: a practical scale." The Lancet 304.7872 (1974): 81-84.

Dowell, Anthony R., et al. "Cheyne-Stokes respiration: a review of clinical manifestations and critique of physiological mechanisms." Archives of internal medicine 127.4 (1971): 712.

Andreas, Stefan, et al. "Cheyne-Stokes respiration and prognosis in congestive heart failure." The American journal of cardiology 78.11 (1996): 1260-1264.

Douglas, C. Gordon, and J. S. Haldane. "The causes of periodic or Cheyne-Stokes breathing." The Journal of physiology 38.5 (1909): 401-419.

Tomlinson, B. E. "Brain-stem lesions after head injury." Journal of Clinical Pathology. Supplement (Royal College of Pathologists). 4 (1970): 154.

Perman, Sarah M., et al. "Timing of neuroprognostication in postcardiac arrest therapeutic hypothermia." Critical care medicine 40.3 (2012): 719.

Towne, A. R., et al. "Prevalence of nonconvulsive status epilepticus in comatose patients." Neurology 54.2 (2000): 340-340.

TEASDALE, GRAHAM, and BRYAN JENNETT. "Assessment of coma and severity of brain damage." Anesthesiology 49.3 (1978): 225.

Green, Steven M. "Cheerio, laddie! Bidding farewell to the Glasgow Coma Scale." Annals of emergency medicine 58.5 (2011): 427-430.

Gill, Michelle R., David G. Reiley, and Steven M. Green. "Interrater reliability of Glasgow Coma Scale scores in the emergency department." Annals of emergency medicine 43.2 (2004): 215-223.

Riechers, Ronald G., et al. "Physician knowledge of the glasgow coma scale."Journal of neurotrauma 22.11 (2005): 1327-1334.