Evaluating depth of coma

While we are all being remarkably patient (we don’t really have a choice, do we?) as Michael’s injuries heal and his state stabilises, I thought it would be useful for what’s to come to explain a bit of how doctors evaluate coma patients. This includes assessing how “deep” the coma is, as well as tracking the patient’s progress as the clinical situation evolves.

Now I’m sure that Michael’s care team will NOT be releasing any of this stuff when they begin lightening his sedation, but I still think it’s useful that we have an idea of what’s going on, how it’s done, and that we can interpret any details that do manage to filter out.

Because by definition a coma is defined as a prolonged state of diminished consciousness making meaningful contact between the patient and his environment impossible, we can’t just ask the patient a series of questions and go from there. What’s needed is a tool to evaluate more basic levels of brain function, in a reproducible, standardised and validated way. This tool is called the Glasgow Coma Score (GCS).

The GCS was described in 1974 by a duo of neurosurgeons working in Glasgow. For those of you interested in the original article, a landmark in neurointensive care, here is the reference:

Assessment of coma and impaired consciousness. A practical scale. Teasdale G, Jennett B; Lancet, 1974, July 13; 2(7872):81-4

The GCS involves observing the patient spontaneously, and if necessary determining his or her response to graded levels of stimulation. The initial stimulus is speaking to the patient. If needed, a painful (but harmless) stimulus is applied. There are several ways of doing this – steady heavy pressure on the forehead, deeply pinching the trapezius muscle, or deep pressure on a fingernail bed.

Three criteria are scored: the patient’s eye opening, motor response, and verbal output. As you can see if you look at the scoring criteria, the points for each parameter go from higher (representing a “higher” level of function) to lower scores, representing “worse” function.

In terms of eye opening, 4 points are assigned if the patients opens his or her eyes spontaneously, 3 points if they open to vocal stimulation, 2 if they only open to pain, and 1 if there is no eye opening at all.

Attention then turns to the patient’s verbal responses. Appropriate, oriented responses to simple questions get 5 points. Confusion or disorientation is scored 4; inappropriate, unrelated words “earn” 3 points. If the patient only makes incomprehensible sounds in response to stimulation, 2 points are given, and as with the eyes, if there is no verbal response only 1 point is given. Obviously this criteria cannot be assessed accurately when the patient is intubated, and this fact is noted, often by assigning a “value” of “T” to this criteria.

Motor responses are extremely important. If the patient follows simple commands (wiggle your toes, move your index finger, etc) he or she gets 6 points. When the response to the painful stimulus is an oriented attempt to remove the stimulus, 5 points are assigned. Next comes a withdrawal response (4 points), an unorganised series of movements representing a primitive response to escape from the stimulus. If the coma is still deeper, the patient will respond to painful stimulation with an abnormal flexion of the arms and/or legs (3 points), a response that originates in mid-levels of the brainstem. Still deeper is abnormal extension, because this is integrated at even lower levels of the brainstem. This is assigned 2 points. And as above, no motor response at all gets 1 point. If there is a difference in the response of the right and left sides, the BEST response is used in scoring (but the “score” of the other side is noted also).

As you can see, scores range from a high of 15 to a low of 3. The GCS score is evaluated quite often (several times a day), and provides a reliable and reproducible way of assessing whether the patient is “emerging”, “plunging”, or staying the same. It is also used to roughly stratify the severity of injury.  Scores from 13-15 are considered to be “mild” (and often correspond to what’s seen in concussion patients). Moderate head injury is present if the score is 9 to 13, while a score from 3-8 is defined as severe head injury. A patient with a score of 8 or less is considered to be in a coma.

The Glasgow Coma Score cannot be reliably evaluated until sedation is off, temperature is normalised, and other factors that could confound the scoring are taken into consideration.

Other elements are also evaluated of course including the size, symmetry and reactivity of the pupils, imaging, sometimes electroencephalography, in order to get a picture of how the patient is progressing and where the problem areas of the brain are.

Hope this helps.

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