Predicting Coma Emergence – The Predictive Tree

Predicting Coma Emergence

By Attorney Gordon S. Johnson, Jr.

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So what are the fundamentals of predicting coma emergence, the Predictive Tree for Coma Emergence in helping to predict a Satisfactory Recovery from Severe Brain Injury?  For a basic understanding of predicting coma emergence, it is necessary to understand the significance of pupillary response and the Glasgow Coma Scale.

Pupillary Response

Pupillary response is what the pupils of the eyes do when exposed to light.  The lens that is the human eye, should respond instantly to a change in light conditions. The pupil is the opening, which exactly as an automatic camera would do, will increase the dilation (size of the opening) with less light, and decrease the size of the opening with more light. If either pupil has an abnormal reaction to light, that is a very disturbing sign after head trauma and plays a part in predicting coma emergence.  [1]

Glasgow Coma Scale – GCS

The Glasgow Coma Scale (“GCS”) is the uniform diagnostic tool used to assess the condition of someone with a traumatic brain injury and helps predicting coma emergence.  It is important for the assessment of those suffering a moderate or severe brain injury but largely irrelevant for those who are conscious when first assessed, as discussed in the webpages above.  It is invaluable to the comatose patient because it can be applied quickly based on the clinical evaluation and predicting coma emergence and can be done with some degree of accuracy, even by EMT’s and other non-physicians.

The GCS scores a brain injured individual in three categories:

  • Eyes Opening
  • Verbal Response and
  • Motor Response.

The oddity in understanding the GCS is that the lowest score in any of these three areas is a one, not a zero.  Thus the lowest possible GCS score is a 3.  The gravest concern for someone in a coma comes when the motor responses are the worst, particularly a two or less.  Verbal and motor response are often lost with even less severe arousal conditions.

A two motor score means that in response to pain there is an extension response or decerebrate posturing. Decerebrate posture is an abnormal body posture that involves the arms and legs being held straight out, the toes being pointed downward, and the head and neck being arched backwards. The muscles are tightened and held rigidly.[2]  A one motor score is means “no response.“

Yet a low Motor Response alone is not grave.  It is when it is combined with abnormal pupillary response that the predicting coma emergence with the  Predictive Tree branches away from some probability of meaningful recovery.  All of those with abnormal pupils and a motor score of 2 or less failed to recover in the Choi study.[3]  With abnormal pupils and a motor score greater than 2, in excess of half had some recovery.  The validity of these two factors has been reaffirmed by subsequent research.  [4]

Figure 1: [5]

Glasgow Coma Scale

Eye Opening Response

  • Spontaneous–open with blinking at baseline  4 points
  • To verbal stimuli, command, speech 3 points
  • To pain only (not applied to face) 2 points
  • No response 1 point

Verbal Response

  • Oriented 5 points
  • Confused conversation, but able to answer questions 4 points
  • Inappropriate words 3 points
  • Incomprehensible speech 2 points
  • No response 1 point

 Motor Response

  • Obeys commands for movement 6 points
  • Purposeful movement to painful stimulus 5 points
  • Withdraws in response to pain 4 points
  • Flexion in response to pain (decorticate posturing) 3 points
  • Extension response in response to pain (decerebrate posturing) 2 points
  • No response 1 point

Head Injury Classification:

  • Severe Head Injury—-GCS score of 8 or less
  • Moderate Head Injury—-GCS score of 9 to 12
  • Mild Head Injury—-GCS score of 13 to 15

What Happens if there is No Emergence from Coma


Teasdale G, Jennett B. Assessment of coma and impaired consciousness. Lancet 1974; 81-84; Teasdale G, Jennett B. Assessment and prognosis of coma after head injury. Acta Neurochir 1976; 34:45-55.

[1] See Neurotrauma, Narayan, Wilberger, Povlishock, McGraw-Hill, 1996, 785-787


[3] Choi SC, et. al., id. Choi study: PVS = 15, Awake 49, Dead = 20.

[4] See Andrews PJ, Sleeman DH, Statham PF, McQuatt A, Corruble V, Jones PA, Howells TP, Macmillan CS. J Neurosurg. 2002 Aug;97(2):326-36. Predicting recovery in patients suffering from traumatic brain injury by using admission variables and physiological data: a comparison between decision tree analysis and logistic regression; and

Park JE, Kim SH, Yoon SH, Cho KG, Kim SH., J Korean Neurosurg Soc. 2009 Feb;45(2):90-5. Epub 2009 Feb 27. Risk Factors Predicting Unfavorable Neurological Outcome during the Early Period after Traumatic Brain Injury.


[5] Disclaimer:

Based on motor responsiveness, verbal performance, and eye opening to appropriate stimuli, the Glascow Coma Scale was designed and should be used to assess the depth and duration coma and impaired consciousness. This scale helps to gauge the impact of a wide variety of conditions such as acute brain damage due to traumatic and/or vascular injuries or infections, metabolic disorders (e.g., hepatic or renal failure, hypoglycemia, diabetic ketosis), etc.

Education is necessary to the proper application of this scale.