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Decision Making Tools May 2012

Decision Making Tools: Illusions of Objectivity


There are a variety of decision-making tools we use on NOLS courses;  several triangles (sea kayaking, bear awareness, risk assessment); and several mnemonics (WADE, WORMS, ALPTRUTH) come to mind.

 

I find these models helpful.  They remind me of factors to consider when making a decision.  They convey expectations of what NOLS wants me to consider when I'm making decisions.  I find them simple, clear and generally useful.  They avoid the trap of morphing a subjective tool into the illusion of an objective tool.

 

As an example of that trap, let's consider the Glasgow Coma Score (GCS), a common tool in medicine.  I have to record a GCS on every patient I see on the ambulance service.   The "score" is intended to give a reliable, objective measure of neurological status based on the sum of the scores on eye opening, verbal ability and motor response.  One of several versions of the GCS looks like this:

 

Eye Opening

Verbal Response

Motor Response

Spontaneous

4

Oriented conversation

5

Obeys commands

6

In response to speech

3

Confused Conversation

4

Localizes Pain

5

In response to pain

2

Inappropriate words

3

Withdraws to Pain

4

None

1

Incomprehensible sounds

2

Flexion

3

 

 

None

1

Extension

2

 

 

 

 

None

1

 

The range is 3-15 with a score of 13 or higher correlating with mild brain injury, 9 to 12 is a moderate injury and 8 or less a severe brain injury. I've been skeptical about this tool.  Correlation is a vague word.  I've seen many patients who have a GCS of 15 who obviously are not right in the head.  Patient's with a GCS less than 8 are obviously very sick or injured.  Patient's in the middle are in a muddle.

 

A few years ago I traveled to Scotland and wandered the streets of Glasgow looking for the origins of the coma score.  My search was fruitless, but later, in a library, I discovered that the GCS was developed in 1974 as a tool to assess and describe changing states of consciousness and to measure duration of coma in a hospital neurological surgical unit.   It was never intended to have numerical scores attached to the descriptors, nor was it intended that the three scales be merged and totaled into a score, but someone went and did the deed.  

 

The quantitative GCS is now a deeply ingrained habit in pre-hospital medicine.  It has been merged with several other "trauma" scoring systems.  Of interest, it has never been validated as an accurate assessment tool and several recent studies have questioned its reliability.1,2   The score is not reproducible.  Line up a bunch of caregivers and you will likely get different GCS scores for the same patient, in part because of the subjectivity in descriptions, in part because it's hard to remember the score, in part because there are several different version of the  GCS is use.   The score does not predict the extent of injury. 3,4  A patient with their eyes open, engaging in oriented conversation and obeying motor commands can also have nausea, headache, visual disturbances and other signs of a brain problem.   One review of the GCS says it's about as accurate as a weather report! 5

 

Enough about that.  You now know why WMI teaches AVPU as an assessment tool.

 

I bring this up to remind us not to fall to the illusion of objectivity in what are often subjective assessments.   Take a model, add some numbers, throw in some technical jargon, package it with creative formatting and there it is, the illusion of objectivity.   This is dangerous. 

 

Validating models is hard.  For better or worse, most of our decisions in the wilderness will remain matters of judgment.   As we create and use these decision-making tools, let's be careful not to create a GCS.

 

by Tod Schimelpfenig

Curriculum Director

NOLS Wilderness Medicine Institute

April  2012

 

 References:

 

1. Gill M, Reiley DG, Green SM. Interrater reliability of Glasgow Coma Scale scores in the emergency department. Ann Emerg Med. 2004;43:215-223.

 

2. Fischer M, Rüegg S, Czaplinski A, et al. Inter-rater reliability of the Full Outline of Unresponsiveness score and the Glasgow Coma Scale in critically ill patients: a prospective observational study. Crit Care. 2010;14:R64.

 

3. Healey C, Osler TM, Rogers FB, et al. Improving the Glasgow Coma Scale score: motor score alone is a better predictor. J Trauma. 2003;54:671-678.

 

4. Gill M, Steele R, Windemuth R, et al. A comparison of five simplified scales to the prehospital Glasgow Coma Scale for the prediction of traumatic brain injury outcomes. Acad Emerg Med. 2006;13:968-973.

 

5. Green S.  Cheerio, Laddie! Bidding Farewell to the Glasgow Coma Scale. Annals of Emergency Medicine 2012;  Vol 58 (5) 427-429.

 

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