Wednesday, August 10, 2016

FOUR Score: Coma scales and prognosis in the ICU

by Drew Rosielle

In neuro-critical care, prediction of outcomes is often tricky because of the wide variability in the ability of the brain to recover and the usual long periods needed before seeing what is the limit of recovery. Most people are familiar with the Glasgow Coma Scale, but back in 2009 Mayo Clinic Proceedings published a study of the FOUR score), which presents some prognostic data for ICU patients. FOUR = 'Full Outline of UnResponsiveness.' (It is also written as 4S. - Ed.)

This was a single institution study (Mayo Rochester) primarily designed to investigate whether the FOUR score is a reliable coma scale when applied in ICUs by non-neuroscience types (it has been studied before in neuro ICUs - this study involved non-neuroscience trained nurses, consulting docs, fellows, and intensivists in several ICUs at Mayo). Part of the context for the score is that the Glasgow Coma Scale, the most commonly used coma scale, measures verbal responsiveness - something which is difficult to do on intubated patients. The 4S measures eye response, motor response, brainstem reflexes, and respiratory pattern and assigns 0-4 ratings to each category (see graphic below). All ICU patients (not all intubated) over a 1 year time frame who had 'abnormal consciousness' and who weren't receiving pharmacologic sedation or paralysis were included for the study. Basically different ICU team members were assigned to do 4S evaluations on these patients, and interrater reliability, etc. was measured.

100 patients were evaluated - 45% intubated - with a broad range of illnesses (at least 40% had some primary CNS pathology such as strokes, 'craniotomy,' etc.). Despite the fact that they noted an inclusion criteria of 'abnormal consciousness,' about a 3rd of the patients were described as 'alert': basically all the non-alert patients either had a primary CNS pathology or anoxic or metabolic encephalopathy (as expected; those patients without those issues would be expected to either be alert or pharmacologically sedated). 33% of the patients died - all of them either by neurologic criteria or after life-prolonging treatments were withdrawn due to poor prognosis.

Basically, the 4S looked good from an interreliability, etc. standpoint, and compared favorably with the GCS. As expected, lower (worse) summative 4S scores were associated with worse outcomes including in-hospital death (e.g. every 1 point decrease in the 4S was associated with a 15% improvement in the odds of in-hospital survival). (Note that is odds not rates - most of the outcomes are presented as odds ratios and not actual event-rates.) The only rates presented are for those 9 patients with the lowest 4S scores (presumably zero): 89% died in-hospital, and one assumes that 6 of these were the ones declared dead by neurologic criteria. Notably, the in-hospital mortality for those with the lowest GCS score (3) was 71%, suggesting perhaps the 4S (as it measures more characteristics than the GCS) can more precisely characterize the very sickest.

That said, from a clinical standpoint one isn't particularly helped by new data that a patient with no signs of consciousness, withdrawal to pain, brainstem reflexes, or spontaneous respirations, without the help of sedating drugs (ie a 4S of 0), is highly likely to die. We knew that already, and of course this paper wasn't intended to really demonstrate anything other than the 4S is a reliable way to measure/stratify degrees of unresponsiveness/coma. It is a reminder to me as a reader of this research how my interests in what data I want presented (in this case gross in-hospital mortality rates for each 4S rank) as I naively hope for answers/clinically-relevant information is not what others find important, even though they have the data. The 4S seems to be a straight-forward and easy to measure coma scale, and perhaps we'll be seeing more of it, including frank outcome data.

Drew Rosielle, MD is a palliative care physician at University of Minnesota Health in Minnesota. He founded Pallimed in 2005. For more Pallimed posts by Drew click here. 

Iyer VN, Mandrekar JN, Danielson RD, Zubkov AY, Elmer JL, Wijdicks EFM. Validity of the FOUR score coma scale in the medical intensive care unit. Mayo Clin Proc. 2009;84(8):694-701. doi:10.1016/S0025-6196(11)60519-3. Open Access PDF

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