gcs-calculation

name	gcs-calculation
description	Extract and calculate Glasgow Coma Scale (GCS) for ICU patients. Use for neurological assessment, consciousness monitoring, or trauma severity scoring.
tier	validated
category	clinical

Glasgow Coma Scale (GCS) Calculation

The Glasgow Coma Scale assesses level of consciousness through three components: Eye opening, Verbal response, and Motor response. This concept extracts and calculates GCS with special handling for intubated patients.

When to Use This Skill

• Neurological status assessment
• Trauma severity scoring
• Sedation monitoring
• Severity scores (SOFA CNS, APACHE, SAPS)
• Consciousness trajectory analysis

GCS Components and Scoring

Response	Score 1	Score 2	Score 3	Score 4	Score 5	Score 6
Eye	None	To pain	To speech	Spontaneous	-	-
Verbal	None	Incomprehensible	Inappropriate	Confused	Oriented	-
Motor	None	Extension	Flexion	Withdraws	Localizes	Obeys

Total GCS Range: 3-15 (lower = worse)

Pre-computed Table

SELECT
    subject_id,
    stay_id,
    charttime,
    gcs,          -- Total GCS score
    gcs_motor,    -- Motor component (1-6)
    gcs_verbal,   -- Verbal component (1-5)
    gcs_eyes,     -- Eye component (1-4)
    gcs_unable    -- 1 if unable to assess (intubated/sedated)
FROM mimiciv_derived.gcs;

MetaVision Item IDs

Component	Item ID	Description
Verbal	223900	GCS - Verbal Response
Motor	223901	GCS - Motor Response
Eyes	220739	GCS - Eye Opening

Critical Implementation Notes

1. Intubated Patients: When verbal response is documented as "No Response-ETT" (endotracheal tube), the verbal component is set to 0 (not 1, not 5) and flagged with gcs_unable = 1. The total GCS is then set to 15 (assumed normal if only intubation prevents assessment). Important: report gcs_verbal = 0 in the output — do NOT replace it with 5. The value 0 is a sentinel meaning "untestable."

2. Component Carry-Forward: If only one or two components are documented at a time, previous values from the past 6 hours are carried forward. This prevents artificially low scores from incomplete charting.

3. Calculation Logic:

   GCS = Motor + Verbal + Eyes
   
   IF current verbal = 0 (intubated) THEN GCS = 15 (but keep gcs_verbal = 0 in output)
   ELSE IF previous verbal = 0 THEN use current components only (don't carry forward)
   ELSE carry forward missing components from past 6 hours
   

4. Sedated Patients: Per SAPS-II guidelines, sedated patients should use pre-sedation GCS. In practice, if documented as "unable to score due to medication", this is flagged.

5. Time Series: Each row represents a charted observation, not an hourly aggregate. Multiple observations per hour are possible.

Example: Worst GCS Per ICU Stay

SELECT
    stay_id,
    MIN(gcs) AS worst_gcs,
    MIN(gcs_motor) AS worst_motor,
    MIN(gcs_verbal) AS worst_verbal,
    MIN(gcs_eyes) AS worst_eyes
FROM mimiciv_derived.gcs
WHERE gcs_unable = 0  -- Exclude intubated/sedated
GROUP BY stay_id;

Example: GCS Categories

SELECT
    CASE
        WHEN gcs <= 8 THEN 'Severe (3-8)'
        WHEN gcs <= 12 THEN 'Moderate (9-12)'
        ELSE 'Mild (13-15)'
    END AS gcs_category,
    COUNT(*) AS n_observations
FROM mimiciv_derived.gcs
WHERE gcs_unable = 0
GROUP BY 1
ORDER BY 1;

Example: First Day Minimum GCS

-- Include ALL patients (intubated patients have gcs=15, gcs_verbal=0)
SELECT
    ie.stay_id,
    MIN(g.gcs) AS first_day_min_gcs
FROM mimiciv_icu.icustays ie
LEFT JOIN mimiciv_derived.gcs g ON g.stay_id = ie.stay_id
    AND g.charttime >= ie.intime - INTERVAL '6' HOUR
    AND g.charttime <= ie.intime + INTERVAL '1' DAY
GROUP BY ie.stay_id;

Example: GCS Trajectory

WITH hourly_gcs AS (
    SELECT
        stay_id,
        DATETIME_TRUNC(charttime, HOUR) AS hour,
        AVG(gcs) AS avg_gcs
    FROM mimiciv_derived.gcs
    WHERE gcs_unable = 0
    GROUP BY stay_id, DATETIME_TRUNC(charttime, HOUR)
)
SELECT
    stay_id,
    hour,
    avg_gcs,
    avg_gcs - LAG(avg_gcs) OVER (PARTITION BY stay_id ORDER BY hour) AS gcs_change
FROM hourly_gcs;

Example: Handle Intubated Patients

-- Option 1: Exclude intubated patients
SELECT stay_id, MIN(gcs) AS min_gcs
FROM mimiciv_derived.gcs
WHERE gcs_unable = 0
GROUP BY stay_id;

-- Option 2: Use motor score only for intubated (mGCS)
SELECT
    stay_id,
    MIN(CASE WHEN gcs_unable = 1 THEN gcs_motor ELSE gcs END) AS min_gcs_or_motor
FROM mimiciv_derived.gcs
GROUP BY stay_id;

References

• Teasdale G, Jennett B. "Assessment of coma and impaired consciousness: A practical scale." Lancet. 1974;2(7872):81-84.
• Teasdale G et al. "The Glasgow Coma Scale at 40 years: standing the test of time." Lancet Neurology. 2014;13(8):844-854.