The Glasgow Coma Scale (GCS) was initially developed to assess the level of brain function following injury. Recently its application has expanded to assess brain function from other neurological etiologies, especially in the critical care setting. The score is calculated by adding assigned values to different levels of function in three main categories: motor, verbal, and eye response. The GCS (Table 192.1) allows for a common language between health care providers during the assessment of neurologically impaired patients. Using this score to stratify the severity of brain injury assists in determining further diagnostic and therapeutic interventions. Its predictive value is limited when the score is used alone; however, when combined with other physiologic and anatomic criteria, it may be more useful in evaluating outcomes.

The severity of traumatic brain injury is often defined by the GCS. A score ≤8 is considered severe injury, 9 to 13 is moderate, and 14 to 15 is mild. The motor score may be the most reliable and accurate component and appears to correlate well with the total GCS score. The use of the motor score alone avoids problems often associated with the collection of the verbal and eye components. The eye portion of the score adds little to the overall predictive ability of the GCS score and can easily be affected by other factors. The verbal response is impossible to determine in intubated patients and has led to the adoption of annotating the GCS score with a T in these patients (e.g., 3T). The GCS is most reliable when used in assessing patients with isolated head injuries; however, there remains variability in calculating the score among different practitioners as well as different institutions.