Some observations on the blink reflex in posttraumatic coma.

Blink reflex studies were carried out on 51 comatose patients with signs of brain stem impairment due to head injury. Twenty-five patients were studied in acute coma on day 1 or 2 after trauma. Twenty-six patients were studied in prolonged coma during days 3-12 after brain injury. Brain stem involvement was divided clinically and by CT scan into secondary lesions due to supratentorial mass displacement and primary lesions due to direct violence to the brain stem. Further, the comatose states were separated by behavioural and EEG signs of sleep into "sleep' and more "alert' states. The blink reflexes were recorded after mechanical and electrical stimulation. Mechanical stimulation appeared to be more effective in evoking late responses than the electrical stimulus. The elicitability of the late responses was also dependent on the time of stimulation. During "sleep', usually accompanied by a spindle-EEG, the late responses were totally absent after both mechanical and electrical stimulation in acute coma. In more "alert' states, usually accompanied by high voltage delta waves in the EEG, the late responses, especially direct R2, could be frequently elicited by mechanical stimulation. These differences decreased during prolonged coma. All patients with signs of secondary brain stem involvement who had at least one late component in the acute stage of coma recovered well. So did all patients, with one exception, with primary brain stem injuries. Early recovery of the blink reflexes in cases of primary brain stem injury was a further favourable sign. Consistent absence of R2 (and R1) in prolonged coma indicated a bad outcome. The presence of all components in prolonged coma was of less prognostic significance than in the acute stage.