[Diagnostic value of the far field acoustic response (FAR) as an objective evaluating method for brainstem injury...

Far Field Acoustic Response (FAR) was repeatedly studied from acute stage to chronic stage of severe head injury in 64 patients for evaluation of the degree of brainstem injury. (1) In acute stage within 7 days after trauma, FAR abnormalities are found in 56% of the subjects with severe head injury. These abnormalities are as follows: (i) Prolongation of latency, disappearance of the 5th wave. (ii) Disappearance of the 1st-5th waves or 2nd-5th waves. The incidence of FAR abnormalities is not correlated to disease categories and age of the subjects. (2) FAR findings reveal more precisely the level of brainstem dysfunction than by clinical assessments of brainstem reflexes and posture, and by computerized tomography. (3) Evaluating results of the FAR recorded within 7 days after trauma are correlated to the outcome 3 or more months after injury in the subjects. Almost of them with alteration of only the 5th wave in FAR improve clinically and electrophysiologicaly at 2-3 weeks after trauma. However any patients with disappearance of the 1st-5th waves in FAR are fatal or fell into the state of vegetation. According to these results, it was concluded that FAR has a important diagnostic value as an objective evaluating method for brainstem dysfunction in patients with severe closed head injury.