Ocular microtremor in brain stem death

OBJECTIVE: This study was undertaken to establish whether measurement of ocular microtremor (OMT) activity could be used as a method to establish brain stem death. Presently, the diagnosis of brain stem death can be made using clinical criteria alone. OMT is a high-frequency, low-amplitude physiological tremor of the eye caused by impulses emanating from the brain stem. There have been a number of reports indicating that the recording of OMT may be useful in the assessment of comatose states and in establishing brain stem viability or death. METHODS: We obtained the OMT recordings of 32 patients suspected of having brain stem death using the piezoelectric strain gauge technique. This method involves mounting the piezoelectric probe in a headset and lowering the rubber-tipped end piece onto the anesthetized scleral surface of the subject. The signal produced is recorded on audiomagnetic tape and later played back and analyzed on an electrocardiographic tape analyzer. RESULTS: In 28 patients, initial clinical assessment confirmed the diagnosis of brain stem death and no OMT activity was recorded from these subjects. In three patients in whom initial clinical assessment demonstrated brain stem function, OMT activity was present; when brain stem death was subsequently diagnosed in these three patients, no OMT activity could be demonstrated. In the remaining patient, two of three OMT recordings demonstrated activity in spite of the absence of clinical evidence of brain stem function. A post mortem revealed bacterial cerebritis in this subject. CONCLUSION: The results suggest that OMT is a sensitive method of detecting brain stem life and that it could play an important role in the assessment of brain stem death.