Ocular microtremor in brain stem death

OBJECTIVE: This study was undertaken to establish whether measurement of oc ular microtremor (OMT) activity could be used as a method to establish brai n stem death. Presently, the diagnosis of brain stem death can be made usin g clinical criteria alone. OMT is a high-frequency, low-amplitude physiolog ical tremor of the eye caused by impulses emanating from the brain stem. Th ere 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 st em 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 metho d involves mounting the piezoelectric probe in a headset and lowering the r ubber-tipped end piece onto the anesthetized scleral surface of the subject . The signal produced is recorded on audiomagnetic tape and later played ba ck and analyzed on an electrocardiographic tape analyzer. RESULTS: In 28 patients, initial clinical assessment confirmed the diagnosi s of brain stem death and no OMT activity was recorded from these subjects. In three patients in whom initial clinical assessment demonstrated brain s tem function, OMT activity was present; when brain stem death was subsequen tly diagnosed in these three patients, no OMT activity could be demonstrate d. In the remaining patient, two of three OMT recordings demonstrated activ ity 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.