Abstracts

Rationale: While magnetoencephalography (MEG) examinations are not infrequently ordered to be done on the same day, e.g. for pre-operative mapping of eloquent cortex prior to resective lesion surgery, these are still elective tests. Adequate sampling of the patient s spontaneous brain activity or multi-sensory evoked field protocols normally dictate a relatively lengthy survey. The sophisticated pre-recording setup required, vulnerability to artifact from acute care instrumentation, and perceived necessity for some degree of patient cooperation; followed by the tedious and lengthy post-processing and interpretation time, has precluded the use of MEG in truly emergent circumstances. Yet the inherent properties of MEG actually make it well-suited for use in acute care situations. It has high te poral and spatial resolution, and once head positioning (HPI) coils have been attached to the scalp, the patient is ready. Methods: The primary obstacles to rapid and safe MEG testing were evaluated and standard operating procedures developed including: 1) Technical feasibility. Issues related to indwelling lines, ventilators, etc. Presence of intensive care personnel, emergency medications, and access to immediate help. 2) Patient safety. Continuous monitoring, immediate entry into the MSR, guarding against most likely risks. 3) Speed of setup and recording. Maximal round-trip time from the ICU established at 1 hr. 4) Timely review, interpretation, and reporting. Focus on answering specific, immediate clinical question. Arranging these solutions required the involvement of nursing, pharmacy, EEG technologists, engineering, as well as the medical staff/fellows. Results: During a one month period (3/16 - 4/14/2010) we performed 3 emergency MEGs which are illustrative of the indications and benefits for stat MEG testing. Patient S was in a coma of unknown origin with frequent waves of widespread body tremor. EEG was unhelpful because the continuous artifact could not be distinguished from seizure activity. The patient was not on a ventilator, so paralytics could not be given to eliminate EMG artifact on EEG. The MEG was recorded in order to ascertain whether the patient s coma was due to seizures. Patient H had had 2 right temporal lobectomies, and was in status epilepticus. The neurosurgically altered anatomy made it impossible to ascertain from EEG from where the focal status was arising. Because of its immunity to alterations in conductivity, the MEG was able to properly identify the origin of the epileptic activity. Patient G underwent a repeat MEG, this time after placement of SEEG electrodes. These invasive electrodes appeared not to be sampling the epileptogenic region, but required immediate explantation. The MEG was carried out just before removal to simultaneously view the SEEG and MEG signals, in order to plan a future invasive investigation. Conclusions: Whole head magnetoencephalography can be safely and rapidly carried out in emergency circumstances. Targeted clinical neurophysiological questions permit truncated recording time and rapid feedback to the neuro-intensivist.