Artikel
Subdural/subarachnoid air collection during surgery in the sitting position unpredictably influences MEP monitoring
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Veröffentlicht: | 8. Juni 2016 |
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Objective: Transcranial motor cortex stimulation and registration of motor evoked potentials (tcMEP) is used for monitoring of the descending motor pathways in complex intracranial and spinal intradural operations. Especially if these operations are done in the sitting position, frontoparietal collection of subdural/subarachnoid air might occur. The thereby increasing the distance from skin to cortex might hamper effective cortical stimulation and, as a consequence, MEP monitoring (“air effect”). The aim of our study was to define the incidence of the “air effect”, to find factors predicting the “air effect” and to develop a strategy how MEP monitoring could be successfully continued.
Method: Out of 414 patients undergoing surgery with neuromonitoring from 01.01.2013 until 31.10.2015, 68 were operated in the sitting position for an intradural spinal or intracranial lesion. The operation files of these patients were screened for a possible “air effect”.
Results: In 16 of 68 patients (23.5%) there was no „air effect“. 19 patients (28%) had only a short-term amplitude extinction. In 33 patients (48.5%), the amplitude extinction persisted. In these patients, the stimulation strength was increased until reaching the baseline amplitude allowing continuation of MEP monitoring in 28 patients. Nine of the 33 patients had a new postoperative deficit, which was severe in 4 and mild in 5. Amplitude reduction was bilateral in 15 patients, and unilateral in 37 patients. Uni- or bilateral “air effect” was not related to the side of the approach. No relation between time point of occurrence of the air effect and specific surgical steps especially initial dura opening could be found.
Conclusions: With 76.5 %, the incidence of the “air effect” influencing MEP monitoring during surgery of intradural spinal and intracranial lesions in sitting position is high. Its occurrence per se, the time point and the laterality is not predictable. Nevertheless MEP monitoring of the descending motor pathways in most cases remained possible despite the “air effect” by increasing the stimulation intensity directly after “air effect” detection.