脳血管障害における術中経頭蓋MEPモニタリングの有用性  [in Japanese] Efficacy of Intraoperative Transcranial Motor Evoked Potential Monitoring in Cerebro-vascular Disease  [in Japanese]

脳血管障害の手術においては,脳動脈瘤クリッピング手術におけるテンポラリークリップの使用に代表されるような一時的な脳血流遮断を行うことが多く,術中の神経学的機能,とくに運動機能のモニタリングが行われることが好ましいと考えられる.運動誘発筋電位モニタリング(MEP)には運動野を直接刺激するもの(D-MEP)と経頭蓋的な高電圧刺激によるもの(TCMEP)がある.D-MEPは,精度は高いが麻酔の影響を受けやすく,容易ではない7).これに対して,TCMEPは吸入麻酔下でも一応は可能で,電極の位置が厳密でなくても導出可能で,同時に四肢すべてのモニタリングも可能(前交通動脈瘤手術などに有用)であり,特に脳血管障害の手術における血流遮断時の運動機能モニタリングに有用であると考えられる.脳血管障害の手術におけるTCMEPのわれわれの経験を報告し,その問題点と対策を考察する.

We clinically examined the efficacy of motor evoked potential (MEP) by transcranial highvoltage electrical stimulation for intraoperative monitoring in cerebro-vascular disease. In 49 neurosurgical operations for cerebro-vascular disease, transcranial MEP (TC.MEP) was recorded by 300-1000 V bipolar stimulation using the screw electrodes with the anode on the affected side. Surface electrodes for electromyographic responses were placed on the bilateral abductor pollicis brevis (APB) and bilateral abductor hallucis (AH) muscles. To remove effects of muscle relaxants on TCMEP, compound muscle action potential (CMAP) by supra-maximum stimulation of the median nerve 2 seconds after transcranial stimulation was recorded in 30 recent operations. In all 40 operations under propofol anesthesia and 6 among 7 cases under volatile anesthesia, MEP was successfully recorded. Postoperative motor paresis occurred in 6 limbs of 4 patients among 54 limbs of 30 patients who had received TCMEP compensated by CMAP by peripheral nerve stimulation and all compensated relative amplitude indexes (CRAls) of these 6 limbs were less than O.2. In contrast, in all 48 limbs of 26 patients who had no postoperative motor dysfunction, CRAI had been more than 0.2. These results suggest that our intraoperative TCMEP monitoring by relatively low-voltage (300-400 V) stimulation and compensated by CMAP after peripheral nerve stimulation was safe, easy (no need to expose the motor cortex), relatively accurate and less invasive, and useful especially in cerebrovascular disease, which often requires a temporary occlusion of the cerebral arteries.