Intraoperative Neurophysiological Monitoring for Endoscopic Transforaminal Lumbar Spine Surgery under General Anesthesia

Percutaneous transforaminal sequestrectomy (PTFES) under endoscopic guidance has proven successful for decompressing lumbar motor nerve roots at the level of the neuroforamen. Nevertheless, nerve root injury is the major complication of this method. For this reason, PTFES has thus far been performed under local anesthesia so that the patient may be questioned about signs of nerve root irritation. A viable alternative seems to be a set-up with the patient under general anesthesia but with the „guidance and control“ of intraoperative motor nerve root monitoring (IOM). Twenty-five patients with an intra- or extraforaminal lumbar disc herniation (IHLD/EHLD) were surgically treated by PTFES under general anesthesia and IOM. There were 6 IHLD, 4 EHLD and 15 combined intra- and extraforaminal HLD. Two of them were at L2/3, 9 at L3/4 and 14 at L4/5. Total intravenous anesthesia was performed using remifentanil and propofol. Neuromuscular blocking agents were used only for intubation but not during surgery. Motor nerve root activity was recorded by free-run EMG for the nerve root exiting through the intervertebral foramen at the level of surgery as well as the ones immediately cranial and caudal to it. The nerve root was visible through the endoscope in 17 cases (68%), covered by intraforaminal fat in 3 cases (12%) and dislocated by the herniated disc in the remaining 5 cases (20%). EMG monitoring was completely uneventful in 7 of the 25 cases (28%). Three cases (12%) already had spontaneous EMG signals in terms of fibrillation potentials before the actual procedure began. Pathological EMG activity in the form of bursts was observed in 12 (48%) cases. Endoscope placement through the foramen caused single or non-repetitive asynchronous EMG activity in 11 cases (44%). Tonic train activity was recorded in 6 cases (24%). The operation was interrupted immediately when burst or train activity occurred. EMG activity was normalized in all cases by modifying the surgical technique. PTFES under IOM guidance is a safe and easy-to-perform technique if combined with intraoperative neurophysiological monitoring techniques. It has the following advantages for the patient: (a) immediate postoperative mobilization, (b) minimal surgical trauma, (c) minimal operation-induced instability and (d) excellent cosmetic results. General anesthesia reduces intraoperative stress to a minimum, thus enabling patients to derive full benefit from this minimally invasive procedure.