PEID is an effective and alternative surgery for the treatment of L5/S1 lumbar disc herniation and even for special cases of L4/5 disc herniation, since this procedure could be easily carried out by spinal surgeons with extensive experience in open surgery and local anatomy. In comparison with percutaneous endoscopic transforaminal discectomy (PETD), the wide space between the L5/S1 interlamina makes it easy to enter the spinal canal, decompress the nerve root and remove the protruded disc.14,15 However, the operating procedure involves entering the spinal canal and retracting the nerve root directly, potentially causing postoperative complications. Commonly, most spinal surgeons prefer to perform PEID to treat L5/S1 disc herniation, while other physicians, such as pain specialists and interventional radiologists, always select PETD for all types of lumbar disc herniation, even those with high iliac crests. In our department, PETD is mostly applied to treat far lateral disc herniation at the L5/S1 level. In regard to long-term clinical efficacy, PEID and PETD do not seem to always differ significantly. 16
Both PETD and PEID, other than the method of anesthesia, truly reflect the nature and techniques of minimally invasive surgery (MIS) in the treatment of degenerative diseases. Endoscopic discectomy is a complicated procedure that relies heavily on patient feedback during surgery. This goes for both the transforaminal approach and the interlaminar approach. General anesthesia has been widely adopted in almost all spinal surgeries due to the ease of controlling vital signs. Nonetheless, general anesthesia also has obvious drawbacks, such as no timely feedback while the patient is unconscious, as well as a higher requirement regarding the skills and experience of surgeons. 17 Relevant studies showed GA may have greater risk of neurological complications, rendering patients unable to cooperate with the surgeon. 17 Compared to those of PETD, the complications of PEID are much more troublesome and serious. 18 Since the spinal canal is opened and the dura matter or nerve root must be retracted during the surgical procedure, complications such as dural avulsion, nerve root damage, and epidural hematoma are more likely to occur 19. In this study, a total of 3 patients among the 29 patients in group GA experienced neurological deficits after the operation, which is as higher proportion than that in the other two groups. Possibly, the lack of a significant difference could be attributed to the small amount of sample. However, the occurrence of nerve injury in patients in group GA, highlights the potential importance of real-time intraoperative patient feedback within these procedures. In the early stage of learning PEID under general anesthesia, junior surgeons might have difficulty in distinguishing nerve root from the surrounding tissue accurately. Although under endoscopic view, the process of inserting working cannula (with an external diameter of 6.9 mm or 6.3 mm) through the ligament flavum and relocating the instrument in the spinal canal might tear the dura directly. Sometimes, to dissect the far migrated discs, the nerve root or dura would be roughly handled and prolonged or strenuously retracted without any reaction from the patients. Fortunately, all 3 patients recovered well after 3 months. Based on our experience, any steps or movement toward the nerve roots should be careful and slow enough to establish a “more controlled” environment and avoid damage because there are no subjective responses from unconscious patients during the operation. Consequently, the operation time and duration of anesthesia increased with the use of general anesthesia (58.75 ± 5.98 minutes, Table 2), and thus, anesthetic accidents or postoperative nausea and emesis are more likely to occur in patients with poor physical condition.20 Mostly, intraoperative neurophysiological monitoring should be considered if general anesthesia is applied, and that may raise treatment expense (data not shown).
Local anesthesia has always been employed by pain specialists and interventional practitioners for the purposes of reducing the risk of nerve injury 21. During this procedure, patients can provide instant feedback on their feelings and communicate their physical information to the doctor, especially any sensations of temporary and sharp pain 22.However, sometimes the sharp pain and agitation could disturb the progress of the surgery (54.23 ± 7.32 minutes, Table 2) and increase the mental burden on surgeons, especially inexperienced novices, because they are always worried about nerve damage while progressing through the procedure, and thus the procedure may have to be stopped.23 In fact, the patients usually had a poor surgical experience under local anesthesia, but the surgeon also usually experienced unpleasant challenges.
For spine surgeons and beginners in the early period of learning PEID, in order to minimize discomfort and pain and allow for real-time communication by receiving continuous feedback from patients to prevent neural damage and help monitor clinical improvements during the operation, we attempted a modified anesthesia method with the assistance of the sensation-motion separation effect of ropivacaine and synergistic effect of sufentanil to maintain a condition of consciousness, painlessness and freedom of movement during the operation. Patients could also move their lower limbs when the surgeons required to identify nerve injury. On the other hand, literatures have suggested the concentration of ropivacaine played important role in the alleviation of pain 24. Kathuria 25 and Zhu 26 et.al separately reported that low concentrations of ropivacaine such as 0.25% or 0.375% could only block the sensory nerves without motor nerves being completely blocked, thus had better effectiveness in pain management when used in EA. Previously we tried different concentrations of ropivacaine according to the body condition of various patients with the help of anesthesiologists, and the concentrations ranged from 0.1–0.375%. For most patients, ropivacaine of 0.2% or 0.25% could be the ideal concentrations and 10 ml total would be a satisfactory volume. Another advantage of MA was the ease in controlling the dosage of anesthetics. Nevertheless, attention should also be paid to individual diversity in pain and drug responses, as well as nerve root anomalies.
It is not surprising that patients undergoing spinal anesthesia had a better intraoperative experience than patients received local anesthesia. Of the 29 patients who received MA, we obtained a satisfactory result that all patients achieved free movement of the lower limbs, and simultaneously did not complain about severe pain (with intra-VAS score of 2.62 ± 1.29, Table 3). Since no difference was identified in the type and location of protrusions (Table 1), the difference in intraoperative pain intensity between groups LA and MA was not associated with operational discrepancies between individuals. Only one patient had lower limb paresthesia, which was found to be caused by an excessive concentration and dosage of anesthetic injection in the attempt to obtain a satisfactory painless condition at the early stage, and the disorder subsided 6 hours later. By receiving indispensable feedback and avoiding unnecessary distractions from the patients, the surgeon could complete the operation in a more leisurely manner, which could explain why the operation period in group MA was significantly shortened (P < 0.001 vs GA and LA).
Another noteworthy matter was the similar recovery rate after surgery in the MA and LA groups. Because of the efficacy of sensation-motion separation and faster metabolism of anesthetics, patients under MA could be resuscitated more quickly from anesthesia than patients under GA, and could immediately cooperate with the routine examination of lower limb activity after leaving the operating table, and thus could return to the wards faster (Table 2). Ye et.al 27 also demonstrated a higher score of postoperative cognitive function in patients received PELD under epidural anesthesia than GA group, suggesting that epidural anesthesia had positive significance for the improvement of cognitive function. In the current study, the ambulation time in group MA, as well as that in group LA, was obviously shorter than that in group GA (P < 0.001). Moreover, vital signs were usually monitored and evaluated for 24 hours before discharge for those who received general anesthesia. Hence, the length of hospital stay in group GA was prolonged (P < 0.001 vs LA and MA).
With regard to the reoperation rate in this study, only one patient in group GA received revision surgery at 2 months postoperation because of a fall while intoxicated, which made it difficult to analyze if there were statistically significant correlations between reoperation rate and different anesthesia method for PEID. Previous studies have suggested that the incidence of recurrence was 5.5% after PEID with annular sealing and 13.5% after PEID without annular sealing, and age was correlated with overall recurrence and late recurrence, whereas operative technique only correlated with early recurrence.22 Noteworthy, here we identified no significant difference in the recurrence rate among the three groups, and the reason for the low reoperation rate in this study may be due to the relatively small sample size and short follow-up period.
In addition, postoperative dysuria is side effect of excessive EA which need to be considered 17,28. Even though that didn’t occur in this study and was reported to normally disappear in hours. In the case of MA, an experienced anesthesiologist is recommended to avoid spinal cord damage/cauda equina damage and for control sensory-motor separation.
According to the current findings, for spinal surgeons who are inexperienced with PEID to treat L5/S1 disc herniation, MA would be superior choice because of its effectiveness in avoiding nerve root injury, increasing the pain tolerance and easing the anxiety of the beginner surgeons, as well as speeding recovery. Our practical experience is, that LA is suggested to be applied once the doctors have gained sufficient operational experience of various endoscopic surgeries in more than 100 cases and have less fear of distractions from patients. After attaining sufficient endoscopic operational experience in more than 200 cases, the surgeon could perform endoscopic surgery perfectly and deal with complex situations, and GA would be more proper for PEID.
Limitations
Retrospective design of the study, limited cases are the main inherent defects which may lead to biases. A larger sample size is needed to corroborate the favorable effect of MA in PEID for treating L5/S1 LDH.