With the improvement of surgical techniques and equipment, PELD has become one of the most common minimally invasive surgeries in spinal surgery practice. Since most surgeons are accustomed to performing posterior spine surgery and are familiar with the anatomy of the posterior spine, PELD via the interlaminar approach is more acceptable to most surgeons than the transforaminal approach.
For lumbar disc herniation at L5/S1, the interlaminar approach takes advantage of a natural anatomical feature (a relatively large interlaminar space), and provides minimally invasive and targeted decompression for the prolapse or sequestration of the nucleus pulposus in the spinal canal. Compared to the transforaminal approach, PELD via the interlaminar approach resulted in greater retraction and manipulation to the dural matter and nerve, which can cause uncomfortable pain and hinder the operation. Thus, most surgeons prefer to perform the endoscopic discectomy through the interlaminar approach under GA. However, GA requires preoperative fasting and is associated with slower recovery and more medical expense.
Several authors have compared the effect of GA and LA on the clinical outcome of PELD via the interlaminar approach. Ye et al included 60 patients with lumbar disc hernia who were treated with PELD with an interlaminar approach.11 At each follow-up of 3, 6 and 12 months after surgery, there was no significant difference in ODI and VAS scores between GA and LA. However, 1 patient in the GA group had intraoperative nerve root injury. There were 2 cases of adverse reactions in the LA group and 6 such cases in the GA group. From the perspective of the intraoperative anesthesia effect, compared with the 100% satisfaction rate of the GA group, only 50% of the patients in the LA group were satisfied with the anesthesia effect. Another study performed by Chen et al included 123 patients with L5/S1 disc herniation.12 They also observed a similar improvement of neurological function; however, one patient developed dural laceration and nerve root injury intraoperatively in the GA group. Transient sensory disturbance was observed in 22 patients (12 in the GA group and 10 in the LA group). Thus, the authors concluded that LA is superior to GA for PELD via the interlaminar approach. Notably, they also found that, although patients in the LA group tolerated the procedure, they experienced varying degrees of discomfort during the operation. This led to further modification in the technique for LA by the two authors. Guan et al. injected the lidocaine into the epidural space with a long needle under endoscopic monitoring.13 Among the reported 120 patients, only one patient developed postoperative cognitive dysfunction (within the GA group). A lower intraoperative VAS score and higher satisfaction reflected the advantages of LA over GA. Unfortunately, however, this study does not mention local anesthetic-related adverse reactions or surgery-related complications, making it difficult to accurately assess the safety of PELD under LA.
Wu et al proposed a technique called stepwise local anesthesia that consists of conventional local anesthesia, epidural injection, and nerve root block procedures, and reported that the anesthetic effect was excellent/good in 97.9% (47 patients) of patients of the stepwise local anesthesia group.14 Nine patients experienced complications associated with local anesthesia, including dyspnea, temporary paresis of the legs, and temporary worsened dysesthesia or numbness in the legs.
Except for Chen et al.,12 who did not elaborate on specific anesthetic drugs, the other three studies reported the specific composition of the LA anesthetic drug.11,13,14 The duration of anesthesia with a single dose of lidocaine may not be long enough for PELD. Instead of using lidocaine alone,13 a mixture of ropivacaine and lidocaine was applied in the Ye et al and Wu et al studies.11,14 We also added ropivacaine with a longer half-life to enhance the anesthetic efficacy and extend the duration of anesthesia. Additionally, the advantage of ropivacaine is that a low concentration of ropivacaine can perform selective sensory blockade and maintain the motor function of neurons, so that nerve function can be monitored in real time through intraoperative lower limb movement.15
We disagree with Wu et al. 's reference to the technique of nerve root block, during which the needle tip is penetrated into the nerve root under endoscopic view.14 Intraneural injections can accelerate the occurrence of nerve block, increase the success rate, and prolong block time.16,17 However, it has also been reported that intraneural injections may cause iatrogenic neurological injury and functional deficits.18–20
Wu et al recommended that, if LA is not satisfactory, nerve root injection can be repeated until the pain is satisfactorily controlled.14 It also suggests that the previous two-step anesthesia may not be as effective. Moreover, repeated administration of the anesthetic compound is the main cause of overdosage, thus increasing the possibility of anesthetic-related adverse reactions. In our modified formula for an anesthetic drug compound, the saline solution is reduced from 30 mL to 20 mL and the anesthetic concentration is increased. The effect of local anesthesia could be enhanced temporarily by injecting 5 mL of lidocaine before the ligamentum flavum is opened. Otherwise, the injected drug will be quickly washed away by the irrigating water, leading to sub-anesthetic results. The total amount of anesthetic is within a safe dose, which greatly reduces the adverse reactions associated with local anesthetics. That explains why there were no adverse reactions in our case series. Although the drug was injected into the epidural space without endoscopic monitoring, dural rupture caused by puncture did not occur because the puncture point was chosen at the central area of the interlaminar space of L5/S1, close to the spinous process. Anatomically, the widest part of the epidural space is in the midline below the spinous process, known as the posterior epidural space. When the disc is protruded, the epidural space plays a compensatory role, reducing the mechanical compression of the nerve root. However, the posterior epidural space is usually the last to be compromised. Thus, epidural administration in this area is quite safe and there is no intraoperative dural puncture injury or occurrence of total spinal anesthesia.
In terms of the efficacy of intraoperative anesthesia, all patients had intraoperative satisfaction scores greater than 7 points, indicating that LAC induces satisfactory pain control throughout the whole surgery. Based on the ideal anesthetic effect, all patients completed thorough neural decompression and achieved significant improvement in symptoms compared with their preoperative symptoms.
The main limitation of our study is the retrospective non-randomized controlled study design. Further studies with a high level of evidence are needed to compare the benefits and safety of gradient local anesthesia with GA for PELD via the interlaminar approach.