**3. SNUH Experience**

Our group have been implementing STN DBS under LA since 2005 initially under sedation using propofol and fentanyl from 2011 to 2014 [93], and under full GA since 2014. To determine if there is a di fference in the clinical outcome of PD patients who received bilateral STN DBS under LA and GA, we compared the clinical outcomes of the consecutive 57 patients who received bilateral STN DBS under LA from 2005 to 2006 and consecutive 90 patients who received bilateral STN DBS under GA from 2014 to 2019. Because our group previously published a study on the clinical course and electrode location of patients who received bilateral STN DBS under LA [114,115], these patients were included for the comparison. After approval by the institutional review board (IRB No. 1904–015–102), we retrospectively reviewed all patient medical records and databases (unpublished data). The scales that evaluated patients were as follows: UPDRS, Hoehn and Yahr (H&Y) Staging, Schwab & England ADL, dyskinesia disability, LEDD, Short Form-36 Health Survey (SF-36), and neuropsychological tests. All clinical evaluations were performed before surgery and 6 months after surgery by experienced neurologists. Patients were evaluated in both o ff- and on-medication states, respectively.

STN DBS under general anesthesia was performed with maintenance of the BIS around 60-70, and MER was administered under general anesthesia. The characteristic discharges of the bilateral STN were identified using MER by LeadPoint (Medtronic, Minneapolis, MN). The permanent quadripolar electrodes were implanted along the proper trajectory to stimulate more sensorimotor region of the STN. The STNs were localized by a combination of brain MRI and intraoperative MER. We did not use an intraoperative macrostimulation technique [15]. The stereotactic frame was removed and the implantable pulse generators (IPG) (Medtronic, Minneapolis, MN, USA) were implanted in a subcutaneous pocket below both clavicles under general anesthesia in a single session. Electrical stimulation was started one day after surgery. The patients also took medications but at a reduced dose compared to their previous dose. The medications and stimulation parameters were progressively adjusted using an Nvision1programmer (Medtronic, Minneapolis, MN, USA) according to the clinical status of the patients.

Statistical analyses were performed using SPSS software (SPSS statistics 18.0; SPSS Inc.). The data for the aforementioned variables were presented as the mean ± standard deviation using unpaired Student t tests. Mann–Whitney U-test and the Wilcoxon signed-ranked test were used for categorical data comparisons as appropriate. *p* values < 0.05 were considered statistically significant. Table 5 represents the patient characteristics and clinical scales of LA and GA cohort before DBS surgery. At baseline before surgery, the GA cohort showed higher LEDD, Beck's Depression Inventory (BDI), and Short Form-36 (SF-36), and lower Beck Depression Inventory than the LA cohort. Table 6 shows the comparison between baseline and 6 months after DBS for each scale in LA and GA cohort. Total UPDRS and UPDRS III showed significant improvement after 6 months compared to baseline, except for LA cohort in on-medication state. H&Y stage and ADL score showed no significant change in the on-medication state in both GA and LA, and significantly decreased in the o ff-medication state. Dyskinesia disability and LEDD were significantly decreased in both GA and LA cohort. There was no significant change in Mini Mental State Examination (MMSE) and BDI after surgery in both groups. Physical health measured by SF-36 increased in both LA and GA cohort, and mental health showed no statistically significant increase. When analyzing the di fference between the LA and GA cohort in the baseline of each item and the change after 6 months, only LEDD showed a significant di fference (*p* < 0.0001). As shown in Figure 1, the degree of reduction in LEDD was greater in the GA cohort than in the LA cohort. We plotted the electrode location in each group based on the plotted position of the electrode in the axial view which is 3.5 mm below the anterior commissure(AC)-posterior commissure(PC) line in the human brain atlas of Schaltenbrand and Wahren (Figure 2). The electrode location on both sides in the LA group (n = 56) were as follows: both within STN (n = 30, 53.6%), only one within STN (n = 18, 32.1%), and both outside STN (n = 8, 14.3%). It was as follow in the GA group (n = 90): both within STN (n = 69, 76.7%), only one within STN (n = 20, 22.2%), and both outside STN (n = 1, 1.1%). There was a significant di fference in the electrode location on both sides between the two groups (*p* = 0.001). Compared to the LA cohort (Figure 2A), the GA cohort (Figure 2B) showed a higher tendency for the electrode to be located within the STN. However, it should be interpreted in consideration of the fact that our group performed DBS surgery under LA in the early days, and under GA after more experienced. As intra- or postoperative complications, one revision and one infection occurred in LA cohort. One patient required revision surgery after 2 months due to inappropriate lead location. The other patient had IPG site infection, which improved after antibiotics treatment. In our center, postoperative MRI was taken 1 month after electrode implantation, so we cannot find post-electrode edema (PEE) in most cases. As recent studies have revealed that PEE is not simply a complication due to venous congestion and has no significant relationship with the number of tracks, further studies on the occurrence pattern of PEE under GA would be required [116–119].


**Table 5.** Patients' characteristics and clinical measurements in patients who underwent bilateral subthalamic nucleus deep brain stimulation under local and general anesthesia.

> \* *p* < 0.05.

**Table 6.** Summary of clinical outcomes of bilateral subthalamic nucleus deep brain stimulation under local and general anesthesia.



**Table 6.** *Cont.*

\* DBS on, \*\* between baseline and follow-up, \*\*\* between two groups: general and local anesthesia.

**Figure 1.** Comparison of clinical outcomes between baseline and 6 months after STN Deep brain stimulation (DBS) under local anesthesia (LA) and general anesthesia (GA) each cohort. ( **A**) Total Unified Parkinson's Disease Rating Scale (UPDRS) and (**B**) UPDRS part III showed significant improvement after 6 months compared to baseline, except for LA cohort medication on state, there was no statistically significant di fference between LA and GA cohort. ( **C**) Hoehn & Yahr stage and ( **D**) Schwab & England

activities of daily living (ADL) showed no significant change in the medication on state in both LA and GA cohort, and no significant difference between two cohorts. (**E**) Dyskinesia disability and (**F**) Levodopa equivalent daily dose (LEDD) were significantly decreased in both LA and GA cohort. Only LEDD showed a significant difference in the change between LA and GA cohort. (**G**) Mini Mental State Examination (MMSE) and (**H**) Beck's Depression Inventory (BDI), showed no statistically significant decrease in both LA and GA cohort. (**I**) Short form -36 (SF-36) physical health and (**J**) Short form -36 (SF-36) mental health showed no statistically significant increase in both LA and GA cohort.

**Figure 2.** Plotting of the electrode location based on the plotted position of the electrode in the axial view which is 3.5 mm below the anterior commissure (AC)–posterior commissure (PC) line in the human brain atlas of Schaltenbrand and Wahren. (**A**) Local anesthesia (LA) cohort, (**B**) General anesthesia (GA) cohort. Compared to LA cohort, the GA cohort showed a higher tendency for the electrode to be located within the subthalamic nucleus (STN).
