Chronic subdural hematoma (CSDH) is a common neurosurgical disease, and the increase is shown as the population aging nowadays. Studies have predicted that CSDH will become the most common brain disease among adults by 2030 (1, 2). When individuals with CSDH develop evident clinical symptoms, conservative therapy is relatively ineffective and surgery is often the only option (3). At present, the main methods of operation for CSDH are craniotomy, twist drilling drainage, and burr hole surgery (4–6). Burr hole surgery is the most effective and simplest method of removing CSDH (7). Previous CSDH research has tended to focus on surgical approaches (7–10), but there have been few investigations on intra-operative anesthetic procedures. For CSDH burr hole surgery, there are two basic forms of anesthesia: local anesthesia (LA) (11) and general anesthesia (GA) (12). Elderly patients carry a higher perioperative risk and are associated with worse outcomes in CSDH (13), therefore, the choice of anesthesia mode is very important for elderly patients (11). However, there is no clear conclusion about how these two kinds of anesthesia impact the surgical procedure and recovery of patients; or which type of anesthesia is more suitable for CSDH burr hole surgery. The goal of this study was to explore the most suitable and effective anesthesia mode for the surgical operation and rehabilitation of patients with CSDH.

This study was approved by the Institutional Review Board of Second Affiliated Hospital of Shantou University Medical College. For the retrospective nature of this study, obtaining informed patient consent was no more required.

A total of 132 patients with CSDH, who underwent burr hole surgery between 1^st January 2013 and 31^st December 2018, were enrolled in this study (Figure 1). Following the exclusion of 27 individuals who did not meet the criteria, 105 individuals with unilateral CSDH were found to be eligible. Among them, there were 51 patients in the LA group and 54 patients in the GA group. The differences were not significant in age, sex, preoperative GCS score, CT value, side of hematoma, hematoma volume, and underlying diseases between the two groups before treatment (P > 0.05), as shown in Table 1. The preoperative symptoms of the patients in both groups are mentioned in Table 2. The most common symptoms of the patients included headache, dizziness, and weakness of limbs, slow reaction time, mental fatigue, vomiting, and slurred speech (Table 2). There were no significant differences in common symptoms of the patients between the two groups (P > 0.05).

In both groups, the operations were completed smoothly and successfully. No initial LA patients had to be switched to GA due to their uncooperative behavior. The anesthesia and operation time of the LA patients was 37.71 (10.55) min, and that of GA patients was 56.04 (8.37) min; the difference being statistically significant (p < 0.001). The time duration from operation to discharge in the LA group was 8.51 (1.49) days, which was significantly shorter than that in GA patients [10.46 (2.34) days; p < 0.001]. The total cost of hospitalization for LA patients was 2,721.54 (504.66) USD, which was significantly less than that for GA patients [3,314.82 (493.52) USD; p < 0.001]. The retention time of the head drainage tube in the LA group was shorter than that in the GA group [(2.55 (0.88) days vs. 3.04 (0.89) days, respectively; p = 0.006]. The number of patients with residual hematoma in the LA group was less than that in the GA group (p = 0.014). However, significant difference between the two groups was not found between the two groups in recurrence rate (p = 1.000) (Table 3).

The main complications observed in the GA group were nausea and vomiting, dyspnea, pneumonia, delayed awakening, and restlessness. While the major complications in the LA group patients were nausea and vomiting, poor wound healing, and brain tissue injury by drainage tube insertion. There were only six cases of complications in LA patients, which has a significantly smaller amount than that of GA patients (p < 0.001) (Table 4). After surgery, all of the patients were released with improved symptoms, and no deaths were reported in any of the groups.

From this current study, it was found that burr hole surgery performed under assisted local anesthesia is safe and more beneficial for patients with CSDH, which was consistent with Seizeur's research (11). Duration of operation (including anesthesia and operating time) in the LA group was much shorter than that in the GA group. The explanation for it is that anesthesia in the LA group does not require continuous intravenous administration of anesthetics to keep the patient sedated, analgesic, and unconscious. As a result, there is no need for anesthetic induction and recovery, as well as tracheal intubation and extubation. Due to residual anesthetics and hemodynamic changes produced by anesthetics, postoperative problems in the GA group were substantially greater than those in the LA group. This study found that patients in the GA group had more respiratory depression and pulmonary infection than those in the LA group. Six patients in the GA group experienced dyspnea after surgery, two of which were due to secretion reflux inhalation into the respiratory tract (the secretion was difficult for patients to cough out); three were due to glossoptosis with the tongue obstructing the throat; and one was due to difficulty in tracheal intubation, where repeated stimulation resulted in laryngeal spasms and also led to a postoperative sore throat. Although the complications of GA, such as airway obstruction and respiratory depression, are mostly reversible, and not all patients will progress to pulmonary infection; the occurrence of similar complications will increase the risk of patients' prolonged hospitalization time suffering and increase their hospitalization costs.

Previous studies revealed that some patients have delayed awakening, hallucinations, mania, and other restless phenomena when GA was administered due to the residual anesthetics (16, 17). In this study, four patients in the GA group had delayed recovery and restlessness after surgery; nausea and vomiting were also common amongst this group. The most common cause of postoperative vomiting is anesthesia side effects and aspiration of vomit is typical, resulting in respiratory obstruction. Blood pressure fluctuations before and after surgery, as well as arrhythmia, are typical problems in GA patients (18). It has also been reported that a high-dose combination of propofol and remifentanil during anesthesia can decrease blood pressure and heart rate, and cause hypoxia and respiratory arrest, which increase the risk of death (19). During this study it was observed that patients in the LA group had no difficulty in breathing, no restlessness, no delayed awakening after the operation; and only a few patients had nausea and vomiting as compared to the GA group. LA patients were also not at risk for airway injury and pain because they do not need to receive tracheal intubation. As LA treatment does not include muscle relaxants or sedatives, these individuals are not at risk for respiratory depression or deleterious effects on blood circulation or gastrointestinal function. In addition, the earlier post-surgery independence of eating and movement also guaranteed better recovery for the patients.

The hospitalization time of the LA patients was significantly shorter than that of the GA patients, which has ultimately reduced their hospitalization costs and the risk of hospital infection. So, LA is particularly suitable for elderly and infirm patients with multiple disorders as well as patients who do not wish to undergo surgery using GA. In contrast to patients with GA, patients with LA can cough to promote hematoma discharge if the hematoma discharge is unsatisfactory during the surgery, which explains why the LA group has fewer patients with residual hematoma after the surgery.

To date, only a few reports are investigating CSDH removal under local anesthesia (20–22). A recent study showed that a series of patients with unilateral and bilateral CSDH successfully underwent burr hole surgery under LA in the sitting position, indicating that LA is safe for the patient with CSDH, even for bilateral CSDH (22). It was found that midazolam sedation combined with LA can achieve the same anesthetic effect as GA during mini-craniotomy of CSDH (21). However, the sedatives employed in the aforementioned method might cause respiratory and cardiac side effects, as well as restlessness and unwillingness to co-operate in some patients during the operation (20). An increased dose of sedatives to calm down such patients may result in deep sedation, respiratory depression, and other complications. Ultimately, some patients may be required to switch to GA with tracheal intubation. The second study showed that three of the patients could not cooperate with the operation under LA combined with sedation, and one of them had to be switched to GA with tracheal intubation; whereas, the other two patients needed a laryngeal mask to be inserted to relieve dyspnea. The failure rate of dexmedetomidine combined with LA for CSDH burr hole surgery was found to be 7.9% (12). Such change from LA to GA with intubation during the surgery makes the whole operation procedure very passive. It delays the operative time and might also cause intracranial or incision infection combined with other complications, causing potential risks to patients.

Most of the patients in this research showed residual hematoma on a CT scan after the operation. However, CT reexamination revealed that most of the residual hematomas were gradually absorbed, with just a few patients requiring reoperation. Previous studies have found that placing a drainage tube under the subgaleal space can play a positive role in draining a hematoma (23), indicating that residual hematomas may flow out of the dural break and gradually infiltrate into the subgaleal space for absorption when brain pulsation and body position changes. Hence, enlarging the incision of the dura mater and hematoma capsule may promote hematoma discharge. Furthermore, the direction of the small infusion tube used during the operation can be changed more flexibly in the hematoma cavity and reach the depth of the hematoma cavity easily, making it more effective to wash out the hematoma than to wash the hematoma cavity directly with a large external drainage tube. During this study, three cases of brain tissue injury caused by the insertion of the drainage tube were reported, as the hematoma cavity was small, making it difficult to insert the tube. To avoid such injury, saline solution was injected to expand the hematoma cavity to aid in drainage tube insertion. A recent randomized clinical study has shown that subperiosteal drain (SPD) is considered to be safer as drain misplacement rates were lower, owing to SPD is not positioned in direct contact to cortical structures (9).

There are still some limitations to this study. Firstly, the patient number in the current study who underwent treatment was too small, which weakened the conclusion of this study that local anesthesia is a safer and more effective anesthesia method than general anesthesia for burr hole surgery of CSDH. Secondly, the major limitation of this study is the retrospective nature, which might lead to a risk of bias. Since this study is a preliminary study from a single center, further multi-center randomized clinical trials should be established with a better follow-up system in order to get more precise conclusions.

From this retrospective study, it was found that CSDH burr hole surgery using local anesthesia might shorten anesthesia and operation time, and hospitalization time, less postoperative complications; ultimately reducing hospitalization costs of the patients as compared to surgery using general anesthesia. It seems that CSDH burr hole surgery using local anesthesia might be beneficial for unilateral CSDH patients with a GCS >12. Further research is still required to confirm this conclusion.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving human participants were reviewed and the present study was approved by the Institutional Review Board of Second Affiliated Hospital of Shantou University Medical College. Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.

JL and AL: conception and design. ZC and JZ: acquisition of data. ZC, HC, BC, and JZ: analysis and interpretation of data. JL and ZZ: drafting the article and critically revising the article. All authors contributed to the article and approved the submitted version.

This study was supported by the Natural Science Foundation of Guangdong Province of China [Grant No. 2021A1515011179] and Science and Technology Planning Project of Guangdong Province of China [Grant No. 2021(88)-4].

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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