The Effects of Different Methods of Anaesthesia for Laparoscopic Radical Gastrectomy with Monitoring of Entropy

Discussion

Kitano et al. first reported the laparoscopy-assisted distal gastrectomy in 1994 (3). After more than 10 years of development, the application of laparoscopic surgery in gastroenteric tumour has become increasingly common (4). However, complete laparoscopic gastrectomy is characterized by a complex operation and long duration, adverse effects on the respiratory cycle resulting from CO₂ pneumoperitoneum, and requirement for early postoperative awakening and activities of patients, etc., increasing the difficulty of anaesthesia. At present, the main clinical anaesthetic methods are TIVA and CIIA. The evaluation of the two methods have always been controversial. This is mostly because the evaluations ignore the influence of the depth of anaesthesia on anaesthetic quality and amount of anaesthetic drugs used. Therefore, this study introduced the same surgical procedure, in which SE was maintained in the range of 45-60, at the same depth of anaesthesia in order to minimize such interference, which improves the confidence level of the study results.

Among the common clinical methods for monitoring the anaesthetic depth, including bispectral index (BIS), auditory evoked potentials, entropy and cerebral state index, the entropy method has the following advantages: (i) It has good correlation with propofol, remifentanil, and sevoflurane (5-7), and is sensitive for rapid response. For instance, RE can be significantly increased about 4 min before the increase of BIS; therefore, it can replace BIS for clinical monitoring (8). (ii) Under shallow anaesthesia, entropy has rapid response to external stimulus, which will cause a stress response (9) and can be used to anticipate harmful stimuli (10). (iii) Entropy can better resist interference (11). The methods for better control of the amount of anaesthetic drugs to be used for individual patients in order to improve quality of anaesthesia and reduce medical costs are rarely reported. Sevoflurane, propofol and remifentanil are novel anaesthetic drugs that are characterized by rapid effect, short duration, and a rapid and smooth recovery. They are commonly used for anaesthesia for significantly reducing the stress response during surgery, maintaining stable intraoperative circulation and achieving rapid postoperative recovery, and hence are ideal for fast-track anaesthesia. Therefore, this study used entropy for monitoring of anaesthetic depth. During surgery, the amount of drugs may be controlled based on variations of entropy values. The results show that during the entire surgery, both groups underwent a similar depth of anaesthesia, which is a depth favourable for comparison with the SE maintained in the range of 45-60; during the perioperative period, both groups have relatively stable haemodynamic characteristics, which indicates that entropy monitoring can give guidance for rational use of anaesthetic drugs so as to avoid injury to patients due to great fluctuations in the depth of anaesthesia.

Stimuli such as trauma and surgery can cause stress responses of patients. Among these stress responses, changes in sympathetic–adrenal medulla system are most active and occur first after stimulation. As important hormones for regulating and maintaining cardiovascular functions, catecholamines are also sensitive indicators reflecting stress response (12). An ideal anaesthetic method should ensure stable haemodynamic characteristics. But more importantly, it should be able to avoid or mitigate the damage due to the stress response during perioperative periods so as to ensure infusion to important organs and homeostasis. In this study, the plasma catecholamine levels in the CIIA group were lower than those in the TIVA group at the following times: upon completion of pneumoperitoneum, intraoperative detection, and immediately after extubation, indicating that at the same depth of anaesthesia, the CIIA method can provide better sedation and analgesic effects, and suppress excessive intraoperative stress responses. This may be because in this mechanism, sevoflurane has hypnotic and analgesic effects on spinal cord (12) and it has a synergistic effect with remifentanil.

In this study, patients in both groups underwent anaesthetic and surgical procedure under the guidance of entropy monitoring. During surgery, both groups showed no significant differences regarding breathing recovery time, extubation time, and awakening time. However, regarding postoperative orientation recovery time, the CIIA group fared better than the TIVA group. This is mainly because sevoflurane can enhance the muscle-relaxant effects of muscle relaxants, extending their duration of action and clinical aging, thereby reducing the amount of muscle relaxants required (13), shortening the postoperative recovery time of muscle tension, so more conducive to patients' early postoperative recovery. Although there were reports that sevoflurane anaesthesia alone can be a major factor in the occurrence of postoperative agitation (14), in this study, patients in the CIIA group only inhaled a little amount of sevoflurane under monitoring. Therefore, the differences regarding the incidence of postoperative adverse reactions, such as agitation, nausea and vomiting, were not statistically significantly different between these groups. According to the 48-h postoperative follow-up survey, patients in both groups had no intraoperative awareness, which indicates that based on entropy monitoring, the depth of anaesthesia can be accurately reflected to prevent intraoperative awareness.

In conclusion, at the same anaesthetic depth, the CIIA method outperforms the TIVA method in suppressing stress response during and obtaining smooth awakening after laparoscopic radical gastrectomy for patients with gastric cancer; therefore, the CIIA method has a better anaesthetic effect.