Discussion
In this Prospective study of the optimal effect-site concentration of REM and propofol to keeping proper depth of anesthesia and promote early postoperation recover under PSI guided anesthesia. We found EC50 of REM at 2.96ng/mL When co-adminstration with 2.5 ug/mL propofol, the PSI, BIS, MAP and HR remained stable during anesthesia, and minimum time of extubation and staying in PACU needed.
Previous research[1, 6, 25] described in detail the importance of multimodal drugs and argued that coadministration of narcotic drugs with different mechanisms usually produces a synergies effect with theoretical advantages, multimodal medications, which can help patients recover more quickly. Compared with propofol, REM has no opioid accumulation effect, mainly used as an analgesic, had the advantage of rapid action, short maintenance time, metabolism by a specific esterase. In this study, we found that when propofol was 2.5ug/mL, the anesthesia process of patients was more stable, that is, the depth of anesthesia, blood pressure and heart rate were less needed to deal with measures. In this group, EC50 of REM could be calculated as 2.96 ng/mL by sequential method. Therefore, this can provide reference for drug concentration collocation in clinical process.
Theoretically, according to the advantages of REM, TCI 2 ug/mL propofol, the extubation time should be the shortest. However, our study showed, compared with other two groups, the patients in middle concentration group experienced the shortest extubation and PACU stay time. According to the preceding report, awakening time from anesthesia relies on various elements, involving age, sex, BMI, operation time, drugs administration[26, 27] and metabolism of muscle relaxants[28, 29]. In this study, these factors make little difference. Another research demonstrates that the increase in plasma propofol concentration was increased by coadministration of REM due to a decreased cardiac and hepatic blood flow[30], and there was a significant increase in REM in the third group, which may account for the results of this study.
Although PSI appeared later than BIS, PSI has many advantages over BIS. In this study, we found that PSI was more sensitive than BIS for the change of anesthesia depth after skin incision, which was in keeping with previous studies, PSI performs better than BIS in detecting consciousness, and less impact of the shock device on the PSI value during surgery[15]. There are several reasons account for this advantage. Firstly, unlike BIS only equipped with 4 electrodes, the SEDLine EEG sensor consists of 6 electrodes: 4 channels (R2, R1, L1, L2), 1 reference channel (CT) and 1 ground channel (CB). It can collect information from both sides of the brain to detect asymmetry in the patient’s electrical activity. Next, this algorithm is improved by considering individual background differences and brain responses of different patients to different anesthetics[12, 31]. Finally, less impact of the shock device on the PSI value during surgery.
Another advantage is that the Sedline® monitored bilateral brain function and symmetry by DSA display. DSA converts complex EEG waveforms into color-comparable EEG. Further, it can show how oscillations in EEG change over time as well as changes in anesthetic drug doses or the intensity of stimulation that could be harmful[32, 33]. A review described three types of EEG changes caused by nociceptive stimulation about general anesthesia: (1) beta arousal, (2) (paradoxical) delta arousal, and (3) alpha dropout[32]. Studies have suggested that in patients with low opioid analgesia, α activity increases, and in patients with satisfactory analgesia, α disappears[34]. In our study, under PSI guide, the concentration of propofol reduced with the required concentration of REM increased in a certain range. This phenomenon showed that sedative synergistic effect of REM was reflected from PSI values which was similar to previous studies[1, 6]. We compared the same group to rule out the effects of different doses of sedative hypnotics, the change in DSA result from REM was observed in different groups of patients. From the comparison of several groups of patients in this study, it can be seen the minimum concentration of REM group α activity increases; however δ wave did not change obviously. The result performed that DSA could help anesthesiologists evaluate sedation and analgesia level dynamically togerther with PSI value compared to BIS applied lonely.
There are some limits to the study. The selected criterias for this study were patients who scheduled for laparoscopic surgery with general anesthesia, which would entail limited stimulation and a relatively smooth operation. Most of the patients were middle-aged healthy women, and demographics and surgery itself had little impact on the results of the study. During the experiment, we made a more detailed choice of patients who needed full uterus (or attachment) removal via laparoscopy, excluding ovarian cyst removal or simple attachment removal of patients. All patients underwent laparoscopic surgeries, but differences in internal pain were observed. Two types of surgeries were relatively short in duration, which could easily cause errors in the results of data analysis. However, only patients who underwent laparoscopic surgery were selected and patients with open abdominal disease were not selected was the first limit of this study. Second, considering the influence of hepatic propofol clearance in our study, the inadequacy was that no detection of plasma concentration at the time of extubation. Besides, the brain waves of propofol were dominated by slow δ wave and α wave oscillations. In our study, REM and propofol were given simultaneously, which may affect the final conclusion. Therefore, to accurately draw the effect of REM on the EEG, further research is needed after excluding influencing factors.