The Role Of Sleep Spindles In Monitoring Of Nociception During General Anesthesia

Objective:Quantifying the nociception during general anesthesia objectively has become a major scientific issue due to the significant individual differences in nociception was observed and the effective biomarkers for the monitoring of nociception remain uncertain.Electroencephalography（EEG）has the characteristics of non-invasiveness and high temporal resolution which has shown its potential in nociception monitoring in general anesthesia.In this light,this study aimed to identify the EEG changes（alpha,beta,delta band and sleep spindle oscillations）associated with nociception during general anesthesia and clarify the underlying mechanism.Methods:（1）A total of 56 patients undergoing selective hysteroscopes under general anesthesia were recruited at Union Hospital,Tongji Medical College,Huazhong University of Science and Technology.Perioperative EEG,electromyography（EMG）and hemodynamic were recorded.Patients were divided into two groups according to whether there was intraoperative EMG arousal（representing nociception）to identify the EEG and hemodynamic changes associated with nociception.（2）To further validate the clinical findings,incisional pain,visceral pain and inflammatory pain models under the existence or absence of analgesia were employed to examine the EEG changes induced by nociception during general anesthesia in male C57BL/6J mice.In addition,non-noxious stimulation and gradient mechanical/visceral stimulations were established to evaluate its specificity in nociception and the correlation between the degree of relative changes and nociception.（3）Mice were randomly divided into hyperpolarization-activated cyclic nucleotide-gated（HCN）2-channel shRNA group and NC shRNA control group.HCN2-adeno-associated virus microinjection was performed to knock down the expression of HCN2channel of thalamocortical（TC）neurons to investigate the role of HCN2 channel in sleep spindle density oscillations changes induced by nociception under general anesthesia.Results:（1）Of the 56 patients,5 patients were excluded for incomplete EEG recordings.In total,the data of 51 patients were analyzed subsequently and 30（58.8%）patients exhibited EMG arousals.No significant difference was observed in age,body mass index,operation time,mean arterial pressure（MAP）and heart rhythm（HR）between the two groups（P>0.05）.Compared with the absence of EMG arousal group,patients with EMG arousal showed a significantly lower sleep spindle density during operation（P=0.030）.In addition,significant differences were observed in the relative change rate of sleep spindle density（P=0.004）,alpha band power（P=0.002）and HR（P=0.005）within two groups.However,no significant change was found in sleep spindle duration（P=0.145）or its relative change rate（P=0.348）.Furthermore,the binary Logistic model constructed based on the above results showed an apparent deviation from the diagonal and had an area under the curve of 0.87.（2）Without analgesia,the HR increased（P=0.002）and sleep spindle density decreased significantly（P=0.002）,with the sleep spindle duration unchanged（P=1.000）after incisional pain model was performed.Subsequently,sufentanil treatment could reverse the increased HR（P=0.005）and decreased density（P=0.043）significantly.Similar results were observed in visceral and inflammatory pain models.However,the three pain models had no significant effect on sleep spindle oscillation and HR of mice with sufficient analgesia（P>0.05）.Non-noxious stimulations made no difference to sleep spindle oscillation,evidenced by no changes detected in its density and duration（P>0.05）.At last,the sleep spindle density gradually decreased with the nociception intensity increased,further analysis showed a remarkable negative correlation between sleep spindle density and intensity of nociception.（3）HCN2 shRNA microinjection significantly reduced the expressions of HCN2channel in TC neurons（P<0.001）.The righting reflex test showed no significant difference in ED₅₀ of propofol between the two groups（85.5%overlapping confidence interval）.Compared with the NC shRNA group,the sleep spindle density in the HCN2shRNA group was significantly increased after general anesthesia（P=0.035）,with its duration unchanged.After the incisional pain model was established,the NC shRNA group exhibited a greater decline in sleep spindle density compared with the HCN2shRNA group（P=0.004）.Conclusions:（1）The changes in sleep spindle density can be considered an objective indicator of nociception during general anesthesia.（2）The decrease in sleep spindle density is associated with intraoperative nociception,it is specific to nociception,and shows a remarkable negative correlation between sleep spindle density and intensity of nociception.（3）The underlying mechanism may be related to the excessive activation of HCN2channels in TC neurons induced by nociception,thereby prolonging the refractory period of sleep spindles.