Craniofacial Electromyogram Activation Response: Another Indicator ofAnesthetic Depth

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• 作者：Dutton ; Robert C. ; Smith ; Warren D. ; Bennett ; Henry L. ; Archer ; Stephen ; Smith ; N. Ty
• 刊名：Journal of Clinical Monitoring
• 出版年：1998
• 出版时间：1998
• 年：1998
• 卷：14
• 期：1
• 页码：5-17
• 全文大小：534 KB

文摘

Objective. After finding that craniofacial EMG preceding a stimulus was apoor predictor of movement response to that stimulus, we evaluated analternative relation between EMG and movement: the difference in anestheticdepth between the endpoint of EMG responsiveness to a stimulus and endpointof movement responsiveness to that stimulus. We expressed this relation asthe increment of isoflurane between the two endpoints. Methods. We measuredEMG over the frontalis muscle, over the corrugator muscle, and between theF$\_p2$ and the mastoid process as patients emerged from generalanesthesia during suture closing of the surgical incision. Anesthesia wasdecreased by controlled washout of isoflurane while maintaining 70%N$\_2$O, and brain isoflurane concentrations($^C$iso$\_Brain$) were calculated. We studied acontrol group of 10 patients who received only surgical stimulation, and 30experimental patients who intermittently received test stimuli in additionto the surgical stimulation. Patients were observed for movement responsesand EMG records were evaluated for EMG activation responses. We defined anEMG activation response to be a rapid voltage increase of at least 1.0µV RMS above baseline, with a duration of at least 30 s, in at leastone of the three EMG channels. Patient responses to stimuli were classifiedas either an EMG activation response without a move response(EMG$^+$), a move response without an EMG activation response(MV$^+$), both an EMG activation response and a move response(EMG$^+$MV$^+$), or no response. We defined theEMG$^+$ endpoint to be the threshold between EMG$^+$response and nonresponse to a stimulus, and estimated$^C$iso$\_Brain$ at this endpoint. We similarly definedthe move endpoint and estimated the move endpoint$^C$iso$\_Brain$. We then calculated the increment of$^C$iso$\_Brain$ at the EMG$^+$ endpointrelative to the move endpoint. Main results. For the 30 experimentalpatients, the initial response to a test stimulus was an EMG$^+$in 14 patients (47%), an EMG$^+$MV$^+$ in 12patients (40%), and a MV$^+$ in 1 patient (3%); noresponse occurred by the time surgery was completed in 3 patients(10%). No response occurred in 7 of the control patients(70%). Of the 14 patients with an initial EMG$^+$ responseto a test stimulus, 9 patients later had a move response. For these 9patients, the increment of $^C$iso$\_Brain$ between theEMG$^+$ endpoint and move endpoint was 0.11 ± 0.04vol% (mean ± SD). Conclusions. Our results suggest that, giventhe circumstances of our study, an EMG activation response by a nonmovingpatient indicates that the patient is at an anesthetic level close to thatat which movement could occur. However, because the first EMG activationresponse may occur simultaneously with movement, the EMG activation responsecannot be relied upon to always herald a move response before it occurs. Ourresults also suggest that EMG responsiveness to a test stimulus may be usedto estimate the anesthetic depth of an individual patient.