Authors: Yoon S-B et al.
Canadian Journal of Anesthesia 72: 1739–1750, 2025
This retrospective cohort study evaluated whether the short tetanic stimulation used during posttetanic count (PTC) monitoring can provoke nociceptive responses in anesthetized surgical patients. PTC monitoring is commonly used when deep neuromuscular blockade is required, particularly when train-of-four responses are absent. The technique involves brief high-frequency electrical stimulation, which raises the question of whether it may produce pain-related physiologic responses even in anesthetized patients.
The investigators reviewed adult patients undergoing ophthalmologic or otolaryngologic surgery between October 2022 and October 2023 who had quantitative neuromuscular blockade monitoring. Nociceptive responses were defined as a 20% or greater increase in heart rate following a five-second tetanic stimulus. Hemodynamic variables and electroencephalographic (EEG) band powers were analyzed to assess physiologic responses to the stimulus. Multivariable logistic regression was used to identify factors associated with these responses.
A total of 732 patients were included in the analysis. Eleven percent of patients were classified as “responders,” meaning they demonstrated a nociceptive response to tetanic stimulation. Among these patients, heart rate increased significantly from an average of 67 beats per minute to 88 beats per minute, representing a 33% increase. Systolic blood pressure also rose from 107 mm Hg to 119 mm Hg, reflecting a 12% increase. These findings suggest that even brief tetanic stimulation may trigger measurable sympathetic activation in a subset of patients.
EEG analysis also demonstrated evidence consistent with nociceptive processing. Responders showed a significant decrease in alpha band power following tetanic stimulation. The reduction in alpha power, approximately 14%, is generally interpreted as cortical activation or arousal associated with nociceptive input. This physiologic pattern supports the idea that the observed hemodynamic changes were not simply random fluctuations but likely reflected a true nociceptive response.
Multivariable regression analysis identified two significant risk factors for nociceptive responses. Lower remifentanil effect-site concentrations were strongly associated with increased likelihood of response, indicating that deeper opioid analgesia reduces the physiologic impact of tetanic stimulation. Lower body weight was also associated with increased responsiveness, although the clinical significance of this association remains unclear.
The authors acknowledge several limitations. The study was retrospective and included only inhalational anesthesia cases, excluding total intravenous anesthesia. Additionally, while physiologic responses were measured, the study did not evaluate whether these responses translated into clinically meaningful outcomes such as intraoperative awareness, postoperative pain, or patient discomfort.
Overall, the findings suggest that short tetanic stimulation during PTC monitoring can produce measurable nociceptive responses in a minority of anesthetized patients, particularly when opioid analgesia is relatively light.
What You Should Know
Posttetanic count monitoring is widely used during deep neuromuscular blockade, but the tetanic stimulus itself may act as a painful stimulus.
This study suggests approximately 11% of anesthetized surgical patients demonstrate physiologic nociceptive responses to the tetanic stimulation used during PTC monitoring.
Lower remifentanil concentrations were the strongest predictor of these responses, suggesting adequate intraoperative analgesia may blunt this effect.
The EEG findings strengthen the physiologic interpretation, showing cortical activation patterns consistent with nociception rather than simple hemodynamic variability.
While interesting, the clinical significance remains uncertain because the study did not evaluate patient-centered outcomes.
Key Points
Short tetanic stimulation during PTC monitoring triggered nociceptive responses in 11% of surgical patients.
Responders experienced a 33% increase in heart rate and a 12% increase in systolic blood pressure.
EEG analysis showed a reduction in alpha band power, indicating cortical activation consistent with nociceptive processing.
Lower remifentanil concentrations were strongly associated with these responses.
Further prospective studies are needed to determine whether these responses have meaningful clinical consequences.
Thank you to the Canadian Journal of Anesthesia for allowing us to summarize this article.