Comparison of the qNOX, qCON and Bispectral (BIS) index responses to noxious stimuli during surgery

Author(s): Ofelia Loani Elvir-Lazo, Roya Yumul, Ruby Wang, Ashley Fejleh, Jason Hager, Paul F White

Background: Monitoring a patient's level of anti-nociception during surgery can minimize autonomic and muscular responses to intraoperative stimuli. Electroencephalogram (EEG)-based tools like Bispectral Index (BIS) (Covidien, Boulder CO, USA), Conox (Fresenius Kabi A. G. Bad Homburg, Germany), and SedLine monitor (Masimo Corp., Irvine, CA, USA) might provide insights into depth of hypnosis (sleepiness) and responses to noxious surgical stimuli. The Conox (qCON and qNOX) was designed to independently assess both sedation and nociception during surgery. The objective of this observational study was to simultaneously compare the responses to specific events during surgery using the qCON, qNOX and BIS index monitors.
Methods: Prior to induction of anesthesia, 59 consenting adult patients undergoing general anesthesia with a laryngeal mask airway (LMA) were simultaneously monitored using BIS and Conox monitors. Monitoring was continuous from induction of anesthesia until return of consciousness after surgery. Both the surgical and anesthetic teams were blinded to the qCON and qNOX values during the operation. Baseline values were recorded prior to and after induction of anesthesia, as well as responses to LMA insertion, and noxious events during surgery (e.g., local anesthetic infiltration, skin incision, painful manipulations during the operation, and skin closure), removal of the LMA device, and upon return of consciousness after the operation. Results: The prediction probabilities (Pk) show significant concordance among comparisons of qCON vs BIS (Pk=0.821, p<0.01), qCON vs qNOX (Pk=0.827, p<0.01), and qNOX vs BIS (Pk=0.743, p<0.05) during anesthesia. During LMA insertion, there were no significant differences in heart rate (HR), mean arterial pressure (MAP), BIS, or qCON values in patients who moved vs. those who did not move; however, qNOX values were significantly higher (p<0.05) in “movers” compared to “nonmovers”. During noxious stimulating events during the operation, there was no significant difference in qCON nor BIS values when comparing movers and nonmovers. However, HR, MAP, and qNOX were significantly higher in movers compared to nonmovers (p<0.05). These findings suggest that qNOX may be capable of serving as a surrogate for sympatheticallymediated responses to noxious stimuli. Logistical regression analysis showed that qNOX was the most accurate predictor of intraoperative movement. The BIS values and hemodynamic changes in HR and MAP were less predictive of patient movements during surgery.
Conclusion: Although there was a strong correlation between BIS and qCON in monitoring hypnotic levels, however, the qNOX values provide useful information for predicting movements in response to noxious stimuli during anesthesia. These preliminary data suggest that higher qNOX values appear to more reliably correlate with inadequate analgesia than either the BIS or qCON values.