Correlations between propofol concentration in exhaled breath and BIS in patients undergoing thyroid surgery

Several clinical studies have reported promising correlations between propofol concentration in exhaled breath (Ce-pro) and the bispectral index (BIS) in patients, suggesting the potential of exhaled propofol measurement as a non-invasive method for adjusting anesthesia depth. However, these studies are still in the validation phase of instrument effectiveness, often limited by small sample sizes or inappropriate instrument selection, and thus lack convincing results regarding these correlations. In this study, one hundred patients aged 18-65, undergoing elective thyroid surgery under general anesthesia were included. The vacuum ultraviolet photoionization and time-of-flight mass spectrometry was employed to monitor Ce-pro at 20 s intervals, alongside continuous BIS measurement. The association between Ce-pro and BIS was analyzed using linear mixed-effects models, with marginalR²used to assess the correlation. The threshold of Ce-pro at awakening was also explored. Additionally, the univariate and multifactorial diagnostic model, including end-of-surgery Ce-pro, were employed to assess the accuracy of predicting delayed recovery. A weak correlation was observed between intraoperative Ce-pro and BIS (marginalR²= 0.348). Predictive models utilizing end-of-surgery Ce-pro levels showed good accuracy (area under the curve (AUC) = 0.75, 95% CI: 0.62-0.89,P= 0.003) in predicting delayed recovery, while the model using end-of-surgery Ce-pro combined with gender, sufentanil dosage, the time from the last administration of sufentanil to the end of surgery, and anesthesia duration demonstrated stronger predicting accuracy (AUC = 0.91, 95% CI: 0.85-0.98,P< 0.001). This study suggests that Ce-pro alone may not reliably predict the depth of anesthesia in clinical practice, but shows promising accuracy in predicting delayed recovery from anesthesia.