Opioid and propofol pharmacodynamics modeling during brain mapping in awake craniotomy

Awake craniotomy (AC) is performed to identify cerebral language center. The challenge of anesthesia is to maintain a calm, comfortable, and cooperative patient during the mapping phase. Response surface models (RSMs) are multidrug modeling algorithms. In this pharmacodynamic study, we investigate the first use of RSM with bispectral index (BIS) to predict patient's response to name calling (RNC) and wakefulness (complete neurological tests) during AC.

The study is performed in two phases. We prospectively enrolled 40 patients who received video-assisted thoracoscopic surgery (VATS) using propofol and fentanyl as the modeling group. Effect-site concentrations (Ce) and BIS values were recorded and a RSM is built from the data set. We verified the RSM retrospectively in AC patients, designated as the validation group. Corresponding BIS values were analyzed for RNC and wakefulness.

A total of 155 data sets of propofol Ce, fentanyl Ce, and BIS pairs were available for modeling. The range of propofol and fentanyl Ce were 0 to 9.95 μg/mL and 0 to 3.69 ng/mL, respectively. Observed BIS ranged from 21 to 98. The model identified an additive interaction between propofol and an opioid. RNC at BIS 64 is predicted by the model and 70 is required for wakefulness.

RSM built from VATS patients is verified with a separate group of AC patient. The BIS target advised for RSM-predicted wakefulness is 70. The model illustrates the timeline to wakefulness during AC under propofol and an opioid. It has implications in guiding, dosing, and estimation of time to wakefulness with propofol and an opioid.