Less general anesthetic is required in patients with regional blocks than in those without, as assessed through commonly used anesthesia monitoring parameters such as blood pressure, heart rate, and bispectral index (BIS). Although intraoperative regional anesthesia has become more widely adopted, few studies have confirmed or monitored its anesthetic-sparing effects. Using recent reports of nonintubated video-assisted thoracoscopic surgery (VATS) by BIS-targeted propofol infusion and intraoperative multilevel thoracoscopic intercostal nerve blocks (TINBs), this retrospective study investigated whether the anesthetic-sparing effect can be realized by reducing the effect-site concentration (Ce) to the targeted BIS level or by reducing the blood pressure at the onset of regional blocks.A retrospective study of a prospectively collected case series of non-intubated VATS.Data on 56 adult patients who underwent nonintubated VATS were collected and analyzed. The mean operative time was 121 ± 32 minutes. BIS levels before and after one-lung ventilation/TINBs and surgery were 48% ± 11% and 47% ± 12%, respectively. The Ce of propofol infusion decreased significantly from 3.4 ± 0.8 μg/mL to 3.0 ± 0.7 μg/mL (p < 0.01) after surgery with TINBs. Blood pressure did not change significantly, whereas the heart rate increased moderately but significantly (77 ± 14 beats/minute to 82 ± 15 beats/minute, p < 0.01).With comparable BIS and blood pressure in the subsequent surgical procedure, the adequacy of anesthesia and the anesthetic component provided by intraoperative TINBs and vagal nerve could be monitored adequately. The anesthetic-sparing effect of intraoperative nerve blocks can be realized when the Ce of propofol infusion was reduced to the target BIS level.