Fig 1.
(A) Specifications of the interface device. (B) The interface device. Four electrodes are integrated into a silicone-coated high-impact polystyrene liner card. (C) The interface device connected to the needle-electrodes and a BIS™ Quatro sensor. BIS: bispectral index.
Fig 2.
The interface device setting for direct and indirect recording.
The setting for the clinical study 2 using BIS™ Bilateral sensors. Left BIS™ Bilateral sensor is attached at the forehead following the manufacturer’s instruction. Two needle-electrodes are inserted subcutaneously adjacent to the LE and LT electrodes and connected to the RE and RT side via the interface device. Arrows designate the signal paths (orange arrows: indirect bispectral index (BIS) recording; green arrows: direct BIS recording). BIS: bispectral index, EEG: electroencephalogram.
Fig 3.
Indirect BIS recording via the interface device (clinical study 1).
(A) The flow of the participants in clinical study 1. (B) Needle-electrodes placement. Electrodes are inserted in four areas (arrows), where electrodes of a conventional BIS™ Quatro sensor are to be placed. (C) A representative plotting of SQI (green), BIS (red), and EMG (blue). The SQI decreases every 10 minutes, corresponding to the automatic impedance check of the BIS system. The period between X: Anesthesia induction until recovery; grey bar: Intubated period; black bar: Surgical procedure; BIS: bispectral index; EMG: electromyogram; SQI: signal quality index.
Table 1.
Patients’ characteristicsa.
Fig 4.
Flow of the participants in clinical study 2.
Fig 5.
(A) A representative captured image of the BIS monitor. The yellow line represents the EEG wave obtained from the left side (direct recording) and the blue line from the right side (indirect recording via the interface device). These two lines are nearly identical. (B-D) Representative BIS (B), EMG (C), and SQI (D) curves from a single patient with a strong agreement between direct and indirect BIS values. Curves from direct recording (orange lines) and indirect recording (blue lines) are superimposed. B’-D’ designate correlation analyses for BIS, EMG, and SQI, respectively. SQI for indirect recording was strongly affected by automatic impedance check every 10 minutes (D, blue line), resulting in the poor correlation coefficient of r2 = 0.6709, but it had a minimal impact on the correlation coefficients in BIS and EMG. The period between X: Anesthesia induction until recovery; grey bar: Intubated period; black bar: Surgical procedure; BIS: bispectral index, EMG: electromyogram, SQI: signal quality index.
Fig 6.
(A-C) Representative BIS (A), EMG (B), and SQI (C) curves from a single patient with an artefact noise in EMG. Curves from direct recording (orange lines) and indirect recording (blue lines) are superimposed. A’-C’ panels designate correlation analyses for BIS, EMG, and SQI, respectively. Due to stimulation of orbicularis oculi muscle, EMG was strongly disturbed (B), and the impedance check strongly affected SQI of direct recording during the orbicularis oculi muscle stimulation (C). Nevertheless, the effect on the BIS agreement was minimal (A’). The period between X: Anesthesia induction until recovery; grey bar: Intubated period; black bar: Surgical procedure period; BIS: bispectral index, EMG: electromyogram, SQI: signal quality index.
Fig 7.
Association between dBIS and indBIS.
(A) Plotting of all BIS values analyzed (2786 pairs of observations, including 2391 with BIS<60 and 395 with BIS ≥60). Red line: the prediction equation determined by the linear mixed model analysis for all data: indBIS = 7.0405 + 0.8286 * dBIS. Blue line: The prediction equation determined by the linear mixed model using stratified data: indBIS = 13.4156 + 0.6953 * dBIS (<60) and indBIS = –19.9564 +1.2515 * dBIS (60+). (B) and (C) Bland-Altman plot. The bias and 95% agreement limits (95%AL) estimated using all data are designated in red (B). The 95% ALs are narrower if it is estimated using dBIS < 60 than those of 60+ (blue lines, C). The dotted lines represent bias and solid lines represent 95% ALs. BIS: bispectral index, ALs: agreement limits.
Table 2.
Leakage currents.