Introduction
To achieve the ideal state of anesthesia, three common and important
goals are needed, namely unconsciousness, inactivity and control of the
autonomic nervous response to surgical stimuli[1, 2]. Clinically,
propofol[3] and remifentanil (REM)[4, 5] are two intravenous
maintenance drugs commonly used in balanced anesthesia. Not only can
satisfactory hypnotic and analgesic effect achieved, but also smaller
concentration needed when the two drugs combined[6].
In the field of anesthesia, it is
important to quantification of drug interactions for better drug
administration[7]. Studies have reported different concentrations
during the combination of propofol and REM under various
conditions[8-10]. The concentration of propofol and REM in
combination that can achieve the goal of early postoperative recovery is
still being explored.
Electroencephalography (EEG) is considered to be an important part of
monitoring organs in anesthesia management[11]. The patient state
index (PSI, SedLine® Root, Masimo Inc., Irvine, CA, USA)[12] is a
reference index provided by the SedLine Brain Monitor, with a reference
range of 0-100 and an ideal anesthetic depth of 25-50 (compared to 40-60
recommended by other monitors). It has been shown to be similar to the
change of the bispectral index (BIS, Medtronic, Minneapolis, Minnesota,
USA) during induction, maintenance and wake-up[13, 14]. Unlike BIS,
PSI would test asymmetries of electrical activity in patients’ brains,
morever, it improved algorithm[15]. Many studies reported the
effect-site concentration of drugs controlling autonomic responses to
stimulation under BIS-guided anesthesia[16-18], there is little
research on the effects of coadministration of propofol and REM on PSI.
Besides, the impact of opioid administration on the BIS during general
anesthesia is debatable[19]. In fact, several investigators have
pointed out that BIS to be insusceptible to opioid addition, whereas
others have reported a hypnotic activity[20]. Therefore, density
spectral array (DSA) was introduced to observe the analgesic effect.
Therefore, we designed a study to find a suitable combination
concentration of propofol and REM which can not only maintain the
appropriate depth with stimulus but also promote early recovery of
patients under the guidance of PSI. Besides, to explore whether the use
of opioid agents (i.e., remifentanil) could confound function of depth
of sedation or anesthesia.