Ethical approval and registration
The present study was registered on the ClinicalTrials.gov website (NCT02440269) and was approved by the Medical Ethics Committee of Southwest Hospital of Third Military Medical University (ethics lot number: 2016 Research No.93). All patients provided informed written consent to participate in the study.
Study design
From June 2016 to August 2018, patients aged 18–60 years old with American Society of Anesthesiologists (ASA) physical status I-II, who underwent laparoscopic surgery for appendicitis, intestinal obstruction, ectopic pregnancy, cholecystitis or liver cancer, were enrolled in this study. Patients were excluded, if they met any of the following criteria: ASA ≥ III, uncontrolled hypertension, pregnancy, severe hepatic and renal dysfunction, history of drug or alcohol abuse, current use of psychotropic medicine, inability to communicate or cooperate before surgery and preoperative critical complications with acute peritonitis or sepsis.
Firstly, 30 patients were sequentially divided into two groups according to the operative time (day or night) using the Narcotrend monitor (MT MonitorTechnik GmbH&Co. KG. Germany). Group ND: Propofol TCI with Narcotrend monitor during the day (8:00–18:00), Group NN: Propofol TCI with Narcotrend monitor during the night (22:00–5:00). After completing the case collection for these two groups with the Narcotrend monitor, the other 30 enrolled patients were sequentially divided into two groups according to operative time (day or night) using closed-loop TCI (Beijing Ideas Co. Ltd. China). Group CLTD: Propofol closed-loop TCI guided by BIS during the day (8:00–18:00), Group CLTN: Propofol closed-loop TCI guided by BIS during the night (22:00–5:00). The period of the day or night referred to in Robinson’s and Scavone’s studies [8, 9], were adjusted and narrowed to a shorter time frame, in order to avoid the potential influence of the time boundary between day and night.
Anesthetic procedure
Patients did not receive pre-anesthetic medication. Non-invasive blood pressure, pulse oximetry, electrocardiogram, body temperature and end-respiratory carbon dioxide concentration were monitored for all patients. Narcotrend and BIS were used respectively for TCI with Narcotrend monitor and Close loop TCI groups mentioned previously.
Oxygen was inhaled at a flow rate of 5L/min for 3 min to remove pulmonary nitrogen. To induce general anesthesia in group ND and NN, midazolam 0.05 mg/kg (Renfu Pharmaceutical Co., Ltd., Yichang, China), sufentanil 0.30 μg/kg (Renfu Pharmaceutical Co., Ltd., Yichang, China), etomidate 0.30 mg/kg (Renfu Pharmaceutical Co., Ltd., Yichang, China) and cisatracurium 0.15 mg/kg (Dongying, Pharmaceutical, Nanjing, China) were used. The anesthetic depth was monitored by the Narcotrend (MT MonitorTechnik GmbH&Co. KG. Germany). The anesthetics used in group CLTD and CLTN for induction, intubation and maintenance included midazolam 0.05 mg/kg, sufentanil 0.30 μg/kg, and cisatracurium 0.15 mg/kg, followed by propofol with closed-loop TCI guided by BIS with a 45–55 target value (Beijing Ideas Co. Ltd. China).
Following endotracheal intubation, the lungs were mechanically ventilated with 50% oxygen combined with 50% air to maintain the pulse oximetry at 95–100% and PetCO2 at 30–40 mmHg. The patients in group ND and NN received TCI of propofol (2.5 μg/ml) and remifentanil (3.0 ng/ml). Patients in group CLTD and CLTN received the propofol closed-loop target-controlled infusion and TCI of remifentanil (3.0 ng/ml) with BIS values of 45–55. Cisatracurium was administrated intermittently via single dose intravenous injection guided by train-of-four stimulation (TOF) monitoring in all groups.
Heart rate (HR) and mean arterial pressure (MAP) were maintained within 20% of baseline values through using cardiovascular drugs. When HR < 40 bpm or MAP < 65 mmHg occurred, atropine (0.5 mg/bolus) or ephedrine (10 mg/bolus) was administered respectively. The fluid volume was supplemented according to the basic principles of intraoperative rehydration. The patients’ body temperatures were maintained within 36–37 °C through heat preservation or fluid heating. The anesthetic depth was monitored closely using the Narcotrend in group ND and NN. If the Narcotrend index was below 20 or above 60, the TCI settings (propofol 2.5 μg/ml and remifentanil 3.0 ng/ml) were adjusted to avoid too deep anesthesia or intraoperative awareness, and these cases were withdrawn from the research protocol. Propofol TCI concentration variations were recorded in group CLTD and CLTN.
Measurements
The primary outcome of this study was to compare the variations in Narcotrend index between group ND and NN. The comparisons of MAP, HR between group ND and NN, as well as the comparisons of propofol TCI concentrations, MAP and HR between group CLTD and CLTN, were secondary outcomes.
Data collection
The Narcotrend index, MAP and HR were recorded in Group ND and NN at the following time points, T1 (5 min before induction), T2 (beginning of mechanical ventilation), T3 (mechanical ventilation for 5 min), T4 (beginning of operation), T5 (operation for 10 min), T6 (operation for 30 min), T7 (end of operation). The propofol TCI concentrations, MAP and HR were recorded in Group CLTD and CLTN at the following time points: T1 (5 min after induction), T2 (beginning of ventilation), T3 (mechanical ventilation for 5 min), and T4 (beginning of operation), T5 (operation for 10 min), T6 (operation for 30 min), and T7 (end of operation).
Patient demographics and surgical characteristics, including duration of surgery, time to extubation, length of PACU stay, intraoperative administration of propofol, remifentanil and cisatracurium, fluid volumes, blood loss, urine output, and ephedrine or atropine use, were recorded.
Statistical analysis
PASS 11.0 (NCSS, Kaysville, UT, USA) was used for sample size analysis. Preliminary investigation indicated that the average value of the Narcotrend index, expressed by mean ± standard deviation (SD), were respectively 49.8 ± 9.3 and 30.7 ± 5.2 in the day and night groups throughout surgery (from T2 to T7). It revealed that a sample size of four patients per group would detect a significant difference with power of 80% and an α coefficient of 0.05. For the supplementary pre-experiments, the average concentration of the propofol closed-loop TCI guided by BIS were respectively 2.87 ± 0.3 μg/ml and 2.47 ± 0.2 μg/ml (mean ± SD) in the day and night groups throughout surgery (from T4 to T7). It was calculated that at least seven cases were needed in each group. Considering that there may be cases of dropout or loss of follow-up during the clinical trial, we decided to enlarge the sample size of each group to fifteen cases.
Statistical analyses were performed using SPSS software (version 19.0; IBM, Armonk, NY, USA). The Kolmogorov–Smirnov test was used to evaluate the normal distribution of continuous data. The normally distributed variables were presented as the mean ± SD. The comparisons of Narcotrend index between groups ND and NN and propofol infusion concentrations between groups CLTD and CLTN were completed using a repeated measurement ANOVA with Bonferroni correction. The data for demographics and surgical characteristics, with normal distribution, were analyzed using an independent samples t-test. The non-normally distributed variables such as gender, ephedrine or atropine use, expressed by ratio, were compared using Fisher’s exact test. P values < 0.05 were considered statistically significant.