Subjects
This study was approved by the Ethics Committee of the Affiliated Hospital of North Sichuan Medical College, Nanchong, China (Approved No. 2018ERR009). Written informed consent was obtained from each child’s guardian. All experiment procedures (consisted of invasive manipulation) and data collection were conducted with prior informed consents. The manuscript adheres to CONSORT guidelines and was registered with the Chinese Clinical Trials Registry at http://www.chictr.org.cn (ChiCTR1800019393, principal investigator: Juan XU, date of registration: Nov. 8, 2018).
This research was conducted between November 2018 and June 2019. Seventy-five child patients, scheduled for laparoscopic herniorrhaphy, with American Society of Anesthesiologists (ASA) physical status I-II, aged between 3 and 7 years, were selected. Exclusion criteria included a history of cardiovascular, brain, liver, kidney, or hematological disease; a history of allergies to inhalation anesthetics or opioids; a history of recent upper respiratory tract infection. The flowchart of patients through the trial is shown in Fig. 1.
Study design
All children were randomly assigned to three groups (R0, R1, R2) with 25 cases in each group according to computer-generated randomization. Children in the three groups were anaesthetized by inhalation of sevoflurane and intravenous infusion of remifentanil with different plasma target concentrations (0, 1, 2, ng ml-1), respectively. During the creation of CO2 pneumoperitoneum, the sympathetic adrenergic response was monitored in all patients. A positive response was defined as an increased heart rate (HR) or mean arterial pressure (MAP) over its baseline value more than 20%. On the contrary, if the increase of HR and MAP was less than 20% of its baseline value, the sympathetic adrenergic response was defined as a negative response. The mean value of MAP or HR measured 3 and 1 min before pneumoperitoneum stimulus was defined as its baseline value. The mean value of HR or MAP measured 1 and 3 min after the pneumoperitoneum pressure maintained stable was defined as its changed value. Patients would be excluded from the experiment if hypotension or bradycardia occurred at the period of determination. Hypotension was defined as systolic blood pressure (SBP) (5th percentile at 50th height percentile), less than 2 x age in years + 65 and was treated with intravenous ephedrine. Similarly, bradycardia was defined as HR < 80 bpm and was treated with intravenous atropine [6, 7].
Anesthesia administration
Induction
All children were fasted for 6 h and not allowed to drink water for 2 h before operation, and not received premedication routinely. Before induction of anesthesia, a venous channel was established and infused with compound sodium chloride solution at a rate of 10 mlˑkg-1ˑh-1. Electrocardiogram, pulse oxygen saturation, non-invasive blood pressure were routinely monitored with a PM-9000 express monitor (Mindray Medical International Limited, Shenzhen, China), and depth of anesthesia was monitored by using bispectral index (BIS) (Canwell Medical International Limited, Zhejiang, China). In each group, anesthesia was induced by inhalation of 7% sevoflurane with 100% oxygen. After children had lost their consciousness, the inhaled sevoflurane concentration was reduced appropriately, and 1 μgkg-1 remifentanil and 0.6 mgkg-1 rocuronium were intravenously injected. After tracheal intubation, sevoflurane concentration was adjusted to a preset end-tidal concentration of 3.0%, 2.2% and 1.4% in group R0, group R1 and group R2, respectively. Sevoflurane concentration was monitored by a multifunctional monitor (Shenzhen Mindray Biomedical Co., Ltd., PM9000). At the same time, remifentanil was administered by target-controlled infusion in each group with the Minto model using a micro pump (TCI-I, ver 4.0, Guangxi VERYARK Technology Co., Ltd). The degree of neuromuscular relaxation (2 Hz for 1.5 s every 11.5 s) was continuously assessed by acceleromyography using a TOF-watch SX system (Veryark-TOF, Guangxi, China), starting when the children were unconscious [8, 9].
Measurement of MACBAR
When the preset end-tidal sevoflurane concentration had maintained stable at least 20 minutes, CO2 pneumoperitoneum was established, and its pressure was set at 9 mmHg with a flow rate of 2 Lmin-1. The first child’s preset end-tidal sevoflurane concentration in each group was obtained from our preliminary test. The next child’s end-tidal sevoflurane concentration for maintenance in each group would be adjusted based on the result of the previous child’s cardiovascular response. If the response was positive (negative), the subsequent child’s end-tidal sevoflurane concentration would be increased (decreased) by 0.2%. The person for recording the data was blinded to the plasma target-controlled remifentanil concentrations used in all groups.
The test was over in each group when six crossing points of a positive versus negative response or a negative versus positive response in the pre and the next child had occurred. The MACBAR of sevoflurane in each group was calculated as the mean value of the end-tidal sevoflurane concentrations corresponding to the six crossing points. After the above test had been done, 0.1 mg kg-1 of midazolam was given intravenously to prevent a potential intraoperative awareness. All the children were received a routine intravenous and inhaled combined anesthesia. The BIS value was maintained between 40 and 60. The administration of sevoflurane and remifentanil were discontinued 5 minutes before the end of operation, and 1.5 μgkg-1 of fentanyl was intravenously injected for analgesia. All children were transferred to the pediatric intensive care unit.
Determination of blood samples
Arterial blood samples (each for 3 ml) were collected 3 min before and after CO2 pneumoperitoneum with sodium-heparin-containing tubes. Soon after, the plasma was separated and frozen at -70°C in a refrigerator until analysis. After the sample collection had been completed, the concentrations of epinephrine (E) and norepinephrine (NE) were measured using a method that has been described previously [3].
Statistical analysis
Statistical analysis was performed using SPSS22.0 software. All measurement data were expressed as mean ± SD. Only these data from the 12 cases at 6 crossing points of a positive (negative) versus negative (positive) response in each group were analyzed. The delta HR, delta MAP, delta E, and delta NE value was calculated as the difference between its change value and baseline value, respectively. One-way analysis of variance (ANOVA) for the complete random design was used to compare the differences of age, weight, MACBAR, delta HR, delta MAP, delta E, and delta NE among the three groups, respectively. The sex constituent ratio was tested by Fisher's exact probability among the three groups. P value <0.05 was considered as a statistical significance.