Effects of Different Ventilation Modes on Airway Pressure and Intracranial Pressure in Patients in the Trendelenburg Position

2.1. Trial design This single-center, parallel-arm, double-blinded, randomized, noninferiority trial was performed at Inner Mongolia Baogang Hospital, The Third Affiliated Hospital of Inner Mongolia Medical University, China, from January 2022 to June 2024. The study adhered to Good Clinical Practice guidelines and the principles of the Declaration of Helsinki. 2.2. Participants This study enrolled patients aged 27-77 years who underwent elective laparoscopic myomectomy at our institution from February 2023 to August 2024. The patients had an ASA classification of I-III. Patients were excluded if they had an allergy to the anesthetic drugs used in the study, adverse effects to the analgesics included, liver cirrhosis or kidney dysfunction, or cardiopulmonary impairment. Patients were also excluded if they were uncooperative, defined as being unable to undergo clinical assessment. This study was approved by the Medical Ethics Committee of Inner Mongolia Baogang Hospital (2023-MER-106) .

2.3. Randomization and blinding Patients who met the inclusion criteria were randomly assigned to one of three groups (PCV, VCV, or PRVC) in a 1:1:1 ratio using a random number table. The anesthesiologists and surgeons performing the anesthesia and assisting with the surgery were only informed of the mechanical ventilation mode to be used. Patients were unaware of their group assignment because mechanical ventilation was initiated after anesthesia induction when they were unconscious. The anesthetic nurses and doctors evaluating the patients postoperatively were also unaware of the group assignments.

2.4. Anesthetic and analgesic managements Anesthesia was administered according to standardized institutional protocols. Patients received 1.5-2 mg/kg propofol, 1-2 mg/kg rocuronium, and 1-2 μg/kg remifentanil for induction. Anesthesia was maintained with inhaled sevoflurane or desflurane, with the inhaled concentration adjusted based on the electroencephalogram (EEG). Remifentanil was continuously infused at 0.05-0.2 μg/kg/min, adjusting blood pressure and heart rate to within ±20% of baseline values.

Thirty minutes before anesthesia emergence, all patients were administered 30 mg ketorolac tromethamine (Chengdu Dominant Pharmaceuticals Co., Ltd., China), 1 μg/kg fentanyl, and 4 mg tramadol (Jiangsu Hengrui Pharmaceuticals Co., Ltd., China), and a patient-controlled analgesia (PCA) device (Y-G-B3, JIANGSU YaGuang Medical Appliance CO., LTD., China) was initiated. The PCA was set to deliver a bolus dose of 15 μg fentanyl with a 10-minute lockout interval and no basal infusion (1 mg fentanyl and 8 mg tramadol mixed in 100 mL of normal saline solution). Data on PCA usage were collected, including the time and dose of each administration.

If the pain remained intolerable despite these measures, rescue analgesia was administered, including 1 μg/kg fentanyl or 30 mg ketorolac tromethamine IV.

2.5. Interventions Patients in the PCV group underwent mechanical ventilation in PC mode after induction. The ventilator (MAQUET Flow-I, MAQUET Italia S.p.A. Via Gozzano 14, 200 92 Cinisello Balsamo, (MI) Italy) settings were as follows: Adjust inspiratory pressure (Pins) to maintain the end-tidal carbon dioxide concentration (ETCO2) at 4.0-5.0 kPa. The investigators used 0.3 L/min of pure oxygen and air each, with an oxygen concentration of 41%.

Patients in the VCV group underwent mechanical ventilation in VC mode after induction. The ventilator was set with a tidal volume of 6-8 ml/kg, positive end-expiratory pressure (PEEP) at 0 cmH2O, a ratio of inspiration to expiration of 1:2, a respiratory rate of 16 breaths per minute, and an oxygen concentration of 41%.

Patients in the PRVC group underwent mechanical ventilation in PRVC mode after induction. The respiratory parameters were the same as those in group Ⅱ.

2.6. Outcome measures Record the following parameters at five time points: before insufflation (T1), 5 minutes after insufflation (T2), 10 minutes after insufflation (T3), 15 minutes after insufflation (T4), and 20 minutes after insufflation (T5). Esophageal pressure (pleural pressure, PES), mean airway pressure (PAWM), peak airway pressure (PAP), arterial carbon dioxide partial pressure (PaCO2), end-tidal carbon dioxide concentration (ETCO2), tidal volume (TV), mean arterial pressure (MAP; calculated as diastolic pressure + 1/3 pulse pressure), heart rate (HR), and optic nerve sheath diameter (ONSD). Since SpO2 was 100% at all time points for each group with no statistical difference, SpO2 is not included in the table.

Esophageal pressure (PES) was monitored using a Swan-Ganz catheter (Swan-Ganz, Edwards Lifesciences LLC, One Edwrds Way, Irvine, CA USA 92614) connected to a monitor (M8003A, Hewlett-Packard-Str. 2, 71034 Boblingen, Germany). Blood chemistry parameters were monitored using a blood gas analyzer (i-STAT1 Analyzer MN:300-G, Abbott Park, IL 60064 USA). Optic nerve sheath diameter (ONSD) was measured using an ultrasound system (On-platform ultrasound system PX, Vianen, Netherlands).

In the Postanesthetic Care Unit (PACU), record the following: Length of stay in PACU, Mean arterial pressure, Heart rate, Postoperative nausea and vomiting, Pain, Rescue antiemetics, Rescue analgesics, Rescue Sulfentanil dose.

2.7. Sample size The hypothesis of this study is that optic nerve sheath diameter (ONSD) can effectively differentiate between groups of different ventilation modes, with the hypothesis that the area under the ROC curve for ONSD is greater than 0.5. Preliminary experiments showed that the area under the ROC curve for ONSD is 0.7. With α=0.05 (one-tailed), β=0.1, and an equal ratio of 1:1:1 between groups, the sample size was estimated using n=Δ2/σ2(zα/2+zβ)2 [11,12]. It was found that at least 25 patients were needed per group. Considering a 20% dropout rate, the study included 30 patients in the PCV group, 30 in the VCV group, and 30 in the PRVC group.

2.8. Statistical analysis The sample size was estimated using the "Diagnostic Test (ROC)" - "Test for One Sample Sensitivity and Specificity" module in PASS 11 software. Data are presented as mean (standard deviation), frequency (%), or median (interquartile range). All statistical analyses were performed using GraphPad Prism version 10.2.3.The Kolmogorov-Smirnov test was performed to investigate the normality of the distribution of continuous variables. An independent t test or Mann-Whitney U test was performed to compare continuous variables, as appropriate. The x2 test or Fisher's exact was performed to compare categorical variables. Repeated-measures analysis of variance was performed to compare changes in some variables over time. Statistical significance was set at P value <0.05.