Effect of positive end-expiratory pressure on pulmonary compliance and pulmonary complications in patients undergoing robot-assisted laparoscopic radical prostatectomy: a randomized control trial

The International Agency for Research in Oncology (IARC) estimated 1,414,259 new cases of prostate cancer and approximately 375,304 prostate-cancer-related deaths worldwide in 2020 [1]. With the continuous advancement of minimally invasive surgery and the rapid development of artificial intelligence-assisted systems, an increasing number of studies have shown that robotic-assisted laparoscopic radical prostatectomy (RARP) is superior to traditional open radical prostatectomy or pure laparoscopic radical prostatectomy in several aspects, such as providing a more specific field, a more delicate operation execution, less trauma, less blood loss, and complete revolutionary treatment [2]. While robot-assisted surgery has benefited prostate cancer patients, the anaesthetic management of patients undergoing RARP surgery, especially managing the physiological changes due to pneumoperitoneum and a vertical head-down position, has become one of the main recent topics in anesthesiology [3, 4]. The establishment of pneumoperitoneum and head-down position can cause serious interference with pulmonary function: first, it affects diaphragm elevation, causing decreased thoracopulmonary compliance, reduced functional residual air volume, and pulmonary atelectasis. This increases the possibility of hypoxemia. Ventilation pressure also rises significantly, which may damage the lungs and increase the occurrence of postoperative pulmonary dysfunction. Pulmonary dysfunction occurs in approximately 5% of patients undergoing surgical procedures under general anaesthesia with tracheal intubation, leading to prolonged postoperative recovery and increased hospital costs [5]. There are many causes of postoperative pulmonary complications, including barotrauma during general anaesthesia [4, 5]. Therefore, perioperative pulmonary protection anaesthetic management is essential to rapid patient recovery. Pulmonary protective ventilation, which combines a low tidal volume (6–8 mL/kg) and positive end-expiratory pressure (PEEP) ventilation, was initially used in patients with respiratory distress syndrome and is now considered beneficial in "healthy lungs" patients under general anaesthesia with tracheal intubation [5, 6]. For laparoscopic procedures requiring CO2 pneumoperitoneum, a "permissive hypercapnia," where small tidal volume ventilation is applied and the arterial blood CO2 partial pressure is permitted to reach ≥ 60–70 mmHg for a short period, was proposed to avoid lung damage from high ventilation pressure [6]. In a study of 40 patients who underwent elective abdominal surgery with individual PEEP value monitoring by thoracic image scanning, a PEEP of 6–16 cmH2O with a median of 12 cmH2O was required to improve pulmonary compliance with pulmonary atelectasis [7]. It has also been suggested that high PEEP levels (10 cmH2O) significantly improve lung compliance and reduce the incidence of atelectasis during mechanical ventilation compared to low PEEP levels and no PEEP ventilation [8, 9].

Most anaesthetized patients treated with RARP surgery have a healthy level of pulmonary function with good lung compliance. There is a lack of systematic studies on whether intraoperative PEEP is required to improve oxygenation and reduce postoperative pulmonary complications in this group. It is essential to guide clinical anesthesiologists in managing the respiratory function of patients undergoing RARP surgery with safer and more effective mechanical ventilation parameters by identifying the appropriate PEEP values. In this study, we investigated the feasibility of a PEEP ventilation strategy for patients undergoing RARP surgery and its effects on ventilation, oxygenation, and Postoperative oxygenation function.

Patients and methods

This prospective randomized, controlled trial was reviewed and approved by the IIT Ethics Review Panel of the Clinical Research Ethics Committee of the First Hospital of Zhejiang University School of Medicine on 06/05/2020 (Session No. 48). The study was registered in the China Clinical Trials Registry (Registration No. ChiCTR2000033380).

Our research follows the ethical standards of the WHO Declaration of Helsinki (1964) and its successive amendments. Studies that are adequately controlled, blinded, randomized, and of sufficient statistical power to confidentially and accurately interpret the effect reported.

Patients

We recruited a total of 120 patients who underwent robotic-assisted laparoscopic radical prostatectomy at the First Hospital of Zhejiang University School of Medicine from July 2020 to June 2021. Written informed consent was obtained from all participants. The inclusion criteria were Patients undergoing RARP, ASA classification I-III. Exclusion criteria were age > 80 years, history of severe cardiopulmonary, hepatic, and renal disease, history of neuromuscular disease, excessive obesity or malnutrition (body mass index, BMI ≥ 30 or ≤ 20), and history of drug allergy. Hemodynamic instability due to positive end-expiratory pressure during the study period and difficulty in maintaining mean arterial pressure above 65 mmHg with intravenous norepinephrine (0.03ug/kg/h) will be terminated. Using SPSS 23 (IBM, Armonk, NY, USA), patients were randomly allocated to three groups (40 patients per group): PEEP0, PEEP5, and PEEP10 groups. Randomization was performed by a researcher not involved in the anesthesia or statistical analysis. The attending anesthetist was given an envelope containing the allocation results. The patient, the surgeon, and the resident anesthetist responsible for the records were blinded to the PEEP level. Nine patients did not meet the inclusion criteria, and six declined to participate. Eight patients were excluded due to issues with recruitment, loss of data records, and loss of follow-up, four patients were excluded due to a change of surgical approach, two patients were terminated due to failure to maintain circulation, and 2 cases were excluded due to failure of pneumoperitoneum time. A flowchart of the study is shown in Fig. 1.

Fig. 1figure 1Anesthesia method

Patients were routinely monitored after admission to the operating room, arterial pressure was measured continuously by proper radial artery puncture placement, and we performed blood gas analysis. Anaesthesia was induced intravenously with etomidate 0.3 mg/kg, fentanyl 4 μg/kg, and rocuronium 0.6 mg/kg, followed by tracheal intubation. All patients were mechanically ventilated using a DrägerFabius GS anaesthesia workstation ( Dräger Medical Center, Lübeck, Germany) with ventilation set to volume-controlled breathing (60% oxygen concentration, 1:1 air mixture), tidal volume set to an initial value of 7 ml/kg based on ideal body weight, frequency 12 times/min, and PEEP set to 0, 5, and 10 cmH2O, respectively, according to randomized groups. The Anaesthetist adjusted the respiratory frequency before pneumoperitoneum (Pnp) to keep the partial pressure of end-expiratory carbon dioxide (ETCO2) at 30–35 mmHg. IfETCO2 ≤ 60 mmHg, Anaesthetist did not adjust the respiratory parameters, but if ETCO2 > 60 mmHg, the increase in respiratory frequency was first adjusted. If ETCO2 continued to rise, the tidal volume was increased appropriately. According to the pretest, Ppeak was generally less than 30cmH2O water column. In addition, we set 40cmH2O as the upper limit to prevent unacceptable levels of high driving or plateau pressure. Anaesthetists set no recruitment manoeuvres for any ventilation modes.

At the beginning of surgery, the Anaesthetist adjusted the position to a 30-degree head-down position according to the surgical needs, and the pneumoperitoneum pressure was adjusted to maintain 13 cmH20.

Anaesthesia maintenance: propofol 4–10 mg/kg/h and remifentanil 8–18 μg/kg/h pumped to keep the BIS value at 40–60. We administered intraoperative rocuronium bromide at 0.6 mg/kg/h to maintain a deep neuromuscular block (NMB). Deep NMB is defined as no responses to train-of-four (TOF) stimulation and 1–2 replies to post-tetanic count (PTC) during neuromuscular monitoring. After pneumoperitoneum, the surgery did not require profound neuromuscular blockade, and we no longer recorded pulmonary compliance indicators as we did in the state of profound neuromuscular blockade. Rocuronium was discontinued at the end of the pneumoperitoneum.

At the end of the surgery, neostigmine (0.05 mg/kg) and atropine (0.1 mg/kg) was intravenously administered under the guidance of the NMB monitor. The patient was extubated in the anaesthesia recovery room (PACU), and Travelling Nurse performed a blood gas analysis before Recovery Room Nurse sent the patient to the general ward. The criteria for discharge from the PACU was an Aldrete score of > 9, as assessed by the anesthesiologist in charge of the PACU before leaving the PACU and returning to the ward. Patients performed a low-dose chest computed tomography (CT) scan the day after the operation. 2.3. Monitoring items and time points.

We monitored patients with ECG, pulse oximetry, temperature, BIS, invasive arterial pressure, ETCO2, and ventilation pressure–volume loop using a CARESCAPE Monitor B650 (GE Medical, Helsinki, Finland) monitor. Blood gas analysis was performed using an ABL-90FLEX analyzer (ApS, Brønshøj, Denmark), and neuromuscular blockade was monitored by accelerated EMG of the thumb adductors using TOF Watch SX (Olga, Dublin, Ireland).

The primary outcome indicators were comparing the effects of applying 0, 5, and 10 cmH2OPEEP on pulmonary compliance (Crs) and driving pressure (ΔP) during pneumoperitoneum in patients undergoing RARP. The secondary outcomes of the study were oxygenation index and pulmonary complications.

Team personnel recorded data at the following six time-points for PEEP0, PEEP5, and PEEP10 groups: after induction, pneumoperitoneum establishment, 30 min after pneumoperitoneum, 60 min after pneumoperitoneum, 90 min after pneumoperitoneum, and at the end of pneumoperitoneum: tidal volume, respiratory rate, end-expiratory carbon dioxide partial pressure, peak airway pressure, plateau pressure, lung compliance, airway resistance, finger oxygen saturation, blood pressure, heart rate, and duration of surgery. Anaesthetist performed blood gas analysis after induction of anaesthesia, 1 h after pneumoperitoneum, and after tracheal extubation. Tracheal extubation time, PACU time, and agitation during the awakening period were recorded in the PACU. Tracheal extubation time was the time from the end of surgery to the tracheal tube removal. PACU time was the time from admission to departure from the PACU. PACU anaesthesia nurses recorded the patient's Riker score; if the Riker score was ≥ 5, we called it awakening agitation.

Follow-up visits were performed on postoperative days 1 and 3 and 1 month postoperatively to record postoperative pain scores, finger pulse oxygen saturation, and postoperative complications.

Statistical analyses

The Kolmogorov–Smirnov test was used to test the normality of the distribution of all variables. Values for peak inspiratory pressure (Peak), mean pressure (Pmean), lung compliance (Crs), airway resistance (Raw), partial pressure of carbon dioxide in the arteries (PaCO2) and the ratio of partial pressure of O2 in the arterial blood to the fraction of oxygen absorbed (PaO2/FiO2) at different time points are expressed as mean and standard deviation. Patient characteristics, time to pneumoperitoneum, time to surgery and time to extubation are expressed as means and standard deviations. One-way ANOVA was used to analyse differences between groups for normally distributed measures, and LSD tests were used for post hoc two-way comparisons. Differences between multiple time points for non-normally distributed actions were analysed using Kruskal–Wallis and one-way analysis of variance (ANOVA) post hoc tests, and Mann–Whitney U tests were used to analyse differences between the two-time points and groups. χ2 tests were used to compare the number of patients with agitation on awakening and the number of patients with postoperative pulmonary complications in all groups.

A pre-test was performed to determine the sample size. The mean Crs at PEEP for pneumoperitoneum (Pnp) 0, 5 and 10 cmH2O were 27 mL/cmH2O, 32 mL/cmH2O and 34 mL/cmH2O with standard deviations of 7, 9 and 10 respectively. considering a P value = 0.05 and a degree of certainty of 0.90, a minimum of 28 patients per group was required to differentiate the Crs in each group.

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