Comparison of Three Methods of PEEP Titration During One Lung Ventilation in Prone Position

Induction of general anesthesia and mechanical ventilation impair respiratory function because of alveoli collapse, decreased functional residual capacity, diminished arterial oxygenation, and even mechanical ventilation-induced injury.In addition, One-lung ventilation during thoracic surgery is prone to ventilator induced lung injury and oxygen toxicity. It is also associated with a profound inflammatory cytokine release which causes excessive neutrophils recruitment that increases pulmonary vascular permeability in both lungs. These reactions often precede systemic inflammatory response syndrome, acute respiratory distress syndrome and pneumonia. Therefore, lung protection and protective ventilation is strongly recommended during thoracic surgery.In contrast to the lateral decubitus position, OLV in the prone position is devoid of the beneficial effect of gravity on preferential redistribution of the pulmonary blood flow to the dependent areas of a lung, possibly resulting in increased V/Q mismatch. Also, the prone position is frequently associated with decreased respiratory compliance and increased peak airway pressure in anesthetized and paralyzed patients when not assuring free abdominal and chest movements, which is further aggravated by CO2 insufflation. Prone positioning during esophagectomy provides several advantages, including shortened operative times and superior surgical view, at the cost of one-lung ventilation (OLV). Intraoperative lung protective ventilation strategy, which includes the combination of low tidal volume and adequate PEEP levels during operation, has been reported to improve respiratory mechanics and reduce the incidence and severity of atelectasis which may prolong hospital stays and increase mortality in surgical patients.Improper PEEP levels have an impact on patient physiology. If the setting level is too low to achieve the desired purpose, it cannot produce the effect of applying PEEP. If the setting level is too high, the pulmonary vascular resistance increases, venous return blood volume decreases, intrapulmonary shunt increases, and arterial oxygen partial pressure level is reduced. Also, it could negatively affect cardiac output and delivery of oxygen to vital organs.Individualization the optimal PEEP level according to the respira¬tory condition of patients has gradually attracted the attention of clinicians. The methods to determine the best PEEP levels include computed tomography scanning, electri¬cal impedance tomography, ultrasound, P-V curve method, best oxygenation titration method, and best lung compliance titration method. Each method has its advantages and disadvantages. Individualized PEEP has advantages over fixed PEEP in improved respiratory mechanics and prevent progressive alveolar collapse.There are few studies on the selection of appropriate PEEP values during one-lung ven¬tilation (OLV) in prone position and the protective effect of PEEP values can be titrated by different titration methods which still requires many prospective studies. Therefore, this study will be conducted to compare PEEP titration using driving pressure versus oxygenation method versus constant PEEP and evaluate their efficacy on oxygenation, ventilation, hemodynamics and PPC for patients undergoing thoracoscopic esophagectomy treated with one lung ventilation in prone position.

Aim of the Study:

The aim of this study is to compare and evaluate the differences between three different PEEP values in patients who will undergo thoracoscopic esophagectomy treated with one lung ventilation in prone position receiving either constant PEEP or driving pressure guided individualized PEEP or oxygenation guided individualized PEEP.

It is hypothesized that the individualized PEEP guided by driving pressure could improve intraoperative oxygenation function, pulmonary mechanics, early postoperative atelectasis, and reduce the incidence of postoperative pulmonary complications(PPCs) for patients undergoing thoracoscopic esophagectomy treated with one lung ventilation in prone position.

Sample Size Calculation:

A pilot study was performed to measure the lung ultrasound score at the end of the surgery to estimate the sample size. Sample size calculations were performed using G. power software (version 3.1.9.7). The means and standard deviations for the D group, O group, and C group were 10.5 + 2.02, 11.7 + 1.2, and 12.5 + 2.5, respectively. Sample size calculations showed that 11 subjects per group will be required to achieve 95% power with a Type I error of 0.05. A total of 42 patients (14 patients per group) will be included in this trial considering an 80% adherence rate.

Methods:

The study will include 42 patients who will be scheduled for thoracoscopic esophagectomy treated with one lung ventilation in prone position under general anesthesia. It will be conducted in Mansoura gastroenterology center over one year and patients will be recruited in june 2023. they will be randomly assigned to 3 equal groups (D group, O group and C group) according to computer-generated table of random numbers using the permuted block randomization method. The group allocation will be concealed in sequentially numbered, sealed opaque envelopes which will be opened only after obtaining the written informed consent.A single investigator will assess the patients for eligibility, obtain written informed consent, open the sealed opaque envelopes containing group allocation and set up the ventilator as specified in the envelope. The study subjects and the resident assessing the outcome will be blinded to the study group.The study protocol will be explained to all patients after enrollment into the study. They will be kept fasting according to pre-operative ASA recommendations prior to surgery. Basic demographic characters including age, sex, and BMI will be recorded. The peri-operative management will be identical in the three groups.

Statistical analysis:- The collected data will be coded, processed, and analyzed using Statistical Package for the Social Sciences (SPSS) program (version 22) for Windows. Normality of numerical data distribution will be tested by Kolmogorov-Smirnov test. Normally distributed numerical data will be presented as mean and standard deviation, and their comparison in different groups will be performed using one-way ANOVA with post-hoc Bonferroni test. Non-normally distributed numerical data will be presented as median and range, and compared nonparametrically using Kruskal-Wallis test followed by Mann-Whitney U test. Categorical data will be presented as number and percentage, and their comparison will be performed using Chi-square test. The all data will be considered significant if P value is ≤ 0.05.