PCV‐VG combined individualized PEEP determination in one‐lung ventilated patients with PEEP step change direction: A randomized controlled trial

Abstract Introduction The efficacy of pressure‐controlled volume‐guaranteed ventilation (PCV‐VG) combined with a gradient‐directional change in positive end‐expiratory pressure (PEEP) during one‐lung ventilation (OLV) in patients who underwent thoracoscopic surgery was investigated. Methods Ninety patients were randomly divided into the PC (PCV‐VG + 5 cm H2O fixed PEEP), PI (PCV‐VG + incremental PEEP titration), and PD (PCV‐VG + decremental PEEP titration) groups. Hemodynamic (heart rate [HR] and mean arterial pressure [MAP]), respiratory mechanics (Ppeak, Pmean, and Cdyn), and arterial blood gas (pH, PaCO2, PaO2, and PaO2/FiO2) indices were evaluated at T1 (10 min of two‐lung ventilation [TLV]), T2 (10 min of OLV), and T3 (10 min of recovery, TLV). Enzyme‐linked immunosorbent assay was performed to detect neutrophil elastase (NE), clara cell secretory protein (CC16), and interleukin‐8 (IL‐8) levels at T1 and T3. Results At T2 and T3, Ppeak was lower in the PI and PD groups than in the PC group, while Pmean and Cdyn were higher than in the PC group. Ppeak in the PD group was lower than that in the PI group; however, Pmean was higher at T2 and T3 (P < 0.05). At T2, PaO2 and PaO2/FiO2 were higher, but PaO2/FiO2 and VD/VT were lower in the PD and PI groups than in the PC group (P < 0.05). NE, CC16, IL‐6, and IL‐8 levels were elevated in all three groups at T3, but the PI and PD groups had lower levels than the PC group (P < 0.05). The incidences of postoperative pulmonary complications (PPCs) and surgical intensive care unit hospitalizations in the PD and PI groups were much lower. Conclusion Gradient‐directed altered PEEP titration could improve respiratory mechanics, arterial blood gases, and inflammatory responses and reduce the incidence of PPCs in patients undergoing thoracoscopic surgery.

Video-assisted thoracoscopic surgery (VATS) is widely used because of small incisions, low bleeding, and quick patient recovery. 1VATs require one-lung ventilation (OLV) to provide a clear and convenient surgical view and sufficient surgical space to minimize compression or strain on cardiopulmonary tissues during surgery. 2 In addition, OLV is performed with a double-lumen bronchial tube or a bronchial blocker to separate the lung on the operative side, effectively isolating the lungs, ensuring oxygen supply to the ventilated lungs, and avoiding the spread of tumor lesions or cross-infection between the two lungs. 3However, non-physiological ventilation often results in hypoxemia due to increased intrapulmonary shunts and an imbalance in the ventilation-blood flow ratio. 4Furthermore, the incidence of postoperative pulmonary complications (PPCs) associated with OLV is as high as 20%, 5 seriously affecting the clinical prognosis of patients.
Pressure-controlled volume-guaranteed ventilation (PCV-VG) is a novel ventilation type, combining the advantages of both volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV). 6PCV-VG automatically adjusts airway pressure according to the mechanical parameters of each breath, which is an important part of the protective ventilation strategy. 7umerous studies have shown that positive endexpiratory pressure (PEEP) increases lung compliance, prevents alveolar collapse, and improves oxygen diffusion, thereby improving pulmonary dynamics and gas exchanges. 8However, it is unreasonable to use fixed PEEP for all patients.The optimal PEEP is determined by "PEEP titration" according to the patient's specific situation, which stabilizes lung function, minimizes lung injury, and achieves lung protection. 9Optimal PEEP titration determined by lung dynamic compliance (Cdyn) is widely used in clinic practice and has been shown to reduce PPCs in patients undergoing abdominal surgery. 7ifferent PEEP titration methods (incremental or decremental) may produce different results with individual PEEP settings; however, the specific differences in their effectiveness are unclear.
This study was conducted to explore the effects of PCV-VG combined with direction-changing PEEP on individualized PEEP determination and lung injury in patients with OLV.The results provide a new perspective on optimizing perioperative anesthesia techniques, reducing intraoperative lung injury, decreasing postoperative complications, and promoting early patient recovery.

| Research participants
The protocol was approved by the Clinical Trial Ethics Committee of the Affiliated Wuxi Fifth Hospital of Jiangnan University (Infectious Diseases Hospital of Wuxi) (No.2023-003-1), and written informed consent was obtained from patients or their families.All procedures are in accordance with the Declaration of Helsinki.
Patients undergoing elective thoracoscopic pulmonary surgery from April 2022 to January 2023 were selected based on the following criteria: (1) age ≥ 18 years; (2) body mass index (BMI) < 35 kg/m2 ; (3) American Society of Anesthesiologists (ASA) classification I-III; and (4) no preoperative blood transfusion.Patient exclusion criteria were as follows: (1) previous history of thoracic surgery; (2) patients with intracorporeal pacemakers; (3) preoperative diagnosis of pneumothorax or pulmonary maculopathy; (4) diagnosis of pulmonary infection, abnormal pulmonary function (FEV1 < 50%), or a history of systemic infection (WBC > 10 Â 10 9 and temperature > 37 C) within the past 1 month; and (5) patients with contraindications to PEEP use, such as high intracranial pressure, hypovolemic shock, and right heart failure.Enrolled patients with any of the following criteria were excluded: (1) surgical approach changed to thoracotomy; (2) intraoperative bleeding ≥ 500 ml; (3) OLV time < 45 min; (4) return to the ward with an endotracheal tube; and (5) peak airway pressure > 40 cm H 2 O on mechanical ventilation during PEEP.According to the above criteria, 90 patients were included in this preliminary study, depending on our ability to recruit patients (a power size calculation revealed a minimum sample size of n = 30 for a power of more than 80% to detect a correlation at a confidence interval of 0.95 and α level of 0.05), retain patients for the duration of the study, and perform intervention and follow-up.Demographic characteristics, including gender, age, BMI, smoking, alcohol use, and clinical information, are shown in Table 1.

| Grouping and anesthetic protocols
Eligible patients were randomly assigned to three study groups (in the ratio of 1:1:1) with a random number generated by using the Statistical Package for Social Sciences software version 22.0 for Windows (IBM SPSS Statistics, 22), based on their registration number in order of referral.The three groups were (i) PC group: as a control group, the patients treated with PCV-VG and received a conventional lung protective ventilation (LPV) strategy during OLV (maintain 5 cm H 2 O fixed PEEP after alveolar recruitment maneuvers (ARM); (ii) PI group: patients who received PCV-VG during OLV combined with an OLV ventilation strategy (applying incremental titration of optimal PEEP after ARM); (iii) PD group: patients who received PCV-VG in combination with a conventional LPV strategy during OLV (applying decremental titration of optimal PEEP after ARM).
Anesthesia and surgical protocols were prepared and performed by the same group of anesthesiologists and surgeons.Electrocardiogram (ECG), heart rate (HR), blood pressure, pulse oxygen saturation (SpO 2 ), and bispectral index (BIS) of the patients were monitored immediately upon arrival in the operating room.Peripheral venous access was opened, and a radial artery puncture catheter was placed under local anesthesia to monitor intraoperative arterial pressure and harvest samples for blood gas analysis (Avance CS2 pro; GE Healthcare, Piscataway, NJ, USA).Anesthesia was administered by intravenous injection of 0.05 mg/kg midazolam, 0.5 μg/kg sufentanil, 0.3 mg/kg etomidate, and 0.2 mg/kg cisatracurium.An endotracheal tube was inserted after complete muscle relaxation, and the position and mechanical ventilation were established.

| Mechanical ventilation settings
The ventilation parameters were the same in all three groups except for PEEP.First, the V T (tidal volume) was calculated based on the predicted body weight (PBW) according to the following equations: PBW = 50.0+ 0.91 Â [height (cm) -152.4] for males and PBW = 45.5 + 0.91 Â [height (cm) -152.4] for females.The fraction of inspired oxygen (FiO 2 ) for two-lung ventilation (TLV) before OLV was 100%, V T was 8 ml/kg PBW, inspiratory/expiratory ratio was 1:2, PEEP was sustained at 5 cm H 2 O, and all ventilation modes were VCV.
OLV was performed in the lateral position, and the parameters were set as V T 5-6 ml/kg, FiO 2 80%, inspiratory/expiratory ratio 1:2, and PEEP values were selected according to the study groups.
ARM was performed at the end of OLV with V T of 8 ml/kg, FiO 2 of 80%, and an inspiratory/expiratory ratio of 1:2.ARM was performed every 45 mins with the same ventilation pattern and PEEP values as in OLV.During ventilation, the respiratory rate was adjusted to maintain the patient's end-tidal carbon dioxide partial pressure (P ET CO 2 ) at 35-45 mmHg.

| ARM and PEEP titration
ARM and PEEP titrations were performed in the PI and PD groups.The patient was positioned laterally, and OLV was started after determining and adjusting the position of DLET (double lumen endotracheal tube) using a fiberoptic bronchoscope.An ARM with 5-10 cm H 2 O PEEP is a very useful and simple method for preventing atelectasis and promoting arteriolar oxygenation. 10ARM was performed on the ventilated side of the lung, and the ventilation mode was changed to PCV.The driving pressure was 20 cm H 2 O, the inspiratory/expiratory ratio was 1:1, and the respiratory rate was 15 breaths/min.PEEP in the PI group started at 0 cm H 2 O and increased by 2 cm H 2 O every 2 min until the Cdyn value reached its maximum value.PEEP in the PD group started at 16 cm H 2 O and decreased by 2 cm H 2 O every 2 min until the Cdyn value reached its maximum, and the optimal PEEP level was maintained until the end of ventilation.The PC group was subjected to the same ARM but without PEEP titration.After the first ARM, the PEEP value was set to 5 cm H 2 O, and the ARM was performed again 2 min later.The PCV was then changed to PCV-VG, and a PEEP of 5 cm H 2 O was maintained until the end of ventilation.If the hemodynamics were not stable (> 30% decrease in MAP) during the operation, the operation was discontinued, and 5-15 mg ephedrine or 0.05-15 mg phenylephrine was administered, depending on recovery.Resume of the study protocol (Supplementary data S-1).

| Data collection and measurement
Patients' hemodynamic indices, HR and MAP were recorded at T 1 (10 min after the initiation of TLV), T 2 (10 min after the initiation of OLV), and T 3 (10 min after the initiation of TLV recovery).V T , PEEP, airway peak pressure (P peak ), airway mean pressure (P mean ), and Cdyn of the patients were also recorded.2][13] Parameters were calculated using the following equation: V D /V T = (PaCO 2 -P ET CO 2 )/PaCO 2 .
A total of 3 ml of radial artery blood samples were collected in anticoagulation tubes at T 1 and T 3 .After centrifuging at 2000 rpm for 15 min at 4 C, the supernatant was stored at À80 C. Commercial enzyme-linked immunosorbent assay (ELISA) kits were employed to analyze the levels of neutrophil elastase (NE), clara cell secretory protein (CC16), and interleukin-8 (IL-8).

| Clinical endpoints
The primary outcome was the occurrence of postoperative pulmonary complications (PPCs) during hospitalization, including pneumonia, pulmonary atelectasis, acute respiratory failure (ARF), acute respiratory distress syndrome (ARDS), and secondary postoperative tracheal intubation.Mortality within 30 days of surgery was also recorded.
The diagnostic criteria for each item of PPCs were as follows: Pneumonia: new infiltrating shadows on chest X-ray and the presence of at least two of the following three indicators: (i) fever (>38.5 C) or hypothermia (<35.58C); (ii) white blood cell count below 4 Â 10 9 /L or > 12.4 Â 10 9 /L; (iii) purulent sputum for diagnosis.
Pulmonary Atelectasis: (i) New infiltrative lung shadow on chest radiography accompanied by interlobular fissures shifting towards the affected side.(ii) Management includes bronchoscopy, chest physiotherapy, or mechanical ventilation.
ARF: Dyspnea at rest; respiratory rate > 25 breaths/ min, PaO 2 /FiO 2 ratio < 200, requiring non-invasive or invasive ventilation (implemented due to hypercapnic acidosis with the partial pressure of carbon dioxide [PaCO2] ≥ 45 mmHg and pH ≤ 7.35). 14RDS was diagnosed according to Berlin's definition: (i) ARF unexplained by cardiac failure or fluid overload; (ii) refractory hypoxemia with PaO 2 /FIO 2 ≤ 200 mmHg on mechanical ventilation; (iii) bilateral opacities on chest imaging; and (iv) presentation within 1 week of a known clinical impairment or worsening of respiratory symptoms. 14econdary outcomes were the length of stay in the surgical intensive care unit (SICU) and the duration of hospital stay after surgery.Length of stay in the SICU was defined as the physical time spent in the ICU, and the duration of hospital stay was defined as the time from the end of surgery until discharge from the hospital.

| Statistical analysis
Statistical analyses were performed using SPSS version 22.0.Statistics of continuous variables conforming to a normal distribution (evaluated by skewness and kurtosis) were described as mean ± standard deviation.One-way analysis of variance (ANOVA) was used for betweengroup comparisons, and the least significant difference-t method was used for two-way comparisons.For continuous variables with skewed distributions, statistics were expressed as median and interquartile spacing, and the non-parametric Kruskal-Wallis H-test was employed for two-way comparisons between groups.Count data were expressed as frequency (rate) and compared using the χ 2 test.P < 0.05 was considered statistically significant.

| The demographic and intraoperative clinical information of patients
Ninety participants were included in this study (Figure 1).As shown in Table 1, demographic characteristics such as age, gender, BMI, and PBW among the participants in three groups (P > 0.05).The operative characteristics, such as the type of surgery, volume of fluids, duration of anesthesia, duration of operation, and duration of OLV were also not significantly different (P > 0.05).The results showed that the baseline clinical characteristics of the three groups of patients were comparable preoperatively.
The optimal PEEP obtained using PEEP decremental titration based on Cdyn was 8.7 ± 2.2 cm H 2 O, and the incremental PEEP titration was 8.2 ± 1.3 cm H 2 O, which was significantly different from the fixed 5 cm H 2 O.

| Clinical endpoint event
There was no significant difference in pneumonia, atelectasis, ARF, or ARDS among the three groups (P > 0.05, Table 2).However, the incidence of total PPCs was significantly lower in the PI and PD groups than in the PC group (P < 0.05, Table 2).In addition, the SICU residence times of the PI and PD groups were significantly shorter than those of the PC group (P < 0.05, Table 2).

| Hemodynamic indices of the three groups
As shown in Table 3, hemodynamic indices were subsequently analyzed.There was no significant difference in HR at T 1 , T 2 , and T 3 among the three groups (P > 0.05).In addition, the same results were observed for MAP, which was not statistically significant at T 1 , T 2 , or T 3 (P > 0.05).Thus, changes in the direction of PEEP had a slight effect on the hemodynamics of the OLA in the patients, but the difference was insignificant.

| Ventilation Analysis
There were no significant differences in the respiratory indices, such as P peak , P mean , and Cdyn, among the three groups at T 1 (P > 0.05).At T 2 , P peak was lower in the PI and PD groups than in the PC group, while P mean and Cdyn were higher (P < 0.05) Additionally, P peak was lower in the PD group than that in the PI group; however, P mean was elevated, while Cdyn was not significantly different between the PD and PC groups.Furthermore, at T 3 , decreased P peak and increased P mean and Cdyn were observed in both the PI and PD groups relative to the PC group.Although the differences in P peak and P mean between the PI and PD groups were significant, the difference in Cdyn was not (Table 4).

| Arterial blood gas variation analysis at different time points
As shown in Table 5, the median PaO 2 was significantly higher at T 2 in the PI and PD groups than that in the PC group (P < 0.05).In addition, PaO 2 /FiO 2 was higher in the PI and PD groups than that in the PC group (P < 0.05).

| The serum concentrations of lung V T biomarkers and inflammatory biomarker concentrations
Concentrations of serum biomarkers associated with pulmonary V T , NE, and CC16 were analyzed at T 1 and T 3 .
As illustrated in Figures 2A-B, NE, and CC16 levels were typically higher at T 3 in all three groups, and the PC group showed higher levels than those in the PI and PD groups (P < 0.05).In addition, the serum inflammatory biomarkers IL-6 and IL-8 were higher at T 3 , and the PI and PD groups showed lower levels than those in the PC group (P < 0.05, Figures 2C-D).PCV-VG combined with an individualized PEEP ventilation strategy significantly reduced inflammation and lung injury.

| DISCUSSION
This randomized controlled trial found that OLV with increasing or decreasing personalized titration of PEEP in PCV-VG mode significantly improved pulmonary air exchange and lung mechanics, and reduced serum inflammation, which contributes to an anti-inflammatory and pulmonary protective effect.In addition, incremental or decremental personalized titration of PEEP in the OLV was effective in suppressing the incidence of postoperative PPCs and reducing the length of stay in the SICU.
VCV, a ventilation model commonly used in clinical practice, ensures stable ventilation but generates high airway pressures, which in turn generates volume injury and leads to uneven gas distribution in the lungs. 15PCV reduces airway pressure and decelerates airflow, but may cause lung injury by exerting traction on the alveoli. 16owever, PCV-VG combines the advantages of VCV and PCV, which allows the use of decelerated airflow in the volume-controlled mode and simultaneously ensures V T T A B L E 4 Comparison of respiratory mechanics indices among the three groups of patients.airflow declaration, reducing airway and alveolar damage from high airway pressures, and protecting the lungs in various fields. 17OLV is usually used in thoracic surgery to isolate bilateral lungs and prevent secretions, infection sources, blood, or tumors from one lung from entering the other, thus protecting the healthy lungs.One-lung anesthesia is required for lung and thoracic surgeries to provide clear vision, shorten the operating time, and reduce unnecessary tissue damage.OLV is an essential form of ventilation for thoracoscopic surgery; however, recent studies have found that improper use of OLV causes lung injury. 18Due to shunting on the nonventilated side of the lung, some blood is not oxygenated, and pulmonary atelectasis occurs on the ventilated side of the lung, resulting in disproportionate ventilation blood flow, which further impairs arterial oxygenation and promotes hypoxemia. 19During anesthesia, when respiratory muscle groups relax and lose tone, the diaphragm moves cephalad, thoracic volume changes, and functional residual air volume and Cydn decrease, eventually causing disproportionate pulmonary ventilation blood flow on the ventilating side. 20From the perspective of a pulmonary protective ventilation strategy, appropriate PEEP during OLV is particularly important to prevent mechanical lung injury caused by V T and pulmonary atelectasis. 21In addition, high FiO 2 was used in this study before OLV because of the high hypoxia, and high FiO 2 is more commonly used in OLV and TLV 22,23 despite the adverse consequences of high oxygen levels, as reported in previous studies. 24ydn is used clinically as an indicator to assess the efficacy of PEEP pulmonary resuscitation. 25Currently, Cydn-based PEEP titration includes incremental and decremental titration methods. 7Previous studies have confirmed that both incremental and decremental titrations reduce intraoperative shunting; however, only decremental titration improves oxygenation and reduces the airway pressure fluctuations required for pulmonary ventilation. 26Another recent study suggested that incremental PEEP titration also improves oxygenation 27 and lung gas distribution uniformity in patients undergoing gynecologic laparoscopy. 28Therefore, patients who underwent OLV during thoracoscopic surgery were included in this study and were studied in conjunction with personalized PEEP titration and PCV-VG.The effectiveness of detecting lung injury using a fixed PEEP titration or incremental or decremental PEEP titrations immediately after ARM was investigated.Additionally, 5 cm H 2 O PEEP was investigated as a fixed PEEP titration based on previous pulmonary protective mechanical ventilation strategies. 29n this study, patients were randomized into three groups based on different PEEP titrations.

Parameters
Hemodynamics, respiratory mechanisms, and blood gas indices during the three phases of TLV (T 1 ), OLV (T 2 ), and TLV (T 3 ) were analyzed.No significant differences in hemodynamic indices were found in individualized PEEP titration changes.In contrast, the respiratory indices of patients with incremental and decremental PEEP titrations were lower than those of patients with fixed PEEP titrations.P mean and Cdyn were higher in the T 2 and T 3 phases.In our study, respiratory mechanics were improved by personalized PEEP titration and did not affect hemodynamic-related factors.Consistently, D'Antini and Rauseo conducted two Italian physiology studies in 2018 and found that OLA application titrated PEEP levels improved patient respiratory mechanics but did not affect hemodynamics. 30,31We also found a more significant decrease in P Peak and a more significant increase in P mean in patients with decremental PEEP titration than in those with incremental PEEP titration, suggesting that decremental PEEP titration improves respiratory mechanics.
Previous studies have demonstrated that OLV and surgical trauma are accompanied by the release of excess inflammatory cytokines and neutrophil elastase, leading to pulmonary infections and systemic inflammation, 7,32 which are responsible for postoperative multiorgan dysfunction and other PPCs.Among the many inflammatory factors that have been strongly associated with lung injury and complication, IL-8 and IL-6, the former to be catalysts for neutrophils and the latter reported to be a manifestation of the acute phase. 33CC16 is an inflammatory mediator that is secreted by Clara cells into the distal lung airway epithelium. 34Accumulating evidence has confirmed an association between CC16 and the occurrence of pulmonary atelectasis and hyperinflation in patients undergoing general anesthesia with mechanical ventilation. 7As one of the most destructive enzymes, NE is stored in neutrophils under physiological conditions and released during inflammation. 35NE breaks down almost the entire extracellular matrix and is an important plasma protein that is released by damaged capillary endothelial cells and alveolar epithelial cells, triggering the onset of acute lung injury. 36Large V T leads to hyperinflation of alveoli at the end of inspiration and repeated opening and atrophy of terminal tracheal alveoli, massive infiltration of neutrophils and macrophages, and release of larger amounts of inflammatory mediators, which, in turn, lead to reduced production and secretion of CC16 proteins, lowering lung tissue defenses and accelerating uncontrolled inflammation.NE and CC16 were employed as markers to indirectly evaluate the degree of lung injury in this study, assisted by the analysis of the inflammatory factors IL-6 and IL-8.It was also observed that NE, CC16, IL-6, and IL-8 levels were elevated in all three groups at T 3 ; however, both incremental and decremental PEEP titrations were reduced compared with fixed PEEP.
PPCs are among the most serious problems in the perioperative period and affect patient morbidity as well as lifetime. 22Although there is greater controversy as to whether incremental PEEP levels are superior to decremental PEEP titration reported in G. Tusman or F. Pet ak, 13,37 PEEP individualization can reduce the incidence, morbidity, and mortality. 38,39Herein, no significant differences were found among the three groups of patients for pneumonia, atelectasis, ARF, or ARDS; however, the total PPCs and SICU stay were lower in patients with incremental or decremental PEEP titration.
However, our study had several limitations.First, limited resources constrained us from recruiting sufficient sample sizes to investigate the clinical outcomes of patients with PPCs and other conditions.To ensure data rigor, this study used strict inclusion and exclusion criteria, which may have biased the results.Therefore, the focus of future research should be on conducting multicenter studies with larger sample sizes to explore and elaborate on the various perspectives in depth.In addition, the correlation between cytokine levels and the PEEP, or driving pressure used was missing from this study, which will be addressed in a subsequent study.Surgical procedures and lung atrophy are factors that can affect serum inflammation levels, warranting further investigation in subsequent studies.Additionally, more detailed hemodynamic monitoring, such as emergency fluid pushing, could not be performed during the procedure.Finally, there is a lack of measurement of intrinsic PEEP at zero PEEP.
In conclusion, the combination of PCV-VG with incremental or decremental PEEP titration ventilation strategies in the OLV showed a favorable effect on intraoperative respiratory mechanics, arterial blood gas indices, and inflammatory response, which reduced the incidence of postoperative PPCs.This study provides a new perspective on ventilation strategies for OLV.

Note:
Date are presented as mean ± Standard deviation (SD) or median (interquartile range).PaCO 2 , partial pressure of arterial carbon dioxide; V D /V T , dead space fraction; PaO 2 /FiO 2 , arterial partial pressure of oxygen/fraction of inspired oxygen.Two-way repeated ANOVA followed by post hoc comparison using Fisher LSD Method.*P < 0.05 vs. PC group.F I G U R E 2 Serum concentration of lung VT biomarkers and inflammatory biomarker concentrations.Perioperative changes in lung VT biomarkers of NE (A) and CC16 (B).The concentration of inflammatory factor markers IL-6 (C) and IL-8 (D) in three groups of patients during the perioperative period.*** P < 0.05, compared with the PC group.
Comparison of the baseline data of subjects.
Â (height in cm -152.4);ASA, American Society of Anesthesiologist; OLV: one-lung ventilation.Two-way repeated ANOVA followed by post hoc comparison using Fisher LSD Method.
Postoperative pulmonary complications and clinical endpoints events.Comparison of the hemodynamic index changes between the three groups.
T A B L E 2Note: Date are presented as n (%) or median (interquartile range).ARF, Acute respiratory failure; ARDS, Acute respiratory distress syndrome.Two-way repeated ANOVA followed by post hoc comparison using Fisher LSD Method.*P<0.05, compared with PC group.T A B L E 3Note: Date are presented as mean ± Standard deviation (SD) or median (interquartile range).HR: heart rate; MAP, mean arterial pressure.Two-way repeated ANOVA followed by post hoc comparison using Fisher LSD Method.
Changes of arterial blood gas at different time points for the patients among the three groups.
Note: Date are presented as mean ± Standard deviation (SD), numbers or median (interquartile range); P peak , peak airway pressure; P mean , mean airway pressure; Cdyn, dynamic compliance.Two-way repeated ANOVA followed by post hoc comparison using Fisher LSD Method.*P< 0.05 vs. PC group.#P < 0.05 vs. PI group.T A B L E 5