Patients will be enrolled in the first 24 hours of admission to the intensive care unit. APACHE-2 and SAPS-2 scores will be noted 24 hours after admission. COVID-19 pneumonia will be confirmed according to World Health Organization (WHO) interim guidance. Level of sedation will be monitored with Ramsey Sedation Scale.~An esophageal balloon will be inserted in order to measure transpulmonary pressure(Ptp). The proper localization will be estimated according to ear-nose-xiphoid length. Localization of the balloon will be confirmed with the Baydur maneuver. Mojoli methods will be used to optimize the balloon filling volume.~All patients will be mechanically ventilated under Intellivent-ASV mode. Initial settings will based on predicted body weight. 45 cmH2O will be determined as target end-tidal carbondiokside (ETCO2) but permissive hypercapnia will be allowed if necessary, to maintain lung protective ventilation. Safe pH value will be determined 7.25 independent from ETCO2 levels in patients who will be applied lung protective ventilation. FiO2 and PEEP will be set to maintain an SpO2 of 88-92%.~Ptpinsp will be calculated by subtracting the esophageal pressure from the alveolar pressure measured during inspiratory pause maneuver. Targeted inspiratory transpulmonary pressure (Ptpinsp) was determined to be below 20 cmH2O. If Ptpinsp exceeds 20 cmH2O, minute-volume (MinVol) will be decreased by 10%. Minvol will be reduced below 100% if necessary, to achieve the target. Expiratory transpulmonary pressure (Ptpexp) will be calculated by subtracting the esophageal pressure from the alveolar pressure measured during expiratory pause maneuver. Targeted Ptpexp was determined from 0 to 3 cmH2O. If Ptpexp is below 0 cmH2O, PEEP will be increased until Ptpexp is positive. If Ptpexp exceed 3 mH2O, PEEP will be decreased until Ptpexp is below 3 mH2O. Transpulmonary pressure will be recorded at the beginning after that at least twice daily morning and evening visits. All measurement will be made in passive condition. Transpulmonary pressure measurement will continue until the patient is awake.
Transpulmonary pressure may be higher in ARDS patients due to decreased respiratory system compliance. The hypothesis is that tidal volumes which are generated by Intellivent- Adaptive support ventilation (ASV) are safe range by transpulmonary pressure.