The relationship of lung recruitability assessment by recruitment to inflation ratio, electrical impedance tomography, and lung ultrasound: The research protocol

Background: Recently, the recruitment-to-inflation ratio (R/I ratio) from the single-breath technique has been proposed for identifying lung recruitability in acute respiratory distress syndrome (ARDS). This technique is based on measuring end-expiratory lung volume (EELV). Also, electrical impedance tomography (EIT) can estimate the EELV, providing the potential role of EIT in measuring the R/I ratio. In addition, the lung ultrasound was proved to identify lung recruitment. However, a study validating those techniques has not been conducted. Methods: We plan to conduct a single-center prospective physiological study on moderate to severe ARDS patients. The R/I ratio by single-breath technique and EIT will be collected before the recruitment maneuver. If the patient has no airway opening pressure (AOP), PEEP of 8 cmH2O will be set as PEEPlow. The PEEPhigh defines as initially set at +10 cmH2O from the PEEPlow. However, if the patients have AOP presence, AOP +10 cmH2O will be set as PEEPhigh The lung ultrasound score (LUS) will be performed at PEEPhigh and PEEPlow during the single-breath technique. Variables that will be used to analyze the relationship are recruited volume (Vrec), R/I ratio, and LUS. Hypothesis: We hypothesize that there are associations between the R/I ratio by both techniques and lung ultrasound score (LUS). Ethics: The study protocol has been approved by the ethics committee of the faculty of medicine, Ramathibodi Hospital, Mahidol University (COA.MURA2021/433).