Transpulmonary pressure and gas exchange during decremental PEEP titration in pulmonary ARDS patients

Selection of the PEEP associated with the best compliance of the respiratory system during decremental PEEP titration can be used for the treatment of patients suffering from ARDS. We describe changes in transpulmonary pressure (Ptp) and gas exchange during a decremental PEEP titration maneuver in subjects with pulmonary ARDS.

Eleven subjects with early ARDS were included. After a recruitment maneuver they were ventilated in volume-controlled ventilation and PEEP was decreased from 30 to 0 cm H2O by steps of 3 cm H2O. Static airway pressure (Paw), esophageal pressure (Pes), Ptp (Paw - Pes), the ratio of dead space to tidal volume (VD/VT), and PaO2 were recorded at each step.

A linear correlation was found between Paw and Ptp. Expiratory Ptp became negative in all subjects when PEEP decreased below 8.9 ± 5.2 cm H2O. VD/VT was 0.67 ± 0.06 with 30 cm H2O of PEEP, and decreased 15.4 ± 8.5% during the maneuver, when PEEP and expiratory Ptp were 10.6 ± 4.1 cm H2O and 1.2 ± 2.8 cm H2O, respectively. VD/VT was significantly higher during ventilation at high (> 18 cm H2O), compared to low, inspiratory Ptp values (P < .001). PaO2 decreased when expiratory Ptp became negative (P < .001).

During decremental PEEP titration we sequentially observed high inspiratory Ptp that stressed lung tissue and increased VD/VT, and negative Ptp, indicating high risk of alveolar collapse, explaining worse oxygenation. PEEP selection based on Ptp and VD/VT in ARDS may help to avoid these situations.