Transpulmonary Pressure and Gas Exchange During Decremental PEEP Titration in Pulmonary ARDS Patients

BACKGROUND: 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 (P_tp) and gas exchange during a decremental PEEP titration maneuver in subjects with pulmonary ARDS.

METHODS: 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 (P_aw), esophageal pressure (P_es), P_tp (P_aw – P_es), the ratio of dead space to tidal volume (V_D/V_T), and P_aO2 were recorded at each step.

RESULTS: A linear correlation was found between P_aw and P_tp. Expiratory P_tp became negative in all subjects when PEEP decreased below 8.9 ± 5.2 cm H₂O. V_D/V_T was 0.67 ± 0.06 with 30 cm H₂O of PEEP, and decreased 15.4 ± 8.5% during the maneuver, when PEEP and expiratory P_tp were 10.6 ± 4.1 cm H₂O and 1.2 ± 2.8 cm H₂O, respectively. V_D/V_T was significantly higher during ventilation at high (> 18 cm H₂O), compared to low, inspiratory P_tp values (P < .001). P_aO2 decreased when expiratory P_tp became negative (P < .001).

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