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 1120 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.