Oesophageal pressure as a surrogate of pleural pressure in mechanically ventilated patients

BACKGROUND: Oesophageal pressure (P(oes)) is used to approximate pleural pressure (P(pl)) and therefore to estimate transpulmonary pressure (P(L)). We aimed to compare oesophageal and regional pleural pressures and to calculate transpulmonary pressures in a prospective physiological study on lung transplant recipients during their stay in the intensive care unit of a tertiary university hospital. METHODS: Lung transplant recipients receiving invasive mechanical ventilation and monitored by oesophageal manometry and dependent and nondependent pleural catheters were investigated during the post-operative period. We performed simultaneous short-time measurements and recordings of oesophageal manometry and pleural pressures. Expiratory and inspiratory P(L) were computed by subtracting regional P(pl) or P(oes) from airway pressure; inspiratory P(L) was also calculated with the elastance ratio method. RESULTS: 16 patients were included. Among them, 14 were analysed. Oesophageal pressures correlated with dependent and nondependent pleural pressures during expiration (R(2)=0.71, p=0.005 and R(2)=0.77, p=0.001, respectively) and during inspiration (R(2)=0.66 for both, p=0.01 and p=0.014, respectively). P(L) values calculated using P(oes) were close to those obtained from the dependent pleural catheter but higher than those obtained from the nondependent pleural catheter both during expiration and inspiration. CONCLUSIONS: In ventilated lung transplant recipients, oesophageal manometry is well correlated with pleural pressure. The absolute value of P(oes) is higher than P(pl) of nondependent lung regions and could therefore underestimate the highest level of lung stress in those at high risk of overinflation.