A fixed correction of absolute transpulmonary pressure may not be ideal for clinical use : Discussion on "Accuracy of esophageal pressure to assess transpulmonary pressure during mechanical ventilation"

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 (R²=0.71, p=0.005 and R²=0.77, p=0.001, respectively) and during inspiration (R²=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.

During controlled ventilation without respiratory muscle activity, absolute oesophageal pressure is higher than the pleural pressure of the nondependent lung regions and could therefore underestimate the highest level of lung stress in that lunghttps://bit.ly/3a95CUh

Should we titrate peep based on end-expiratory transpulmonary pressure?-yes

Ventilator management of patients with acute respiratory distress syndrome (ARDS) has been characterized by implementation of basic physiology principles by minimizing harmful distending pressures and preventing lung derecruitment. Such strategies have led to significant improvements in outcomes. Positive end expiratory pressure (PEEP) is an important part of a lung protective strategy but there is no standardized method to set PEEP level. With widely varying types of lung injury, body habitus and pulmonary mechanics, the use of esophageal manometry has become important for personalization and optimization of mechanical ventilation in patients with ARDS. Esophageal manometry estimates pleural pressures, and can be used to differentiate the chest wall and lung (transpulmonary) contributions to the total respiratory system mechanics. Elevated pleural pressures may result in negative transpulmonary pressures at end expiration, leading to lung collapse. Measuring the esophageal pressures and adjusting PEEP to make transpulmonary pressures positive can decrease atelectasis, derecruitment of lung, and cyclical opening and closing of airways and alveoli, thus optimizing lung mechanics and oxygenation. Although there is some spatial and positional artifact, esophageal pressures in numerous animal and human studies in healthy, obese and critically ill patients appear to be a good estimate for the "effective" pleural pressure. Multiple studies have illustrated the benefit of using esophageal pressures to titrate PEEP in patients with obesity and with ARDS. Esophageal pressure monitoring provides a window into the unique physiology of a patient and helps improve clinical decision making at the bedside.