Which lung should CPAP be applied to improve ventilation-perfusion mismatch?

The correct application of CPAP (Continuous Positive Airway Pressure) to improve ventilation-perfusion mismatch is best directed to the non-dependent lung. This choice is based on the principles of pulmonary physiology and how CPAP functions to enhance oxygenation.

In a situation where there is a mismatch between ventilation and perfusion, typically seen in conditions such as acute respiratory distress syndrome (ARDS) or other forms of lung injury, the non-dependent lung is the area that may not be receiving adequate ventilation due to gravity and the positioning of the patient. Applying CPAP to the non-dependent lung helps to open up collapsed or poorly ventilated alveoli, increasing the surface area available for gas exchange. This can lead to improved ventilation in previously hypoventilated regions and, consequently, better oxygenation and overall gas exchange efficiency.

In contrast, directing CPAP to the dependent lung may not yield the same benefits because this lung area is often already optimized for perfusion due to gravity, while its ventilation may be compromised. The aim of using CPAP in these cases is to improve ventilation to areas that are not receiving adequate airflow, hence targeting the non-dependent lung will generally produce more favorable outcomes regarding ventilation-perfusion matching and overall respiratory mechanics.