Positive end-expiratory pressure ventilation increases extravascular lung water due to a decrease in lung lymph flow

Area of Science:

• Physiology
• Critical Care Medicine

Background:

• Positive end-expiratory pressure (PEEP) is a cornerstone in managing respiratory failure, aiming to enhance gas exchange and lung aeration.
• The precise impact of PEEP on extravascular lung water (EVLW) remains an area requiring further elucidation.
• Understanding PEEP's effects on lung fluid dynamics is crucial for optimizing mechanical ventilation strategies.

Purpose of the Study:

• To prospectively investigate the effects of PEEP on EVLW and pulmonary lymph flow (QL) in a physiological animal model.
• To determine the reversibility of PEEP-induced changes in EVLW and QL.

Main Methods:

• A prospective laboratory experiment was conducted on twelve adult sheep.
• Measurements included cardiopulmonary hemodynamics, EVLW, QL, and arterial blood gases under varying PEEP levels (0 and 10 cmH2O).
• Animals were mechanically ventilated in an awake state, with PEEP adjusted over a two-hour baseline, two hours at 10 cmH2O, and a return to baseline.

Main Results:

• Increasing PEEP to 10 cmH2O significantly increased EVLW (498 ± 40 to 630 ± 58 ml) and decreased QL (7 ± 1 to 5 ± 1 ml/h).
• These changes in EVLW and QL were reversible upon reducing PEEP back to baseline levels.
• Cardiac output remained unaffected by the changes in PEEP.

Conclusions:

• The application of PEEP leads to a reversible increase in EVLW in the lungs.
• This increase in EVLW is associated with a corresponding decrease in pulmonary lymph flow.
• PEEP influences lung fluid balance, highlighting the need for careful monitoring during mechanical ventilation.