What does a flat pressure-volume loop indicate during mechanical ventilation?

A flat pressure-volume loop during mechanical ventilation typically indicates a decrease in lung compliance, which can occur when there is increased PEEP (Positive End-Expiratory Pressure). Increased PEEP raises the baseline pressure in the lungs and can make it more difficult for the lungs to expand during inspiration. As a result, the pressure needed to produce a change in volume is greater, resulting in a flatter loop.

The characteristics of the pressure-volume loop allow clinicians to assess the mechanics of breathing and lung function. A flat loop suggests that even with increased pressure, the change in lung volume is minimal, indicating poorer lung compliance, which can be a response to high levels of PEEP. Therefore, the presence of a flat loop is indicative of the effects of increased PEEP, affecting how the ventilator needs to be adjusted to match the patient’s pulmonary mechanics.