Which of the following best describes intrapleural pressure during mechanical ventilation with PEEP?

Intrapleural pressure refers to the pressure within the pleural cavity, the space between the lungs and the chest wall. In a healthy, spontaneously breathing individual, intrapleural pressure is typically negative, which aids in lung expansion. However, during mechanical ventilation, particularly when positive end-expiratory pressure (PEEP) is applied, the dynamics of intrapleural pressure change.

Positive end-expiratory pressure involves delivering a certain amount of pressure during the end of expiration to ensure that the alveoli remain inflated and to improve oxygenation. When PEEP is applied, it effectively raises the baseline pressure in the lung. As a result, the intrapleural pressure becomes less negative or can even be mildly positive during certain phases of the ventilatory cycle, especially when the ventilator is actively delivering a breath.

Thus, during mechanical ventilation with PEEP, the increase in intrapleural pressure that accompanies the application of positive pressure ventilation leads to a state where the pressure is no longer negative but has reached a positive level at certain points in the respiratory cycle. This positive pressure enables the benefits of mechanical ventilation while preventing the collapse of alveoli.