In the case of increasing PEEP for a patient with ARDS on ventilatory support, what is the expected physiological response?

Increasing PEEP (Positive End-Expiratory Pressure) in patients with ARDS (Acute Respiratory Distress Syndrome) typically results in increased intrathoracic pressure. PEEP helps to keep the alveoli open at the end of expiration, which can improve oxygenation by increasing functional residual capacity and recruiting collapsed alveoli. However, this increase in lung volume and the pressure from the additional PEEP leads to elevated intrathoracic pressure.

As the intrathoracic pressure rises, it can affect the hemodynamics of the patient, potentially leading to decreased venous return to the heart. This response highlights the hemodynamic interplay between ventilatory mechanics and cardiovascular function in critically ill patients. Understanding this physiological mechanism is crucial for managing patients with ARDS effectively.

The other potential responses to increased PEEP, such as decreased oxygenation and improved lung compliance, are not typically expected; PEEP is generally implemented to enhance oxygenation and is often accompanied by a decrease in compliance due to pressure effects. Additionally, the cardiac output may diminish due to the increased intrathoracic pressure affecting blood return, but the immediate and direct effect of increasing PEEP is the elevation of intrathoracic pressure itself.