Pathophysiology and clinical applications of PEEP in acute brain injury

Mechanical ventilation is a life-sustaining treatment needed in patients with acute brain injury to maintain airway permeability, optimize gas exchange, and prevent secondary brain damage. Positive end-expiratory pressure (PEEP), a key component of mechanical ventilation, helps prevent atelectasis, improve oxygenation, and stabilize alveolar recruitment, offering potential benefits in terms of lung protection. However, neurological tolerance of PEEP can be poor in brain-injured patients. The variability in lung and chest-wall elastance, lung recruitability, cardiac function, and fluid status, as well as the integrity of cerebral autoregulation, further complicates the recommendations for the safe range of PEEP in this patient population. This review aims to explore the physiological effects of PEEP on the brain-heart-lung interplay, focusing on the direct and indirect influences of PEEP on intracranial and cerebral perfusion pressures, as well as cerebral perfusion. We also discuss the need for individualized mechanical ventilation settings to balance the respiratory benefits of PEEP against its potential adverse effects on cerebral perfusion.