Brain Monitoring During PEEP-Based Respiratory Therapy in Critically Ill Patients

Acute brain injury is frequently accompanied by respiratory dysfunction requiring mechanical ventilation because of impaired consciousness, respiratory insufficiency, or the need for airway protection. Positive end-expiratory pressure (PEEP) and lung recruitment maneuvers (RM) are commonly applied to improve oxygenation and prevent alveolar collapse. Although these interventions are essential components of lung-protective ventilation, increases in intrathoracic pressure may influence venous return, systemic hemodynamics, cerebral perfusion, carbon dioxide homeostasis, and cerebral blood flow. Such physiological alterations may subsequently affect cortical activity and neurovascular coupling, particularly in patients with impaired cerebrovascular regulation. However, the cerebral effects of ventilator interventions remain incompletely understood in neurocritical care populations.

This prospective, single-center study is designed to investigate brain-lung interactions during mechanical ventilation in patients admitted to a neurocritical care unit. The study focuses on the dynamic relationships among ventilator settings, cerebral electrophysiological activity, cerebral hemodynamics, and systemic physiological responses during clinically indicated recruitment maneuvers and PEEP adjustments.

During routine respiratory management, participants will undergo predefined ventilator interventions consisting of recruitment maneuvers and PEEP modifications according to the study protocol. Physiological signals will be continuously recorded throughout baseline, intervention, and recovery periods. This design allows assessment of cerebral responses to controlled changes in intrathoracic pressure and respiratory support while minimizing interference with standard clinical care.

Multimodal physiological monitoring will be performed simultaneously throughout the study period. Monitoring modalities include scalp electroencephalography (EEG), transcranial Doppler ultrasonography (TCD), invasive arterial blood pressure monitoring, end-tidal carbon dioxide monitoring, pulse oximetry, and routine intensive care monitoring. Physiological signals from multiple monitoring devices will be synchronized and recorded using a dedicated multimodal data acquisition platform. High-resolution recordings of cerebral electrophysiological activity, cerebral blood flow velocity, arterial blood pressure, respiratory parameters, and end-tidal carbon dioxide will allow assessment of rapid physiological responses occurring during ventilator interventions. Continuous acquisition of synchronized physiological signals will permit integrated evaluation of respiratory, cardiovascular, and cerebral responses.

EEG recordings will be analyzed using quantitative electrophysiological methods to characterize cortical activity. Spectral analysis will be performed to assess changes across conventional frequency bands, including relative delta activity and other power-based indices reflecting alterations in cortical functional state. Cerebral blood flow dynamics will be evaluated using TCD-derived cerebral blood flow velocity measurements. Simultaneous recordings of arterial blood pressure and end-tidal carbon dioxide will provide complementary information regarding cerebral perfusion and respiratory physiology.

A central component of the study is the investigation of neurovascular coupling during mechanical ventilation. Integrated analysis of EEG activity and cerebral blood flow oscillations will be performed to characterize physiological coupling between neuronal activity and cerebral circulation. Relationships among cerebral electrophysiological activity, cerebral blood flow velocity, systemic hemodynamics, respiratory variables, and ventilator settings will be explored to better understand mechanisms underlying brain-lung interactions. These analyses will provide insight into how ventilator-induced physiological changes may influence cerebral function and cerebrovascular regulation in critically ill patients.

By providing simultaneous assessment of respiratory, hemodynamic, and neurophysiological responses during ventilator interventions, this study aims to improve understanding of the physiological mechanisms linking mechanical ventilation and brain function. The findings may contribute to the development of individualized ventilatory strategies that optimize respiratory support while preserving cerebral physiological stability in patients with acute brain injury.

Inclusion criteria

• Age ≥18 years.
• Admission to the neurocritical care unit with acute brain injury requiring intensive care management.
• Receiving invasive mechanical ventilation.
• Undergoing clinically indicated recruitment maneuvers and positive end-expiratory pressure (PEEP) adjustments.
• Availability of an adequate temporal acoustic window for transcranial Doppler monitoring.
• Written informed consent obtained from the participant or a legally authorized representative.

Exclusion criteria

• Pregnancy.
• Hemodynamic instability precluding recruitment maneuvers or PEEP adjustments.
• Severe cardiac dysfunction judged by the treating physician to contraindicate study procedures.
• Inability to obtain adequate transcranial Doppler signals.
• Conditions preventing EEG monitoring, including extensive scalp injury or dressings that preclude electrode placement.
• Withdrawal of informed consent.