PEEP titrated mechanical ventilation

Enrolled patients will receive a sequential, step-wise increase in positive end-expired pressure from 5 cmH2O to 15 cmH2O. Intracranial pressure, transpulmonary pressure, vitals, and mechanical ventilator data will be measured at each increment. PEEP will be increased by increments of 5 cmH2O. The mode of mechanical ventilation (pressure or volume control), inspiratory time and fraction of inspired oxygen (FIO2) will be determined by the critical care team caring for the patient. In the event that PEEP is set > 5 cmH2O, measurements will be obtained from that starting point and increased to a maximum of 15 cmH2O. The physiologic measurements will be obtained at regular intervals (within 5 minutes at each PEEP level) throughout the PEEP titration period.

Intracranial pressure will be measured and recorded using the existing intracranial pressure monitoring device placed previously as part of the patient's routine care. The association between positive end expiratory pressure and intracranial pressure will be analyzed as the primary outcome.

Transpulmonary pressure will be measured and recorded using an esophageal balloon catheter placed for research purposes. The association between transpulmonary pressure change with titration of PEEP and intracranial pressure will be analyzed as a secondary outcome.