Effect of positive end-expiratory pressure on intracranial pressure in post cranial surgery using ultrasonic imaging measurement the optic nerve sheath diameter

Background: While positive end expiratory pressure (PEEP) is beneficial for oxygenation, it may potentially increase intracranial pressure (ICP): especially in post-cranial surgical patients. The optic nerve sheath diameter (ONSD) is the non-invasive method of ICP measurement. Our study focuses on the association between PEEP and intracranial pressure (ICP) in post-cranial surgery patients using optic nerve sheath diameter (ONSD) as a surrogate marker. Method: A prospective non-randomized interventional study was conducted on post-cranial surgical patients who required mechanical ventilation with ages 16-80 years, initial PEEP at 5 mmH2O were included in this study. Patients with intracranial hypertension (defined as ICP ≥22 mmHg), a history of traumatic brain injury, or cardiopulmonary disease at enrollment were excluded from the study. ONSD measurement was performed at varying PEEP levels from 5 to 20 cmH2O. Result: In adult (18-60 years) patients who had post-cranial surgery within 72 hours and required a mechanical ventilator, ONSD corresponding to ICP significantly increased when PEEP exceeded 13 cmH2O. PEEP more than 15 cmH2O resulted in a significant increase in ONSD exceeding 5.5 mm (corresponding to ICP > 22 mmHg); Mean arterial pressure (MAP) significantly decreased with an increase in PEEP value (p < 0.001). PEEP 20 cmH2O reduced MAP to below 65 mmHg. Conclusion: PEEP less than 15 cmH2O can be safely applied to post-cranial surgical patients, whereas PEEP more than 20 cmH2O may be harmful due to both ICP elevation and MAP decrement for these patients.