Evaluating the impact of varying positive end-expiratory pressure on intracranial pressure via optic nerve sheath diameter sonography in adults with brain injury

Background Traumatic brain injury(TBI) is a significant cause of mortality and disability in adults. Intracranial pressure(ICP) is typically measured invasively, while the noninvasive measurement of optic nerve sheath diameter(ONSD) is gaining popularity as a surrogate. Positive end-expiratory pressure(PEEP), a key component of mechanical ventilation, has been found to affect ICP. This study aimed to evaluate the effect of different PEEP values on ONSD and to correlate these changes with direct ICP measurements. Material and methods This prospective observational study enrolled 12 adult patients with severe TBI admitted to the ICU, requiring invasive ICP monitoring. The ONSD was examined using ultrasound at PEEP levels of 5,7,10,and 12cmH 2 O, while the ICP was measured concurrently using an external ventricular drain(EVD). Results Increasing PEEP from 7 to 10 cmH 2 O significantly increased the right ONSD(P = 0.002) but did not significantly affect the left ONSD(P > 0.016). The mean ONSD increased significantly with each incremental step in PEEP(P < 0.016). ICP also increased significantly when PEEP was changed from 7 to 10 cmH 2 O(P = 0.002), but it remained within a normal range(ICP < 20 mmHg). Importantly, increasing PEEP did not significantly affect cerebral perfusion pressure(CPP) (P > 0.016). An ONSD > 5.30 mm was found to predict an ICP > 17 cmH 2 O with 83.33 % sensitivity and 82.79 % specificity(AUC = 0.904, P < 0.001). Conclusion In patients with TBI and normal baseline ICP, PEEP can be safely increased up to 12 cmH 2 O without compromising CPP. The mean ONSD can be used as a reliable, noninvasive tool to monitor for PEEP-induced changes in ICP, with an ONSD of 5.30 mm serving as a critical threshold.