Data Sheet 1_Positive end-expiratory pressure increases intracranial pressure but does not affect PRx, regardless of body position, in a porcine ARDS model.docx

BackgroundPositive end-expiratory pressure (PEEP) and prone positioning are key components in the management of acute respiratory distress syndrome (ARDS), improving gas exchange and protecting the lung via enhanced lung recruitment and homogenization of lung aeration. However, higher intrathoracic pressures may increase intracranial pressure (ICP) or impair cerebral autoregulation, as reflected by vascular reactivity. This study investigated whether stepwise PEEP elevations affect ICP, the pressure reactivity index (PRx), and brain tissue oxygenation (PbO2) in a porcine ARDS model, comparing prone and supine positions, and whether baseline physiological variables modify the ICP response.
MethodsTwelve anesthetized pigs with bronchial lavage–induced ARDS were studied in a randomized crossover design with stepwise PEEP increases (5, 10, 15, and 20 cmH2O) in prone and supine positions while maintaining stable arterial carbon dioxide tension and cerebral perfusion pressure. Intracranial pressure, PRx, and PbO2 were continuously monitored, and effects of PEEP and position were analyzed using linear mixed-effects models and analysis of variance.
ResultsIncreasing PEEP was associated with a progressive rise in ICP, whereas PRx remained unchanged across PEEP levels and body positions. PbO2 showed a non-significant upward trend with increasing PEEP, while the PbO2/PaO2 ratio remained stable. Higher baseline pulmonary artery pressure was associated with larger ICP increases, whereas higher baseline respiratory rate was associated with attenuated responses.
ConclusionIn this porcine ARDS model, moderate PEEP escalation resulted in a modest increase in ICP without impairment of cerebrovascular reactivity, with similar effects in prone and supine positions, suggesting that lung protective ventilation strategies may be compatible with stable intracranial physiology when arterial carbon dioxide tension and cerebral perfusion pressure are controlled.