Intracranial pressure responsiveness to positive end-expiratory pressure is influenced by chest wall elastance: a physiological study in patients with aneurysmal subarachnoid hemorrhage

BACKGROUND: Respiratory system elastance (E(RS)) is an important determinant of the responsiveness of intracranial pressure (ICP) to positive end-expiratory pressure (PEEP). However, lung elastance (E(L)) and chest wall elastance (E(CW)) were not differentiated in previous studies. We tested the hypothesis that patients with high E(CW) or a high E(CW)/E(RS) ratio have greater ICP responsiveness to PEEP. METHODS: An esophageal balloon catheter was placed to measure esophageal pressure. PEEP was increased from 5 to 15 cmH(2)O. Airway pressure and esophageal pressure were measured and E(L), E(CW) and E(RS) were calculated at the two PEEP levels. Patients were classified into either an ICP responder group or a non-responder group based on whether the change of ICP after PEEP adjustment was greater than or less than the median of the overall study population. RESULTS: The magnitude of the increase in esophageal pressure (median [interquartile range]) at end-expiratory occlusion was significantly increased in the responder group compared with that in the non-responder group (4.1 [2.7–4.1] versus 2.7 [0.0–2.7] cmH(2)O, p = 0.033) after PEEP adjustment. E(CW) and the E(CW)/E(RS) ratio were significantly higher in ICP responders than in non-responders at both low PEEP (p = 0.021 and 0.017) and high PEEP (p = 0.011 and 0.025) levels. No significant differences in E(RS) and E(L) were noted between the two groups at both PEEP levels. CONCLUSIONS: Patients with greater ICP responsiveness to increased PEEP exhibit higher E(CW) and a higher E(CW)/E(RS) ratio, suggesting the importance of ECW monitoring. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12883-018-1132-2) contains supplementary material, which is available to authorized users.