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

Abstract

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 cmH₂O. 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] cmH₂O, 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.