title: Changes in cerebral compartmental compliances during mild hypocapnia in patients with traumatic brain injury.
abstract: The benefit of induced hyperventilation for intracranial pressure (ICP) control after severe traumatic brain injury (TBI) is controversial. In this study, we investigated the impact of early and sustained hyperventilation on compliances of the cerebral arteries and of the cerebrospinal (CSF) compartment during mild hyperventilation in severe TBI patients. We included 27 severe TBI patients (mean 39.5 ± 3.4 years, 6 women) in whom an increase in ventilation (20% increase in respiratory minute volume) was performed during 50 min as part of a standard clinical CO(2) reactivity test. Using a new mathematical model, cerebral arterial compliance (Ca) and CSF compartment compliance (Ci) were calculated based on the analysis of ICP, arterial blood pressure, and cerebral blood flow velocity waveforms. Hyperventilation initially induced a reduction in ICP (17.5 ± 6.6 vs. 13.9 ± 6.2 mmHg; p < 0.001), which correlated with an increase in Ci (r(2) = 0.213; p = 0.015). Concomitantly, the reduction in cerebral blood flow velocities (CBFV, 74.6 ± 27.0 vs. 62.9 ± 22.9 cm/sec; p < 0.001) marginally correlated with the reduction in Ca (r(2) = 0.209; p = 0.017). During sustained hyperventilation, ICP increased (13.9 ± 6.2 vs. 15.3 ± 6.4 mmHg; p < 0.001), which correlated with a reduction in Ci (r(2) = 0.297; p = 0.003), but no significant changes in Ca were found during that period. The early reduction in Ca persisted irrespective of the duration of hyperventilation, which may contribute to the lack of clinical benefit of hyperventilation after TBI. Further studies are needed to determine whether monitoring of arterial and CSF compartment compliances may detect and prevent an adverse ischemic event during hyperventilation.
authors.affiliation: Academic Neurosurgery Unit, Department of Clinical Neurosciences, University of Cambridge, Cambridge, United Kingdom. emmanuel.carrera@chuv.ch
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Carrera
authors.forename: Luzius A
authors.initials: LA
authors.lastname: Steiner
authors.forename: Gianluca
authors.initials: G
authors.lastname: Castellani
authors.forename: Peter
authors.initials: P
authors.lastname: Smielewski
authors.forename: Christian
authors.initials: C
authors.lastname: Zweifel
authors.forename: Christina
authors.initials: C
authors.lastname: Haubrich
authors.forename: John D
authors.initials: JD
authors.lastname: Pickard
authors.forename: David K
authors.initials: DK
authors.lastname: Menon
authors.forename: Marek
authors.initials: M
authors.lastname: Czosnyka
mesh_terms: D000328:Adult; D001930:Brain Injuries / Q000150:complications* / Q000175:diagnosis / Q000473:pathology*; D003187:Compliance / Q000502:physiology; D005260:Female; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D006985:Hyperventilation / Q000473:pathology / Q000503:physiopathology*; D016857:Hypocapnia / Q000175:diagnosis / Q000209:etiology* / Q000473:pathology*; D019586:Intracranial Hypertension / Q000473:pathology / Q000503:physiopathology* / Q000517:prevention & control; D008297:Male; D011446:Prospective Studies; D015599:Trauma Severity Indices