Cerebral metabolism is not affected by moderate hyperventilation in patients with traumatic brain injury

Abstract

Background Hyperventilation-induced hypocapnia (HV) reduces elevated intracranial pressure (ICP), a dangerous and potentially fatal complication of traumatic brain injury (TBI). HV decreases the arteriolar diameter of intracranial vessels, raising the risk of cerebral ischemia. The aim of this study was to characterize the effects of moderate short-term HV in patients with severe TBI by using concomitant monitoring of cerebral metabolism, brain tissue oxygen tension (PbrO 2 ), and cerebral hemodynamics with transcranial color-coded duplex sonography (TCCD). Methods This prospective trial was conducted between May 2014 and May 2017 in the surgical intensive care unit (ICU) at the University Hospital of Zurich. Patients with nonpenetrating TBI older than 18 years of age with a Glasgow Coma Scale (GCS) score < 9 at presentation and with ICP monitoring, PbrO 2 , and/or microdialysis (MD) probes during ICU admission within 36 h after injury were included in our study. Data collection and TCCD measurements were performed at baseline (A), at the beginning of moderate HV (C), after 50 min of moderate HV (D), and after return to baseline (E). Moderate HV was defined as arterial partial pressure of carbon dioxide 4–4.7 kPa. Repeated measures analysis of variance was used to compare variables at the different time points, followed by post hoc analysis with Bonferroni adjustment as appropriate. Results Eleven patients (64% males, mean age 36 ± 14 years) with an initial median GCS score of 7 (IQR 3–8) were enrolled. During HV, ICP and mean flow velocity (CBFV) in the middle cerebral artery decreased significantly. Glucose, lactate, and pyruvate in the brain extracellular fluid did not change significantly, whereas PbrO 2 showed a statistically significant reduction but remained within the normal range. Conclusion Moderate short-term hyperventilation has a potent effect on the cerebral blood flow, as shown by TCCD, with a concomitant ICP reduction. Under the specific conditions of this study, this degree of hyperventilation did not induce pathological alterations of brain metabolites and oxygenation. Trial registration NCT03822026 . Registered on 30 January 2019.

VENTILatOry strategies in patients with severe traumatic brain injury: the VENTILO Survey of the European Society of Intensive Care Medicine (ESICM)

“…Currently, hyperventilation is suggested only in case of emergency with lifethreatening risk of cerebral herniation [22]. However, recent findings suggested that mild, short-term hyperventilation is able to reduce ICP, without a clinically significant reduction of cerebral oxygenation and metabolism [23]. In fact, most responders aimed to a target of 36-40 mmHg of CO 2 , and only a minority accept mild hypercapnia, even in the absence of intracranial hypertension.…”

Peranan Hiperventilasi terhadap Penurunan Tekanan Intrakranial dalam Kasus Bedah Saraf

“…CBF dapat diukur, secara langsung atau tidak langsung, dengan sejumlah metode, namun tidak satupun yang dengan mudah tersedia di samping tempat tidur di lingkungan ICU. 3 Pengukuran CBF dengan radioaktif 131Xe, telah diperkenalkan untuk penggunaan klinis pada 1970-an, namun teknik ini kemudian dilarang untuk digunakan secara klinis karena bahaya radiasinya. Setelah pengenalan pemindai CT multislice yang lebih cepat, pemindaian Xe-CT menjadi teknik standar untuk mengukur CBF dengan menggunakan Xe yang stabil dan non-radioaktif selama pemindaian CT otak.…”

“…Xe yang terinhalasi, yang secara bebas terdifusi dari paru-paru ke pembuluh darah, dan dari pembuluh darah otak ke jaringan otak, dapat dideteksi di otak menggunakan pemeriksaan CT scan karena meningkatkan pelemahan sinar-x. 3 24 jam pertama setelah cedera otak traumatik, terdapat kekhawatiran khusus bahwa kondisi hiperventilasi akan meningkatkan risiko iskemia.…”

“…Studi klinis telah berfokus pada oksimetri bulbus jugularis dan pemantauan tekanan oksigen jaringan otak (PbrO 2 ). 3 Dalam oksimetri bulbus jugularis, SjO 2 dipantau baik secara terus-menerus menggunakan teknik fiber optik kontinyu atau intermiten disertai dengan pengambilan sampel darah. 9 Oleh karena itu, teknik umum ini memberikan informasi mengenai ekstraksi oksigen dari drainase vena cerebral.…”

“…Selain itu, pedoman tersebut menyatakan bahwa "penggunaan terapi hiperventilasi profilaksis (PaCO2 < 35 umum diberikan pada pasien dengan cedera otak traumatik, khususnya jika hiperventilasi perlu dilakukan. 1,3,9…”