Effect of hyperventilation on cerebral blood flow in traumatic head injury: clinical relevance and monitoring correlates

Coles, Jonathan, Minhas, P.S., Fryer, Tim, Smielewski, P., Aigbirhio, Franklin I., Donovan, Tim, Downey, S.P., Williams, G., Chatfield, D., Matthews, J.C., Gupta, A.K., Carpenter, T. Adrian, Clark, J.C., Pickard, John D. and Menon, David K. (2002) Effect of hyperventilation on cerebral blood flow in traumatic head injury: clinical relevance and monitoring correlates. Critical Care Medicine, 30 (9). pp. 1950-1959. Full text not available from this repository.

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Abstract

Objective: To investigate the effect of hyperventilation on cerebral blood flow in traumatic brain injury.

Design: A prospective interventional study.

Setting: A specialist neurocritical care unit.

Patients: Fourteen healthy volunteers and 33 patients within 7 days of closed head injury.

Interventions: All subjects underwent positron emission tomography imaging of cerebral blood flow. In patients, PaCO2 was reduced from 36 +/- 1 to 29 +/- 1 torr (4.8 +/- 0.1 to 3.9 +/- 0.1 kPa) and measurements repeated. Jugular venous saturation (SjvO2 ) and arteriovenous oxygen content differences (AVDO2 ) were monitored in 25 patients and values related to positron emission tomography variables.

Measurements and main results: The volumes of critically hypoperfused and hyperperfused brain (HypoBV and HyperBV, in milliliters) were calculated based on thresholds of 10 and 55 mL.100g(-1).min(-1), respectively. Whereas baseline HypoBV was significantly higher in patients ( p<.05), baseline HyperBV was similar to values in healthy volunteers. Hyperventilation resulted in increases in cerebral perfusion pressure (p <.0001) and reductions in intracranial pressure (p <.001), whereas SjvO2 (>50%) and AVDO2 (<9 mL/mL) did not exceed global ischemic thresholds. However, despite these beneficial effects, hyperventilation shifted the cerebral blood flow distribution curve toward the hypoperfused range, with a decrease in global cerebral blood flow (31 +/- 1 to 23 +/- 1 mL.100g(-1).min(-1); p<.0001) and an increase in HypoBV (22 [1-141] to 51 [2-428] mL; p<.0001). Hyperventilation-induced increases in HypoBV were apparently nonlinear, with a threshold value between 34 and 38 torr (4.5-5 kPa).

Conclusions: Hyperventilation increases the volume of severely hypoperfused tissue within the injured brain, despite improvements in cerebral perfusion pressure and intracranial pressure. Significant hyperperfusion is uncommon, even at a time when conventional clinical management includes a role for modest hyperventilation. These reductions in regional cerebral perfusion are not associated with ischemia, as defined by global monitors of oxygenation, but may represent regions of potentially ischemic brain tissue.

Item Type: Article
Journal or Publication Title: Critical Care Medicine
Publisher: Lippincott, Williams & Wilkins for Society of Critical Care Medicine
ISSN: 1530-0293
Departments: Faculty of Health and Science > Medical and Sports Sciences > Health and Medical Sciences
Depositing User: Insight Administrator
Date Deposited: 17 Oct 2011 08:08
Last Modified: 17 Oct 2017 11:26
URI: http://insight.cumbria.ac.uk/id/eprint/1045

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