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BJA Advance Access published online on November 17, 2006
British Journal of Anaesthesia, doi:10.1093/bja/ael308
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© The Board of Management and Trustees of the British Journal of Anaesthesia 2006. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
Accepted September 21, 2006

Clinical Investigation

Enhanced upper respiratory tract airflow and head fanning reduce brain temperature in brain-injured, mechanically ventilated patients: a randomized, crossover, factorial trial

B. A. Harris 1 *, P. J. D. Andrews 1, and G. D. Murray 2

1 Intensive Care Unit (Ward 20), University of Edinburgh, Western General Hospital, Crewe Road South, Edinburgh EH4 2XU, UK
2 Division of Community Health Sciences, University of Edinburgh Medical School, Teviot Place, Edinburgh EH8 9AG, UK

* To whom correspondence should be addressed.
B. A. Harris, E-mail: b.harris{at}ed.ac.uk


  Abstract

Background. Heat loss from the upper airways and through the skull are physiological mechanisms of brain cooling which have not been fully explored clinically.

Methods. This randomized, crossover, factorial trial in 12 brain-injured, orally intubated patients investigated the effect of enhanced nasal airflow (high flow unhumidified air with 20 p.p.m. nitric oxide gas) and bilateral head fanning on frontal lobe brain temperature and selective brain cooling. After a 30 min baseline, each patient received the four possible combinations of the interventions--airflow, fanning, both together, no intervention--in randomized order. Each combination was delivered for 30 min and followed by a 30 min washout, the last 5 min of which provided the baseline for the next intervention.

Results. The difference in mean brain temperature over the last 5 min of the preceding washout minus the mean over the last 5 min of intervention, was 0.15°C with nasal airflow (P=0.001, 95% CI 0.06-0.23°C) and 0.26°C with head fanning (P<0.001, 95% CI 0.17-0.34°C). The estimate of the combined effect of airflow and fanning on brain temperature was 0.41°C. Selective brain cooling did not occur.

Conclusion. Physiologically, this study demonstrates that heat loss through the upper airways and through the skull can reduce parenchymal brain temperature in brain-injured humans and the onset of temperature reduction is rapid. Clinically, in ischaemic stroke, a temperature decrease of 0.27°C may reduce the relative risk of poor outcome by 10-20%. Head fanning may have the potential to achieve a temperature decrease of this order.

Keywords: brain, cooling; brain, injury; brain, temperature; stroke.
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B. A. Harris, P. J. D. Andrews, I. Marshall, T. M. Robinson, and G. D. Murray
Forced convective head cooling device reduces human cross-sectional brain temperature measured by magnetic resonance: a non-randomized healthy volunteer pilot study
Br. J. Anaesth., March 1, 2008; 100(3): 365 - 372.
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