Abstract TP63: High-flow Oxygen Reduces Cerebral Blood Flow
Background: Normobaric high-flow oxygen (NBO) is often used in the pre-hospital and emergency setting following acute stroke, extrapolating evidence of benefit following myocardial infarction. However, in the context of impaired cerebral autoregulation following acute stroke, it is important to establish the effect of high-flow oxygen on cerebral blood flow (CBF). A study in healthy volunteers has demonstrated good visit-to-visit reproducibility of transcranial Doppler (TCD)-estimated CBF velocity (CBFV: surrogate for CBF) measurements with NBO - coefficient of variation 3.85%, comparable to previous studies on air.
Methods: We studied the effect of NBO on CBFV in subjects following TIA, acute stroke, previous stroke and in healthy volunteers. Bilateral CBFV recordings were performed using TCD. Four minute assessments were repeated during inhalation of air and NBO (80% oxygen), in random order. Repeated measures ANOVA was used to analyse difference between air and oxygen.
Results: 33 subjects were recruited (17 volunteers, 7 acute stroke, 5 TIA, 4 previous stroke). Age: mean (SD) 58 (15) years, male 64%. There were no inter-hemispheric differences in CBFV, therefore we averaged values from both hemispheres. Mean (SD) CBFV was 47 (11) on air; 45 (11) on NBO. Mean CBFV was significantly lower during NBO administration, in the whole population (2.1 + 0.6 cm/s, within subjects effect p=0.003). There was no significant between-group interaction (p=0.99).
Discussion: NBO is associated with a significant fall in CBFV which may be deleterious in the setting of acute stroke. In the absence of any clear benefit, high-flow oxygen should not be used routinely in patients with acute stroke. Further research is required to establish the effects on other cerebral haemodynamic parameters, including autoregulation and cerebrovascular reactivity.
- © 2012 by American Heart Association, Inc.