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Crit Care Med. 2008 Jan;36(1):273-81.

Effect of hyperoxia on regional oxygenation and metabolism after severe traumatic brain injury: preliminary findings.

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1
University Division of Anaesthesia, University of Cambridge, Addenbrooke's Hospital, Cambridge, UK.

Abstract

OBJECTIVE:

To determine the effect of normobaric hyperoxia on cerebral metabolism in patients with severe traumatic brain injury.

DESIGN:

Prospective clinical investigation.

SETTING:

Neurosciences critical care unit of a university hospital.

PATIENTS:

Eleven patients with severe traumatic brain injury.

INTERVENTIONS:

Cerebral microdialysis, brain tissue oximetry (PbO2), and oxygen-15 positron emission tomography (15O-PET) were undertaken at normoxia and repeated at hyperoxia (FiO2 increase of between 0.35 and 0.50).

MEASUREMENTS AND MAIN RESULTS:

Established models were used to image cerebral blood flow, blood volume, oxygen metabolism, and oxygen extraction fraction. Physiology was characterized in a focal region of interest (surrounding the microdialysis catheter) and correlated with microdialysis and oximetry. Physiology was also characterized in a global region of interest (including the whole brain), and a physiologic region of interest (defined using a critical cerebral metabolic rate of oxygen threshold). Hyperoxia increased mean +/- sd PbO2 from 28 +/- 21 mm Hg to 57 +/- 47 mm Hg (p = .015). Microdialysate lactate and pyruvate were unchanged, but the lactate/pyruvate ratio showed a statistically significant reduction across the study population (34.1 +/- 9.5 vs. 32.5 +/- 9.0, p = .018). However, the magnitude of reduction was small, and its clinical significance doubtful. The focal region of interest and global 15O-PET variables were unchanged. "At-risk" tissue defined by the physiologic region of interest, however, showed a universal increase in cerebral metabolic rate of oxygen from a median (interquartile range) of 23 (22-25) micromol x 100 mL(-1) x min(-1) to 30 (28-36) micromol x 100 mL(-1) x min(-1) (p < .01).

CONCLUSIONS:

In severe traumatic brain injury, hyperoxia increases PbO2 with a variable effect on lactate and lactate/pyruvate ratio. Microdialysis does not, however, predict the universal increases in cerebral metabolic rate of oxygen in at-risk tissue, which imply preferential metabolic benefit with hyperoxia.

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