Assessment of a Non-Invasive Brain Oximeter in a Sheep Model of Acute Brain Injury

Abstract

Introduction

Evidence suggests treatments guided by brain oxygen levels improve patient outcomes following severe traumatic brain injury; however, brain oxygen levels are not routinely monitored as an effective non-invasive method has not been established. We undertook a study, in a sheep model of acute brain injury, to assess a new non-invasive brain oximeter. The monitor uses the principles of pulse oximetry to record a pulse and oxygen levels.

Methods

We studied 8 sheep. An acute increase in intracranial pressure was induced with an injection of blood into the cranial vault. The temporal changes in the brain oximeter, intracranial pressure and cerebral perfusion pressure were recorded. Simultaneous conventional skin pulse oximetry was also recorded to assess the possible influence of skin blood flow on the brain oximeter signal.

Results

At baseline, a pulsatile waveform consistent with the brain circulation was obtained in 7 animals. The baseline brain pulse was quite distinct from the simultaneous conventional skin pulse and similar in shape to a central venous pressure waveform. Injection of blood into the cranial vault triggered an immediate increase in intracranial pressure and fall in cerebral perfusion pressure, by 60-s cerebral perfusion pressure recovered. The brain oximeter oxygen levels demonstrated similar changes with an immediate fall and recovery by 60 s. Periods of high intracranial pressure were also associated with high-frequency oscillations in the brain pulse waveform; there was, however, no change in the conventional skin pulse oximeter pulse waveform.

Conclusion

The brain oximeter detected acute changes in both oxygen levels and the brain pulse waveform following an increase in intracranial pressure levels. The brain oximeter could assist clinicians in the management of acute brain injury.

Video abstract

Point your SmartPhone at the code above. If you have a QR code reader the video abstract will appear. Or use:

https://youtu.be/wbf5tjsC3pw

Keywords:

• oximetry
• traumatic brain injury
• brain
• sheep

Abbreviations

CPP, cerebral perfusion pressure; ICP, intracranial pressure; RR_m, modified ratio of ratios; NIR, near infrared; SO₂, oxygen saturation; RR, ratio of ratios; TBI; traumatic brain injury.

Availability of Data and Materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Author Contributions

All authors contributed to the data analysis, drafting or revising the article, gave final approval of the version to be published and agree to be accountable to all aspects of the work. Protocol/project development was performed by BD, RT, CC; data collection or management was done by BD, RT, CC; data analysis was performed by BD; manuscript writing and editing were done by BD, RT, CC.

Disclosure

This research received no specific grant from any funding agency in the public or not-for-profit sectors. Dr Dixon has a financial interest in Cyban Pty Ltd, that is developing the brain oximeter. In addition, Dr Dixon has a patent pending for a Brain oximeter. The Preclinical Imaging and Research Laboratories, South Australian Health and Medical Research Institute and Dr Turner received fees from Cyban Pty Ltd, during the conduct of the study. The authors report no other conflicts of interest in this work.

Additional information

Funding

This research received no specific grant from any funding agency in the public or not-for-profit sectors and was funded by Cyban Pty Ltd.