Tissue oxygenation indices of cerebrovascular autoregulation in healthy volunteers: a comparison of two NIRS devices

ABSTRACT

Background

Correlation coefficients between blood pressure and cerebral oxygen saturation measured using near-infrared spectrometry may be used to derive the tissue oximetry index of cerebral autoregulation. Cerebral oxygen saturations demonstrate poor agreement between near-infrared spectrometers however it is unclear if measurements of autoregulation are similarly specific to the equipment used.

Methods

Cerebral oxygen saturation was monitored bilaterally in 74 healthy volunteers using both the FORE-SIGHT and EQUANOX monitors in random order. The tissue oximetry index was calculated during changes in blood pressure induced by isometric handgrip manoeuvres and the mean bias and limits of agreement were calculated.

Results

Tissue oximetry index measured by FORE-SIGHT was higher than EQUANOX (0.21 ± 0.16 versus 0.15 ± 0.17, P < 0.001) and limits of agreement were −0.24 to 0.36. Baseline cerebral oxygen saturation by FORE-SIGHT was lower than EQUANOX by 1.48% (CI95% 0.63–2.33) and limits of agreement ranged from −11.8% to 8.8%.

Conclusions

The substantial bias and wide limits of agreement for the tissue oximetry index as a measure of cerebral autoregulation indicate that values must be treated as specific to models of near-infrared spectrometers.

KEYWORDS:

• Spectroscopy
• near-infrared
• cerebrovascular circulation/physiology
• arterial pressure/physiology
• healthy volunteers
• homeostasis

Disclosure statement

The authors have no conflicts of interest to declare.

Author contributions

A.P. and M.C.: study design, patient recruitment, data collection, data analysis and preparation of the manuscript. B.C.: study design, data collection and manuscript review. M.J., A.A. and A.C.: study design and manuscript review.

Compliance with ethical standards

Ethical approval was obtained from the South Western Sydney Local Health District Human Research Ethics Committee (HREC/14/LPOOL/135). Written informed consent was obtained from all participants.

Additional information

Funding

Equipment used in this study was funded by a previous infrastructure grant from the University of New South Wales.

Notes on contributors

Alexander Peng

Alexander Peng is a critical care senior resident medical officer at Blacktown Hospital. He is a conjoint associate lecturer with Western Sydney University.Matthew Chua is a critical care senior resident medical officer at Nepean Hospital. He is a conjoint associate lecturer with the University of New South Wales.

Matthew J. Chua

Matthew J. Chua is a critical care senior resident medical officer at Nepean Hospital. He is a conjoint associate lecturer with the University of New South Wales.

Bernard Chan

Bernard Chan is Junior Medical Officer in the Junior Medical Staff Unit at Royal North Shore Hospital.

Matthias Jaeger

Matthias Jaeger is a Neurosurgeon at Wollongong Public and Private Hospitals. He is a Fellow of the Australasian College of Surgeons and a Conjoint Associate Professor at the University of New South Wales. His research interests have been around intracranial pressure, cerebral blood flow regulation and its clinical monitoring.

Anders Aneman

Anders Aneman is a Senior Staff Specialist at the Intensive Care Unit, Liverpool Hospital, a Conjoint Professor at the University of New South Wales and a Clinical Professor at Macquarie University, Sydney, Australia. He has extensive expertise in cardiovascular research including the cerebral circulation.

Alwin Chuan

Alwin Chuan is a Conjoint Associate Professor in Anaesthesia at the University of New South Wales and Anaesthetist at Liverpool Hospital in Sydney. He has research expertise in cerebral oximetry, cerebrovascular autoregulation and clinical research.