Inhouse R&D
Non-invasive CO2 detection for patients on life support
01
The Patient Proposition
Every year hundreds of millions of patients having operations and intensive care need life support for their breathing. This requires nurses and doctors to take multiple blood tests every day to measure the levels of CO2 and adjust the ventilator settings.
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We asked ourselves if we could create a device that could be used to measure the CO2 levels without needing blood tests.
02
What we learnt from existing research
The change in the colour of haemoglobin is well known for a range of different gases - such as oxygen and carbon monoxide - as well as when haemoglobin becomes degraded.
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However, we were surprised and encouraged that we could not find any previous research documenting colour changes in haemoglobin due to CO2.
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Source original data from Determination of Hemoglobin and its Derivatives. Advances in Analytical Chemistry, (1966) Vol 8. pp 141-187
03
Existing clinical devices
Non-invasive devices called pulse oximeters already exist to measure oxygen levels in the blood by measuring the change in colour of the blood molecule called haemoglobin that carries oxygen around the body.
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We wondered if a similar mechanism could be used to measure CO2 levels in the same familiar form factor.
04
Designing a test device
We designed a simple device that would collect light that has passed through a finger and analyse the changes in colour over time.
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To achieve this we would need to analyse the wavelengths of light across the entire spectrum and not just at a couple of discrete wavelengths like a standard pulse oximeter measuring O2 levels.
05
Our device build
Our test device was built for under £100
Light is collected from the sample chamber using a fibre optic cable. This light is then passed to a spectroscope that spread out into its constituent colour wavelengths. A CCD device then captured the intensity of each wavelength of light that was then passed to a Raspberry Pi where the spectra of colours was analysed.
06
Our Initial Results
The spectroscope was calibrated using lasers of known wavelength to maximise the spectral width and resolution, as well as ensuring the stability of the instrument.
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Initial testing of software was performed by collecting colour spectra from test tubes filled with standardised solutions filled with dyes.
07
STOP/GO - results from Dervieux et al
In late 2020, as we were starting the next phase using real haemoglobin solutions, a group in France published their results.
This group was equally surprised that the CO2 spectra of haemoglobin was unpublished and are the first to showed that CO2 only causes very small changes in the colour of haemoglobin... too small to detect in for a real world device. Hence we made a STOP decision on the R&D project
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Check out their impressive research at J. of Biomedical Optics, 25(10), 105001 (2020). doi.org/10.1117/1.JBO.25.10.105001
Lessons we will be applying to our next R&D project
A clear high-value patient need is a better starting point that being tied to trying to find a use for a specific technology.
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Failing fast and failing cheap avoids the need to raise external finance and hence avoids dilution of ownership and consumption of valuable management time on managing stakeholders.
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Focus project decision making on achieving proof of concept rather than distractions..