Novel approach to monitor local tissue ischemia associated with pressure ulcers using an optical fibre carbon dioxide sensor†

Abstract

In this paper, we describe the development of a novel approach to monitor local tissue ischemia associated with pressure ulcer using an optical fibre carbon dioxide sensor. Carbon dioxide (CO₂) is a potential biomarker for local tissue ischemia associated with pressure ulcer (PU) formation. Skin CO₂ measurement during loading could provide an earlier indicator for pressure induced tissue damage. This study presents a reflection mode optical fibre CO₂ sensor (OFCS) that was fabricated and evaluated for measuring skin CO₂ during mechanical loading. The optical fibre tip was coated with organically modified silica gel (ormosil) film (thickness 7.23 ± 0.52 μm) containing thymol blue using a dip coating process. Thymol blue has an absorption peak at a wavelength of ~600 nm with an amplitude proportional to CO₂ concentration. The OFCS had a typical response time of approximately 60 seconds and a recovery time of 400 seconds for a 0–5.5% CO₂ range. OFCSs were tested on the human skin of six healthy volunteers with corresponding CO₂ peak values ranging from 145 ppm to 429 ppm with a percent error range of 6–32.2%. The increase in CO₂ emitted from the skin during loading offers future promise for alerting the early stage of PU formation.