A new fibre optic photoplethysmographic sensor for the assessment of splanchnic organ perfusion

• Main Author: Hickey, Michelle
• Published: City University London 2010
• Subjects: 615.84
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.508374

A new reflectance fibre optic photoplethysmographic (PPG) sensor, comprising of red (660 nm) and infrared (850 nm) emitters, a photodiode and 600 ?m fibre optic cables, was developed to allow for the intraoperative assessment of PPG signals and the preliminary estimation of SpO2 from splanchnic organs. An identical peripheral sensor was also developed to allow for the qualitative and quantitative comparison between PPG signals obtained from splanchnic organs and those from the traditional peripheral site (finger or toe). A three channel instrumentation system (splanchnic PPG, peripheral PPG, and ECG) and software algorithms implemented in LabVIEW allowed for the continuous acquisition of PPG and ECG signals and the estimation of SpO2. The feasibility of the fibre optic sensors to allow for sufficient illumination of the tissue and to adequately detect PPG signals was explored and validated in the laboratory. A detailed investigation to determine the optimal transmitting-receiving fibre separation distance, found that the optimum separation distance was between 3 mm and 4 mm. An in vivo evaluation of the fibre optic splanchnic PPG sensor on 20 patients under-going open laparotomy demonstrated that good quality PPG signals can be obtained from the surface of the small bowel, large bowel, liver and stomach. Due to underlying differences in vasculature, the splanchnic ac and dc PPG signals were found to be of larger amplitudes than those obtained from the periphery, and statistical analysis showed that there is a statistical significant difference between splanchnic and peripheral PPG signals. Also, preliminary estimation of SpO2 from the uncalibrated fibre optic splanchnic sensor showed good agreement between the SpO2 estimated at the periphery. The results from the clinical measurements have confirmed that fibre optic pulse oximetry might be the way forward in monitoring splanchnic perfusion.