A Novel Photoplethysmography Sensor for Vital Signs Monitoring from the Human Trachea.

James M May,Tracey Fitchat,Saowarat Snidvongs,Shankar Ramaswamy,Justin P Phillips,Panayiotis A Kyriacou

doi:10.3390/bios9040119

Abstract

Current pulse oximeter sensors can be challenged in working accurately and continuously in situations of reduced periphery perfusion, especially among anaesthetised patients. A novel tracheal photoplethysmography (PPG) sensor has been developed in an effort to address the limitations of current pulse oximeters. The sensor has been designed to estimate oxygen saturation (SpO2) and pulse rate, and has been manufactured on a flexible printed circuit board (PCB) that can adhere to a standard endotracheal (ET) tube. A pilot clinical trial was carried out as a feasibility study on 10 anaesthetised patients. Good quality PPGs from the trachea were acquired at red and infrared wavelengths in all patients. The mean SpO2 reading for the ET tube was 97.1% (SD 1.0%) vs. the clinical monitor at 98.7% (SD 0.7%). The mean pulse rate for the ET sensor was 65.4 bpm (SD 10.0 bpm) vs. the clinical monitor at 64.7 bpm (SD 9.9 bpm). This study supports the hypothesis that the human trachea could be a suitable monitoring site of SpO2 and other physiological parameters, at times where the periphery circulation might be compromised.

Highlights

Pulse oximetry is perhaps the most important development in patient monitoring in the last forty years, its limitations are well known and well documented [1,2,3,4]
Despite improvements in the accuracy of pulse oximetry brought about by advances in signal processing over the last decade or so [5], reliable and dependable SpO2 readings still depend on adequate periphery perfusion, especially in anaesthetised patients
An initial clinical study, performed in patients undergoing general anaesthesia showed that reliable oesophageal signals could be obtained in all subjects, and that the optical pulse signals were significantly larger in amplitude than those obtained from a probe placed on the finger

Summary

Introduction

Pulse oximetry is perhaps the most important development in patient monitoring in the last forty years, its limitations are well known and well documented [1,2,3,4]. There is a recognised need for improved pulse oximetry performance in some groups of vulnerable patients, especially as current coping methods only compromise patient safety and place an unwanted burden on the surgical team as they try to restore monitoring. To overcome this limitation, Kyriacou et al described an internally placed reflectance pulse oximetry system in 2001 that allowed detailed investigation of SpO2 measurements and the photoplethysmography (PPG) signals, from which the SpO2 signals are derived from the oesophageal wall [7]. A follow-on clinical study [8,9]

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Conclusion