Jones, D. P.

Kyriacou, P. A.

Langford, R. M.

Pal, S. K.

City Research Online

Kyriacou, P. A., Pal, S. K., Langford, R. M. & Jones, D. P. (2004). Investigation of oesophageal pulse oximetry in burns patients. Paper presented at the Annual National Conference of the Institute of Physics and Engineering in Medicine (IPEM), 6-8 Sep 2004, York, UK. City Research OnlineOriginal citation: Kyriacou, P. A., Pal, S. K., Langford, R. M. & Jones, D. P. (2004). Investigation of oesophageal pulse oximetry in burns patients. Paper presented at the Annual National Conference of the Institute of Physics and Engineering in Medicine (IPEM), 6-8 Sep 2004, York, UK. Permanent City Research Online URL: http://openaccess.city.ac.uk/14320/ Copyright & reuseCity University London has developed City Research Online so that its users may access the research outputs of City University London's staff. Copyright © and Moral Rights for this paper are retained by the individual author(s) and/ or other copyright holders.  All material in City Research Online is checked for eligibility for copyright before being made available in the live archive. URLs from City Research Online may be freely distributed and linked to from other web pages. Versions of researchThe version in City Research Online may differ from the final published version. Users are advised to check the Permanent City Research Online URL above for the status of the paper.EnquiriesIf you have any enquiries about any aspect of City Research Online, or if you wish to make contact with the author(s) of this paper, please email the team at publications@city.ac.uk.Investigation of oesophageal pulse oximetry in burns patients  P A Kyriacou1, S K Pal2, R M Langford3 and D P Jones4 1School of Engineering and Mathematical Sciences, City University, London EC1V 0HB UK 2St Andrew’s Centre for Plastic Surgery & Burns, Broomfield Hospital, Chelmsford, Essex, CM1 7ET 3Anaesthetic Laboratory & Department, St.Bartholomew’s Hospital, London EC1A 7BE, UK 4Medical Electronics & Physics, Department of Engineering, Queen Mary University of London, London E1 4NS, UK  Background and purpose  Pulse oximetry is widely used in anaesthesia and intensive care monitoring. It is a valuable, non-invasive optical monitoring technique used for continuous measurement of arterial blood oxygen saturation (SpO2). Sites for pulse oximeter sensors are frequently difficult to find in patients with major thermal injury. Standard sites such as fingers or toes may be affected by the burn, unsuitable due to the use of tourniquets during surgery, or in some cases absent. Therefore blood oxygen saturation readings are often unobtainable at just the time when they would be most valuable.  An oesophageal SpO2 probe has been designed to record reliable photoplethysmographic (PPG) signals and SpO2 values from the oesophagus of burns patients.  Method  A reflectance oesophageal pulse oximetry sensor has been constructed comprising miniature electro-optical devices [1 2]. An electrically isolated PPG processing system was developed to detect and pre-process simultaneously the red and infrared AC and DC PPG output signals. Oesophageal AC and DC PPG traces (obtained at red and infrared wavelengths) were digitised by a 16-bit data acquisition card. The digitised PPG signals were further analysed by a Virtual Instrument implemented in LabVIEW. Oesophageal PPG signals were displayed simultaneously on a laptop computer. The design of the Virtual Instrument incorporated algorithms allowing the online estimation of oesophageal SpO2.   Seven patients with major burns admitted to burns intensive care were recruited for the study. The five men and two women ranged in age between 26 and 52 years. The total body surface area burnt ranged between 28% and 90%. A nasogastric tube containing the reflectance pulse oximetry sensor was placed in each patient’s oesophagus. The PPG signals were recorded at various depths in the oesophagus. Arterial blood samples were taken for estimation of oxygen saturation using a CO-oximeter. Linear Regression analysis was used to compare the blood oxygen saturation results from the oesophageal pulse oximeter with those from CO-oximetry. Results  Measurable PPG traces were obtained from the oesophagus in all patients. The oesophageal PPG signals recorded from all patients were of good quality and large amplitude. The optimal monitoring oesophageal depth ranged from 13 cm to 20 cm, measured from the upper lip (mean  SD: 15.6  1.8 cm).  A plot of SpO2 readings obtained from the reflectance oesophageal pulse oximeter (OES SpO2) against the SaO2 values from the CO-oximeter is shown in Figure 1. The equation of the best fit linear regression line is: (OES SpO2) = 33.278 + 0.666 (CO-ox SaO2)  (the solid line in Figure 1); r2 = 0.49; Standard Error of Estimate (SEE) = 0.64; p<0.001. The dashed line represents the line of identity.  CO-ox SaO2 %90 92 94 96 98 100Oesophageal SpO2 %9092949698100 Figure 1: Plot of SpO2 measurements obtained from the oesophageal pulse oximeter against SaO2 from the CO-oximetry for 7 patients.  Conclusions  The aim of this investigation was to evaluate the reliability of oesophageal pulse oximetry in major burns patients. Good quality oesophageal PPG signals with large amplitudes were measured from various depths within the oesophagus. The optimal monitoring oesophageal depth ranged from 13 cm to 20 cm, measured from the upper lip. It was found that the oesophageal pulse oximeter saturation results were in good agreement with those from the CO-oximeter (see Figure 1). In summary, the data suggest that oesophageal reflectance pulse oximetry may be a reliable and useful alternative method for monitoring continuous oxygen saturation in major burns patients.  References    [1] Kyriacou P A, Powell S, Langford R M, and   Jones D P. Oesophageal pulse oximetry utilizing reflectance photoplethysmography IEEE Trans. on Biomed. Eng., 2002: 49(11): 1360-1368. [2] Kyriacou P A, Powell S, Langford R M, and   Jones D P. Evaluation of oesophageal pulse oximetry in patients undergoing cardiothoracic surgery. Anaesthesia, 2003: 58: 422–

Investigation of oesophageal pulse oximetry in burns patients

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