A novel, non-invasive, optical device for the measurement of total haemoglobin and stroke volume, and for the identification of fluid responsiveness – initial clinical evaluation
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Date
2019-10
Authors
Broderick, Alan Jonathan
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University College Cork
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Abstract
Haemoglobin is a molecule present in red blood cells and is essential for adequate oxygen delivery to tissues. It is measured frequently in many clinical situations, particularly intraoperatively. Until recently, it was only possible to measure haemoglobin through blood testing which is an invasive process and requires some time to process. Devices have been developed in the last number of years to minimise both the invasiveness and time needed to measure haemoglobin. More recently, devices are available that provide instant or continuous results without requiring blood samples but these have not been universally accepted into clinical practice.
Stroke volume is the amount of blood ejected from the heart at each heartbeat, and is one of the determinants of cardiac output (which is also responsible for ensuring adequate tissue oxygen delivery). It varies across many clinical states, particularly following major haemorrhage or reduced cardiac function. The analysis of variations in stroke volume during the respiratory cycle (i.e. between the end of a complete exhalation and the end of the following complete exhalation) has been shown to predict when a patient’s stroke volume could be improved by administering intravenous fluid. Successfully identifying such ‘responders’ can lead to earlier appropriate treatment, and also avoid over-treatment.
However, at present the most reliable methods of measuring stoke volume or predicting fluid responsiveness involve the use of invasive devices which have the potential to be harmful.
A novel device has been developed which uses the absorbance of red and near-infrared light across a finger tip as the basis for the measurement of both haemoglobin and stroke volume, along with the prediction of fluid responsiveness. This is non-invasive and would allow for the continuous measurement of these physiological parameters, with potential for more efficient and timely treatment.This thesis presents the first clinical evaluation of the two functions of this novel device across three studies.
The first study investigated the measurement of haemoglobin by this device across twenty five patients undergoing heart surgery who each underwent four samples. The second study looked into the measurement of haemoglobin in one hundred pregnant women during their twenty- week antenatal clinic visit. In both studies, the results from the device were compared with the standard laboratory method of measurement. The third study investigated the device’s ability to measure stoke volume and to predict fluid responsiveness in twenty patients undergoing heart surgery.
The results of these studies showed that the device is currently not suitable for use in clinical practice as a replacement for the more established methods of measurement one each case. Some explanation is offered regarding the poor results.
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Keywords
Photoplethysmography , PPG , Haemoglobin , Fluid responsiveness , Point-of-care medical devices , Intraoperative monitoring , Non-invasive monitoring , Medical devices , Stroke volume , Clinical evaluation
Citation
Broderick, A. J. 2019. A novel, non-invasive, optical device for the measurement of total haemoglobin and stroke volume, and for the identification of fluid responsiveness – initial clinical evaluation. MD Thesis, University College Cork.