In-airway molecular flow sensing: A new technology for continuous, non-invasive monitoring of oxygen consumption in critical care
Ciaffoni L., O'Neill DP., Couper JH., Ritchie G., Hancock G., Robbins PA.
There are no satisfactory methods for monitoring oxygen consumption in critical care. To address this, we adapted laser absorption spectroscopy to provide measurements of O2, CO2 and water vapour within the airway every 10 ms. The analyser is integrated within a novel respiratory flowmeter that is an order of magnitude more precise than other flowmeters. Such precision, coupled with the accurate alignment of gas concentrations with respiratory flow, makes possible the determination of O2 consumption by direct integration over time of the product of O2 concentration with flow. The precision is illustrated by integrating the balance gas (N2/Ar) flow, and showing that this exchange was near zero. Measured O2 consumption changed by <5% between air and O2 breathing. Clinical capability was illustrated by recording O2 consumption during an aortic aneurysm repair. This device now makes possible easy, accurate, and non-invasive measurement of O2 consumption for intubated patients in critical care.