In-airway molecular flow sensing: A new technology for continuous, noninvasive monitoring of oxygen consumption in critical care

There are no satisfactory methods for monitoring oxygen consumption in critical care. To address this, we adapted laser absorption spectroscopy to provide measurements of O(2), CO(2), and water vapor within the airway every 10 ms. The analyzer is integrated within a novel respiratory flow meter that is an order of magnitude more precise than other flow meters. Such precision, coupled with the accurate alignment of gas concentrations with respiratory flow, makes possible the determination of O(2) consumption by direct integration over time of the product of O(2) concentration and flow. The precision is illustrated by integrating the balance gas (N(2) plus Ar) flow and showing that this exchange was near zero. Measured O(2) consumption changed by <5% between air and O(2) breathing. Clinical capability was illustrated by recording O(2) consumption during an aortic aneurysm repair. This device now makes easy, accurate, and noninvasive measurement of O(2) consumption for intubated patients in critical care possible.