Large changes in PaO2 oscillation amplitude with respiratory rate are not measurement artifact

Highlights • Real time detection of cyclical atelectasis is fundamental for individualised mechanical-ventilation therapy in ARDS. • Intra-arterial oxygen sensors could be used to detect the breath-by-breath oscillations in PO2 during cyclical atelectasis. • The fidelity with which oxygen sensors can detect these arterial PO2 oscillations depends on the sensors’ speed of response. • We present a system for testing fast-response fibre optic oxygen sensors under simulated conditions of cyclical atelectasis. • We show that a prototype fibre optic oxygen sensor, compatible with clinical use, can detect rapid PO2 changes in vitro.
Two challenges in the management of Acute Respiratory Distress Syndrome are the difficulty in diagnosing cyclical atelectasis, and in individualising mechanical ventilation therapy in real-time. Commercial optical oxygen sensors can detect PaO2 oscillations associated with cyclical atelectasis, but are not accurate at saturation levels below 90%, and contain a toxic fluorophore. We present a computer-controlled test rig, together with an in-house constructed ultra-rapid sensor to test the limitations of these sensors when exposed to rapidly changing PO2 in blood in vitro. We tested the sensors’ responses to simulated respiratory rates between 10 and 60 breaths per minute. Our sensor was able to detect the whole amplitude of the imposed PO2 oscillations, even at the highest respiratory rate. We also examined our sensor's resistance to clot formation by continuous in vivo deployment in non-heparinised flowing animal blood for 24 h, after which no adsorption of organic material on the sensor's surface was detectable by scanning electron microscopy.