Relevance of laser spectroscopy OF-CEAS (optical feedback cavity enhanced absorption spectroscopy), for the measurement of carbon monoxide in healthy volunteers

Introduction: Endogenous production of carbon monoxide (CO), measured in exhaled air (eCO), increases with oxygen toxicity and pulmonary inflammation. The OF-CEAS is a measurement technique by laser spectroscopy which allows a very low detection threshold of CO (10 -3 ppm) and real-time measurements (5Hz). The objective was to evaluate the monitoring of eCO by OF-CEAS in subjects breathing a gas mixture enriched with O2. Methods: eCO was monitored in 30 healthy volunteers who breathed in a ventilator circuit of an anesthesia workstation with a fraction of inspired O2 (FiO2) ranged from 21 to 100% in increments of 5 minutes. Results: The mean concentration of eCO was 5.2 ± 5.9 ppm at 21% FiO2. The COe amounted to 20.5 ± 22.4 ppm at 100% then back down to 5.4 ± 6.2 ppm when returning to 21%. For each subject, initial content of eCO was multiplied by a factor 3 with 100% FiO2, regardless of smoking or non-smoking status. Discussion: The elevation of eCO under 100% FiO2 was probably due to a shift, by O2, of CO attached to hemoglobin. Endogenous CO overproduction in response to hyperoxia was probably not a predominant mechanism in our study. Conclusion: OF-CEAS device has shown its accuracy and convenience in operating room environment. Its sensitivity and speed of analysis make it a potentially useful tool for clinical studies on lung inflammation.