Measurement of carbon monoxide in simulated expired breath

Environmental carbon dioxide (CO) detectors used as an early warning method have been adapted to measure CO concentration in expired breath. This technique has been validated in smokers with relatively low CO concentrations, but its applicability to poisoning has not been demonstrated.

To compare the reliability of toxicologically significant CO measurements performed using a portable CO detector with those obtained using infrared spectrometry, the standard method for blood CO concentration determination.

Experimental study with a CO detector and infrared spectrometer. A balloon simulated respiratory movements and an expired breath. Balloon gas mixtures contained CO, in one of 21 different concentrations from 100 to 600 parts per million (ppm) in air. CO concentration was measured directly with the portable CO detector and two gas samples obtained at the beginning and end of the simulated expired breath were diluted, with validation, for spectrometric measures.

Portable CO detector concentrations were compared with the mean value of the reference method. Simple linear regression was performed using ANOVA to evaluate the parallel between the model with the reference method.

Portable CO detector concentration measurements were perfectly linear (R2=0.989, P<10(-3)) over a concentration range of 46-645 ppm. The difference from the reference plot was significant (P<0.01).

Given the linearity of the measurements, the underestimation by the portable CO detector at higher concentrations can be corrected mathematically. A portable CO detector should measure CO in expired breath efficiently and reliably.