Exhaled carbon monoxide in mechanically ventilated critically ill patients: influence of inspired oxygen fraction.

OBJECTIVE: To assess the feasibility of exhaled carbon monoxide (CO) measurements in mechanically ventilated critically ill adult patients and to determine the influence of inspired oxygen fraction on this measurement. DESIGN: Prospective physiologic study. SETTING: Medical ICU in a community hospital. PATIENTS: The study was performed on nine mechanically ventilated patients with varying diagnoses. MEASUREMENTS AND RESULTS: Carbon monoxide concentration was determined with an infrared CO analyzer on exhaled breath collected at the outlet of the ventilator. We assessed the stability of exhaled carbon monoxide concentration over a 4-hour period and determined its course during a 7-hour period after inspired oxygen fraction had been abruptly increased from baseline to 1. Carbon monoxide was detected in exhaled breath in each patient at a higher concentration than in inspired gas (0.64 +/- 0.1 ppm vs 0.25 ppm, approximately). Exhaled carbon monoxide did not vary during a 4-hour period in five hemodynamically stable patients. When inspired oxygen fraction was increased from baseline (0.52 +/- 0.04) to 1, exhaled carbon monoxide concentration increased abruptly from baseline (0.63 +/- 0.13 ppm) to a peak value of 1.54 +/- 0.16 ppm within 15 min and returned slowly to baseline values within 7 h. CONCLUSION: CO was easily detected in the exhaled breath of mechanically ventilated patients and CO lung excretion was markedly but transiently dependent on inspired oxygen fraction. Other studies are warranted in order to determine the different factors that might influence CO lung excretion in critically ill patients.

[Humidification and aspiration of the respiratory tract in patients with mechanical ventilation]. / Humidification et aspiration des voies aériennes du malade sous ventilation mécanique.

Mechanical ventilation through endotracheal prosthesis, suppresses the nose functions and stops elimination of secretions. It is mandatory to heat artificially, humidify insufflated gas and to suction tracheobronchial secretions. Heating humidifiers are very efficient for the first purpose but heat and moisture exchangers, a little less efficient, seem to be a good alternative as they are easiest to use and offer a good bacterial protection. Tracheobronchial suctioning has to be carried out at least each four hours and at the best as soon as adventitious sound are heard in the chest. Suction catheters have to be atraumatic; vacuum has to be between -200 to -400 cm H2O; catheter have not to be pushed further than the carina; suction hypoxemia can be reduced by shortening suction maneuver, by using suction catheter with little diameter, by conducting the suction on mechanical ventilation.