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Uptake of inhaled nitric oxide in acute lung injury
U N Westfelt1, S Lundin, O Stenqvist
1Department of Anaesthesiology and Intensive Care, Sahlgrenska University Hospital, Sweden.
Background:
Despite the widespread use of inhaled nitric oxide (NO), little is known of its pulmonary uptake in patients with acute respiratory failure.
Methods:
Fourteen patients with acute lung injury (ALI) and ongoing NO therapy were studied. Three doses of NO (5, 10 and 40 ppm) were given for 20 min and at each dose level the following parameters were recorded: minute ventilation, inspiratory NO conc., mixed expired NO conc., end-tidal NO conc., mixed expired CO2 conc., end-tidal CO2 conc, and arterial CO2 tension. Total uptake was calculated and correlated to the total amount of NO inhaled, the amount of NO administered to the alveolar space, and the amount of NO administered to the perfused alveolar space.
Results:
About 35% of the total amount of NO delivered is taken up by the lungs, 70% of NO administered to the alveolar space is taken up, and 95-100% of the NO administered to perfused alveolar space is taken up. The size of the alveolar dead space varied between 10 and 60% of the alveolar space. At 40 ppm of inhaled NO there was no difference between inspired and mixed expired NO2 concentration, indicating that there is no significant NO2 formation taking place in the lungs during NO inhalation at the concentrations studied.
Conclusions:
Practically all NO administered to the perfused alveolar space is taken up. The total uptake differs from that of healthy persons probably because of differences in the alveolar dead space.