ABSORPTION OF NITROGEN-DIOXIDE AND NITRIC-OXIDE BY SODA LIME

Inhaled nitric oxide (NO) is used for the treatment of pulmonary hyper tension as a selective pulmonary vasodilator. However, NO is oxidized rapidly to the more toxic nitrogen dioxide (NO2). Elimination of NO2 f rom inspired gas is essential for safe clinical use NO. We therefore i nvestigated the efficacy of soda lime in absorbing NO2 from NO2-contai ning gases. Commercially available soda limes (Soda sorb and Wake lime -A), were exposed to the following six gas mixtures containing NO and NO2 in a hypoxic carrier gas for 20 min: No, 1: NO 40 ppm; No. 2: NO 3 5 ppm and NO2 5 ppm; No, 3: NO 30 ppm and NO2 10 ppm; No. 4: NO 20 ppm and NO2 20 ppm; No, 5: NO 10 ppm and NO2 30 ppm; and No. 6: NO2 40 pp m. Both types of soda lime completely absorbed the NO2 in all samples when it was present (Nos 2-6). NO concentration in these gas mixtures was reduced by an amount equal to the NO2 absorbed by soda lime. NO wa s absorbed minimally when NO2 was not present in the mixture. Nitrite was detected from the Wako lime-A granules exposed to the test gas by the chemical analysis. These findings suggest that soda lime completel y absorbs NO2 by chemical neutralization, but NO is absorbed as simult aneously absorbed NO2 only where NO and NO2 coexist. Therefore, we con clude that soda lime is useful for NO2 absorption during NO inhalation therapy but NO monitoring from a point distal to the soda lime is req uired for precise control of inspired NO concentration.