Acute lung injury causes alveolar collapse with decrease in lung compliance and resting lung volume, resulting in a mismatch between ventilation and perfusion (Va/Q). The Va/Q mismatch accounts entirely for the severe arterial hypoxemia observed during acute lung injury. Application of continuous positive airway pressure (CPAP) recruits additional lung units for gas exchange and improves Va/Q matching.”
Inhalation of nitric oxide (NO) in concentrations ranging from 5 to 80 parts per million (ppm) has been shown to cause selective pulmonary vasodilation” and to improve pulmonary gas exchange in patients with acute lung injury. Because NO is r^Hdly inactivated by binding to hemoglobin, inhai^jn of NO results in pulmonary vasodilation limited to ventilated lung areas. Inhalation of 36 ppm NO in patients with acute lung injury selectively improved perfusion of ventilated lung areas, resulting in a redistribution of blood flow from nonventilated to ventilated lung units and in improved pulmonary oxygen transfer. canadian health&care mall
We hypothesized that recruitment of lung units with CPAP should augment the effect of NO inhalation on Va/Q matching. To test this hypothesis, we examined changes in the continuous Va/Q distributions during application of CPAP and inhalation of low concentrations of NO in dogs with oleic acid-induced lung injury. After approval by the local laboratory animal care and use committee, 10 mongrel dogs weighing 22 to 28 kg (24.6 ±2.4 kg; mean±SD) were anesthetized with intravenous pentobarbital sodium, 12 mg/kg, followed by an infusion of 20 /-tg/kg/min. Each animal was placed in a supine position, and the trachea was intubated with a 9-mm internal diameter cuffed tracheal tube (Mallinckrodt, Argyle, NY). All dogs breathed room air spontaneously at ambient airway pressure throughout instrumentation. A catheter was inserted into the right femoral artery. A 7-French, thermistor-tipped, triple-lumen, pulmonary artery catheter (93A-131-7F, Baxter Edwards Critical-Care, Irvine, Calif) was placed through the right femoral vein.