Inhaled nitric oxide delivery by anesthesia machines

Inhaled nitric oxide (NO) is a selective pulmonary vasodilator used to treat intraoperative pulmonary hypertension and hypoxemia. In contrast to NO delivered by critical fare ventilators, NO delivered by anesthesia machines can be complicated by rebreathing. We evaluated two methods of administering NO intraoperatively: via the nitrous oxide (N2O) flowmeter and via the INOvent (Datex-Ohmeda, Madison, WI). We hypothesized that both systems would deliver NO accurately when the fresh gas flow (FGF) rate was higher than the minute ventilation ((V) over dot E). Each system was set to deliver NO to a lung model. Rebreathing of NO was obtained by decreasing FGF and by simulating partial NO uptake by the lung. At FGF greater than or equal to (V) over dot E (6 L/min), both systems delivered an inspired NO concentration ([NO]) within approximately 10% of the [NO] set, At FGF < (V) over dot E and complete NO uptake, the N2O flowmeter delivered a lower [NO] (70 and 40% of the [NO] set at 4 and 2 L/min, respectively) and the INOvent delivered a higher [NO] (10 and 23% higher than the [NO] set at 4 and 2 L/min, respectively). Decreasing the NO uptake increased the inspired [NO] similarly with both systems. At 4 L/min FGF, [NO] increased by 10%-20% with 60% uptake and by 18%-23% with 30% uptake. At 2 L/min, [NO] increased by 30%-33% with 60% uptake and by 60%-69% with 30% uptake. We conclude that intraoperative NO inhalation is accurate when administered either by the N2O flowmeter of an anesthesia machine or by the INOvent when FGF greater than or equal to (V) over dot E. Implications: Inhaled nitric oxide (NO) is a selective pulmonary vasodilator. In a lung model, we demonstrated that NO can be delivered accurately by a N2O flowmeter or by a commercial device. We provide guidelines for intraoperative NO delivery.