Hemodynamic and gas exchange responses to inhalation of nitric oxide in patients with the acute respiratory distress syndrome and in hypoxemic patients with chronic obstructive pulmonary disease

Objective: Inhalation of nitric oxide (NO) can improve oxygenation and decrease mean pulmonary artery pressure (MPAP) in patients with the acute respiratory distress syndrome (ARDS). It is not known whether inhaled NO exerts a similar effect in hypoxemic patients with chronic obstructive pulmonary disease (COPD). Design: Prospective clinical study. Setting: General intensive care unit in Sabadell, Spain. Patients: Nine mechanically ventilated COPD patients (mean age 72±2 years; forced expiratory volume in 1 s 0.91±0.11 l) and nine ARDS patients (mean age 57±6 years; mean lung injury score 2.8±0.1) Measurements and results: We measured hemodynamic and gas exchange parameters before NO inhalation (basal 1), during inhalation of 10 ppm NO (NO-10), and 20 min after NO was discontinued (in basal 2) in the ARDS group. In the COPD group, these parameters were measured before NO inhalation (basal 1), during different doses of inhaled NO (10, 20, and 30 ppm), and 20 min after NO was discontinued (basal 2). A positive response to NO was defined as a 20% increment in basal arterial partial pressure of oxygen (PaO₂). MPAP and pulmonary vascular resistance (PVR) decreased significantly, while other hemodynamic parameters remained unchanged after NO-10 in both groups. Basal oxygenation was higher in the COPD group (PaO₂/FIO₂ (fractional inspired oxygen) 190±18 mmHg) than in the ARDS group (PaO₂/FIO₂ 98±12 mmHg), (p<0.01). After NO-10, PaO₂/FIO₂ increased (to 141±17 mmHg, p<0.01) and Qva/Qt decreased (39±3 to 34±3%, p<0.01) in the ARDS group. There were no changes in PaO₂/FIO₂ and Qva/Qt when the NO concentration was increased to 30 ppm in the COPD group. In both groups, a correlation was found between basal MPAP and basal PVR, and between the NO-induced decrease in MPAP and in PVR. The NO-induced increase in PaO₂/FIO₂ was not correlated with basal PaO₂/FIO₂. In the ARDS group, six of the nine patients (66%) responded to NO and in the COPD group, two of nine (22%) (p=0.05). Conclusions: NO inhalation had similar effects on hemodynamics but not on gas exchange in ARDS and COPD patients, and this response probably depends on the underlying disease. Received: 19 December 1995 Accepted: 28 September 1996