Inhaled and exhaled nitric oxide

Inhaled nitric oxide (NO) is used to treat various cardiopulmonary disorder s associated with pulmonary hypertension. The rationale is based on the fac t that NO, given by inhalation, only dilates those pulmonary vessels that p erfuse well-ventilated lung units. As a result, pulmonary gas exchange is i mproved while pulmonary vascular resistance is reduced and pulmonary blood flow is increased. Inhaled NO has been succesfully applied to treat persist ent pulmonary hypertension of the newborn, reducing the need for extracorpo real life support. Although pulmonary hypertension and altered vasoreactivi ty contribute to profound hypoxaemia in adult and paediatric acute respirat ory distress syndrome (ARDS), the benefit of inhaled NO still remains to be established in patients with ARDS. ARDS is a complex response of the lung to direct or indirect insults, leading to pulmonary vasoconstriction and va rious inflammatory responses. Recent randomized trials suggest that inhaled NO only causes a transient improvement in oxygenation. Whether this effect is important in the long-term management of ARDS remains to be established . NO, measured in the exhaled breath, is an elegant and non-invasive means to monitor inflammation of the upper and lower respiratory tract. In the no rmal upper airways, the bulk of exhaled NO originates from the paranasal si nuses. Exhaled NO is increased in nasal allergy and decreased in cystic fib rosis, nasal polyposis and chronic sinusitis. That NO production is increas ed in asthmatic airways is also well established. However, several question s still need to be addressed, in particular evaluation of the sensitivity a nd specificity of the measurement techniques, and assessment of the broncho dilator action of endogenous NO.