Prolonged inhalation of low concentrations of nitric oxide in patients with severe adult respiratory distress syndrome. Effects on pulmonary hemodynamics and oxygenation.
BACKGROUND
Nitric oxide (NO) inhalation selectively decreases pulmonary artery hypertension and improves arterial oxygenation in patients with the adult respiratory distress syndrome (ARDS). In this study of patients with severe ARDS, we sought to determine the effect of inhaled NO dose and time on pulmonary artery pressure and oxygen exchange and to determine which patients with ARDS are most likely to show this response.


METHODS
Thirteen patients with severe ARDS (hospital mortality 67%) inhaled 0-40 parts per million (ppm) NO. Seven of these patients continued to breathe 2-20 ppm NO for 2-27 days.


RESULTS
Inhaling 5-40 ppm NO decreased mean pulmonary artery pressure in a dose-related fashion (from 34 +/- 7 to 30 +/- 7 mmHg at 20 ppm NO). Systemic arterial pressure did not change. The ratio of arterial oxygen tension to inspired oxygen fraction increased (from 126 +/- 36 to 149 +/- 38 mmHg) and the venous admixture decreased (from 31.2 +/- 5.5 to 28.2 +/- 5.2%) without a clear dose-response effect. During prolonged NO inhalation, 2-20 ppm NO effectively reduced mean pulmonary artery pressure (38 +/- 7 vs. 31 +/- 6 mmHg) and increased arterial oxygen tension (79 +/- 10 vs. 114 +/- 27 mmHg) without evidence of tachyphylaxis. The decrease of pulmonary vascular resistance during NO inhalation correlated with the level of pulmonary vascular resistance without NO (r = -0.72). The reduction of venous admixture correlated with the level of venous admixture without NO (r = -0.78).


CONCLUSIONS
Long-term NO inhalation at low concentrations selectively decreases mean pulmonary artery pressure and improves arterial oxygen tension in patients with ARDS. The selective pulmonary vasodilation effect is most pronounced in ARDS patients with the greatest degree of pulmonary vasoconstriction.
Department of Anaesthesia, Massachusetts General Hospital, Harvard Medical School, Boston.
L M
LM
Bigatello
W E
WE
Hurford
R M
RM
Kacmarek
J D
JD
Roberts
W M
WM
Zapol
D000280:Administration, Inhalation; D000328:Adult; D000368:Aged; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D006801:Humans; D006976:Hypertension, Pulmonary / Q000097:blood* / Q000188:drug therapy*; D008875:Middle Aged; D009569:Nitric Oxide / Q000008:administration & dosage*; D010100:Oxygen / Q000097:blood*; D010313:Partial Pressure; D011652:Pulmonary Circulation / Q000187:drug effects*; D012128:Respiratory Distress Syndrome / Q000097:blood* / Q000188:drug therapy* / Q000503:physiopathology; D013618:Tachyphylaxis / Q000502:physiology
D009569:Nitric Oxide; D010100:Oxygen