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Association Between Inhaled Nitric Oxide Treatment and Long-Term Pulmonary Function in Survivors of Acute Respiratory Distress Syndrome
Study Question: Does inhaled nitric oxide (iNO) improve pulmonary function six months post-treatment in acute respiratory distress syndrome (ARDS) survivors compared to placebo?
Study Description: This article was an a priori-defined analysis of data from ARDS survivors (n = 92) who took part in a multicenter, randomized, blinded, placebo-controlled study comparing low-dose iNO (5 ppm) and inhaled placebo (nitrogen gas). Patients with a partial-pressure-of-arterial-oxygen-to-fraction-of-inspired-oxygen (PaO2/FiO2) ratio ≤ 250 mm Hg due to causes other than severe sepsis were included. Exclusion criteria were: non-pulmonary organ failure at randomization; sepsis-induced ARDS; need for vasopressors; severe head injury; and the presence of severe burns. The study drug was continued until the end of trial (28 days), death, or adequate oxygenation with FiO2 ≤ 0.40 and PEEP ≤ 5 cm H20. Pulmonary function tests (PFTs) were performed in survivors six months post-treatment.
Results: Thirty percent of those who survived the trial completed the 6-month assessment. The remainder of patients died prior to follow-up (7%), were lost to follow-up (16%), or did not have PFT results available (47%). Baseline characteristics, oxygenation, and respiratory parameters were clinically similar between groups. The mean PaO2/FiO2 ratio at baseline was 140.5 vs 136.1 mm Hg. At 6 months, patients treated with iNO had improved: total lung capacity (TLC; 5.54 L vs 4.81 L; p = 0.026); % predicted TLC (93.3% vs 76.1%; p < 0.001); FEV1 (80.2% vs 69.5%, p = 0.042); forced vital capacity (FVC; 83.8% vs 69.8%; p = 0.019); and FEV1/FVC (96.1% vs 87.9%; p = 0.033). There were no significant differences in FEV1, FEV1/FVC, functional residual capacity or carbon monoxide diffusion.
Conclusion(s): ARDS survivors who receive iNO have improved PFTs at 6 months post-treatment.
Perspective: Because pre-morbid pulmonary function was unknown, six-month data was unavailable for the majority of ARDS survivors and exclusion criteria were restrictive, the findings in this analysis are very challenging to interpret and generalize. iNO has not been shown to improve ARDS mortality, thus utilizing this medication outside of salvage therapy for severe ARDS likely remains unwarranted at the present time.