Background: Pulmonary hypertension may occur after cardiovascular surgery, and inhaled nitric oxide (iNO) is expected to reduce pulmonary artery pressure and improve oxygenation. Pulmonary hypertension can occur even after cardiopulmonary bypass because of microemboli, ischemia, sedimentation of blood cells or stress reaction. iNO is a pulmonary vasodilation therapy in which nitric oxide (NO) is administered directly into the alveoli via the airways. iNO is transported to the alveoli by both convection and diffusion and is rapidly absorbed into the tissues where it relaxes vascular smooth muscle. NO binds to Hb (hemoglobin) in blood vessels and is inactivated within seconds. Therefore, it does not act on systemic vasodilation and selectively dilates only pulmonary vessels. However, sudden weaning can pose the risk of causing serious hypoxia and rebound hypertension. The purpose of this study is to investigate oxygenation response to initiation and withdrawal of iNO. Methods: The study population included intubated adult iNO patients who had pulmonary hypertension (mean PAP ≥ 20 mm Hg) after cardiac surgery, admitted to the ICU. A retrospective chart review was conducted to P/F ratio, weaning time, rebound, and mortality rate. The study site was a 400-bed hospital in Osaka, Japan. 12 ventilated patients identified the date of iNO use (April 1, 2022–March 31, 2023) were enrolled in the study group. AINOMAX (Mallinckrodt Pharma) was used as an NO inhaler for adults. Wilcoxon signed-rank test was used to analyze the data. Institutional Review Board (IRB) approval was obtained. Results: There was not significant difference in P/F ratio between pre and post initiation of iNO therapy (104.1 81.9–174.3 vs. 155.5 111.8– 220.8, P > .05). There was significant difference in P/F ratio between pre and post withdrawal of iNO therapy (234.5 209.8–303.8 vs. 191.6 153.8– 235.3, P < .05). Median of iNO therapy time, total weaning time, and 1 ppm to 0 ppm weaning time were 93 hours 24 min, 8 hours 38 min, and 48 min 30–127, respectively. Rebound occurred in one patient (8 %). 1 ppm to 0 ppm weaning time of the patient with rebound was 20 min. Mortality rate was 33.3%. Conclusions: Oxygenation response to withdrawal of iNO differed in adult patients with pulmonary hypertension after cardiac surgery. Patients with pulmonary hypertension after cardiovascular surgery had a mortality rate of 33.3% and weaning must be performed carefully to avoid rebound.Table1 Subjects Patients, n=12Male, n (%)9(75.0)Age, mean ±SD66.9±9.9Mortality rate, n (%)4(33.3)±Values are mean ±SDTable 2 Results Pre-intiationPost-intiationρ ValuePre-withdrawalPost-withdrawalρ ValuePaO2/FiO2104.1 81.9–174.3155.5 111.8– 220.80.11234.5 209.8–303.8191.6 153.8– 235.30.004Data are median IQR
Masami Sana (Sun,) studied this question.