The patient was admitted to our unit at 45 days of life (day 0) for moderate to severe dehydration due to acute gastroenteritis. Interesting data include: preterm newborn of 32 weeks gestational age with adequate birth weight (2,060 g) and Down's syndrome, diagnosed in the first week of life of TF. Prior to admission he had not presented any hypoxic crisis. His weight curve was adequate. Ultrasound (Sonos 100 CF, Hewlett Packard, Massachusetts, USA) showed a pulmonary stenosis gradient of 70 mmHg, baseline O2 saturation was 92% with O2 at 0.5 bpm in nasal goggles, non-invasive mean arterial pressure (MAP) ranged between 50 and 55 mmHg (50-90 percentile for his age). On the third day he presented acute hypovolaemic shock due to severe diarrhoea, requiring volume expansion, intubation and connection to mechanical ventilation (MV). After a good clinical response, the patient was extubated after 6 hours with good clinical and gasometric tolerance. On the fifth day he started with progressive dyspnoea, cyanosis, bilateral crackles without wheezing, requiring reintubation and connection to MV (Babylog 8000 plus, Dräger Medizintechnik GMBH. Lübeck, Germany). Respiratory syncytial virus (RSV) testing in nasal mucus was negative. On day 8 he developed progressive oligoanuria with generalised oedema (maximum weight gain of 16% on day 9) and increased oxygen requirements (FiO2: 100%), with significant decrease in lung compliance and severe refractory hypoxaemia (transcutaneous saturation < 70%). Invasive MAT remained higher than 45 mmHg (5th percentile for her age: 43 mmHg): there was no pathological thermal gradient or coagulopathy. On auscultation, the heart murmur changed characteristics, becoming shorter and less intense (suggestive of suprasystemic PPH). Prone ventilation achieved only slight improvement for 2-3 hours (oxygenation index [OI] from 19 to 16) and the patient could not tolerate positive end-expiratory pressure (PEEP) increases greater than 8 cmH2O (desaturation and systemic hypotension). After ruling out infundibular spasm by ultrasound and verifying PPH (reversal of ventricular septal defect [VSD] shunt), treatment was started with ONI at 40 bpm. Subsequently, after a good response, it was maintained at 20 bpm. ONI and nitrous oxide (NOxPUMP plus, Bedfont Scientific Ltd, Upchurch Kent, England) were continuously monitored, the latter being maintained in ranges below 3 ppm.

The patient was also treated with dopamine perfusion at 8 µg/kg/minute. Chest X-ray showed bilateral alveolar infiltrates and mild pulmonary oligoperfusion. Bronchoalveolar lavage isolated Pseudomonas aeruginosa and antibiotic treatment was started. On day 12, resolution of the acute renal failure and oedema was observed, without having received treatment with renal function replacement agents. From day 30, a progressive improvement in respiratory dynamics was observed, tolerating the progressive weaning of ONI (previously it had not been possible to reduce it to less than 15 ppm because the patient could not tolerate it). On day 35 the patient was extubated.