A 53-year-old female with hemophagocytic lymphohistiocytosis (HLH) was admitted to the intensive care unit (ICU) because of respiratory failure. Immediately after admission, her airway was established using a cuffed 7.0-mm tracheal tube. Her chest X-ray showed severe bilateral infiltrates, and blood gas showed moderate level of acute respiratory distress syndrome (ARDS). Immediately after beginning of mechanical ventilation, high positive end-expiratory pressure (PEEP) combined with low tidal volume was applied. Her respiratory status gradually improved. Two weeks after commencement of mechanical ventilation, finally, her trachea was extubated. However, she developed mild hypoxemia with standard oxygen therapy and was suffering from tenacious secretion. HHFNC therapy at 40 L/min with an FIO2 of 0.5 (Optiflow system™, MR850 heated humidified RT202 delivery tubing; Fisher and Paykel Healthcare Ltd., Auckland, New Zealand) was applied through nasal cannula (Optiflow™; Fisher and Paykel, Auckland, New Zealand), and a mini tracheostomy cannula (Portex™ Mini-Trach™ II, Smith Medical, Kent, UK) was placed to treat her sputum. Her oxygenation was improved, and FIO2 was decreased to 0.35. Four days later, she complained of respiratory discomfort. Her oxygenation worsened and hemodynamic status also deteriorated. Specifically, FIO2 was 0.35 and PaO2 was about 60 mmHg, and PaCO2 was less than 30 mmHg because of respiratory acceleration (35 per minute). In hemodynamics, blood pressure itself was maintained, but it became sinus tachycardia of about 100 to 130 times per minute. Her chest X-ray revealed a localized pneumothorax and subcutaneous emphysema (Fig. 1a). A subsequent chest CT showed massive pneumomediastinum and a localized right-side pneumothorax, and subcutaneous emphysema were confirmed (Fig. 2). Regarding these air leaks, they seemed difficult to release. We decided to observe her course with changing HHFNC therapy to the standard oxygen therapy (5 L/min of O2 administration through a standard oxygen mask). She could not improve subjective discomfort easily, but her oxygenation and hemodynamic status gradually improved. On the next day, it was confirmed by a chest X-ray that the localized pneumothorax and emphysema disappeared (Fig. 1b).
Moreover, she had a lung with bulla, and it is undeniable that the bulla ruptured due to cough caused by suction after extubation, and the pressure by HHFNC was applied to it and pneumothorax occurred.