Acute Respiratory Distress Due to Methane Inhalation
A 21-year-old man, non-smoker, was admitted to the emergency department (ED) in a drowsy mentality after exposure to methane gas. He had started working at a medical gas supply company 3 months ago. He had worked without any respiratory protective devices. While opening a methane gas tank, assuming it was a nitrogen tank, he was accidently exposed in a gas supply room, approximately 10×10 m. There was no window and the doors were kept closed in the room. When the methane tank was opened, gas escaped from the tank for about one minute. Immediately after exposure, he sought refuge in a room inside of the gas supply space and soon lost consciousness. Approximately, 4.5 hours after exposure he was admitted to the ED.\nWhen he arrived at the ED, his vital signs were as follows: blood pressure, 160/100 mm Hg; heart rate, 130 beats/min; respiratory rate, 28 breaths/min; temperature, 36.2℃; and O2 saturation measured by pulse oxymeter (SpO2), 75% of room air. His oropharynx was found to be normal. There was a bilateral decrease in breathing sounds without wheezing, stridor or crackles on pulmonary auscultation. He was immediately intubated because he was cyanotic and in respiratory distress. Initial blood gas during intubation with 10 L/min oxygen supply showed pH 7.268, PCO2 34.5 mm Hg, PO2 77.2 mm Hg, HCO3- 15.3 mmol/L, and SaO2 93.3%. Electrocardiography showed sinus tachycardia. Serum blood urea nitrogen, creatinine, and lactate were 11 mg/dL, 0.8 mg/dL, and 14.0 mmol/L, respectively. Initial chest radiograph showed bilateral ill-defined air-space consolidations on both perihilar areas, which mimics pulmonary edema but heart and great vessels appeared unremarkable (). A computed tomography (CT) scan of the chest showed bilateral symmetric air-space consolidation and ground glass opacity at the dependent portion of the lungs (). After mechanical ventilation (MV) with fraction of inspired oxygen (FiO2) of 0.6, his SpO2 increased to 98%. Four hours after MV he gained an alert mentality. Subsequent blood gas analysis showed a pH 7.36, PCO2 34.5 mm Hg, PO2 77 mm Hg, HCO3- 15.3 mmol/L, and SaO2 95.0% under MV (synchronized intermittent mandatory ventilation; SIMV; FiO2 of 0.4). He received albuterol nebulizer treatment. Peripheral blood tests showed the following: white blood cells, 14,550/mm3 (neutrophils, 36%; lymphocytes, 58%; and eosinophils, 2%); hemoglobin, 15.9 g/dL; and platelets, 296,000/mm3. Four hours after arriving at the ED, he was weaned from MV to 4 L/min nasal cannula with SpO2 96%. The next day, a chest radiograph showed resolution of bilateral airspace consolidations (). He was admitted to the intensive care unit for 24 hours and subsequently transferred to the general ward when oxygen was no longer required. A pulmonary function test was performed 4 days after exposure. The results were as follows: forced vital capacity (FVC), 3.3 L (68% predicted); forced expiratory volume in one second (FEV1), 3.0 L (74% predicted); FEV1 to FVC ratio, 90%; and total lung capacity, 4.2 L (70% predicted). A single-breath carbon monoxide diffusing capacity (DLco) was 24.5 mL/min/mm Hg (83% predicted). His symptoms resolved and he was discharged after 5 days without medication. Ten days after discharge, the follow-up chest CT scan showed a complete resolution of previous bilateral air-space consolidations (). The follow-up pulmonary function test showed recovery from the restrictive ventilatory defect.