Chemical Pneumonitis

Chemical pneumonitis is lung inflammation caused by direct injury from inhaled or aspirated chemical agents rather than infection or immune sensitisation. Causes include aspiration of gastric acid (Mendelson syndrome), hydrocarbon ingestion with aspiration (kerosene, petrol, paraffin), inhalation of irritant gases, vapours and fumes, ingestion of corrosives, and aspiration of mineral oil, lipoid substances and some medicines.

Kerosene (paraffin) poisoning in children is a leading cause in Kenyan households where the fuel is stored in drink bottles. Low viscosity, low surface tension and high volatility make hydrocarbons spread across the airway, so as little as 1 to 2 mL aspirated can cause severe pneumonitis.

Pathology is loss of surfactant, bronchiolar and alveolar epithelial necrosis, haemorrhage, oedema and then secondary bacterial infection.

Most survive; deaths occur from hypoxaemic respiratory failure or ARDS. Fever and infiltrates appear within hours and resolve over 1 to 2 weeks.

• Immediate: coughing, choking, gagging, vomiting, dyspnoea.
• Within 30 minutes to 6 hours: tachypnoea, grunting, wheeze, crackles, cyanosis, fever.
• Hydrocarbon odour on breath; drowsiness or agitation if systemic absorption (central nervous system depression), arrhythmia with halogenated or aromatic compounds (sensitisation of the myocardium to catecholamines).
• Gastric acid aspiration: wheeze, tachypnoea and hypoxaemia within 2 hours; pink frothy sputum in severe cases.
• Complications: ARDS, pneumatocele, pneumothorax, pleural effusion, secondary bacterial pneumonia, bronchiolitis obliterans.
• Red flags: SpO2 below 92 percent on air, respiratory rate above 60 in infants, seizures, coma, dysrhythmia.

• History: agent, volume, time, route, and vomiting.
• Observe for 6 hours with pulse oximetry; asymptomatic with normal examination and radiograph at 6 hours means safe discharge.
• Chest radiograph at presentation and at 6 hours (may lag clinical onset): perihilar and basal alveolar infiltrates, and may be unilateral (right lower zone) if aspirated.
• Arterial blood gas for hypoxaemia; PaO2/FiO2 below 300 indicates ARDS physiology.
• Blood tests: full blood count (leucocytosis common and non-specific), glucose, electrolytes, ECG for dysrhythmia, liver and kidney function in systemic toxicity.
• Culture of sputum or tracheal aspirate if the fever persists beyond 48 hours.
• Exclude bacterial pneumonia, foreign body aspiration, cardiogenic pulmonary oedema, and ingestion of other toxins (organophosphate, ethylene glycol).

• Do not induce vomiting, do not perform gastric lavage, do not give activated charcoal (it does not bind hydrocarbons and increases vomiting).
• Remove contaminated clothing, wash skin with soap and water, irrigate eyes with 1 to 2 litres of normal saline.
• Oxygen: titrate to SpO2 94 percent or more; continuous positive airway pressure 5 to 8 cmH2O for persistent hypoxaemia.
• Bronchospasm: salbutamol 2.5 mg (child under 5 years) or 5 mg (older child and adult) nebulised every 4 to 6 hours as needed. Avoid adrenaline and other catecholamines where possible in hydrocarbon exposure because of myocardial sensitisation.
• Corticosteroids and prophylactic antibiotics do not improve outcome. Give antibiotics only for proven or strongly suspected bacterial infection: amoxicillin clavulanate 25 to 45 mg/kg (amoxicillin component) orally or 30 mg/kg intravenously every 8 hours for 5 to 7 days in children; adults amoxicillin clavulanate 1.2 g intravenously every 8 hours for 5 to 7 days.
• Severe respiratory failure: intubation and lung protective ventilation (tidal volume 6 mL/kg predicted body weight, PEEP 8 to 12 cmH2O, plateau pressure 30 cmH2O or less); prone positioning for PaO2/FiO2 below 150 for 12 to 16 hours daily; extracorporeal support in specialist units.
• Gastric acid aspiration: suction the airway, oxygen, supportive ventilation; no empirical antibiotics unless the patient has a bowel obstruction, is on acid suppression, or fails to improve in 48 hours.
• Admission criteria: any respiratory symptoms, abnormal radiograph, SpO2 below 94 percent, or impaired consciousness.
• Follow up: chest radiograph at 2 weeks; spirometry at 6 weeks if symptoms continue.
• Prevention: store fuel in labelled original containers out of children's reach; counselling of caregivers.