What is the treatment for a patient with chemical pneumonitis, possibly with pre-existing respiratory conditions such as asthma or Chronic Obstructive Pulmonary Disease (COPD)?

Treatment of Chemical Pneumonitis

For chemical pneumonitis, immediately discontinue exposure to the offending agent and initiate supportive care with supplemental oxygen; glucocorticoids should be administered for moderate to severe cases (grade 2-4), while mild cases may be managed with observation alone. 1, 2

Immediate Management Steps

Exposure Cessation and Initial Assessment

• Remove the patient from the chemical exposure source immediately and assess severity based on symptoms (dyspnea, cough, hemoptysis), gas exchange abnormalities (hypoxemia), and radiologic findings 1, 3, 4
• Recognize that initial chest radiographs can be normal for up to 48 hours after significant exposures, so delayed imaging is critical if clinical suspicion remains high 5
• Monitor vital signs at least twice daily including temperature, respiratory rate, pulse, blood pressure, and oxygen saturation 6

Severity Grading and Treatment Algorithm

Grade 1 (Mild):

• Minimal symptoms with limited radiographic changes 1
• Manage as outpatient with close monitoring every 2-3 days 1
• Supportive care with observation may be sufficient 1
• Repeat chest CT before considering any re-exposure 1

Grade 2 (Moderate):

• New or worsening dyspnea, cough, or reduced exercise tolerance with radiographic infiltrates 1
• Initiate oral or intravenous glucocorticoids (specific dosing: prednisone 0.5-1 mg/kg/day or equivalent) 1, 2
• Hospitalization may be required for initial treatment and monitoring 1
• Minimum 4-6 week steroid taper to prevent recrudescence 1

Grade 3-4 (Severe):

• Severe dyspnea, significant hypoxemia, or extensive radiographic abnormalities 1
• Hospitalization is mandatory with intensive monitoring 1
• High-dose intravenous glucocorticoids (hydrocortisone 50 mg IV every 6 hours or methylprednisolone 1-2 mg/kg/day) 1, 7
• Supplemental oxygen targeting SaO₂ >92% and PaO₂ >8 kPa 6
• Consider noninvasive or invasive mechanical ventilation if respiratory failure develops 1
• For refractory cases not improving after 48 hours on corticosteroids, add infliximab, mycophenolate mofetil, or IV immunoglobulin 1

Respiratory Support Considerations

Oxygen Therapy

• Initiate controlled oxygen therapy immediately for hypoxemic patients 6
• In patients with pre-existing COPD, use controlled oxygen delivery targeting PaO₂ ≥6.6 kPa (approximately 50 mmHg) without pH falling below 7.26 to avoid CO₂ retention 6
• For patients without COPD, target SaO₂ >92% 6
• Consider high-flow nasal oxygen if standard oxygen therapy fails 6

Mechanical Ventilation

• Noninvasive ventilation should be considered particularly in patients with pre-existing COPD who develop respiratory failure 1
• Invasive mechanical ventilation may be necessary for severe cases with refractory hypoxemia or hypercapnia 1

Special Considerations for Pre-existing Respiratory Disease

COPD Patients

• Continue regular bronchodilators throughout treatment 8
• Use controlled oxygen delivery to avoid precipitating hypercapnic respiratory failure 6
• These patients face higher risk of poor outcomes and require more intensive monitoring 1
• Consider early noninvasive ventilation before respiratory failure becomes severe 1

Asthma Patients

• Maintain regular controller medications (inhaled corticosteroids, long-acting bronchodilators) 8
• Chemical pneumonitis may trigger bronchospasm requiring increased bronchodilator therapy 1
• Monitor peak flows and consider systemic corticosteroids earlier in the treatment course 1

Pre-existing Interstitial Lung Disease (ILD)

• These patients are at significantly higher risk for worse outcomes with odds ratios for fatal outcomes of 2.27 compared to those without ILD 1
• Greater CT extent of pre-existing ILD portends higher risk of fatal outcome 1
• More aggressive early treatment with glucocorticoids is warranted 1

Monitoring and Follow-up

Short-term Monitoring (First 72 Hours)

• Assess clinical response at 72 hours using temperature, respiratory rate, heart rate, blood pressure, and oxygen saturation 8, 6
• Measure C-reactive protein on days 1 and 3-4, especially if clinical parameters are unfavorable 8, 6
• Clinical improvement should occur within 72 hours; if not, conduct full reinvestigation including chest CT and consider broadening therapy 6

Long-term Follow-up

• Delayed diagnosis is associated with higher severity and less reversibility, resulting in residual lung damage including fibrosis 1
• Pulmonary function testing should be performed at 1 month and repeated at 3-6 months to assess for persistent restrictive defects or diffusion impairment 3, 4
• Some patients may develop chronic complications including bronchiectasis, bronchiolitis obliterans, or permanent lung destruction 5
• Radiologic pulmonary infiltrates typically resolve within 1-2 weeks with appropriate treatment, but pulmonary function abnormalities may persist for months 3, 2

Critical Pitfalls to Avoid

• Do not delay treatment while awaiting diagnostic confirmation—early intervention with glucocorticoids for moderate-to-severe cases improves outcomes 1, 2
• Do not provide uncontrolled high-flow oxygen in patients with COPD or any obstructive component, as this can precipitate hypercapnic respiratory failure 6
• Do not use rapid steroid tapers (less than 4 weeks)—recrudescence of symptoms has been reported with rapid tapering 1
• Do not assume normal initial chest radiographs exclude significant injury—repeat imaging at 24-48 hours if clinical suspicion remains 5
• Ensure adequate hydration to maintain optimal secretion clearance, but avoid volume overload in patients with reduced lung compliance 6