Aspiration Pneumonitis

Aspiration pneumonitis is a chemical lung injury caused by inhalation of sterile gastric contents (acid, with a pH below 2.5, and a volume above 25 mL or 0.3 mL/kg) into the lower airway, without a primary bacterial infection. It differs from aspiration pneumonia, which is a bacterial infection that follows the aspiration of oropharyngeal secretions colonised with bacteria.

• The injury happens in two phases: an initial direct chemical burn of the airway epithelium within minutes, followed 2 to 4 hours later by an inflammatory response with neutrophil infiltration, cytokine release, increased capillary permeability, alveolar oedema and surfactant inactivation. This leads to hypoxaemia, which usually peaks at 24 to 48 hours.
• Settings and risk factors: reduced level of consciousness (anaesthesia and sedation, seizures, stroke, head injury, alcohol or drug intoxication, cardiac arrest), swallowing disorders (neurological disease, Parkinson disease, motor neurone disease, dementia, oesophageal disease), vomiting and bowel obstruction, gastro oesophageal reflux, enteral tube feeding, a recent endoscopy or intubation, obesity, pregnancy (labour and caesarean section), and old age.
• It occurs in about 1 in 3000 anaesthetics, and is a major cause of death from anaesthesia. About 5 to 10% of patients develop acute respiratory distress syndrome, and mortality is about 5% overall and over 30% in those with respiratory failure.
• Aspiration pneumonitis and pneumonia are difficult to separate in the first 48 hours, since both cause fever, hypoxia and infiltrates.

• A witnessed event (vomiting, regurgitation, a seizure, loss of consciousness, or a swallowing episode with choking), followed within 2 to 5 hours by cough, wheeze, breathlessness, tachypnoea, tachycardia, fever, and cyanosis. In unwitnessed cases, new hypoxia or respiratory failure in a high risk patient suggests aspiration.
• Frothy or pink sputum, and gastric particles in the mouth or airway. Auscultation shows crackles, wheeze or bronchial breathing, usually over the right lower lobe or the posterior segments of the upper lobes (supine patients) and the apical segment of the lower lobes.
• Fever is common, and does not distinguish pneumonitis from infection. Hypotension and shock can occur with extensive injury.
• Mild cases show only cough and transient hypoxia that resolve within 24 to 48 hours.
• Differential diagnosis: aspiration pneumonia, community acquired or hospital acquired pneumonia, pulmonary oedema, pulmonary embolism, acute respiratory distress syndrome from other causes, asthma, foreign body aspiration, anaphylaxis, and pneumothorax.
• Red flags: oxygen saturation below 92% on room air, respiratory rate above 30, hypotension, altered consciousness, large volume or particulate aspiration, bilateral infiltrates, a rising oxygen requirement, and failure to improve at 48 hours.
• Complications: acute respiratory distress syndrome, secondary bacterial pneumonia (in 20 to 30%), lung abscess, empyema, pneumothorax, bronchiectasis, chronic aspiration with fibrosis, and respiratory failure.

• Clinical, based on a witnessed or probable aspiration event in a patient at risk, with the acute onset of respiratory symptoms and hypoxia.
• Assess oxygen saturation and respiratory rate, and arterial blood gases for patients with hypoxia.
• Chest X-ray: new infiltrates in the dependent lung segments (right lower lobe, posterior segments of the upper lobes, apical segments of the lower lobes) that appear within 2 to 24 hours. The X-ray is normal in the first hour. CT of the chest is used for complications or diagnostic doubt.
• Full blood count, C-reactive protein, procalcitonin (a low level supports pneumonitis), urea and electrolytes, glucose, lactate and blood cultures in febrile or unwell patients.
• Sputum or endotracheal aspirate for Gram stain and culture when pneumonia is suspected.
• Bronchoscopy for removal of particulate matter, or when there is lobar collapse, or foreign body is suspected.
• Look for the cause of aspiration: swallowing assessment (bedside, then videofluoroscopy or fibreoptic endoscopic evaluation), neurological examination, reflux evaluation, and medicines (sedatives, anticholinergics).

• Immediate care at the time of aspiration:
  • Place the patient in the lateral position (or head down tilt in witnessed vomiting), and suction the oropharynx and, if intubated, the trachea, before the first positive pressure breath.
  • Give oxygen to keep oxygen saturation at 94 to 98%, by face mask or high flow nasal cannula (30 to 60 L/min).
  • Bronchoscopic removal of solid particles.
  • Do not perform saline lavage, which spreads acid.
• Supportive care:
  • Monitor in a high dependency or intensive care unit for those with hypoxia, increased respiratory effort or large volume aspiration.
  • Non-invasive ventilation or mechanical ventilation with lung protective settings (tidal volume 6 mL/kg of predicted body weight, plateau pressure below 30 cm of water, positive end expiratory pressure 5 to 15 cm of water) for respiratory failure. Prone position for 12 to 16 hours daily in severe acute respiratory distress syndrome.
  • Intravenous fluids to maintain perfusion, and vasopressors for shock.
  • Bronchodilators (salbutamol 2.5 to 5 mg nebulised) for wheeze.
  • Corticosteroids do not improve outcome and are not recommended.
• Antibiotics: not given routinely for aspiration pneumonitis. Begin antibiotics when there is no improvement or worsening at 48 hours, a persistent fever beyond this time, purulent sputum, a rising inflammatory marker, or when risk factors for bacterial pneumonia are present (bowel obstruction, gastric colonisation from acid suppression, poor oral hygiene or dental disease, a hospital stay, prolonged aspiration).
  • Community onset aspiration pneumonia: amoxicillin clavulanate 625 mg orally 8 hourly (or 875/125 mg 12 hourly), or 1.2 g IV 8 hourly, for 5 to 7 days. Penicillin allergy: clindamycin 300 to 450 mg orally 6 to 8 hourly (or 600 mg IV 8 hourly), or moxifloxacin 400 mg once daily, or doxycycline 200 mg on day 1, then 100 mg once daily.
  • Hospital acquired or severe disease: piperacillin tazobactam 4.5 g IV 6 to 8 hourly, or ceftriaxone 2 g IV once daily with metronidazole 500 mg IV 8 hourly, or meropenem 1 g IV 8 hourly, adjusted by culture, local resistance, and renal function. Add vancomycin 15 to 20 mg/kg IV 8 to 12 hourly when meticillin resistant Staphylococcus aureus is a concern.
  • Lung abscess or empyema: prolonged therapy for 3 to 6 weeks with drainage as needed.
  • Routine anaerobic cover is not needed when the oropharynx is not heavily colonised, except with lung abscess or empyema.
• Prevent recurrence:
  • Swallow assessment and speech and language therapy: modify food and fluid texture, give compensatory positioning (chin tuck), supervised feeding, and small, slow mouthfuls.
  • Enteral feeding when oral feeding is unsafe: nasogastric tube feeding with the head raised 30 to 45 degrees, post-pyloric feeding for high risk patients, and gastrostomy for prolonged need (over 4 weeks). Gastrostomy does not eliminate aspiration risk.
  • Oral hygiene: toothbrushing twice daily, and chlorhexidine 0.12 to 0.2% mouthwash 15 mL twice daily for those who are ventilated.
  • Treat reflux (omeprazole 20 to 40 mg once daily), and avoid unnecessary acid suppression, which increases bacterial colonisation.
  • Review sedatives, opioids, anticholinergics and antipsychotics, and keep patients upright for meals and for 30 to 60 minutes afterward.
  • Pre-operative fasting (6 hours for solids, 2 hours for clear fluids), rapid sequence induction with cricoid pressure in high risk patients, and non-particulate antacid (sodium citrate 30 mL orally) in obstetric patients, with omeprazole 40 mg the night before and morning of surgery.
• Special groups:
  • Pregnancy: high risk in labour and caesarean section, so fasting, antacid prophylaxis (sodium citrate 30 mL) and regional anaesthesia are used. Treat injury with oxygen and supportive care, and use amoxicillin clavulanate for infection.
  • Children: after a witnessed event give oxygen and observe for 6 hours, and treat infection with amoxicillin clavulanate 25 to 30 mg/kg of amoxicillin IV or orally 8 to 12 hourly. Consider foreign body, swallowing disorders and reflux in recurrent cases.
  • Elderly and dementia: swallow assessment, texture modification, oral care, and careful feeding. Discuss goals of care when swallowing is unsafe.
  • Neurological disease: early swallow assessment, nutrition, and tube feeding when needed.
  • Renal impairment: adjust doses of piperacillin tazobactam, meropenem, vancomycin, and amoxicillin clavulanate.
• Follow up: review at 24 to 48 hours for response, and arrange chest X-ray at 6 weeks for those with persistent signs, smokers, and patients above 50 years. Refer to a respiratory physician for lung abscess, empyema, bronchiectasis, or recurrent aspiration, and to speech and language therapy and gastroenterology for dysphagia.