Feature

Aspiration Pneumonitis

Aspiration Pneumonia

Basic definition

Acute chemical lung injury caused by inhalation of sterile gastric contents

Infectious pneumonia due to aspiration of oropharyngeal secretions colonized with bacteria

Nature of process

Chemical / inflammatory (non-infectious initially)

Infectious (bacterial)

Primary insult

Gastric acid (low pH), bile salts, enzymes, food particles

Pathogenic bacteria from oral cavity

Sterility at onset

Sterile at onset

Non-sterile from onset

Common clinical scenario

Witnessed aspiration during: anesthesia induction, overdose, alcohol intoxication, seizures, head injury

Chronic micro-aspiration in: stroke, dementia, poor oral hygiene, alcoholism

Aspiration event

Usually witnessed and large-volume

Often unwitnessed, recurrent micro-aspiration

Time course of symptoms

Abrupt onset (minutes to hours)

Insidious onset (days)

Latency after aspiration

Symptoms within 1–6 hours

Symptoms appear 24–72 hours or later

Fever

Absent or low-grade initially

Common, persistent

Cough

Acute cough, choking episode

Productive cough common

Sputum

Usually minimal or absent

Purulent, foul-smelling sputum

Dyspnea

Prominent and sudden

Progressive

Hypoxemia

Severe, early

Moderate, progressive

Tachypnea

Common

Common

Chest pain

Rare

Possible pleuritic pain

Systemic toxicity

Minimal initially

Prominent (sepsis features common)

Inflammatory markers (CRP, PCT)

Mild or normal early

Elevated

Leukocyte count

Normal or mild leukocytosis

Marked leukocytosis

Arterial blood gas

Acute hypoxemic respiratory failure

Hypoxemia ± respiratory alkalosis/acidosis

Radiological onset

Rapid (within hours)

Delayed

Chest X-ray pattern

Patchy, bilateral or dependent infiltrates

Lobar or segmental consolidation

Typical lobes involved (upright)

Right lower lobe

Right lower lobe

Typical lobes involved (supine)

Posterior segments of upper lobes, superior segments of lower lobes

Same

CT chest findings

Ground-glass opacities, dependent consolidation

Consolidation ± cavitation

Cavitation

Rare

Common (anaerobes)

Lung abscess

No

Yes

Empyema

Rare

Possible

Bronchiectasis (chronic)

No

Can develop

Pathophysiology – key mechanism

Acid causes epithelial injury → ↑ permeability → alveolar flooding → ARDS

Bacterial infection → inflammation → necrosis

pH of aspirate relevance

pH < 2.5 strongly injurious

Less relevant

Volume relevance

> 0.3 mL/kg high risk

Small repeated volumes sufficient

Common organisms

None initially

Anaerobes (Prevotella, Fusobacterium), Streptococcus, Gram-negative bacilli

Role of anaerobes

None

Major role

Blood cultures

Negative

May be positive

Sputum culture

Non-diagnostic

Useful

BAL findings

Neutrophilic inflammation, sterile cultures

Positive bacterial cultures

Progression

May resolve in 24–48 h or progress to ARDS

Progressive without antibiotics

ARDS risk

High

Lower

Sepsis risk

Low initially

High

Natural course without antibiotics

Often improves spontaneously

Worsens

Mainstay of treatment

Supportive care only

Antibiotics essential

Antibiotics role

NOT indicated initially

Indicated

When antibiotics may be started

If no improvement after 48–72 h or secondary infection suspected

From diagnosis

Preferred antibiotics

None initially

Beta-lactam/beta-lactamase inhibitor (e.g., amoxicillin-clavulanate, piperacillin-tazobactam)

Anaerobic coverage

Not required

Required

Steroids

Not routinely recommended

Not routine

Oxygen therapy

Frequently required

Often required

Mechanical ventilation

Common in severe cases

Less common

Outcome

Good with supportive care

Good with appropriate antibiotics

Mortality

Related to ARDS severity

Related to sepsis, comorbidities

Prevention strategies

Aspiration precautions peri-intubation

Oral hygiene, swallowing assessment