What is the impact of pneumonia on the lung?

Impact of Pneumonia on the Lung

Pneumonia causes significant damage to the lungs through primary viral infection, secondary bacterial infection, or mixed viral-bacterial processes, leading to inflammation, consolidation, and potential complications including empyema, respiratory failure, and long-term sequelae.

Pathophysiological Effects on Lung Tissue

Primary Viral Pneumonia

• Characterized by rapid onset of breathlessness within 48 hours of fever 1
• Initially dry cough that may become productive of blood-stained sputum
• Physical findings include cyanosis, tachypnea, bilateral crepitations, and wheeze
• Radiographic findings: bilateral interstitial infiltrates predominantly in mid-zones, though focal consolidation can occur
• Can progress to respiratory failure with high mortality (>40%) despite intensive care support 1
• Death often occurs within seven days of hospital admission in fatal cases

Secondary Bacterial Pneumonia

• More common than primary viral pneumonia (up to four times more frequent) 1
• Typically develops during early convalescent period (4-5 days from initial symptoms)
• Chest radiography usually shows lobar pattern of consolidation
• Mortality ranges from 7% to 24% 1
• Common pathogens include:
  • Streptococcus pneumoniae
  • Staphylococcus aureus (associated with higher incidence of lung abscess formation - 14% vs 2%)
  • Haemophilus influenzae
  • Groups A, C, and G β-hemolytic streptococci

Mixed Viral-Bacterial Pneumonia

• Concurrent bacterial and viral infection
• Radiographically shows lobar consolidation superimposed on bilateral diffuse lung infiltrates
• High mortality rate (>40%), similar to primary viral pneumonia 1

Complications of Pneumonia

Pleural Complications

• Parapneumonic effusions develop in approximately 40% of bacterial pneumonias requiring hospitalization 1
• Persistent fever despite adequate antibiotic treatment should raise suspicion for empyema
• Pleural fluid is best evaluated by ultrasound examination

Respiratory Complications

• Acute Respiratory Distress Syndrome (ARDS) presents with:
  • New or worsening respiratory symptoms within one week of known clinical insult
  • Bilateral lung opacities on chest imaging 1
• Respiratory failure requiring mechanical ventilation
• Organized pneumonia can develop when pneumonia does not resolve adequately 2
  • Characterized by persistent fever, non-productive cough, progressive dyspnea, malaise, fatigue, weight loss
  • Physical examination reveals inspiratory crackles

Systemic Complications

• Sepsis and septic shock 1
• Metastatic infections in up to 10% of patients with pneumococcal bacteremic pneumonia 2:
  • Meningitis
  • Arthritis
  • Endocarditis
  • Pericarditis
  • Peritonitis
• Non-infectious complications that can delay radiographic resolution 2:
  • Renal failure
  • Heart failure
  • Pulmonary embolism with infarction
  • Acute myocardial infarction

Treatment Response and Failure

Treatment Failure

• Occurs in 20-30% of cases, defined as persistence or worsening of clinical signs 3
• Requires 48-72 hours for most patients to respond to appropriate antibiotic therapy
• Causes of non-response include:
  • Host factors (immunosuppression, chronic lung disease)
  • Incorrect antibiotic dosing
  • Atypical or resistant pathogens
  • Septic complications
  • Non-infectious conditions mimicking pneumonia

Management of Non-Responding Pneumonia

• Re-evaluation is necessary if a child remains pyrexial or unwell 48 hours after admission 1
• Consider:
  • Appropriateness of drug treatment and dosage
  • Lung complications such as empyema or lung abscess
  • Host factors including immunosuppression or coexistent disease
  • Rapid initiation of appropriate antimicrobial treatment (within first 2 hours of hospitalization) is crucial 2

Long-Term Impact

• Pneumonia can lead to chronic lung disease, especially in premature infants 1
• Organized pneumonia can develop as a sequela, requiring specific treatment
• Structural changes to lung architecture may persist after resolution of acute infection
• Recurrent pneumonia can lead to bronchiectasis and permanent lung damage

Pneumonia represents a significant threat to lung health with both immediate and potential long-term consequences, requiring prompt diagnosis, appropriate treatment, and vigilant monitoring for complications.