pneumonia

• Pneumonia: 

  • inflammation of lung parenchyma associated with alveolar filling with exudate  

  • Pneumonia can result from a variety of causes including infection  

  • Also can occur secondary to chemical or physical injury to the lungs  

  • Pneumonia may also be described as idiopathic (unknown) when infectious causes have been excluded  
• Epidemiology: 

  • Pneumonia is very common in UK affecting 1 in every 100 people each year  

  • Although more than 100 strains of microorganism cause pneumonia only a few are responsible for most cases  

  • The most common causes of pneumonia are viruses and bacteria  

  • Less common causes of infectious pneumonia are fungi and parasites 

   
• Pathophysiology: 

  • Symptoms of infectious pneumonia are caused by invasion of lungs by microorganisms and by immune system's response to that infection  

  • Organisms invade spaces between cells and between alveoli via connecting pores  

  • This invasion triggers the immune system 

  • Neutrophils engulf and kill organisms  

  • White blood cells (mainly lymphocytes) activate chemical cytokines (proinflammatory mediators creating dilation) which allow fluid to leak into the alveoli  
• Main problems: 

  • The combination of cell destruction and fluid-filled alveoli interrupts the normal transportation of oxygen into the blood 

  • Affected alveoli can no longer be used for ventilation causing hypoxemia (low o2 in blood) 

  • Affected alveoli remain patent with no loss of volume (no atelectasis)  

  • This airless state is called consolidation 

   
• Review criteria for diffusion: 

  • In accordance with Fick’s law  

  – Concentration / pressure gradient  

  • No fresh inspired air reaching alveoli 
  • Therefore reduced alveolar partial pressure exerted (PAO2 )  
  • Reduced concentration / pressure gradient to facilitate diffusion 

   
• Review criteria for diffusion: 

  • In accordance with Fick’s law  

  – Gas solubility 

  • Small amounts of O2 dissolved in fluid  
  • But O2 poorly soluble so reduced gas exchange 

   
• Review criteria for diffusion: 

  • In accordance with Fick’s law  

  – Thickness of alveolar membrane  

  • Presence of inflammatory fluid in interstitium and exudate in alveoli increase distance for diffusion   
  • With disease progression alveolar membrane can become fibrotic and thickened 

   
• Review criteria for diffusion: 

  • In accordance with Fick’s law  

  – Surface area of alveolar membrane  

  • Areas of consolidated lung “blocked” and unable to participate in gas exchange 
  • Reducing area of alveolar membrane  
  • Makes very small contribution to hypoxaemia 

   
• Review criteria for diffusion: 

  • In accordance with Fick’s law  

  – V/Q coupling 

  • Pneumonic areas consolidated and unventilated  
  • Would expect perfusion to also be reduced due HPVC  
  • However, presence of inflammatory cytokines reverses HPV  
  • Continued perfusion of nonventilated airspaces produces V/Q mismatch termed “Shunt” 
  • Main cause of hypoxaemia in pneumonia 

   
• Symptoms: 

  • Typical symptoms associated with pneumonia  

  – Cough  

  – Chest pain  

  – Fever and rigors  

  – Rapid shallow breathing / SOB  

  – Haemoptysis (coughing up blood)  

  – Weight loss  

  – ? Sputum production 
• Auscultation: 

  • Reduced breath sounds over pneumonic area  

  • Bronchial breath sounds transmitted from trachea and main airways  

    – Indication of consolidation  

  • Inspiratory crackles before pneumonia organises or during resolution of consolidation 

   
• Complications: 

  • Respiratory & circulatory failure 

  • Pleural effusion 

  • Empyema 

  • Abscess  

   
• Management: 

  • High flow O2 therapy  

  • Antibiotics if bacterial in origin  

  • Fluid resuscitation  

  • Positioning to maximise V/Q  

  • Analgesia for chest pain  

  • Airway clearance techniques if productive of sputum  

  • Ventilatory support (non-invasive / invasive)