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Pneumonia – Pathophysiology, clinical manifestations, complications

Pathophysiology of Pneumonia

Pneumococcal pneumonia is the most common cause of bacterial pneumonia and is caused by streptococcus pneumonial organism S. Pneumonia also called as pneumococcus can infect the upper respiratory tract ,the blood and the nervous system. The organisms are generally found in the nose and the throat.When it invades the lung, pneumonia can occur.

The pathophysiology of all the other types of pneumonia is similar except the cause .

There are four characteristic stages of the disease process

  1. CONGESTION :- After the pneumococcus reach the alveoli, there is an out pouring of fluid into the alveoli. The organism multiply in the serous fluid, and the infection is spread. The pneumococci damages the host by their over whelming growth & by interfering with lung function.
  2. RED HEPATIZATION :- There is massive dilation of the capillaries and alveoli are filled with the organism, neutrophills, RBC’s fibrin. The lung appears red and granular. Similar to liver which is why the process is called hepatization.
  3. GRAY HEPATIZATION :- Blood flow decreases and leucocytes and fibrin consolidate in the affected part of the lung.
  4. RESOLUTION :- Complete resolution & healing occurs if there are no complication. The exudate becomes lysed and is processed by the macrophages. The normal lung tissue is restored and the persons gas exchange ability returns to normal.


  • The most common symptoms of pneumonia are
    • Cough (with some pneumonias you may cough up greenish or yellow mucus, or even bloody mucus)
    • Fever, which may be mild or high
    • Shaking chills
    • Shortness of breath (may only occur when you climb stairs)
  • Other symptoms include
    • Confusion, especially in older people
    • Excess sweating and clammy skin
    • Headache
    • Loss of appetite, low energy, and fatigue
    • Sharp or stabbing chest pain that gets worse when you breathe deeply or cough
    • On physical examination signs of pulmonary consolidation. Such as dullness on percussion, increased fremitus, cracles may be found
    • Pneumonia may also manifest itself with a more gradual onset, a dry cough, extrapulmonary manifestations like headache, myalgia, fatigue, sore throat, nausea, vomiting and diarrhea. These manifestations are classically produced by M.pneumoniae
    • Initial manifestations of viral pneumonia are highly variable, characterised by chills, fever, dry non productive cough and extrapulmonary symptoms .

In children typical symptoms are

  • Tachypnea
  • Chest in-drawing
  • Stridor,wheeze

Complications of pneumonia

  1. Pleurisy: Inflammation of the pleura
  2. Pleural effusion: (Transudate fluid in the pleural space). It develops in 40% of the hospitalized patients with pneumococcal pneumonia, usually the effusion is sterile and is reabsorbed within 2 weeks occasionally it requires aspiration by thoracentesis
  3. Atelectasis : Collapsed (airless) alveoli of one of the part of lobe may occur. These area usually clear with deep breathing exercises, and effective coughing
  4. Becteremia : It is bacterial infection in the blood, occurs in 30% of the patients with pneumococcal infection and is associated with 20% mortality, this rate can go upto 60% in case of elderly
  5. Lung abscess : It is not common, usually occurs in S.aureus infections and Gram negative pneumonias
  6. Empyema: Accumulation of the purulent exudates in the pleural cavity. It is treated with antibiotics and chest tube drainage system.
  7. Pericarditis: Results from spread of the infecting organism from an infected pleura to pericardium.
  8. Meningitis: Can be caused by S pneumoniae. The patient is disoriented, confused.
  9. Endocarditis: when organism attacks the endocardium of the heart.