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Pneumonia

illustration human lungs
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What is Pneumonia

Pneumonia is a disease of the lung. The lung is composed of large airways (beginning with the trachea and then two main bronchi), which branch out to form smaller airways (segmental bornchi and bronchioles) which finally lead to the alveoli – the small air sacs where gas exchange takes place.

Pneumonia represents an acute lower respiratory tract infection – it affects the lung parenchyma, alveoli and small airways. When the lung tissue becomes infected (whether it is bacteria, viruses, or fungi) there is inflammation of the lung tissue which leads to an exudate filling the alveoli and small airways – which impairs gas exchange.

Statistics on Pneumonia

Pneumonia is a common disease world-wide. 5 million children die of pneumonia each year. The incidence of community-acquired pneumonia is 10-15/1000 person years; the incidence of hospital admission is 1-3/1000 person years.

Pneumonia is mostly more common during winter (although Legionella is more common during summer).

Risk Factors for Pneumonia

Although pneumonia can occur in anyone (everybody can come into contact with an infective carrier), certain patients are at higher risk:

  • Patients with any chronic lung disease or a structurally abnormal lung are especially prone. In particular, patients who suffer from COPD or an airway-obstructing tumour are at high risk;
  • Patients who spend long periods of time in hospital are more likely to contract pneumonia, as are immuno-compromised patients;
  • People who cannot protect their own airway are at a very high risk of contracting aspiration pneumonia (pneumonia due to inhalation of gastric and oropharyngeal contents). This includes people with a lowered conscious state (coma or anaesthesia), oesophageal disease (achalasia or GORD), stroke;
  • Natural lung defences are impaired by smoking, alcohol, pulmonary oedema or congestion.

Progression of Pneumonia

There are several ways of classifying pneumonia. One method is by the origin of the infective organism.

  • Community-acquired pneumonia is the most frequent type and may be primary or secondary to lung abnormality/disease;
  • The common organisms responsible are viruses (e.g. influenza), or certain bacteria;
  • The so-called “atypical pneumonias” are also classified as community-acquired. This subcategory includes slightly different species who tend to produce a more different clinical picture and are treated differently;
  • Nosocomial pneumonia is defined as pneumonia contracted more than 48 hours after admission to hospital and is due to more virulent organisms;
  • Aspiration pneumonia is commonly due to chemical damage and secondary infection by bacteria.

Complications of pneumonia include fibrosis, pleural effusion, lung abscess, empyema, septicaemia, septic shock or respiratory failure.

How is Pneumonia Diagnosed?

A number of tests can and should be performed if pneumonia is suspected.

  • Pneumonia is often defined by the presence of abnormalities on a chest x-ray. Some complications (abscess or empyema) can also be seen on the chest x-ray;
  • A full blood count and CRP will demonstrate infection (leukocytosis and raised platelets);
  • Liver and kidney function tests may be done – these may be affected in the process;
  • The offending bacteria or virus may be cultured or the antibody against it detected;
  • Oxygen saturations and their response to therapy should be monitored;
  • Arterial blood gas sampling can be done if hypoxia is suspected.

Prognosis of Pneumonia

A number of clinical parameters have been shown to be associated with increased mortality in patients with pneumonia. Some of these include:

  • Age over 60;
  • Presence of underlying lung disease;
  • Respiratory rate (too fast or slow);
  • Pulse (too fast or slow);
  • Temperature (too high or low);
  • Hypotension (low blood pressure); or
  • Hypoxia (low oxygen in the blood).

Clinical parameters that increase the risk or death include: high urea, low albumin, white cells (too low or extremely high) and bacteraemia. Mortality amongst hospital admissions has been reported as 6-24%.

How is Pneumonia Treated?

  • Patients with pneumonia should be monitored carefully;
  • Oxygen should be given to maintain good blood saturations. Assisted ventilation may be required;
  • Empirical antibiotics should be chosen on the likely origin; specific hospital protocols vary but a good combination for mild-moderate community-acquired pneumonia is amoxicillin and roxithromycin. Length of therapy should be judged by clinical response;
  • Pain control and intravenous fluids are often required;
  • Chest physiotherapy may be helpful in some cases;
  • The pneumococcal vaccine is recommended for the elderly, people with severe chronic disease and those who are immuno-suppressed.

Pneumonia References

  1. Cotran RS, Kumar V, Collins T, Robbins SL. Robbins Pathologic Basis of Disease (6th edition). Philadelphia: WB Saunders Company; 1999. Book
  2. Kumar P, Clark M (eds). Clinical Medicine (4th edition). Edinburgh: WB Saunders Company; 1998. Book
  3. Talley NJ, O’Connor S. Clinical Examination: A systematic guide to physical diagnosis (3rd edition). Eastgardens, NSW: MacLennan & Petty; 1996. Book
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Dates

Posted On: 26 May, 2003
Modified On: 20 May, 2011

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