Pneumonia - Prognosis

Complications of Pneumonia

Abscess. An abscess in the lung is a thick-walled, pus-filled cavity that forms when infection has destroyed lung tissue. It typically occurs as a result of aspiration pneumonia, when a mixture of organisms is carried into the lung. Abscesses can cause hemorrhage (bleeding) in the lung if untreated, but antibiotics that target them have significantly reduced their danger. Abscesses are more common with Staphylococcus aureus or Klebsiella pneumoniae, and uncommon with Streptococcus pneumoniae.

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Respiratory Failure. Respiratory failure is one of the top causes of death in patients with pneumococcal pneumonia. Acute respiratory distress syndrome (ARDS) is the specific condition that occurs when the lungs are unable to function and oxygen is so severely reduced that the patient's life is at risk. Failure can occur if pneumonia leads to mechanical changes in the lungs (ventilatory failure) or oxygen loss in the arteries (hypoxemic respiratory failure).

Bacteremia. Bacteremia, bacteria in the blood, is the most common complication of pneumococcus infection, although it rarely spread to others sites. Bacteremia is a frequent complication of infection from other gram-negative organisms, including Haemophilus influenzae.

Pleural Effusions and Empyema. The pleura are two thin membranes that line the chest and lungs:

The visceral pleura cover the lungs.
The parietal pleura cover the chest wall.

In some cases of pneumonia, the pleura become inflamed, which can result in breathlessness and acute chest pain when breathing.

In about 20% of pneumonia cases there is build-up of the fluid between the pleural membranes. Ordinarily the narrow zone between the two membranes contains only a tiny amount of fluid, which lubricates the lungs. This build-up of fluid in the pleural space is known as pleural effusion.

In most cases, particularly in Streptococcus pneumoniae, the fluid remains sterile (no bacteria are present), but occasionally it can become infected and even filled with pus, a condition called empyema. Empyema is more likely to occur with specific organisms such as Staphylococcus aureus or Klebsiella pneumoniae infections. The condition can cause permanent scarring.

Collapsed Lung. In some cases, air may fill up the area between the pleural membranes causing the lungs to collapse. This is called pneumothorax. It may be a complication of pneumonia (particularly Streptococcus pneumoniae ) or of the invasive procedures used to treat pleural effusion.

Pneumothorax occurs when air leaks from inside of the lung to the space between the lung and the chest wall. The lung then collapses. The dark side of the chest (right side of the picture) fills with air from outside of the lung tissue.