Pathophysiology of Pleural Infection

There are three main stages in the development of pleural infection. This is shown in the diagram below.

Figure 2. Stages of pleural infection

Key points to note: [4, 8, 9]

• More than half of patients with pneumonia develop para-pneumonic effusions. If the fluid becomes infected an empyema results
• Primary empyemas can also develop in patients without evidence of underlying pneumonia
• Empyemas require drainage
• The most commonly found bacteria in pleural infection are aerobic organisms (gram positive and gram negative)
• Common gram positive bacteria include streptococcal and staphylococcal species
• Common gram negatives include E. Coli, Pseudomonas spp, Haemophilus influenzae and Klebsiella spp
• Staphylococcus aureus is a common pathogen in patients following surgery, trauma or chest drain insertion
• The most common associated underlying disease processes present in patients with empyemas are:

1. Diabetes mellitus (commonest)
2. Malignancy
3. COPD
4. CNS disease

• Approximately one-third of patients presenting with empyema have no underlying health problems.