CHAPTER 7 Ian Hunt1 and Najib M. Rahman2 1 St. George’s Hospital, London, UK 2 Oxford Centre for Respiratory Medicine, Churchill Hospital, Oxford, UK Pleural infection is the presence of infected fluid or material in the pleural space, and includes both empyema (the presence of frank pus) and complicated parapneumonic effusion (the presence of bacteria or evidence of bacterial infection). Pleural infection is a life‐threatening condition, even in young people. In the UK, the mortality is 20%, the risk of death being higher in the elderly. Early medical intervention is associated with better outcomes. A significant proportion (20%) will require a thoracic surgical procedure to treat the acute illness or prevent long‐term complications. Pleural infection typically develops from a parapneumonic effusion although an iatrogenic pleural infection may complicate thoracic or oesophageal surgery or chest drain insertion (Box 7.1). The origins of cardiothoracic surgery can probably be traced back to the management of empyema in Ancient Greece. Hippocrates described how those afflicted, often from battlefield chest wounds, were typically sweaty and feverish with sunken eyes, curled fingernails and warm fingers. Those that survived the initial illness developed spontaneous discharge of pus through the chest wall (empyema necessitans). This was sometimes assisted by cautery or incision. There was a recognition even then that assisted open drainage performed too early resulted in death, although it would take another two thousand years to relearn these lessons. The management of empyema changed little for two millennia. However, the advent of the underwater seal prevented death from pneumothorax (or sucking chest wound) seen with open drainage performed too early in the disease process. During the First World War, the US Army Empyema Commission investigated the high mortality associated with empyema treatment. Their subsequent recommendations on nutrition, obliteration of the pleural space, closed tube drainage and timing of intervention reduced death rates significantly. The discovery of antibiotics and advances in anaesthetic techniques in the first half of the twentieth century enabled the development of the medical and surgical treatment of empyema that forms the basis of present day care. In particular, modern keyhole video‐assisted thoracic surgery (VATS) techniques allow effective treatment of even the most severe forms of pleural infection. It is estimated that over 50% of patients with pneumonia will develop a parapneumonic effusion. The majority of these are ‘simple’ effusions (i.e. will resolve with antibiotic treatment alone). However, in a proportion, bacteria translocate to the pleural fluid and establish infection, at which point antibiotics alone will not resolve the infection. Overall, around 8% of patients with pneumonia develop an infected pleural collection. There are three stages in the development of a pleural infection: Around 60% of patients with pleural infection have positive pleural fluid cultures while only 12% have positive blood cultures. Therefore, throughout treatment, in around 40% of cases there will be no identifiable causative organism. Streptococcus species and Staphylococcus aureus are most often seen in community‐acquired parapneumonic empyemas. Gram‐negative bacteria (e.g. Escherichia coli, Haemophilus influenzae and enterococci) and anaerobes (e.g. Bacteroides species) are also commonly isolated. Hospital‐acquired empyemas (both iatrogenic and parapneumonic) are often caused by methicillin‐resistant Staphylococcus aureus (MRSA), Staphylococcus aureus, enterococci and Pseudomonas aeruginosa. Untreated, pleural infection may resolve spontaneously but this is highly unlikely. The patient is at risk of a complication of the empyema: The patient’s condition may range from asymptomatic to severely septic. There is not always a history of a predisposing pneumonia. The patient’s signs and symptoms will depend on their age, comorbidities, severity of the underlying pneumonia, and the size and stage of the pleural infection. Symptoms include shortness of breath, chest pain, cough and fever. Unlike other infections, pleural infection can develop as an indolent illness over weeks to months with weight loss, cachexia and general malaise. In association with the chest X‐ray findings, this is often referred as a potential cancer. Hypoxia and fever are common findings. Cardiovascular signs (hypotension and tachycardia) are present in toxic patients, while examination of the chest may reveal a dull percussion note with reduced vocal resonance and air entry consistent with a pleural effusion. In longer term pleural infections, digital clubbing and contraction of the hemithorax may occur. The diagnosis of pleural infection should be suspected if a patient fails to respond clinically to adequate treatment of pneumonia within 48–72 hours. Inflammatory markers (white cell count (WCC) and C‐reactive protein (CRP)) remain raised and an effusion may be present on chest X‐ray. Blood cultures should be performed as they may reveal the underlying organism. A thoracic ultrasound and pleural fluid aspiration should be performed. Thoracic ultrasound will confirm the presence of an effusion. Ultrasound is now mandatory for guiding aspiration or drainage of pleural fluid, and it may demonstrate additional diagnostic information – ultrasound is highly sensitive (more than CT) for the detection of septations (Figure 7.1). Figure 7.1 Thoracic ultrasound showing heavily septated complicated parapneumonic effusion. Diagnostic aspiration and analysis of pleural fluid is the most important test in guiding management. Aspiration of frank pus or turbid fluid is diagnostic of an empyema. Non‐purulent fluid should be checked for pH (using a blood gas analyser); an acidic pleural aspirate (pH <7.2) is diagnostic of complicated parapneumonic infection. This is usually associated with a low pleural glucose (<3.4 mmol/L) and high LDH (>1000 IU/L). The fluid should also be sent for Gram stain and culture, and recent evidence suggests sending pleural fluid in ‘blood culture bottle’ media can increase microbiological yield. Additionally, it should be sent for cytological analysis if an underlying malignancy is suspected. CT scanning can be helpful if doubt remains around the diagnosis of empyema or if an underlying cause such as malignancy is suspected. CT in pleural infection will typically demonstrate the presence of enhancing visceral and parietal pleural surfaces (known as the ‘split pleura’ sign) and may demonstrate underlying lung consolidation and other abnormalities such as parenchymal lung abscess. Pleural thickening is almost always seen. There is often an associated reactive mediastinal lymphadenopathy. A CT scan is essential in those patients being considered for surgery as it helps the surgeon decide the best approach and type of operation and may guide the position of the surgical ports. Magnetic resonance imaging (MRI) does not generally provide any additional information, but may be useful in selected younger patients to reduce radiation dose. The goals are to treat the underlying cause of the pleural infection, drain the infected pleural fluid and eliminate the pleural space while simultaneously addressing nutrition, mobility and the prevention of thromboembolic disease. Antibiotics and chest drainage are the cornerstones of initial medical management. While some patients with empyema can be relatively asymptomatic, others may be profoundly septic and moribund. There may be respiratory compromise secondary to the original pneumonia. In addition, the mass effect of the fluid or pus may compress the underlying lung causing further respiratory embarrassment. Signs of sepsis and haemodynamic compromise may also be present. It is essential therefore that resuscitation and restoration of normal physiological parameters are performed first. This may involve the administration of oxygen, respiratory support, fluid boluses or the use of vasopressors. Antibiotic therapy should be started immediately and cover all likely bacteria as dictated by the probable underlying cause. The microbiology of community‐acquired and hospital‐acquired pleural infection are distinct, and different from pneumonia. Antibiotics may later be rationalised in the light of positive pleural or blood cultures. Initial treatment should cover Gram positives and anaerobes in community‐acquired infection, and cover MRSA and resistant Gram negatives in hospital‐acquired infection until culture results are known. The optimal duration of treatment is unknown but a total treatment course of around 4–6 weeks is typical, with at least 1 week of intravenous treatment. Penicillins and cephalosporins have good pleural penetration but aminoglycosides are not effective in the pleural space and should be avoided. Box 7.2 details the indications for drainage of the effusion. An intercostal chest drain should only be inserted under ultrasound guidance, and ideally should be placed in a dependent position. Although it has been a widely held view that a large bore drain (>20 Fr) should be used, there is no conclusive evidence for this, and smaller bore drains appear to be equally effective. Smaller bore drains should receive regular sterile saline flushes to maintain patency.
Pleural Infection
Pathology
Bacteriology
Natural history
Symptoms and signs
Diagnosis
Thoracic ultrasound scan
Pleural fluid aspiration
Further imaging
Medical management
Initial care
Antibiotics
Chest tube drainage
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