Critical Care Medicine

Mediastinal & pleural infections (purulent pericarditis, mediastinitis, empyema)

Mediastinal and pleural infections

Synonyms

Pericarditis

Mediastinitis

Empyema

Related conditions

Bronchopleural fistula, lung abscess, sternal wound infection and esophageal perforation

1. Description of the problem

What every clinician needs to know

Purulent pericarditis is a suppurative infection of the pericardial space. The process typically results from extension of a myocardial or annular abscess into the pericardial space. Purulent pericarditis can also result from bloodstream infections, immunosuppression and direct exposure during cardiac surgery. The usual infectious agents include enterococcus, Streptococcus viridans, candida or E coli.

Mediastinitis is a suppurative infection of the central compartment of the chest. The process usually develops as a result of contamination from an esophageal injury, airway injury or postoperative sternal wound infection. Neck (pharyngeal) infections that "descend" to involve the mediastinum are also occasionally seen. Mediastinitis can result in rapid clinical deterioration secondary to overwhelming sepsis. A rapid clinical diagnosis is essential to reducing morbidity and mortality, and early surgical drainage is critical in addition to intravenous antibiotic therapy.

Empyema is a suppurative infection of the pleural cavity that is usually related to extension of a necrotizing pneumonia or lung abscess. Empyema can also occur in the setting of a bronchopleural fistula after a pulmonary resection, esophageal perforation or other cause of mediastinitis, or trauma. Gram-positive organisms such as Staph aureus and Staph pneumoniae are more commonly involved compared to Gram-negative organisms, such as Klebsiella and Pseudomonas. Empyema has three phases:

  1. Exudative phase.

  2. Fibropurulent phase.

  3. Organized phase.

Prompt drainage of purulent fluid and re-expansion of the lung parenchyma is the cornerstone of management of empyema.

Clinical features

  1. Patients usually present with a fever and elevated white blood cell count. Chest pain is also common.

  2. Patients may present with hypotension and clinical signs of sepsis (rare with empyema alone).

  3. Chest radiographs will demonstrate a pleural effusion, pneumomediastinum or an enlarged cardiac silhouette (pericarditis).

  4. A CT scan of the chest may demonstrate a pleural effusion, evidence of aerodigestive tract injury (air in mediastinal soft tissues), a pericardial effusion or inflammation stranding of the mediastinal fat.

  5. Patients may present in the early postoperative period after esophagectomy or cardiac surgery.

  6. Patients can rapidly deteriorate, requiring mechanical ventilatory support and vasopressor support.

Key management points

Patients who present with mediastinal and pleural infections require rapid recognition of the disease process and immediate intervention. Prompt broad spectrum antibiotic therapy should be initiated until the infectious agent is identified. Admission to an intensive care unit is preferable for close monitoring of vital signs and organ function. Two large bore IV catheters, a Foley catheter and an arterial line should be placed. A Swan-Ganz catheter should be considered in hemodynamcally unstable patients.

Source control of the infectious process is a high priority when managing mediastinal and pleural infections. For example, mediastinitis secondary to an esophageal perforation should prompt an urgent thoracic surgery consultation. The esophageal perforation requires timely repair to prevent ongoing contamination of the mediastinum as well as drainage of purulent contents. Delay in diagnosis and source control will ultimately result in increased morbidity and mortality.

Patients who present with empyema should undergo either tube thoracostomy for unilocular, phase I collections or surgical drainage (VATS or open thoracotomy, as necessary) for multilocular, phase 2 or 3 collections.

2. Emergency Management

Stabilizing the patient

  1. Evaluate the airway, breathing and circulation initially. Patients with hypoxia and respiratory distress should be intubated and placed on mechanical ventilation. IV access should be established and intravenous antibiotics should be initiated without delay. Vasopressor agents may be necessary to treat hypotension.

  2. Place a Foley catheter, arterial line and possibly a central venous catheter. Patients should be admitted to an intensive care unit for close monitoring of vital signs and organ function.

  3. Imaging studies, including chest radiography, computed tomography scans and echocardiography should be performed to determine the etiology of the mediastinal or pleural infection. A barium swallow and/or EGD may be required to rule out esophageal injury.

  4. Thoracic surgical consultation should be obtained. Patients with mediastinitis will require surgical exploration for drainage and control of the source of infection, such as esophageal perforation or deep sternal wound infection. Patients with empyema should have a tube thoracostomy or surgical drainage performed to drain all purulent pleural fluid and re-expand the lung completely. Patients with purulent pericarditis should undergo immediate drainage of the pericardial space with pericardial window.

Management points not to be missed

  1. Initiate broad spectrum antibiotic therapy.

  2. Obtain prompt cardiothoracic surgical consultation.

  3. Admit to the intensive care for invasive monitoring.

  4. Prompt surgical intervention should be performed for debridement, drainage and control of the source of infection.

3. Diagnosis

Diagnostic criteria and tests

Purulent pericarditis

  1. History of recent endocarditis, bacteremia or cardiac surgery.

  2. Echocardiography and pericardiocentesis with gram stain/culture.

  3. CT scan of the chest.

Mediastinitis

  1. History of recent thoracic or cardiac surgery or esophageal event (e.g. instrumentation, emesis).

  2. Chest radiograph.

  3. CT scan of the chest.

  4. Barium esophagram and/or EGD.

Empyema

  1. History of recent pneumonia or thoracic surgery.

  2. Chest radiography.

  3. Exudative pleural fluid chemistries, low pleural fluid pH.

  4. Gram stain and culture of pleural fluid (often negative if prior antibiotics administered).

Normal lab values

Normal values for pleural fluid obtained by Thoracentesis

  1. Appearance: serous color.

  2. pH greater than 7.2.

  3. Protein concentration less than 30 g/dL.

  4. LDH less than 2-3 times the upper limit if normal serum LDH.

  5. Glucose greater than 60 mg/dL.

Establishing the diagnosis

Drainage of frank pus from the pleural cavity, pericardium or the mediastinum is diagnostic of a suppurative infection in these spaces. Few things cause mediastinal air on imaging in a febrile patient other than mediastinitis. Few things cause loculated pleural fluid in a febrile patient other than empyema.

Other possible diagnoses

Purulent pericarditis could be confused with a simple pericardial effusion, with a fever from another source.

Empyema could be confused with parapneumonic (uninfected) pleural effusions (culture negative, WBC counts below 500/cc, normal pH), lung abscess without pleural collection, malignant pleural effusion, chylothorax or hemothorax.

Confirmatory tests

A thoracentesis with analysis of the fluid will confirm the diagnosis of empyema. However, when the diagnosis is clear clinically, thoracentesis can be skipped in favor of direct drainage with a chest tube. The drainage of frank pus from the pleural cavity is diagnostic of empyema. A pH of less than 7.2, a WBC count greater than 1000/cc and a glucose less than 60 mg/dL would be highly suggestive of an empyema, even with negative cultures (when patient received antibiotics prior to sampling, which is usually the case).

4. Specific Treatment

First line therapy

The first line medical therapy for mediastinitis, empyema and purulent pericarditis includes broad spectrum antibiotics and complete drainage. These should be pursued simultaneously. Patients should be promptly referred to thoracic surgery for drainage, debridement, decortication of the lung when necessary and repair of any aerodigestive injuries.

Drugs and dosages

  • Pipercillin-tazobactam 3.375 gm IV Q 6 hours.

  • Vancomycin 1 gm IV Q 12 hours.

  • Flagyl 500 mg IV Q 8 hours.

  • Fluconazole should be added initially if there is a concern for esophageal injury.

Antibiotics should be begun intravenously, but approximately 5 days after complete drainage can be converted to oral to complete an at least 2 week postoperative course. The antibiotics can be narrowed to exclude vancomycin if no MRSA identified and antifungals if no fungus identified on cultures, assuming the patient did not receive antibiotics against these organisms prior to the taking of culture. It is always recommended to continue anaerobic coverage for the duration of therapy, given the false negative rate of anaerobic cultures.

Refractory cases

Patients with refractory cases of empyema or mediastinitis (after initial drainage) should have repeat imaging studies to look for undrained collections. These patients may require a repeat operation to repair missed injuries or undrained abscess collections. In descending mediastinitis from a pharyngeal source, two operative debridements are almost always required, and three or more may even be necessary.

5. Disease monitoring, follow-up and disposition

Expected response to treatment

Patients who receive prompt surgical drainage, broad-spectrum antibiotic therapy and supportive care for empyema or mediastinitis generally respond clinically within 48 hours if they have not already developed multi-organ system failure. They have a good prognosis for recovery and discharge from the hospital. Elderly patients with multiple comorbid conditions, such as diabetes, coronary artery disease, COPD and chronic renal failure are at increased risk for in-hospital mortality. In addition, patients who develop multiple organ failure are also at increased risk for mortality.

Incorrect diagnosis

A wrong diagnosis should be suspected in patients with no clinical signs of infection ( i.e. normal WBC, no fever, stable vital signs). Also, failure to respond to complete surgical drainage and antibiotics should prompt a search for other sites of infection (e.g. secondary endocarditis).

Follow-up

After discharge from the hospital, patients who were treated for mediastinitis, empyema or purulent pericarditis should maintain routine follow up with their primary care physician. A surgical follow up visit should be scheduled for 2-3 weeks after the discharge. Follow up chest radiograph will be performed routinely, and CT scan may be indicated to evaluate adequacy of surgical drainage if abnormal CXR findings and/or persistent fever.

Pathophysiology

Empyema

The potential space between the parietal pleura and visceral pleura normally contains small amounts of circulating, sterile fluid that can become infected by an adjacent pneumonia or bronchopleural fistula, or seeded by bacteremia or trauma. There are three stages in the progression of empyema. In the exudative phase, pleural fluid increases in volume and is characterized by a low WBC count and LDH level. At this point, the fluid is generally not loculated and simple chest tube placement can be successful in completely draining it.

In the fibropurulent phase, fibrin, bacteria and leukocytes accumulate in the pleural fluid. During this stage, loculation of the pleural fluid often occurs and the fluid becomes more acidic. Successful treatment at this stage usually requires VATS.

In the organized phase, fibroblasts proliferate and generate a pleural peel that encases the lung. The lung becomes entrapped by this visceral pleural peel at this stage, and it will not re-expand to fill the thorax unless formal decortication (removal of this peel) is performed surgically. This can sometimes be performed by VATS but often requires thoracotomy.

Mediastinitis

The most common causes of mediastinitis include post-sternotomy wound infection, perforation of the esophagus and extension of a head and neck infection into the mediastinum. Sternal wound infections can result in mediastinitis in up to 3% of sternotomy procedures and is associated with a 5-10% mortality rate. Patients with diabetes, obesity, steroid therapy and bilateral internal mammary artery take-downs (reducing the sternal blood supply) are at increased risk.

Spontaneous esophageal rupture (Boerhaave's syndrome), iatrogenic perforation after instrumentation, or creation of an esophageal hole by an ingested bone or other foreign body, results in direct contamination of the mediastinum. Patients can quickly develop sepsis if the esophageal injury is not repaired and the mediastinal collections are not drained adequately. Patients with peritonsillar abscess, Ludwig Angina, mastiditis, epiglottitis, and sinusitis can develop descending mediastinitis into the middle and posterior mediastinum.

These head and neck infections can extend into the mediastinum along fascial planes covering the esophagus and trachea. All of these mediastinal infections can rupture through the mediastinal pleura into the pleural space as well, creating a secondary empyema which must also be managed.

Purulent pericarditis

Purulent pericarditis can develop as a result of an extension of a myocardial infection, direct extension of a thoracic infection, hematogenous spread, post-surgical infection or an extension of a subdiaphragmatic infection.

Epidemiology

Approximately 60,000 patients develop pleural infections in the United States each year. Between 40-60% of pneumonias will be associated with parapneumonic effusions.

Approximately 5-10% of parapneumonic effusions will develop into empyema. Empyema is more common in men, with a male to female ratio of 2:1. Elderly patients are more commonly affected compared to children.

In the antibiotic era, purulent pericarditis is a very rare condition. A recent review described 33 cases among an inpatient population of 593,600.

The incidence of postoperative mediastinitis associated with sternotomy ranges from 0.4-5%. Major risk factors include diabetes, obesity, vascular disease, prolonged surgical procedure and bilateral internal mammary artery harvest. The incidence of descending mediastinitis from deep neck infections is rare in the antibiotic era but is still seen at major centers about once yearly. Unfortunately, esophageal perforation with associated mediastinitis remains quite common.

Prognosis

Patients with mediastinitis, empyema and purulent pericaditis should be treated with broad spectrum antibiotics, supportive care and surgical drainage. The prognosis depends on the timeliness of surgical intervention and treatment. Prognosis is excellent if diagnosis is made promptly, the source of the infection is controlled promptly (e.g. repair of esophageal perforation), and infected fluid and tissues are promptly and completely debrided. Delayed treatment may result in multisystem organ failure and death. Straightforward parapneumonic empyema is less urgent than mediastinitis, as patients with empyema tend to be chronically, rather than acutely ill.

Special considerations for nursing and allied health professionals.

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What's the evidence?

Purulent pericarditis

Sagrista-Sauleda, J, Barrabes, JA, Permanyer, G, Soler-Soler, J. "Purulent pericarditis: Review of a 20-year experience in a general hospital". J Am Coll Cardiol. vol. 22. 1993. pp. 1661.

(This paper is a retrospective review of the clinical course of 19 patients diagnosed and treated for purulent pericarditis. This reference also reports the clinical outcomes of the 19 patients after they were treated. Interestingly, 15 of the 19 patients were alive at 35 month follow-up.)

Maisch, B, Seferovic, PM, Ristic, AD. "Guidelines of the diagnosis and management of pericardial diseases executive summary; The task force of the diagnosis and management of pericardial diseases of the European society of cardiology". Eur Heart J. vol. 25. 2004. pp. 587.

(This reference is a comprehensive review on the diagnosis and management of pericardial diseases, including purulent pericarditis. The recommendations are based on expert opinion and review of the literature.)

Empyema

Light, RW, Girard, WM, Jenkinson, SG, George, RB. "Parapneumonic effusions". Am J Med. vol. 69. 1980. pp. 507.

(This reference establishes guidelines that help predict when a parapneumonic effusion will progress to an empyema. Pleural fluid with a pH between 7.00 and 7.20 and a LDH above 1,000 IU/1,1000 ml should be drained with a chest tube according to the authors.)

Colice, GL, Curtis, A, Deslauriers, J. "Medical and surgical treatment of parapneumonic effusions: an evidence-based guideline". Chest. vol. 118. 2000. pp. 1158.

(This reference reviews the data in the literature for surgical intervention for parapneumonic effusions. The authors offer a risk stratification for patients with parapneumonic effusions that were likely to progress to empyema and require surgical intervention.)

Wurnig, PN, Wittmer, V, Pridun, NS, Hollaus, PH. "Video-assisted thoracocscopic surgery for pleural empyema". Ann Thorac Surg. vol. 81. 2006. pp. 309.

(This reference is a retrospective review of 130 patients who underwent VATS for treatment of fibropurulent empyema. Only three of the patients required conversion of open thoracotomy and most of the VATS patients achieved good functional results postoperatively. The study concludes that VATS is alternative to open thoracotomy.)

Mediastinitis

El Oakley, RM, Wright, JE. "Postoperative mediastintis: Classification and management". Ann Thorac Surg. vol. 61. 1996. pp. 1030.

(This reference reviews the current literature for the management and treatment of complicated median sternotomy wounds and proposes a classification system for postoperative mediastinitis.)

Chen, KC, Chen, JS, Kuo, SW. "Descending necrotizing mediastintis: A 10 year surgical experience in a single institution". J Thorac Cardiovasc Surg. vol. 136. 2008. pp. 191.

(This reference is a retrospective review of 18 patients treated with cervical drainage for descending necrotizing mediastinitis. The mortality rate was 17%, which underscores the importance of urgent surgical drainage of cervical infections that extend into the superior mediastinum.)
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