Empyema

 

Empyema

PKGhatak, MD

Empyema is defined as an accumulation of pus in the pleural space.

The surface of the lung and the inner surface of the chest wall is lined with a thin layer of serous tissue, leaving a minimal space in between known as pleural space. The pleural membrane is covered by just one layer of mesodermal epithelium upon a connective tissue layer consisting of collagen and elastic fibers. A thin film of pleural fluid bathes both the parietal (chest wall) and visceral(lung) pleura and acts as a lubricant; that makes the lungs expand and contract without any friction during breathing. The pleural fluid is formed by the parietal pleura and the fluid is removed by the lymphatics of this layer, so pleural fluid formation and removal go on continuously. The visceral pleura gets its blood supply from the bronchial arteries and has no sensory nerve supply, so the visceral pleura is pain insensitive, whereas, the parietal pleura is richly supplied with pain fibers from the intercostal nerves and also receives blood supply from the intercostal blood vessels.

In pneumonia usually, more fluid is formed in the pleural space, but the presence of fluid is not easily detected by examination or by simple chest x-rays. CT scan can detect in 15 to 30 % of cases minimal pleural effusion called Parapneumonic pleural effusion. As pneumonia resolves, so also the parapneumonic pleural effusion.

About 6 % of children and 5% of adults with community acquired pneumonia develop parapneumonic empyema. When pleura effusion is infected by the extension of infection, the fluid becomes cloudy and thick. If the infected fluid has the following characteristics, then the effusion is called Empyema: fluid pH is less than 7.2 (normal blood pH is 7.4), glucose less than 60 mg/dl. LDH is three times the upper limit of serum LDH or LDH over 1000 IU/dl, WBC over 50,000/ml, protein over 3,000 mg/dl. Gram stains identify the presence of bacteria.

Risk factors.

In children, empyema often results when pneumonia is treated with inappropriate antibiotics. For those who are not fully immunized, chickenpox is followed by pneumonia, and the use of Ibuprofen in pneumonia.

In adults, the risk factors are homelessness, pulmonary emphysema, Pulmonary tuberculosis, IV drug use, not receiving pneumonia vaccine, alcoholics, HIV infection, and immunosuppression by disease or therapy, and lung abscess. 35 % of anaerobic lung access is associated with empyema.

Both adults and children are at risk of empyema following prolonged chest tube drainage of bloody pleural effusion from a gunshot wound of the chest/ lung, knife wound, or automobile accident resulting in lung contusion, rib fracture, or pneumothorax.

Post-Surgical Empyema.

Following lobectomy and pneumonectomy due to malignancy or other diseases, if the lung fails to fill up the pleural cavity, then prone to empyema. This may be a special problem in the removal of bullous lesions in emphysema patients. Other causes of Empyema are Bronchopleural fistula, esophageal pleural fistula, perforated duodenal ulcer, amoebic liver abscess, perforated colon diverticulitis, and peritonitis the infection may spread to the pleural cavity and foreign bodies in pleural space like infected fragments of a projectile.

Common bacterial empyema.

The common bacteria is Streptococcus pneumonae type1. In community acquired pneumonia, the Streptococcus pneumonae type1 accounts for nearly 50% of postpneumonic empyema, Staphylococcus aureus followed by anaerobic bacteria infections. Viral parapneumonic and tubercular pleural effusion may also lead to empyema.

Symptoms and Diagnosis.

Persistent temperature elevation- often to 101F or higher, shortness of breath, chest pain, weight loss, anorexia, and general debility are common symptoms. On examination decreased or absent breath sound on one side of the chest, dullness on percussion. Leukocytosis with a shift to the left, toxin granules and Doehle bodies in the neutrophils are present. Chest x-ray shows pleural fluid. Ultrasound detects and delineates empyema easily and is usually repeated for monitoring purposes. CT chest is helpful in trauma cases and also in difficult cases.

Diagnostic thoracentesis is almost universal in all cases of more than minimal pleural effusion. In empyema, the pleural fluid is thick, difficult to aspirate, and cloudy to milky white. The other features will match the characteristics listed above.

Empyema fluid is sent to the lab for aerobic and anaerobic cultures and also for fungi and mycobacteria cultures. Gram stain of empyema fluid shows the presence of bacteria.

Treatment.

Closed tube drainage with a vacuum assisted closure device is inserted by Thoracoscopy. A wide bore chest tube Malicote 10-14F, Pigtail 8 -12F, or 28-32F French catheter is generally suited. Thoracoscopy can also detect septa, loculation, compartmentalization of fluid and that can be removed at the same time. That makes empyema drainage easier. Thoracoscopic lysis of adhesion is generally repeated.

Fibrinolytic enzymes like deoxyribonuclease DNase or tissue plasminogen activator tPA are injected into the pleural cavity and usually repeated in order to liquefy thick fluid.

Antibiotics are administered by IV and guided by culture and sensitivity tests.

In closed tube drainage of empyema, the lung should expand fully in 14 days.

If the lung fails to expand then re-culture of fluid, review of the entire case, use of multiple antibiotics, or other surgical measures are called for.

Open drainage.

If the empyema fluid is so thick that even the French 32 size catheters are not draining fluid then a wide area of the wound is created over the empyema. A large bore chest tube is inserted in the dependent part of the empyema and the other end of the tube is drained into a colostomy bag. The cavity is irrigated daily with mild antiseptic fluid, or the cavity is packed with saline moistened surgical gauge and changed daily. The cavity size should decrease gradually and the wound should seal in 4 to 5 months.

Open flap or Eloesser flap.

In this procedure, a wide incision is made just over the diaphragm, the most dependent part of the pleural cavity. A large skin and muscle flap is created. 1 to 3 ribs are resected to make a large opening into the chest cavity and the skin-muscle flap is stitched in a way creating a one-way opening for drainage making drainage of empyema easier. One way flap prevents air entry at the same time empyema is drained.

Decortication.

In the previous generation, tubercular empyema was the primary reason for this surgical operation. But occasionally some empyema fails to heal by the above methods and decortication is required.

If the lung does not expand to fill the chest cavity in 140 days. This procedure is considered. It is a major open thoracic surgery procedure, and many sick patients may not be able to withstand this procedure.

In this procedure, the entire pleura is stripped away and all cellular/fibrinous materials are removed. The lung with stripped away thick covering expands readily and the operative wound heals in 3 to 4 weeks.

The incidence of empyema has been declining over the past decades but in recent years the empyema incidence began creeping upwards. Early diagnosis and proper closed drainage and antibiotic therapy should resolve empyema in 2 to 3 weeks. The decision to open drainage of Empyema should be made after a thorough review of therapy and should be delayed until it is proven to be the only option available.

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