Introduction and Epidemiology
Empyema thoracis is a common cause of morbidity in the pediatric population. In 1983 it was estimated that 0.6% of pediatric pneumonias were complicated by empyema , but more recent studies indicate that the incidence is increasing. One study estimated that anywhere from 10-30% of pediatric patients hospitalized with pneumonia are complicated by empyema. 
While the mainstay of parapneumonic effusion treatment is antibiotics, surgical interventions and drainage procedures have always played a role in the treatment of empyema. This purpose of this article is to provide an overview of pediatric empyema and discuss the role of video assisted thoracoscopic surgery (VATS) in its treatment.
Causes and Pathogenesis
Empyema thoracis is defined as a purulent pleural effusion. While cases are most commonly parapneumonic (a complication of bacterial pneumonia), other rarer causes include traumatic introduction, iatrogenic introduction, and spread from other infections of the tracheobronchial tree and esophagus .
In the case of parapneumonic empyema, infection occurs from either direct bacterial spread across visceral pleura, or by free intrapleural rupture of peripherally located lung abscesses.  Along with bacteria, neutrophil permeability (not normally located in pleural space) increases as well, leading to an increase in multiple chemotactic factors and activation of the coagulation cascade. Higher procoagulant activity leads to fibrin deposition within the pleural space.
Empyemas have classically been into 3 stages, which follow the progression of their pathogenesis [4,5]:
Stage I (exudative phase)- Pleural membranes swell considerably and a thin exudative fluid is leaked into the pleural space (simple parapneumonic effusion).
Stage II (fibrinopurulent phase)- There is a deposition of fibrin leading to septation and loculations, with an increase in white cells and fluid thickness (complicated parapneumonic effusion) and ultimately frank pus (empyema).
Stage III (organizing phase)- Massive influx of fibroblast activity leads to formation of collagen fibers over visceral and parietal pleura, with development of a thick “pleural peel” that prevents lung re-expansion.
The presentation of empyema mirrors that of bacterial pneumonia. Patients often present with shortness of breath, dyspnea, fever, and cough. With increasing inflammation the patient may experience pleuritic chest pain, and possibly abdominal pain and vomiting. In severe cases splinting of the affected side can occur.
Pertinent findings on physical exam include decreased breath sounds, crackles, and dullness to percussion on affected side.
CBC- will show leukocytosis.
Blood cultures- should be sent on all patients with parapneumonic effusion as they may indicate causative organism.
Sputum cultures- Although rare, if patient is producing sputum it should be sent for culture to help identify causative organism.
Pleural fluid analysis- Although diagnostic taps of pleural fluid are not routinely performed in the pediatric population, any pleural fluid obtained should be sent for microbiological analysis . A differential cell count can also be performed, as results may indicate further need to test for mycobacterium and malignancy. Fluid will often be sterile due to prior antibiotic administration, but may still have diagnostic value. There is otherwise little evidence that chemical analysis of pleural fluid has any relevance to clinical course. .
Imaging selection is an integral part in the management of parapneumonic effusions, as evidenced by their use in many treatment algorithms [3, 5, 7-11]. Plain films should be performed on all patients with possible parapneumonic effusion, but are ineffective at distinguishing between parenchymal consolidation and pleural fluid . For the evaluation of pediatric empyema, the use of ultrasound vs CT has previously been a topic of controversy. Two studies suggest that ultrasound is superior to CT in identifying and locating the presence of fibrin septations compared to CT(13, 14) . However, it is important to note that ultrasound is often more operator dependent than CT scan, which may limit its utility in clinical management at certain institutions. While some surgeons feel CT scanning is more valuable for preoperative planning [8, 15], with increasing concerns for adverse effects of radiation in the pediatric population, most physicians today prefer ultrasound imaging as a diagnostic modality of choice following plain film [5, 7, 10, 16].
Advantages of VATS
Regardless of drainage procedure used, the majority of children with parapneumonic effusions often have favorable long term outcomes [17, 18]. This is especially true when compared to adults as they usually do not have chronic underlying lung pathology. However, once empyema (presence of solid components in pleural fluid with imaging, or pus in thoracentesis sample) has been diagnosed, debridement with VATS has been found to have advantages. Multiple studies have indicated that in comparison to thoracentesis or chest tube alone, the use of VATS significantly decreases the length of hospital stay [19-23]. Other groups of studies [11, 22, 24] indicate that performing VATS as the primary intervention early in the hospital course (up to 4 days depending on the study) decreases the length of hospital stay.
VATS vs Fibrinolytics
The above findings caused VATS to be considered the gold standard of empyema treatment for a period of time, until the advent of “chemical debridement,” using fibrinolytic instillation through thoracostomy tube. To date, there have been three prospective randomized trials [25-27] comparing the use of fibrinolysis to VATS in the treatment of pediatric empyema. All three studies found no significant difference in length of hospital stay or failure rate. Two of the studies [26,27] found no difference in length of post-operative fever. However, two of the studies [25,26] did find a significant difference in cost, with fibrinolysis treatment costing less.
Although one group has challenged the surgical failure rate of the above studies as being too high through a large retrospective series , APSA now recommends that chemical debridement should be considered first line therapy with operative management reserved for patients who fail . However, they do note that VATS remains an equivalent treatment option, particularly in situations where thoracostomy tube insertion and fibrinolysis requires general anesthesia.
VATS Surgical Technique
The surgical technique for using VATS in the treatment of empyema has been well described [8, 11, 16, 24, 28]. The procedure is performed under general anesthesia using single or double lumen endotracheal intubation with either one or two lung ventilation depending on the size of the child. The patient should be placed in the left or right lateral decubitus position (with the affected lung up) depending on disease location. Supine positioning with the affected side elevated 45 degrees has also been described. The first trocar is placed in the 5th or 6th intercostal space at the mid-axillary line, through which a 30-degree telescope is inserted. From there, two additional ports are placed under thoracoscopic guidance. Port size can be 5 to 10 mm depending on patient size. If necessary, continuous flow of carbon dioxide can be used to ensure lung deflation but is not always required. If used it is important to avoid mediastinal displacement which can lead to decreased oxygenation, and venous return to the heart. Once accessed, free fluid and loculations are evacuated and fibrous adhesions are separated. Any fibrin clots and pleural debris should be removed with ring forceps or biliary stone clamps. If there is any necrotic lung tissue, it should be carefully preserved to avoid a postoperative continuous air leak. Once the procedure is completed, one or more chest tubes should be placed under thoracoscopic visualization. Lung re-expansion should be confirmed by chest x-ray after the procedure.
Submitted by Michael Cox, M.D.
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