Pleural empyema is a condition leading to a significant burden on health care systems due to protracted hospitalisations. Mortality rates of up to 15% have been reported (10). Treatment ranges from non-surgical interventions such as antibiotic therapy and chest tube placement to thoracoscopic or open surgery.
60 years ago, the American Thoracic Society (ATS) first described the evolution of empyema as a continuous process that subdivides into three stages:
Exudative phase: first 48 hours, initial bacterial infection causes an increased permeability of local tissue resulting in parapneumonic effusion. Usually resolves with adequate antibiotic therapy.
Fibropurulent phase: bacterial invasion, turbid fluid, and development of fibrin membranes, possibly leading to chambered fluid collections and captured lung.
Organisational phase: Characterised by transformation of fibrin membranes into thick tissue which may lead to widespread restriction of the lung.
A stage adapted and effective therapy requires the clinicians to make decisions based on the understanding of the patient’s clinical history, the local antimicrobial resistance patterns as well as the pharmacological characteristics of the antibiotic agents. Ideally, antibiotic therapy should be based on culture results. Intravenous antibiotics are the cornerstone of all treatment methods; intrapleural administration has no place in the therapy of pleural empyema.
In all effusions > 10 mm in pleural ultrasound, diagnostic pleural fluid collection via thoracocentesis should be performed as a diagnostic tool. If the obtained fluid is purulent or cloudy as a near certain sign of pleural infection, a chest tube should be placed as a continuous therapeutic drainage (8). Ongoing pleural drainage in the setting of known pleural infection is a requirement for effective treatment. There is no evidence for increased effectiveness with increasing size of the tube drain (< 14 vs > 14 Fr.) (11). Image guided drainage application can be useful in early-stage empyema with minimal presence of septations.
Video assisted thoracic surgery (VATS) should be considered for all patients with stage 2 empyema requiring surgical intervention. In the setting of empyema, VATS has proven benefits compared to thoracotomy in postoperative outcomes. These include improved postoperative pain control, shorter length of hospital-stay and reduction in 30-day overall mortality (12). The AATS consensus guidelines recommend VATS as the first line approach for stage II and II/III pleural empyema (8).
There are few contraindications for VATS, including a severe coagulopathy making the procedure unsafe, or the patient’s inability to tolerate one-lung-ventilation, meaning a thoracoscopic approach is virtually impossible. Conversion from VATS to open surgery is necessary in case of uncontrollable bleeding, injury to structures which cannot be repaired thoracoscopically, and failure to achieve complete evacuation of the pleural cavity and inability to facilitate lung expansion.
Stage 3 empyema necessitates surgical intervention as pleural drainage procedures have proven to be ineffective treatment options for chronic empyema. Stage 3 empyema is characterised by granulation tissue developing into a peel compressing the visceral pleural surface, which inhibits the expansion of the lung. Continuation of this process results in contraction of the hemithorax with mediastinal shift and rib narrowing of the affected side. Decortication has the aim of eliminating infectious material and achieving re-expansion of the lung by removing the constricting peel (8, 13). Formal decortication is the removal of the visceral and parietal pleura. Pleural debridement refers to removal of granulation tissue in the pleural cavity. The evacuation of infectious material from the pleural space is the aim of both approaches, with formal decortication assumed to be superior in terms of lung expansion. Studies have shown debridement and formal decortication to show similar results regarding resolution of empyema collection and lung re-expansion (14). Muscle flaps or omentum flaps have been shown to be effective therapeutic options (15, 16).
Intrapleural fibrinolysis has been subject of many discussions. The British Thoracic Society published guidelines on the management of pleural diseases in 2010, where it was stated that routine intrapleural fibrinolysis cannot be recommended. However, since then the results of the 2 largest randomised control trials on the subject, the Multicenter Intrapleural Sepsis Trials 1 and 2 (MIST1 and MIST2) have been published. While MIST1 did not demonstrate reduced mortality, frequency of surgery or length of hospital stay, MIST2 demonstrated that a combination of intrapleural tissue plasminogen activator and DNase had a statistical improvement in pleural drainage and reduction in length of hospital stay and the need for surgical intervention (17). All evidence considered, The American Association for Thoracic Surgery (AATS) consensus guidelines for the management of empyema do not routinely recommend the use of intrapleural fibrinolysis as a treatment option (8).
The first report of intrathoracic NPWT using a vacuum assisted closure (VAC) device was a case study reported in 2006, where NPWT was used to close an OTW (18).
There are various known risk factors which impair treatment success. Recently, attempts have been undertaken to improve patient triage and guide clinicians when deciding on the optimal treatment options for individual patients based on different risk factors. The RAPID Score (renal, age, purulence, infection source, and dietary factors) is a clinical risk score which was developed to identify patients at higher risk of death at presentation and may be used to formulate individual treatment strategies accordingly (9). It has since been validated in a prospective observational cohort study (19). We conducted our study with the aim of validating the RAPID score and possibly identifying further risk factors which impact patient outcomes. Demographics, comorbidities as well as perioperative risk factors were analysed. As well as confirming that the RAPID score does in fact accurately predict deteriorating patient outcomes with increasing scores, we were able to demonstrate that certain comorbidities as well as perioperative risk factors negatively impact surgical treatment outcomes in terms of higher 90-day mortality rates. These are currently not included in the RAPID score. When deciding on the best course of treatment, it is often not clear which patients benefit from early surgical intervention and which would be better conservatively treated with antibiotics and drainage. For example, increasing mortality rates with increasing age could be due to biological factors or a surgeons’ reluctancy to treat pleural empyema surgically early on. Evidence that for stage 2 and 3 empyema surgical therapy has superior outcomes to tube thoracostomy alone (20, 21) could support this.
In this current study we investigated a wide range of variables including demographics, comorbidities, cause of empyema, clinical data as well as 90-day mortality to identify factors which correlated with significantly higher 90-day mortality rates.
Diabetes, renal insufficiency and immunosuppression all led to significantly higher 90-day mortality rates in patients which were surgically treated for pleural empyema. In line with previous reports ROC analysis of the RAPID score showed that increasing RAPID scores did predict higher 90-day mortality. Adding the above comorbidities to the RAPID score further improved the predictive value in terms of 90-day mortality rates for patients undergoing surgery for pleural empyema. Diabetes, renal insufficiency and immunosuppression on their own had an even higher predictive value.
Of the perioperative risk factors, transfusions as well as postoperative bleeding with the need for revisional surgery were the only factors which significantly increased the 90-day mortality.
While keeping blood loss and therefore the need for blood transfusion to a minimum when operating for any pathology is logical and should always be aimed for, these are factors which cannot be considered when initially deciding on a certain course of treatment. It is therefore not feasible to include these in any preoperative risk analysis or risk score.
In our study, adjusting the RAPID score by including diabetes, renal insufficiency and immunosuppression significantly improved the predictive value of the score for the 90-day mortality. While a wide range of variables was investigated, the small sample size and retrospective nature of the analysis at a single center obviously limit the strength of the results. Prospective studies with larger sample sizes with the aim of validating the proposed adjustment of the RAPID score may show that this is in fact sensible and that an adjusted RAPID score could in fact help when deciding on early treatment strategies for patients presenting with pleural empyema.