Empyema

Patient outlook is variable. Some patients respond fully to antibiotic treatment and chest drain insertion within a couple of weeks. However, approximately 24% do not respond and require surgery.[8]Shen KR, Bribriesco A, Crabtree T, et al. The American Association for Thoracic Surgery consensus guidelines for the management of empyema. J Thorac Cardiovasc Surg. 2017 Jun;153(6):e129-46. https://www.jtcvs.org/article/S0022-5223(17)30152-6/fulltext http://www.ncbi.nlm.nih.gov/pubmed/28274565?tool=bestpractice.com ​ Most patients will recover fully, but a small number will develop chronic pleural thickening causing restricted ventilation or chronic pleural infection.

Mortality following empyema is approximately 15% to 20% and is higher in patients with significant comorbidities or immunocompromise.[3]Rahman NM, Davies RJO. Effusions from infections: parapneumonic effusion and empyema. In: Light RW, Lee YCG, eds. Textbook of Pleural Disease. 2nd ed. London: Hodder & Stoughton; 2008:341-66.[23]Maskell NA, Davies CW, Nunn AJ, et al. UK controlled trial of intrapleural streptokinase for pleural infection. N Engl J Med. 2005 Mar 3;352(9):865-74. http://www.nejm.org/doi/full/10.1056/NEJMoa042473#t=article http://www.ncbi.nlm.nih.gov/pubmed/15745977?tool=bestpractice.com

Factors associated with a worse 3-month mortality include elevated serum urea, elderly age, non-purulent effusion, hospital-acquired infection, and low serum albumin levels, collectively known as the RAPID [Renal (urea), Age, fluid Purulence, Infection source, Dietary (albumin)] score.[25]Rahman NM, Kahan BC, Miller RF, et al. A clinical score (RAPID) to identify those at risk for poor outcome at presentation in patients with pleural infection. Chest. 2014 Apr;145(4):848-55. http://www.ncbi.nlm.nih.gov/pubmed/24264558?tool=bestpractice.com Of these variables, only elderly age has been associated with an increased need for surgery at 3 months. Although it seems counter-intuitive that non-purulent effusions would be associated with worse outcomes, this may be explained by the clinical observation that frankly purulent effusions appear to have less loculations and as a result are more likely to fully drain without the need for additional intervention such as intrapleural enzyme therapy or surgery.

Outcome based on the American College of Chest Physicians categorisation of parapneumonic effusions

Category 1 empyemas: free-flowing pleural effusion, <10 mm on lateral decubitus chest x-ray (CXR), thoracentesis (pleural aspiration) not required; a very low risk of poor outcome.

Category 2 empyemas: moderate free-flowing effusion (less than half of haemithorax), Gram stain and culture negative, pH >7.2; a low risk of poor outcome.

Category 3 empyemas: large or loculated pleural effusion or pleural thickening, or positive Gram stain or culture, or pH <7.2; a moderate risk of poor outcome.

Category 4 empyemas: aspiration of frank pus; a high risk of poor outcome.

Abnormalities on chest x-ray

Although invariably abnormal at discharge, most CXR changes resolve within 3 to 6 months with some residual pleural thickening. A repeat CXR should be taken 4 to 6 weeks after discharge.

Impaired pulmonary function

Some patients develop restrictive pulmonary function as a result of residual pleural thickening following chest tube removal. This pleural thickening resolves in most patients within several months and pulmonary function is usually near normal after 3 to 6 months. If reduced pulmonary function persists after 6 months and the patient is symptomatic, surgical decortication (a major thoracic operation involving the evacuation of pus and debris from the pleural space and removal of fibrous tissue from the visceral and parietal pleura) should be considered.