Management of Parapneumonic Effusions

Annotation for Point B

Gross purulence (empyema) evident at the time of thoracentesis is unusual but constitutes an indication for prompt video-assisted thoracoscopic surgery (VATS) decortication.⁷ In all other circumstances, the pleural fluid should be submitted for laboratory analysis. A common oversight in the SICU is to pursue the distinction of an exudative versus transudative effusion, that is, via Light’s criteria: protein greater than 0.5 serum, LDH greater than 0.6 serum, or LDH greater than two-thirds normal serum.²⁹ But the critical issue is whether the parapneumonic fluid collection is infected, and most of the pleural collections in the SICU are exudative. The most cost-effective means to analyze this is to measure the pH of the pleural fluid using a standard blood gas analyzer, available in most SICUs. A pH less than 7.2 is the threshold, although less than 7.3 is considered high risk.^4,7-9,30-34 This is a level I diagnostic evidence. A notable exception is a Proteus infection where the pH may exceed 7.4 because of ammonia production.⁸ An alternative diagnostic criterion is a pleural fluid glucose less than 60 mg/dL when infection is suspected.³ This is a level I diagnostic evidence. Because the evolution of an empyema may extend for days to weeks and the early phase is a sterile effusion, a repeat diagnostic thoracentesis should be done in any patient with a persistent unexplained systemic inflammatory response syndrome and unilateral pleural effusion.^7-9