Clinical Significance of Pleural Lactate Measurement in Critically Ill Patients with Parapneumonic Pleural Effusion.

Objective: Pleural fluid pH measurement is recommended for tube thoracostomy decisions in complicated parapneumonic pleural effusions. However, pleural fluid pH may be affected by blood pH in critically ill patients with common systemic acid-base disorders. We aimed to investigate the use of pleural fluid lactate to distinguish culture-positive parapneumonic effusions from other pleural effusions.

Material and methods: This prospective observational study included 121 eligible patients (51 female and 70 male). All patients with pleural effusion who underwent thoracentesis were assessed. Pleural fluid lactate was measured by a blood gas analyzer.

Results: Of the 121 patients, 30 (24.8%) were transudate and 91 (75.2%) were exudate. Of the 91 patients with exudative pleural effusion, 61 were diagnosed as culture-negative parapneumonic, 13 as culture-positive parapneumonic, 9 as malignant, and 8 as other exudative effusion. There was a strong positive linear association between serum pH and pleural fluid pH (R = 0.77, P < .001). The post hoc tests for pleural fluid lactate revealed there was a significant difference between culture-positive parapneumonic versus culture-negative parapneumonic groups (P = .004), culture-positive parapneumonic versus transudative effusion groups (P < .001), culture-negative parapneumonic versus transudative effusion groups (P = .008) and lastly; malignant effusion versus transudative effusion groups (P = .001). Receiver operating characteristics curve analysis for culture-positive parapneumonic indicated a cutoff of 4.55 mmol/L for pleural fluid lactate to have a sensitivity of 76.9% and a specificity of 84.3% (positive predictive value: 37%, negative predictive value: 96.8%).

Conclusion: A cutoff of 4.55 mmol/L of pleural fluid lactate can be used as a useful tool to distinguish culture-positive parapneumonic effusions from other effusions in critically ill patients.