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exudative-pleural-effusions-pathogenesis-and-lab-findings

Exudative Pleural Effusions: Pathogenesis and Lab Findings Authors: Sravya Kakumanu Reviewers: Ben Campbell *Tara Lohmann * MD at time of publication Chylothorax Damage to thoracic duct Leakage of lymphatic fluid into pleural space Pulmonary embolism Clot obstructs blood flow to lung Infarcted lung tissue Lung infection (e.g. pneumonia, tuberculosis) Lung infection signals inflammatory response Systemic Lupus Rheumatoid Erythematosus (SLE) arthritis (RA) Autoimmune antibodies localize to pleura Pleural tumors (primary or secondary from metastatic cancer) Inflammatory cells migrate to affected site and release cytokines ↑ Permeability of pleural capillaries ↑ Fluid leakage across capillaries Exudative Pleural Effusion Cancer invades lymphatic drainage of pleural space (PS) ↓ Drainage of pleural fluid (PF) from pleural space If infectious etiology Tumor invasion = inflammatory response See Pleural Effusions: X-ray Findings and Physical Exam Findings of Lung Diseases slides ↑ Permeable pleural capillaries allow ↑ protein and cell leakage into pleural space If pleural tumour: Release of cancer cells into pleural space Cancer cells on PF cytology 60-75% sensitive for malignancy If rheumatoid arthritis: Release of auto-antibodies into pleural space Auto-antibodies initiate inflammatory response in pleural space ↑ Inflammatory cells have ↑ glucose metabolism in pleural space Sterile PF with mildly elevated white blood cells, normal pH, normal glucose ↑ Inflammation at infection site damages endothelium of pleura Pleural Infection Stage I: Simple Parapneumonic Effusion ↑ Inflammatory cells and bacterial cells in pleural space have ↑ glucose metabolism in pleural space Bacterial invasion from infected parenchymaà pleural space < 40mg/dL glucose in PF ↑ Activation of coagulation cascade and ↓ fibrinolytic activity ↑ Deposition of fibrin clots/membranes within pleural space creates loculated effusion (compartmentalized effusion due to septations in pleural space) ↑ Production of lactate dehydrogenase (LDH) (LDH maintains NAD+ supply during ↑ glucose metabolism) ↑ CO2 production pH of PF < 7.20 ↑ CO2 production pH of PF < 7.20 < 3.3mmol/L glucose in PF Pleural Infection Stage II: Complicated Parapneumonic Effusion Loculated effusion OR bacteria present OR ↓ pH + ↓ glucose ↑ Fibroblast proliferation creates thickened pleura ↑ Pus in pleural space Pleural Infection Stage III/Empyema: Loculated effusion and pus in pleural space PF/serum protein ratio ≥ 0.5 PF/serum LDH ratio ≥ 0.6 Light’s Criteria: Any criteria can be met to be an exudative pleural effusion PF LDH ≥ 2/3 upper limit of normal Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published August 9, 2022 on www.thecalgaryguide.com