Transudative Pleural Effusions: Pathogenesis and Lab Findings
Authors: Sravya Kakumanu Reviewers: Ben Campbell, *Yan Yu, *Tara Lohmann * MD at time of publication
Cirrhosis
Cirrhotic liver ↑ pressure in hepatic veins
Ascites:
Leakage of fluid from hepatic capillariesàperitoneal cavity
Negative intrathoracic pressure on inspiration and ↑ intra-abdominal pressureàfluid leakage from abdominal space into pleural space across diaphragmatic defects
L heart failure (most common)
Left ventricle unable to pump sufficient blood into systemic circulation
Backup of blood in pulmonary veins
↑ Hydrostatic pressure
in pulmonary veins
Pulmonary embolism
R ventricle unable to pump blood due to clot in pulmonary artery
Backup of blood in systemic veins
↑ Hydrostatic pressure
in veins draining parietal pleura
Nephrotic syndrome
Damaged glomerulus has ↑ permeability to plasma proteins in blood
↑ Loss of proteins through urine
↓ Oncotic pressure
in systemic capillaries (including within parietal pleura)
Normally, permeable pleural capillaries do not allow protein leakage into the pleural space
↑ Interstitial fluid leakage across intact pulmonary or pleural capillaries into pleural space
Transudative Pleural Effusion
Absence of bacteria and inflammatory cells in pleural space
No increase in cellular activity in pleural space
Normal levels of glucose metabolism in pleural space = low lactate dehydrogenase (LDH) (LDH increases when glucose metabolism, particularly glycolysis, increases to maintain supply of NAD+)
Large accumulation of pleural fluid (PF) pressing against lung tissue and mediastinum
Lung atelectasis (lung collapse)
See Pleural Effusions: X- ray Findings and Physical Exam Findings of Lung Diseases slides
PF/serum protein ratio < 0.5 PF LDH < 2/3 upper limit of normal Light’s Criteria: All three criteria must be met to be a transudative pleural effusion PF/serum LDH ratio < 0.6 See Hypoxemia: Pathogenesis and Clinical Findings slide for pathophysiology and signs of hypoxemia Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published August 9, 2022 on www.thecalgaryguide.com