Respiratory · General Medicine
Pleural Effusion
Also known as Pleural effusion · Hydrothorax · Transudative effusion · Exudative effusion · Parapneumonic effusion · Empyema · Hepatic hydrothorax · Chylothorax
Pleural effusion is an accumulation of fluid in the normally near-dry pleural space. It is classified by Light's criteria (1972) as a transudate (systemic cause: heart failure, cirrhosis, nephrotic syndrome, peritoneal dialysis, myxoedema, pulmonary embolism) or an exudate (local pleural disease: parapneumonic, malignancy, tuberculosis, pulmonary embolism, autoimmune, pancreatitis, chylothorax, haemothorax). Diagnosis rests on chest X-ray, thoracic ultrasound (loculation, septation, guidance) and diagnostic thoracentesis with pleural fluid analysis (protein, LDH, glucose, pH, cell count, Gram stain and culture, cytology, ADA, triglycerides, NT-proBNP). Treatment is cause-directed, with drainage for a complicated parapneumonic collection (pH under 7.20, glucose under 60 mg/dL, frank pus), intrapleural tPA plus DNase for a loculated empyema, and talc pleurodesis or an indwelling pleural catheter for a recurrent malignant effusion.
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Red flags
- Tension pleural effusion — severe respiratory compromise with hypotension and tracheal deviation away from the side; emergency needle decompression then intercostal drain
- Empyema — infected pleural fluid (frank pus, pH under 7.20, glucose under 60 mg/dL); requires immediate chest drain plus intravenous antibiotics with mandatory anaerobic cover, intrapleural tPA plus DNase if loculated and failing drainage, surgical decortication if failed medical therapy
- Massive haemothorax after blunt or penetrating trauma — immediate large-volume drainage or ongoing bleeding; large-bore intercostal drain, resuscitation with blood, thoracic surgery referral
- Chylothorax (pleural fluid triglycerides over 110 mg/dL or chylomicrons present) — investigate thoracic duct injury, lymphoma, post-surgical leak
- Re-expansion pulmonary oedema — rare after large-volume thoracentesis; stop draining for chest discomfort or a pleural pressure below minus 20 cm of water rather than at an arbitrary volume limit
Meet the patient
A 68-year-old former smoker arrives with two weeks of progressive breathlessness and a sharp, pleuritic pain over the right base that has eased as he became more breathless. He is tachypnoeic; the right base is stony dull with absent breath sounds and reduced vocal resonance, and the trachea is pushed slightly to the left.[2]
The two questions that decide his next 24 hours are the two that decide every pleural effusion: is the lung pushed away by fluid, or pulled in by collapse? (the trachea answers at the bedside — pushed away means effusion), and once you have confirmed fluid, is it a transudate or an exudate? (the tap answers that). Hold those two questions and everything below slots into place.[1]
Light's criteria — the one fork that runs everything
A pleural effusion is not a diagnosis; it is a sign of an underlying disease. The single most powerful diagnostic step, introduced by Richard Light in 1972 and unchanged in half a century, is to classify the fluid as a transudate or an exudate. That one distinction collapses a differential of dozens of causes into two manageable lists, and it dictates which further fluid tests are worth sending.[1][2]
Light's criteria compare simultaneous serum protein and LDH against the pleural fluid. The effusion is an exudate if any ONE of the three holds:[1][13]
- Pleural fluid protein divided by serum protein over 0.5
- Pleural fluid LDH divided by serum LDH over 0.6
- Pleural fluid LDH over 200 U/L[13]
The criteria are highly sensitive but less specific. In the prospective series that tested them head-to-head against the albumin gradient, Light's criteria correctly identified every exudate, but five patients with congestive heart failure were misclassified as exudates — four of them after diuretic therapy — and about a quarter of heart-failure effusions fall into the exudative range biochemically.[13][14] The two rescue tests for that trap are pleural fluid NT-proBNP — at a cut-off of 4000 ng/L it identified cardiac effusions with about 92 per cent accuracy and correctly reclassified every patient Light's criteria had mislabelled — and, where natriuretic peptide assays are unavailable, the serum-to-pleural-fluid albumin gradient, where a gradient over 1.2 g/dL supports a transudate.[15][13][14]
The four mechanisms — and which fork they land on
A transudate forms when systemic Starling forces are disturbed across a normal pleura; an exudate forms when the pleura itself is diseased. Recognising the mechanism predicts the transudate-exudate split before the tap.[1][10]
- Increased hydrostatic pressure (transudate). Pulmonary venous pressure rises in left heart failure, mitral stenosis, fluid overload and constrictive pericarditis; pleural effusion results from increased interstitial fluid in the lung due to elevated pulmonary capillary pressure.[14]
- Decreased oncotic pressure (transudate). Hypoalbuminaemia from cirrhosis, nephrotic syndrome or severe malnutrition lowers plasma oncotic pressure. Hepatic hydrothorax is the paradigm — ascites tracks through small diaphragmatic defects into the negative-pressure pleural space, typically producing a unilateral right-sided effusion.[12]
- Increased capillary permeability (exudate). Inflammation from pneumonia, autoimmune disease, pulmonary embolism with infarction, pancreatitis or drugs opens intercellular junctions and lets protein-rich fluid leak in — the fibropurulent stage of a parapneumonic effusion is the classic example.[16]
- Impaired lymphatic drainage (exudate). Obstruction by tumour or nodes raises back-pressure and traps protein, so even normal-constituency fluid accumulates as an exudate.[1]
The benign (non-malignant) effusions outnumber the malignant ones by at least three to one, and in recent United States epidemiological data 75 per cent of resource allocation for pleural effusion management is spent on non-malignant effusions (excluding empyema) — yet they do not follow a benign course, with mortality that matches and sometimes exceeds malignant effusions.[10]
The epidemiology is the epidemiology of its causes, and the side matters at the bedside. Heart-failure effusions are typically bilateral, but when unilateral they are more commonly right-sided — so a unilateral right-sided effusion in heart failure is a common explanation, not a reason to chase an alternative cause first.[14]
In tuberculosis-endemic regions pleural tuberculosis remains one of the most frequent causes of a pleural exudate, particularly in tuberculosis-endemic areas and in people living with HIV.[21] The incidence of pleural infection in adults has been continuously increasing over the past two decades, particularly in older adults with comorbidities, and management requires a prolonged hospitalisation — 14 days on average in contemporary series.[17]
At the bedside — stony dull and shifted away
The classical symptom triad is progressive exertional dyspnoea, pleuritic chest pain and a dry cough. Dyspnoea is the commonest and most reliable symptom; pleuritic pain arises from the parietal pleura (the visceral pleura is insensate) and therefore points to an exudative cause — pneumonia, pulmonary embolism, autoimmune — rather than a transudate. The pain often eases as fluid accumulates and separates the inflamed pleural surfaces.[2]
Examination yields one of the most distinctive bedside findings in medicine. The affected hemithorax is expanded, moves less on respiration, and is dull to percussion. The percussion note is "stony dull" — a dense, thud-like quality distinct from the woody dullness of consolidation, because fluid transmits vibration poorly. Breath sounds and vocal resonance are reduced or absent over the fluid, and a pleural rub may sit at the upper margin where the two pleural surfaces still rub. The trachea and apex beat are deviated away in a massive effusion.[2]
Everyone forgets the trachea. Effusion pushes the mediastinum away; collapse pulls it toward. That single sign separates the two at the bedside before any imaging, and it is the discriminator examiners listen for.[4]
The differential of dullness with reduced breath sounds
The bedside finding of dullness with reduced breath sounds has a focused differential, and the examiner expects you to distinguish each by the features that separate them.[2][4]
Pleural effusion
- Stony dull percussion, reduced breath sounds and vocal resonance
- Trachea deviated AWAY in massive effusion
- CXR: meniscus sign, blunted costophrenic angle, mediastinal shift away
- Ultrasound confirms fluid; thoracentesis diagnostic
Consolidation (pneumonia)
- Dull but woody, not stony; bronchial breathing and increased vocal resonance
- Crackles and wheeze; fever, productive cough, sepsis
- Trachea central; CXR: alveolar opacification with air bronchograms
- Responds to antibiotics; small reactive effusion may coexist
Collapse or atelectasis
- Dull with reduced breath sounds — but trachea deviated TOWARD the lesion
- Volume loss: shifted mediastinum, narrowed intercostal spaces
- CXR: opacification with volume loss, no meniscus
- Causes: mucus plug, foreign body, tumour, pneumothorax (compressive)
Raised hemidiaphragm
- Dullness high in the axilla, normal breath sounds above
- Phrenic nerve palsy (lung cancer, mediastinal tumour, post-CABG)
- CXR: elevated dome; fluoroscopy sniff test shows paradoxical ascent
- No fluid meniscus; ultrasound confirms no effusion
The discriminator line: trachea away equals effusion; trachea toward equals collapse; bronchial breathing with increased resonance equals consolidation.[2]
Diagnostic thoracentesis — what to send, what to skip
The investigation proceeds in two phases: confirm the effusion (imaging), then identify the cause (pleural fluid analysis). The cornerstone is the diagnostic thoracentesis with pleural fluid interpreted through Light's criteria.[1][4]
Tap every unexplained unilateral effusion, every bilateral effusion with discordant appearances, and any effusion that does not resolve with heart failure treatment. Perform it under ultrasound guidance — ultrasound confirms fluid, and it is one of the most useful tests for detecting the loculated or septated collections that mark a complicated parapneumonic effusion.[16]
The first and decisive step is to apply Light's criteria to the fluid, comparing simultaneous serum protein and LDH. Once classified as a transudate, no further fluid tests are usually needed — the workup shifts to the systemic cause. Once it is an exudate, a panel of additional tests refines the diagnosis:[1][13]
- Glucose — under 60 mg/dL (about 3.3 mmol/L), together with a low pH and a high LDH, defines the fibropurulent stage of a parapneumonic collection.[16]
- pH — under 7.20 marks a complicated parapneumonic effusion; meta-analysis of the primary studies found pH the most accurate single discriminator (area under the ROC curve 0.92, versus 0.84 for glucose and 0.82 for LDH), with decision thresholds falling between 7.21 and 7.29 depending on cost-prevalence considerations.[19]
- Cell count — neutrophils point to bacterial infection or its complications; lymphocytes point to tuberculosis or malignancy. Tuberculous effusions are characteristically lymphocyte-rich, straw-coloured and free-flowing.[21]
- Gram stain and culture, AFB — bacterial and mycobacterial; tuberculous pleural effusions have a characteristically low yield on mycobacterial culture, so a negative culture never excludes tuberculosis.[21]
- Cytology — pooled diagnostic sensitivity for a malignant effusion is 58.2 per cent (range 20.5 to 86.0 across studies); it is highest for lung adenocarcinoma (83.6 per cent) and ovarian cancer (85.2 per cent) and lowest for lung squamous carcinoma (24.2 per cent) and mesothelioma (28.9 per cent).[20]
- ADA — at a threshold around 40 U/L (studies used 40 plus or minus 4 IU/L) the summary sensitivity for tuberculous pleural effusion is 0.93 and the specificity 0.90.[22]
- Triglycerides — over 110 mg/dL (about 1.24 mmol/L), or chylomicrons on lipid electrophoresis, defines a chylous effusion.[23]
The macroscopic appearance gives the first clue: serous and straw-coloured (transudate or early exudate), bloody (malignancy, trauma, PE, iatrogenic), turbid or purulent (empyema), milky white (chylothorax or pseudochylothorax), food particles (oesophageal rupture).[2][23]
PLEURAL
- PProtein and LDH ratio — Light's criteria (protein ratio over 0.5, LDH ratio over 0.6, LDH over 200 U/L) separate transudate from exudate
- LLow glucose — under 60 mg/dL with a pH under 7.20 marks a complicated parapneumonic collection
- EEmpyema — frank pus, or a complicated collection that antibiotics alone cannot resolve; it needs drainage
- UUse ultrasound for every tap — it finds the loculated, septated collections that define a complicated effusion
- RRepeat cytology if negative — pooled sensitivity is only 58 per cent, and lowest (29 per cent) in mesothelioma
- AADA around 40 U/L in a lymphocytic effusion — tuberculous pleuritis (sensitivity 0.93, specificity 0.90)
- LLipids and peptides — triglycerides over 110 mg/dL means chylothorax; NT-proBNP over 4000 ng/L means cardiac
The drainage thresholds — pH, glucose, pus
The decision to drain a parapneumonic effusion rests on the fluid biochemistry: a pH under 7.20, a glucose under 60 mg/dL, or a high LDH mark the fibropurulent stage, in which antibiotic therapy alone is not enough for resolution and an invasive procedure — pleural drainage or surgery — is required; frankly purulent fluid is empyema by definition.[16] Meta-analysis of the primary studies confirms the hierarchy: pleural fluid pH had the highest diagnostic accuracy (AUC 0.92), retaining the top position even after frankly purulent effusions were excluded (AUC 0.89), with decision thresholds between 7.21 and 7.29.[19]
Parapneumonic effusions stratify into three stages that map directly onto management:[16]
Stage I — Exudative
- Simple accumulation of pleural fluid alongside the pneumonia
- Free-flowing, usually anechoic on ultrasound
- Antibiotics for the pneumonia alone are usually sufficient
Stage II — Fibropurulent
- Bacterial invasion of the pleural cavity; neutrophilic, fibrinous, often loculated
- pH under 7.20, glucose under 60 mg/dL, high LDH
- Antibiotics alone are not enough — chest drainage or surgery is required
- Intrapleural fibrinolytic-enzymatic therapy when the tube fails or surgery is not suitable
Stage III — Organised
- Scar tissue formation with loculation and septation
- Complex (non-anechoic, loculated or septated) on ultrasound
- Drainage plus surgical clearance; intrapleural therapy for those not fit for surgery
Resuscitation — the four time-critical effusions
Most effusions are managed electively, but a small number present as time-critical emergencies in which the resuscitation reflex precedes the diagnostic workup. The dangerous scenarios are tension pleural effusion, massive haemothorax, empyema with septic shock, and severe hypoxaemia from a large malignant effusion.[2][5]
Tension pleural effusion is rare but lethal — a large effusion under pressure that shifts the mediastinum away, compresses the great veins, and produces hypotension, tachycardia, marked dyspnoea and hypoxaemia. Immediate management is emergency needle aspiration followed promptly by an intercostal chest drain.[2]
Massive haemothorax is a surgical emergency. Most cases of haemothorax follow blunt or penetrating chest trauma, and the criteria for surgical intervention in the initial haemothorax are well defined; what remains controversial is the best approach to a retained haemothorax after the initial drain. Drain the chest, resuscitate with intravenous crystalloid and blood, correct coagulopathy, and involve thoracic surgery early.[27]
Empyema with septic shock requires simultaneous resuscitation and source control: intravenous fluids, vasopressors for refractory hypotension, antimicrobial therapy with mandatory anaerobic coverage, and chest-tube drainage — the two key components of pleural infection management — escalating to surgery or intrapleural fibrinolytics when sepsis persists despite standard measures.[17][6]
The one procedural limit everyone must know — and its evidence: re-expansion pulmonary oedema is the feared complication of therapeutic thoracentesis, but in a prospective series of 185 large-volume thoracenteses (a litre or more removed) clinical oedema occurred in only one patient (0.5 per cent) and radiographic-only oedema in four (2.2 per cent), with no association with the volume removed, the pleural pressure or the pleural elastance. The evidence therefore supports draining a large effusion to completion, stopping for chest discomfort or an end-expiratory pleural pressure below minus 20 cm of water, rather than stopping at an arbitrary volume.[25]
Parapneumonic effusion and empyema — MIST-2 changed the rule
Antibiotics for pleural infection must cover anaerobes — anaerobic coverage is mandatory, because anaerobes are a major cause of pleural infection — and the expected spectrum differs between community-acquired and healthcare-associated infection, so the regimen must be chosen accordingly.[17] Conventional teaching is a minimum of four weeks of treatment, though that figure rests on expert opinion; a randomised trial comparing a short course (14 to 21 days) with a long course (28 to 42 days) in medically stabilised patients found no significant difference in treatment failure (16.7 versus 12.5 per cent).[18]
Intrapleural tPA plus DNase was established by the MIST-2 trial (Rahman 2011): in a blinded two-by-two factorial trial, 210 patients with pleural infection received double placebo, tPA plus DNase, tPA alone, or DNase alone, each for three days. The combination significantly increased pleural drainage (mean change in pleural opacity minus 29.5 versus minus 17.2 per cent with placebo), reduced surgical referral at three months (4 versus 16 per cent) and shortened the hospital stay by a mean of 6.7 days. The trap examiners love: tPA alone and DNase alone were no better than placebo, and DNase alone actually increased surgical referral (39 versus 16 per cent).[6] Intrapleural fibrinolytic-enzymatic therapy is the option when a chest tube fails to clear a loculated collection or the patient is not suitable for surgery.[16][17]
Surgical decortication is indicated for failed medical therapy — persistent sepsis despite standard measures — with intrapleural fibrinolytic therapy recommended for poor surgical candidates.[17] The RAPID score (Rahman 2014) — Renal (urea), Age, Purulence, Infection source, Dietary (albumin) — stratifies three-month mortality into low (0 to 2), medium (3 to 4) and high (5 to 7) risk; in the MIST-2 validation cohort a high-risk score carried an odds ratio of 14.1 for death at three months.[9]
Malignant effusion — IPC or talc, take your pick
A malignant effusion is a symptom-control problem layered on an oncology problem. The fluid is usually an exudate, and pleural fluid cytology makes the diagnosis in 58.2 per cent of cases overall — highest in lung adenocarcinoma (83.6 per cent) and ovarian cancer (85.2 per cent), lowest in mesothelioma (28.9 per cent), which usually needs a pleural biopsy instead.[20][11]
The TIME2 trial (Davies 2012) compared an indwelling pleural catheter with chest tube and talc slurry pleurodesis: dyspnoea improved in both groups with no significant difference over the first 42 days (mean visual-analogue dyspnoea score 24.7 versus 24.4 mm), the IPC group was significantly better at six months (difference minus 14.0 mm), and the initial hospitalisation was dramatically shorter (median 0 versus 4 days) — at the cost of more adverse events (21 of 52 versus 7 of 54) and fewer further pleural procedures (3 versus 12).[7] The IPC-Plus trial (Bhatnagar 2018) then showed that talc slurry instilled through an existing IPC produced successful pleurodesis at 35 days in 43 per cent versus 23 per cent with placebo (hazard ratio 2.20), without excess harm — combining the convenience of an IPC with the pleurodesis effect.[8]
Current practice therefore presents IPC and talc pleurodesis as equivalent first-line options for dyspnoea relief, with the choice guided by lung re-expansion (a trapped lung precludes pleurodesis) and expected prognosis.[3][7] Mesothelioma-related effusions deserve pleural biopsy — image-guided or thoracoscopic — for diagnosis, with BAP1 or MTAP loss and CDKN2A homozygous deletion as the basic molecular markers, and the effusion managed with tunnelled pleural catheters, alone or combined with aerosolised talc during a diagnostic thoracoscopy.[11]
The specific-cause one-liners that earn marks
Tuberculous pleuritis is treated with antituberculous regimens identical to those used for pulmonary tuberculosis.[21] The effusion is typically an exudate that is lymphocyte-rich, straw-coloured and free-flowing with a high ADA and a characteristically low yield on mycobacterial culture — up to 80 per cent of patients also have parenchymal involvement on chest imaging. Where tuberculosis prevalence is high, a lymphocyte-predominant exudate with a high ADA carries a positive predictive value of 98 per cent; in low-prevalence areas the absence of both makes tuberculosis very unlikely and pleural biopsy should be performed to confirm the diagnosis, and to obtain culture and susceptibility testing where drug resistance is prevalent. Initial pleural drainage may have a role in symptom relief and in hastening resolution.[21]
Hepatic hydrothorax develops in 5 to 10 per cent of patients with liver cirrhosis, typically as a unilateral, right-sided pleural effusion with concomitant ascites, from small diaphragmatic defects (pleuroperitoneal connections) that let ascitic fluid migrate directly into the pleural cavity.[12] Never put a chest tube: in a 10-year series of 17 patients drained this way, 16 suffered at least one complication — acute kidney injury in 11, pneumothorax in 7, empyema in 5 — and six were dead within three months, whereas six of seven who received TIPS survived.[26] Medical management is sodium restriction and diuretic therapy, with thoracentesis for symptomatic relief; refractory cases go for TIPS, as definitive treatment or a bridge to liver transplantation — the only curative option.[12]
Chylothorax is a lymphocyte-predominant effusion caused by thoracic duct leakage into the pleural space, defined by a pleural fluid triglyceride concentration over 110 mg/dL (about 1.24 mmol/L) or the presence of chylomicrons; chylous effusions from a duct leak alone are typically protein-discordant exudates with a low LDH, and fluid that falls outside that pattern should prompt a search for a coexisting cause, because that changes management.[23]
Rheumatoid pleuritis has a distinctive fluid signature — high LDH with low pH and low glucose; it usually occurs in middle-aged men, and a contemporary series found most patients were over 60, with milder fluid abnormalities (lower LDH, higher pH) in older patients and a distinctly higher mortality than previously reported.[28]
A consultant confession: distinguish chylothorax from pseudochylothorax. A true chylothorax is from a thoracic duct leak and has triglycerides over 110 mg/dL; a pseudochylothorax (cholesterol pleurisy, chyliform effusion) is a cholesterol-rich effusion of chronic inflammatory disease — 88.5 per cent of published cases were tuberculosis or rheumatoid arthritis — with a milky exudate, lymphocyte predominance in 61.1 per cent, cholesterol crystals (89.7 per cent sensitive) and a cholesterol-to-triglyceride ratio over 1 (97.4 per cent sensitive), and it is not managed with a low-fat diet.[24][23]
Chest tubes — the smallest effective drain
The modern principle is the smallest effective drain. A small-bore Seldinger drain, inserted under ultrasound guidance, is preferred for most free-flowing effusions, complicated parapneumonic effusion and many empyemas, because it is more comfortable and equally effective when correctly placed; a larger-bore drain is reserved for frank pus, haemothorax and large-volume air leaks. The BTS recommends ultrasound guidance for every pleural drain.[4]
Drain care matters: assess output and swing regularly, keep the tube patent, never clamp a chest tube in a ventilated patient or a pneumothorax, and remove it once the effusion has resolved and the lung re-expanded.[4]
When it goes wrong — the preventable list
- Missing empyema — a parapneumonic collection with pH under 7.20 or glucose under 60 mg/dL is complicated and needs drainage, because antibiotic therapy alone is not enough for its resolution.[16]
- Putting a chest tube in hepatic hydrothorax — 16 of 17 patients in one series suffered complications including acute kidney injury, pneumothorax and empyema; use sodium restriction, diuretics, therapeutic thoracentesis, and TIPS or transplantation for refractory disease.[26]
- Stopping a therapeutic tap too early out of fear of re-expansion oedema — clinical oedema complicated only 0.5 per cent of 185 large-volume thoracenteses; drain to completion but stop for chest discomfort.[25]
- Pleurodesis in a trapped lung — pleurodesis cannot succeed if the lung does not re-expand; choose an indwelling pleural catheter instead.[3]
- Mislabelling a diuretic-treated cardiac effusion as an exudate — rescue with pleural fluid NT-proBNP (4000 ng/L cut-off, 92 per cent accuracy) or the serum-to-pleural albumin gradient over 1.2 g/dL.[15][13]
- Missing a tuberculous effusion in a high-burden setting — a lymphocytic exudate with a high ADA carries a positive predictive value of 98 per cent for tuberculosis.[21]
- Giving DNase alone in empyema — MIST-2 showed it increased surgical referral to 39 per cent; only tPA plus DNase together works.[6]
Prognosis, disposition, and the score that sets both
The prognosis of a pleural effusion is the prognosis of its cause. Transudative effusions generally improve with treatment of the underlying disease. Pleural infection carries considerable morbidity and remains life-threatening — more than 30 per cent of patients with pleural infection either die or require surgery — and the RAPID score quantifies that risk at three months from age, urea, albumin, hospital-acquired infection and non-purulence.[6][9]
Malignant pleural effusion is a marker of advanced disease with a limited median survival measured in months, and the choice between pleurodesis and an indwelling catheter is guided by lung re-expansion, performance status and expected prognosis.[3][7]
Disposition follows the cause and the patient's physiology. Outpatient management suits a stable transudate with a treatable cause and a small exudate under investigation. Inpatient management is required for drainage, sepsis, massive or tension effusion, haemothorax, diagnostic uncertainty, and significant comorbidity — pleural infection alone averages 14 days of hospitalisation.[17] Every patient needs a follow-up chest X-ray to document resolution, because a non-resolving effusion mandates reinvestigation.[4]
Special populations
In the elderly, heart failure, pneumonia and malignancy all rise with age, reserve is lower, and the incidence of pleural infection is increasing fastest in older adults with comorbidities — lower the threshold for inpatient management.[17] In pregnancy, a large or symptomatic effusion always needs a workup rather than reassurance, with heart failure, pulmonary embolism and infection the leading considerations.[14]
The immunocompromised are at risk for a broader spectrum of infection — bacterial, mycobacterial (including non-tuberculous), fungal and parasitic — and a wider differential for an exudative effusion, including tuberculosis at any CD4 count.[21] The anticoagulated patient needs the INR checked and corrected before thoracentesis, and a bloody effusion in an anticoagulated patient still needs investigation for malignancy and pulmonary embolism.[4]
In tuberculosis-endemic regions, pleural tuberculosis is one of the most frequent causes of a pleural exudate, and a lymphocyte-predominant exudate with a high ADA carries a positive predictive value of 98 per cent there; in low-prevalence areas the absence of both makes tuberculosis very unlikely and pleural biopsy is required to confirm the diagnosis — and to obtain culture and susceptibility testing where drug resistance is prevalent.[21] In asbestos-exposed populations, mesothelioma is the concern: diagnosis usually requires a pleural biopsy — image-guided or thoracoscopic — with loss of BAP1 or MTAP expression and homozygous CDKN2A deletion as the basic molecular markers, and pleural fluid cytology is least sensitive for it (pooled 28.9 per cent), so a cytology-negative effusion in an exposed patient is not reassurance.[11][20]
The evidence — BTS, MIST-2, TIME2
The British Thoracic Society Pleural Disease Guideline 2010 — Roberts on the malignant effusion, Hooper on investigation of a unilateral effusion, Davies on pleural infection — set the framework for contemporary practice.[3][4][5] Contemporary syntheses restate its algorithm: chest imaging with ultrasound first, thoracentesis interpreted through Light's criteria, then cause-directed fluid tests; drainage for the complicated parapneumonic collection (pH under 7.20, glucose under 60 mg/dL); antimicrobial therapy with anaerobic cover plus chest-tube drainage for pleural infection, escalating to surgery or intrapleural fibrinolytics on failure.[16][17]
The 2011 MIST-2 trial transformed loculated empyema: intrapleural tPA plus DNase, each given daily for three days, improved drainage, cut surgical referral and shortened hospital stay — neither agent alone works, and DNase alone is harmful.[6] The 2014 RAPID score then provided a validated three-month mortality risk score for pleural infection.[9]
For malignant effusion, TIME2 (2012) showed an indwelling pleural catheter gave dyspnoea relief equivalent to talc pleurodesis at 42 days (24.7 versus 24.4 mm on a visual-analogue scale) with better dyspnoea at six months, and IPC-Plus (2018) showed talc instilled through an existing IPC increased pleurodesis rates (43 versus 23 per cent at 35 days). Together they established IPC and talc pleurodesis as equivalent first-line options.[7][8][3]
The ERS 2024 statement on benign pleural effusions (Sundaralingam) synthesises the contemporary approach to a diagnostic approach to transudates, heart failure, hepatic hydrothorax, end-stage renal failure, benign asbestos-related effusion, post-surgical effusion and nonspecific pleuritis — and quantifies the burden: non-malignant effusions are at least three times more common than malignant ones and absorb 75 per cent of United States pleural-effusion resource allocation.[10]
The mantra, and the mnemonic
TRANSUDATE
- TTransudate versus exudate — Light's criteria decide (protein ratio over 0.5, LDH ratio over 0.6, or LDH over 200 U/L)
- RRight-sided when a heart-failure effusion is unilateral — but they are typically bilateral
- AAlbumin gradient over 1.2 g/dL, or NT-proBNP over 4000 ng/L, rescues a diuretic-confounded cardiac effusion
- NNever put a chest tube in hepatic hydrothorax — sodium restriction, diuretics, thoracentesis, TIPS or transplant
- SStony dull, reduced breath sounds, trachea AWAY — the effusion bedside sign
- UUltrasound every tap and every drain — it finds the loculated, septated collections
- DDrain a parapneumonic effusion with pH under 7.20, glucose under 60 mg/dL or frank pus
- AADA around 40 U/L in a lymphocytic effusion — tuberculous pleuritis (sensitivity 0.93)
- TtPA plus DNase, each daily for three days, for the loculated empyema that will not drain (MIST-2) — never either alone
- EEmpyema in three stages — exudative, fibropurulent, organised — and the drain escalates with them
The mantra: transudate or exudate decides everything — Light's criteria first, tap under ultrasound, drain when pH, glucose or pus demand it.[1]
[13] [15] [16] [6]Ward-round test — three stems, thirty seconds each
Stem 1 — the patient from the top of the topic (answer)ShowHide
The 68-year-old with two weeks of progressive dyspnoea, stony dull right base, trachea pushed left. CXR confirms a large right effusion. What is your next step, and what single result changes management most? Model: Confirm with ultrasound, then diagnostic thoracentesis under ultrasound guidance and apply Light's criteria. The single result that changes management most is the pH: a parapneumonic effusion with pH under 7.20 or glucose under 60 mg/dL is complicated and goes straight to a chest drain, because antibiotics alone will not resolve it; otherwise the transudate-exudate split and the fluid panel (cell count, Gram stain and culture, cytology, ADA, triglycerides) direct the cause hunt.[16][19][13]
Stem 2 — the loculated empyema that will not drain (answer)ShowHide
A 55-year-old with a parapneumonic effusion has a chest drain in place but remains febrile, and the drain output is poor. CT shows a multiloculated collection. What do you add, and what must you NOT add alone? Model: This is a loculated complicated parapneumonic effusion or empyema failing simple drainage. Add intrapleural tPA plus DNase, each daily for three days (MIST-2), which increased drainage, cut surgical referral from 16 to 4 per cent and shortened hospital stay by a mean of 6.7 days. Do not give DNase alone — MIST-2 showed it increased surgical referral to 39 per cent; do not give tPA alone either, as it was no better than placebo. Continue antibiotics covering community pathogens and anaerobes, and call thoracic surgery early for persistent sepsis despite standard measures.[6][17]
Stem 3 — the cirrhotic with a right effusion (answer)ShowHide
A 60-year-old with decompensated cirrhosis has a large right pleural effusion and tense ascites. The registrar wants to put a chest drain. What is the right call? Model: This is hepatic hydrothorax — a transudate tracking through diaphragmatic defects. Do NOT put a chest drain: a 17-patient series recorded complications in 16 — acute kidney injury in 11, pneumothorax in 7, empyema in 5 — with six deaths within three months. Treat with sodium restriction and diuretic therapy, offer therapeutic thoracentesis for symptomatic relief, and refer refractory disease for TIPS or liver transplantation, the only curative option — six of seven TIPS patients in that series survived.[12][26]
References28ShowHide
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