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Pleural effusion
Is it a transudate, an exudate — or pus? Most bilateral effusions in heart failure don't need a tap. A unilateral or unexplained effusion does: an ultrasound-guided sample, sent for the right tests, gives you the answer. Built for revision, not live patient decisions.
Settle them, and check the basics
how breathless? is it pus?Red flags — what each should make you think
Use ultrasound before every pleural procedure. Blind taps cause pneumothoraces and liver and spleen injuries. And if the patient has heart failure with bilateral effusions, treat the heart failure first: tap only if it's atypical (unilateral, febrile, pleuritic pain, or not responding).
First actions
- O₂Oxygen to target
- USSBedside ultrasound
- 💉Diagnostic tap if unexplained
- 🚰Therapeutic aspiration if breathless
- ☎Respiratory team
Understand the patient — transudate or exudate
Light's criteriaLight's criteria — exudate if any one is met
- Pleural fluid protein / serum protein above 0.5
- Pleural fluid LDH / serum LDH above 0.6
- Pleural fluid LDH above two-thirds of the upper limit of normal for serum LDH
Send a serum protein and LDH at the same time as the tap.
Causes
- Transudates — heart failure, cirrhosis (hepatic hydrothorax), nephrotic syndrome, hypoalbuminaemia, hypothyroidism, peritoneal dialysis
- Exudates — parapneumonic/empyema, malignancy (lung, breast, lymphoma, mesothelioma), TB, PE, rheumatoid/SLE, pancreatitis, drugs
What the fluid tells you
- pH below 7.2 (in suspected infection) → complicated parapneumonic effusion → chest drain
- Frank pus → empyema → drain
- Blood-stained → malignancy, PE, trauma; haematocrit above 50% of blood → haemothorax
- Low glucose → infection, rheumatoid, malignancy, TB
- Lymphocytes → TB, malignancy; milky → chylothorax
Work A–E — assess and act as you go
The diagnoses you must not miss
tap to open eachWhat points toward it, what would rule it in, and how to manage it.
Pneumonia not improving, persistent fever, rising CRP, effusion.
USS-guided tap: pus, positive Gram stain/culture, or pH below 7.2.
Chest drain, IV antibiotics with anaerobic cover; respiratory; consider intrapleural therapy or surgery if not draining.
Trauma, procedures, anticoagulation, falling Hb.
CXR/USS, tap haematocrit, CT.
Large-bore drain, resuscitation, reverse anticoagulation, cardiothoracic review.
Severe breathlessness, whole hemithorax opaque, shift away.
CXR, USS, cytology.
Therapeutic aspiration (about 1.5 L), then definitive plan: indwelling pleural catheter or pleurodesis; oncology.
Cough, breathlessness, hypoxia after rapid large-volume drainage.
Clinical, CXR.
Stop drainage, oxygen, supportive care. Prevent it: limit volume removed, stop if symptoms appear.
Investigate — what to order, when, and what it tells you
test with a question in mindUltrasound
Pleural fluid
Bloods
Imaging
How the plan comes together
disposition · handoveroutpatient
Small stable effusion with an obvious cause (e.g. treated HF), or after diagnostic tap with results to follow and urgent respiratory clinic follow-up.
admit
Empyema, haemothorax, large symptomatic effusion, drain needed, or significant underlying illness.
Hand over: tap results, drain status, volume removed, plan.
Ultrasound first, tap the unexplained effusion, send paired serum tests, and check the pH whenever infection is possible. A pH below 7.2 means a drain. Nicely done getting here.
Clerking template
copy or downloadPleural effusion — documentation structure
A structure and prompt list to help you document and think systematically. It is not a completeness check and cannot guarantee nothing is missed — use your trust's own proforma, your seniors, and your clinical judgement.
Test yourself
active recallCover the answer, say it out loud, then reveal. Retrieval beats re-reading.
0 / 10 knownFrequently asked questions
quick answersWhat are the red flags for pleural effusion?
- Fever + effusion + sepsis — think empyema
- Pleural pH below 7.2 — think complicated parapneumonic — drain
- Trauma or anticoagulated, blood on tap — think haemothorax
- Massive effusion, mediastinal shift — think urgent therapeutic drainage
- Weight loss, smoker, asbestos — think malignancy / mesothelioma
- Breathless after draining a lot — think re-expansion pulmonary oedema
What is the initial management of pleural effusion?
- Oxygen to target — sit up
- Bedside ultrasound — size, septations, safe site
- Diagnostic tap if unexplained — protein, LDH, pH, glucose, cytology, MC&S
- Therapeutic aspiration if breathless — remove no more than about 1.5 L at a time
- Respiratory team — empyema, malignant or recurrent effusions
Always alongside senior support and your local guideline.
What diagnoses must you not miss in pleural effusion?
- Empyema / complicated parapneumonic effusion — fever won't settle
- Haemothorax — trauma · anticoagulated
- Massive / malignant effusion — mediastinal shift
- Re-expansion pulmonary oedema — after drainage
Open each one in the must-not-miss section for what points toward it, how to rule it in, and how to manage it.
What investigations should a junior doctor order for pleural effusion?
- Ultrasound — Before any pleural procedure.
- Pleural fluid — Protein, LDH (with serum), pH (blood gas analyser), glucose.
- Bloods — Serum protein, LDH.
- Imaging — Size, shift.
Admit or discharge: how is the plan decided for pleural effusion?
- Outpatient — Small stable effusion with an obvious cause (e.g. treated HF), or after diagnostic tap with results to follow and urgent respiratory clinic follow-up.
- Admit — Empyema, haemothorax, large symptomatic effusion, drain needed, or significant underlying illness.
Is there a clerking template for pleural effusion?
Yes — there is a clerking template for pleural effusion on this page, structured as presenting complaint, red flags asked, history, examination (A–E), investigations, differentials, plan and escalation. You can copy it or download it as a Word document. Jump to the template.
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