Malignant ascites and pleural effusion — Rapid

Synopsis

Identify cancer-related peritoneal or pleural fluid without overlooking infection, thrombosis, heart, liver or renal disease, obtain safe diagnostic samples and select therapeutic drainage, pleurodesis, indwelling catheter, diuretic and tumour treatment by physiology and recurrence pattern.

Malignant fluid is a clinical-pathological diagnosis: cancer can coexist with heart failure, cirrhosis, infection, pulmonary embolism, renal disease or treatment toxicity.
First-line imaging for a suspected pleural or abdominal collection is ultrasound because it confirms fluid, estimates distribution and makes aspiration safer.
All pleural procedures should use contemporaneous thoracic ultrasound by a trained operator; never rely on a historic skin mark after position changes.
A first unexplained pleural effusion usually needs ultrasound-guided diagnostic aspiration for protein, LDH, pH when infection is possible, glucose, cell count, culture and cytology.
Pleural fluid meeting Light’s criteria is exudative, but this does not prove malignancy; cytology sensitivity varies substantially by tumour type.
If cytology is negative and suspicion remains, contrast CT and image-guided or thoracoscopic pleural biopsy provide the reference tissue diagnosis rather than repeated low-yield fluid samples.
A first or atypical ascites presentation needs diagnostic paracentesis for cell count, culture, albumin, total protein and cytology, with additional tests guided by pancreatic, chylous or urinary suspicion.
A serum–ascites albumin gradient of at least 11 g/L supports portal-hypertensive physiology and predicts a better chance of response to spironolactone-based diuresis.
First-line relief of tense symptomatic malignant ascites is ultrasound-guided therapeutic paracentesis, stopping or slowing for pain, hypotension or physiological deterioration.
Routine albumin replacement after malignant-ascites drainage is not supported in the same way as cirrhotic large-volume paracentesis; individualise for mixed portal disease and circulatory risk.
For repeatedly recurrent malignant ascites, a tunnelled peritoneal catheter can allow smaller home drainage and reduce hospital procedures when patient and carers can manage it.
For recurrent symptomatic malignant pleural effusion with expandable lung, offer a choice of indwelling pleural catheter or talc pleurodesis based on admission, preference and treatment goals.
For non-expandable lung, an indwelling pleural catheter is usually preferred because pleurodesis requires visceral and parietal pleura to appose.
During one pleural aspiration, drain slowly and generally no more than 1.5 litres, stopping for chest tightness, pain, persistent cough, hypotension or worsening breathlessness.

Key red flags

Marked respiratory distress, new oxygen need, hypotension or tracheal and mediastinal shift with a large pleural collection requires same-day specialist drainage assessment.

Fever, pleuritic pain, pus, pleural-fluid pH at or below the guideline drainage threshold or loculation suggests pleural infection requiring antibiotics and chest drainage.

Abdominal guarding, rebound, fever, lactate rise or free gas suggests perforation, ischaemia or secondary peritonitis rather than uncomplicated malignant ascites.

Sudden pleuritic pain, haemoptysis or disproportionate hypoxaemia can indicate pulmonary embolism even when a pleural effusion is visible.

Oliguria, hypotension, acute kidney injury or severe hyponatraemia after large-volume drainage requires circulatory, fluid and medicine reassessment.

A unilateral exudative effusion, pleural thickening or recurrent bloody fluid without secure pathology needs tissue diagnosis rather than repeated symptom-only aspiration.

New leakage, erythema, tunnel pain, cloudy fluid or failure to drain from an indwelling catheter requires prompt obstruction and infection evaluation.

Pleural infection

Fever, pleuritic pain, purulent fluid, loculation or low fluid pH with sepsis requires antibiotics and urgent drain pathway.

Investigation priorities

First-line pleural or abdominal ultrasoundFirst stepFirst line

Confirm fluid, depth, septation, solid disease and a safe contemporary path for aspiration or catheter placement.

Management branches

New pleural effusionSample safely, then secure tissue when needed

A new unilateral or otherwise unexplained pleural collection occurs in a patient with possible cancer.

Assess respiratory stability, infection and thromboembolic features and obtain chest imaging and contemporaneous thoracic ultrasound before any needle procedure.
Perform ultrasound-guided aspiration for biochemistry, culture and cytology and use contrast CT to map pleural, lung and nodal targets.
If cytology is non-diagnostic and suspicion remains, obtain image-guided core or thoracoscopic biopsy with sufficient material for lineage and molecular testing.

Key medicines

Spironolactone-based diuresis for selected ascitesWhen portal-hypertensive physiology is likely, start spironolactone commonly at 100 mg orally each morning, adding furosemide 40 mg daily if needed and titrating cautiously to weight, symptoms, renal function and electrolytes.Monitor potassium, sodium, creatinine, pressure and daily weight; stop or reduce for hypotension, renal injury, severe sodium change or potassium disturbance and review interacting renin–angiotensin medicines.

Sterile graded talc pleurodesisGive 4 g sterile graded talc as slurry through a correctly positioned chest drain or by thoracoscopy under the specialist pleural protocol after confirming adequate lung apposition.Provide analgesia, discuss fever and pain and avoid ungraded talc; pleurodesis is unlikely to succeed with substantial non-expandable lung or uncontrolled pleural infection.

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