Malignant Ascites

Malignant ascites is an abnormal accumulation of peritoneal fluid caused by cancer, through peritoneal carcinomatosis, liver metastases, portal vein involvement or lymphatic obstruction. It causes distension, discomfort, breathlessness and anorexia, and indicates advanced disease with a median survival of 1 to 4 months.

It accounts for about 10% of ascites. The commonest cancers are ovarian (about 35%), pancreatic, gastric, colorectal, breast, endometrial and hepatocellular carcinoma. Up to 15% to 50% of patients with advanced intraperitoneal cancer develop it, and the cause is unknown in about 20% of cases.

Pathophysiology. Peritoneal carcinomatosis increases vascular permeability through VEGF and other factors, and tumour obstruction of subdiaphragmatic lymphatics reduces drainage (peritoneal type, SAAG under 11 g/L). Liver metastases or portal vein thrombosis cause portal hypertension (SAAG 11 g/L or more), and some patients have a mixed picture with coexistent cirrhosis.

• Progressive abdominal distension and weight gain with loss of muscle mass.
• Abdominal pain, early satiety, nausea, vomiting, constipation and heartburn.
• Dyspnoea, reduced mobility, lower limb oedema, hernia and scrotal or vulval oedema.

Red flags.

• Fever or abdominal tenderness (infected ascites).
• Respiratory distress from tense ascites, renal impairment or hypotension.

• Ultrasound to confirm ascites and guide paracentesis; contrast CT for the cause (primary tumour, peritoneal nodules, liver metastases, portal vein thrombosis).
• Diagnostic paracentesis: cell count and differential, culture, albumin (with serum albumin for the gradient), protein (over 25 g/L in peritoneal carcinomatosis), LDH, cytology with a cell block (sensitivity about 97% in peritoneal carcinomatosis), CEA. Triglycerides if chylous.
• Serum urea, creatinine, electrolytes, liver tests, albumin and clotting.
• Laparoscopic biopsy if cytology is negative and cancer is suspected.

Differential diagnosis.

• Cirrhotic ascites, portal vein thrombosis and Budd-Chiari syndrome
• Heart failure, nephrotic syndrome and constrictive pericarditis
• Tuberculous peritonitis and pancreatic ascites
• Chylous ascites from lymphoma

Treatment relieves symptoms in line with prognosis and patient wishes.

Paracentesis. Therapeutic paracentesis gives rapid relief and is the main treatment for peritoneal type ascites.

Remove up to 5 L at a time (larger volumes if the patient is stable), with albumin for volumes over 5 L.

• Dose: albumin 20% 6 to 8 g for each litre of ascites removed, given IV over 1 to 2 hours during or immediately after paracentesis of more than 5 L. Maximum 100 g in one session.
• Monitoring: blood pressure, creatinine, sodium, signs of fluid overload.
• Adjustment: omit for small volume paracentesis in non-cirrhotic ascites, reduce in heart failure, give for any volume when cirrhosis and renal impairment coexist.

Diuretics. Useful for ascites with portal hypertension (SAAG 11 g/L or more); little benefit in peritoneal carcinomatosis.

Spironolactone 100 mg orally once daily in the morning, increased every 3 to 5 days by 100 mg to 400 mg daily. Add furosemide 40 mg orally once daily, increased in parallel to 160 mg daily. Use for ascites with portal hypertension (serum ascites albumin gradient 11 g/L or more). The maximum is spironolactone 400 mg and furosemide 160 mg daily.

Monitoring:

• sodium, potassium, creatinine and weight (target loss of 0.5 kg daily without oedema and 1 kg daily with oedema) every 3 to 5 days at first
• blood pressure

Adjustment:

• stop for sodium under 125 mmol/L, potassium over 6 mmol/L, a creatinine rise of over 50%, or encephalopathy
• reduce the dose for gynaecomastia (use amiloride) or cramps
• avoid NSAIDs

Indwelling drains. A tunnelled peritoneal catheter allows home drainage (for example 1 to 2 L each day or on alternate days) in patients with recurrent ascites and expected survival of weeks to months. Risks are infection, catheter blockage and protein loss.

Cancer directed therapy. Systemic chemotherapy or targeted therapy for chemosensitive tumours (ovarian, breast, lymphoma, germ cell). Selected patients have heated intraperitoneal chemotherapy or cytoreduction.

Other measures. Dietary advice (small frequent meals), sodium restriction only in portal hypertension, treatment of nausea and constipation, and thromboprophylaxis.

Enoxaparin 40 mg subcutaneously once daily is given for thromboprophylaxis during active disease and for 4 weeks after surgery (therapeutic dosing of 1 mg/kg twice daily if thrombosis is established). The maximum is 40 mg daily for prophylaxis.

Monitoring:

• platelet count at baseline and every 2 to 4 weeks
• creatinine
• signs of bleeding
• anti-Xa level in obesity or renal impairment

Adjustment:

• 20 mg daily when creatinine clearance is under 30 mL/min
• hold for platelets under 50 x 10^9/L or active bleeding
• time the dose at least 12 hours before and 4 hours after a neuraxial procedure

Monitoring. Weight, abdominal girth, renal function and electrolytes after paracentesis or diuretic therapy. Catheter site checks and prompt treatment of peritonitis.

Referral and escalation.

• Referral to oncology and palliative care for symptomatic ascites.
• Same day assessment for suspected peritonitis, haemodynamic instability or acute kidney injury.

Special groups.

• Cirrhosis with malignancy: manage diuretics and albumin with hepatology input.
• Frail or end-of-life patients: tunnelled catheter and community nursing support.
• Pregnancy: individualised management with obstetric and oncology teams.