Ascites and peritoneal disease: Viva

Branch 1: Recognising and classifying the ascites

The candidate should recognise that progressive abdominal distension with shifting dullness and a fluid thrill in a child with biliary atresia is ascites, and that its appearance marks the transition from compensated to decompensated cirrhosis. The key first investigation is ascitic fluid analysis, and the key calculation is the serum-ascites albumin gradient. A strong candidate would explain that the gradient is calculated by subtracting the ascitic albumin from the serum albumin, and that a gradient of 11 g per litre or more indicates portal hypertension. ^[2]

If the examiner presses on the significance, the candidate should explain that the gradient correctly classifies the cause in over 97 per cent of cases and has replaced the older transudate-exudate concept based on total protein. In this child, with underlying biliary atresia, the gradient should be 11 g per litre or more, confirming portal-hypertensive, cirrhotic ascites. The candidate should also send the fluid for cell count, culture, and total protein, and should request an abdominal ultrasound with Doppler to assess the liver architecture, portal vein patency, and splenomegaly. ^[2]

A strong candidate would acknowledge that while cirrhosis is the most likely cause, the gradient and the fluid analysis are what separate cirrhosis from cardiac ascites, Budd-Chiari syndrome, and the non-portal causes such as nephrotic syndrome and tuberculosis. This is why ascitic fluid analysis is never optional, even when the diagnosis seems obvious. ^[1]