A 48-year-old woman with hepatitis C virus (HCV) infection and biopsy-proven cirrhosis (Child-Pugh Class B) presents with progressive abdominal distension, ankle swelling, and a 3 kg weight gain over 2 weeks. On examination, she has shifting dullness, hepatomegaly, and a serum albumin of 2.9 g/dL. Abdominal ultrasound shows ascites and no focal lesions. Ascitic fluid analysis reveals: total protein 1.2 g/dL, SAAG 1.8 g/dL, cell count 150 WBC/μL (85% lymphocytes), and negative bacterial culture. Which of the following best explains the mechanism of ascites formation in this patient?

Explanation

## Mechanism of Ascites in Cirrhosis **Key Point:** Ascites in cirrhosis results from **portal hypertension** combined with **renal sodium retention** (secondary to splanchnic vasodilatation and activation of RAAS/SNS), NOT from infection or acute inflammation. ### Pathophysiology: The Underfilling Hypothesis ```mermaid flowchart TD A[Cirrhosis with fibrosis]:::outcome --> B[Increased intrahepatic resistance]:::outcome B --> C[Portal hypertension]:::outcome C --> D[Sinusoidal hypertension]:::outcome D --> E[Splanchnic arteriolar vasodilatation]:::outcome E --> F[Decreased effective arterial blood volume]:::outcome F --> G[Activation of RAAS and SNS]:::action G --> H[Renal sodium and water retention]:::action H --> I[Ascites formation]:::outcome C --> J[Increased capillary hydrostatic pressure]:::outcome J --> I K[Decreased plasma oncotic pressure<br/>from hypoalbuminaemia]:::outcome --> I ``` ### Key Features Supporting This Diagnosis | Feature | Interpretation | |---------|----------------| | **SAAG 1.8 g/dL** | >1.1 g/dL = portal hypertension (cirrhosis). SAAG correlates with portal pressure gradient. | | **Low ascitic protein (1.2 g/dL)** | Transudative ascites typical of portal hypertension, NOT exudative (which would suggest infection or malignancy). | | **Low WBC (150/μL)** | Rules out spontaneous bacterial peritonitis (SBP), which requires ≥250 PMN/μL. Lymphocyte predominance is typical of cirrhotic ascites. | | **Negative culture** | No bacterial infection. | | **Low serum albumin (2.9 g/dL)** | Reflects hepatic synthetic dysfunction and contributes to decreased plasma oncotic pressure. | | **Shifting dullness + ankle swelling** | Clinical signs of fluid overload from sodium retention. | **High-Yield:** The **SAAG** (Serum-Ascites Albumin Gradient) is the gold standard for determining the cause of ascites: - SAAG ≥1.1 g/dL = portal hypertension (cirrhosis, Budd-Chiari, portal vein thrombosis) - SAAG <1.1 g/dL = non-portal hypertensive causes (peritoneal carcinomatosis, tuberculosis, nephrotic syndrome) **Mnemonic: RAAS in Cirrhosis — "SALTY"** - **S**planchnic vasodilation - **A**ctivation of RAAS - **L**ow effective blood volume - **T**ubular sodium reabsorption - **Y**ield = ascites ### Clinical Pearl The patient's **gradual onset** (2 weeks) and **transudative profile** (low protein, low WBC, negative culture) confirm portal hypertension as the cause, NOT acute infection or malignancy. [cite:Robbins 10e Ch 18; Harrison 21e Ch 297]