Transvenous Pressure Measurements and Liver Biopsy

Clinical Relevance

Chronic inflammation of the liver results in hepatic fibrosis and leads ultimately to cirrhosis. Portal hypertension is the hallmark of liver cirrhosis and is defined as a portal pressure gradient (pressure gradient between portal vein and inferior vena cava [IVC]) of greater than 5 mmHg. The portal pressure gradient is considered clinically significant when greater than 10 mmHg. Portal hypertension is classified as prehepatic, hepatic, or posthepatic, depending on the anatomical site of flow impedance. The most commonly encountered etiologies of cirrhosis, such as excess alcohol consumption and viral hepatitis, lead to fibrosis at the level of the hepatic sinusoids and subsequently hepatic portal hypertension. Portal hypertension leads either directly or indirectly to most clinical sequelae of cirrhosis except jaundice.

The hepatic venous pressure gradient (HVPG) is considered the gold standard for evaluating the portal pressure gradient in cirrhotic patients with hepatic portal hypertension. HVPG is the difference between wedged hepatic venous pressure and the free hepatic venous pressure (FHVP). The HVPG correlates closely with stage and outcomes in cirrhosis and accurately predicts mortality. HVPG also plays a role in preoperative screening for liver resection and monitoring response to medical treatments.

Indications

• Diagnosis and classification of portal hypertension

• Assessment of severity and prognostication

• Assessment of response of portal hypertension to pharmacological therapy (β-blockers)

• Preoperative assessment of cirrhotic patients before surgical resection

• Monitoring response of portal hypertension to transjugular intrahepatic portosystemic shunt

Contraindications

There are no absolute contraindications to HVPG measurement. However, occluded hepatic veins (e.g., patients with Budd-Chiari syndrome) will prevent access to the hepatic venous system. Uncontrolled coagulopathy should be corrected. If the patient is allergic to iodinated contrast media, CO ₂ can be used for venography.

Equipment

• Vascular sheath 6–8 F

• Multipurpose catheter

• 0.035-inch hydrophilic and J- or straight-tip standard wire

• End-hole or occlusion balloon catheter

• Pressure transducers and monitors

Technique

Access to the hepatic venous system is typically via a right internal jugular vein puncture. However, common femoral or antecubital vein approaches are possible. Measurements are performed after catheterization of the right or middle hepatic veins.

Wedged hepatic venous pressure may be measured in two ways. First, an end-hole catheter should be advanced as far as possible into a hepatic vein until it wedges in the vessel lumen. Alternatively, a balloon-tip catheter can be used, with inflation of the balloon in the hepatic vein to occlude the lumen. Occlusion of the hepatic vein is confirmed by slow injection of contrast, which demonstrates static flow without reflux of contrast or washout via collateral flow to other hepatic veins. With a wedged end-hole catheter, parenchymal blush and reflux into the portal system can be seen. The balloon catheter technique is more reproducible and accurate because it averages pressure over a larger volume of hepatic parenchyma. ^{, ,}

Free hepatic venous pressure is the pressure recorded within the hepatic veins. Catheter position (proximal/distal) within the hepatic vein affects the measured FHVP due to flow interference by the catheter. Consequently, FHVP should be measured close to the hepatic venous confluence within 1 to 3 cm of the IVC. When using a balloon catheter, the balloon must be deflated. IVC pressure should then be recorded at the level of the hepatic venous confluence. A pressure difference of greater than 1 to 2 mmHg between the FHVP and IVC pressure implies inadequate catheter position or hepatic vein obstruction, and pressure measurements should be repeated.

Measured hepatic venous pressures are affected by the relative position of transducers to the heart. In view of this, transducers should be positioned at the level of the right atrium (midaxillary line). Pressure transducers must be “zeroed” to air and an appropriate scale for venous pressure measurements selected on the monitoring device such that pressure tracings are well visualized. Pressure tracings should be allowed to stabilize over at least 60 seconds before the pressures are recorded. Pressure measurements should be repeated two to three times and an average measurement obtained. Marked variability in recorded pressures is likely to reflect measurement error. Deep sedation and general anesthesia affect the accuracy of HVPG measurements and tend to underestimate the awake value. Therefore, hepatic venous pressure measurements should be obtained using local anesthesia and conscious sedation only.

There is debate in the literature as to whether HVPG should be calculated using the FHVP or IVC/right atrial pressures. Most authors recommend using the FHVP measured close to the hepatic venous confluence. Rossle et al. found relative obstruction of the hepatic vein by the measuring catheter resulted in inaccurate FHVP measurements, a problem compounded by narrow hepatic veins encountered in cirrhotic livers. These authors recommend that HVPG is calculated from either IVC or right atrial pressure. However, measurement of IVC and right atrial pressure also suffer from significant potential limitations. Accurate measurement of IVC pressure can be technically challenging because measurement of pressures just a few centimeters above or below the level of the hepatic venous confluence can cause significant measurement error due to transmitted intraabdominal pressure and caudate lobe hypertrophy. Accuracy of HVPG when calculated from the right atrial pressure measurements has also been questioned because changes in intraabdominal pressure in the presence of ascites and obesity may affect the portoatrial pressure gradient but not the portohepatic pressure gradient.

Complications

Complications after transvenous hepatic pressure measurements are uncommon and are usually minor. Puncture site complications may occur but are typically limited to hematoma and pain. Self-limiting arrythmias may be encountered when passing a catheter across the right atrium.

Postprocedure and Follow-up Care

A short period of bed rest is recommended after the venous puncture and conscious sedation (if used) as per institutional preference.