Anesthesia Toolbox Question:

Which of the following statements BEST describes a feature of hepatic blood flow?

A. Hepatic blood flow is primarily regulated by changes in response to hepatic metabolic activity  X

B. The hepatic artery compensates for changes in portal blood flow  ✔

C. The Portal vein supplies 75% of the liver’s blood flow and 25% of its oxygen  X

Read the discussion and key information below.

Discussion:

The liver receives a dual blood supply from the portal vein and the hepatic artery. The portal vein supplies 75% of the blood but only 50-55% of the liver’s oxygen requirement. The hepatic artery supplies only 25% of the blood volume but 45-50% of the oxygen. The normal hepatic blood flow is 1500cc/min and does represent between 20-30% of the total cardiac output. In a healthy liver, total blood flow is constantly maintained through intrinsic regulation called the hepatic arterial buffer response, which is the ability of the hepatic artery to produce compensatory flow changes in response to changes in portal venous flow. An increase in hepatic arterial blood flow is capable of buffering 25-60% of a decrease in portal flow. Portal blood flow is determined by the degree of vasoconstriction in the splanchnic arterioles. The hepatic artery can compensate for increases or decreases in portal venous flow. However, the portal venous system cannot compensate for changes in hepatic artery flow. This becomes significant with arterial hypotension or bleeding and decreased hepatic artery flow leading to hepatic dysfunction. The metabolic activity of hepatic parenchymal cells does not directly control the hepatic arterial flow.

Key Information:

The liver receives blood supply from the portal vein and hepatic artery. The portal vein supplies 75% of blood but only 50-55% of liver’s oxygen requirement. The hepatic artery supplies 25% of blood but only 45-50% of oxygen. The normal hepatic blood flow is 1500 cc/min and 20-30% of total cardiac output. The intrinsic regulation is maintained by autoregulation and the hepatic arterial buffer response (the ability for the hepatic artery to compensate for changes in portal blood flow).

References: 

Lautt WW. Hepatic vasculature: a conceptual review. Gastroenterology. 1977;73(5):1163-9. PMID 332580

Eipel C, Abshagen K, Vollmar B. Regulation of hepatic blood flow: the hepatic arterial buffer response revisited. World of Gastroenterology. 2010; 16(48): 6046-6057. PMID 21182219

Hepatic and GI physiology and Anesthesia consideration – (videocast Randy Schell)

Mackey, D. C., Butterworth, J. F., Mikhail, M. S., Morgan, G. E., & Wasnick, J. D. (2013). Morgan & Mikhail's clinical anesthesiology (5th ed.). New York, N.Y.: McGraw-Hill Education LLC.

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