Liver or Hepatic Anatomy and Physiology for anesthesiology

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The anesthesiologist's most critical aspect of liver anatomy is its blood supply. 

The liver derives its blood supply from the hepatic artery and portal vein. These two blood vessels receive about 20%–25% (≈1500 mL/min) of cardiac output. 

The hepatic artery provides approximately 25% of the blood flow to the liver, with the portal vein providing the remaining 75%. 

The portal vein receives blood specifically from the stomach, intestines, pancreas, and spleen and carries it into the liver through the porta hepatis. While there may be some variations between individuals, the hepatic portal vein is usually formed by the convergence of the superior mesenteric vein and the splenic vein, referred to as the splenic-mesenteric confluence.

The hepatic artery arises from the common hepatic artery, a branch of the celiac artery. It runs alongside the portal vein and the common bile duct to form the portal triad. 

Owing to the difference in oxygen content of portal venous blood compared to hepatic artery blood, about half of the liver’s oxygen supply is derived from the portal vein and half from the hepatic artery. 

When portal vein blood flow decreases, there is a corresponding increase in hepatic artery blood flow. It is thought that this effect is due to locally produced adenosine that accumulates in low-flow states, causing arterial vasodilation and thus increasing hepatic artery blood flow. This physiologic response is critical in maintaining relatively constant blood flow and adequate oxygen supply to the liver. 

Blood exits the liver from the hepatic veins.

Typically blood travels from the portal vein through the low-resistance hepatic sinusoids into the hepatic veins, then into the vena cava and finally into the right atrium. In a healthy liver, the portal venous pressure is generally only 1–5 mm Hg higher than the hepatic veins. This pressure difference is the driving force of blood flow through the liver. In cirrhosis, fibrosis causes an increase in intrahepatic vascular resistance and thus impedes blood flow through the liver. This creates higher portal pressures. 

Reference: Stoelting's Anesthesia and Co-Existing Disease: 7th edition 

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