No abstract

Hepatic hypoxia occurs during liver surgery and transplantation. The critical level associated with irreversible hepatocellular damage is unknown. Measurement of hepatic tissue oxygenation and hepatic vein oxygen partial pressure (HVPO₂) reflects oxygen supply and consumption. Near infrared spectroscopy (NIRS) can be used to monitor hepatic oxyhaemoglobin (HbO₂), deoxyhaemoglobin (Hb) and cytochrome oxidase (Cyt Ox) oxidation. This study compared regional hepatic tissue oxygenation (HbO₂, Hb and Cyt Ox) using NIRS with HVPO₂. The use of tissue oxygenation measured by NIRS and HVPO₂ as indicators of hepatic tissue hypoxia was also investigated. Large Landrace pigs (n = 5) underwent laparotomy and liver exposure. Systemic and hepatic haemodynamics were monitored continuously. NIRS probes were placed on the liver to record continuously HbO₂, Hb and Cyt Ox. Graded hypoxaemia was achieved by stepwise reduction of the fraction of inspired oxygen (FiO₂) from 30% (baseline) to 4%. A significant decrease in hepatic arterial blood flow and total hepatic blood flow was seen with severe hypoxaemia while there was no significant change to portal vein blood flow. Oxygen partial pressures in the hepatic artery, portal vein and hepatic vein decreased progressively with all grades of hypoxaemia. There was an immediate reduction of hepatic HbO₂ and simultaneous increase in hepatic Hb with all grades of hypoxaemia. Hepatic Cyt Ox was reduced significantly only with FiO₂ ≤10%. A significant correlation (p < 0.001) was found between the changes in hepatic oxygenation parameters measured by NIRS and HVPO₂. HVPO₂ measurement did not predict the reduction in intracellular tissue oxygenation demonstrated by NIRS with a decrease of Cyt Ox oxidation. In conclusion there was a good correlation between the tissue oxygenation parameters measured by NIRS and HVPO₂. However, the reduction of intracellular oxygenation found with severe hypoxaemia was demonstrated only by NIRS.

This study shows the potential of monitoring the degree of I/R injury by measuring hepatic tissue intracellular oxygenation.