Measurement of hepatic tissue hypoxia using near infrared spectroscopy: Comparison with hepatic vein oxygen partial pressure

Hepatic hypoxia occurs during liver surgery and transplantation. The critic al level associated with irreversible hepatocellular damage is unknown. Mea surement of hepatic tissue oxygenation and hepatic vein oxygen partial pres sure (HVPO2) reflects oxygen supply and consumption. Near infrared spectros copy (NIRS) can be used to monitor hepatic oxyhaemoglobin (HbO(2)), deoxyha emoglobin (Hb) and cytochrome oxidase (Cyt Ox) oxidation. This study compar ed regional hepatic tissue oxygenation (HbO2, Hb and Cyt Ox) using NIRS wit h HVPO2. The use of tissue oxygenation measured by NIRS and HVPO2 as indica tors of hepatic tissue hypoxia was also investigated. Large Landrace pigs ( n = 5) underwent laparotomy and liver exposure. Systemic and hepatic haemod ynamics were monitored continuously. NIRS probes were placed on the liver t o record continuously HbO(2), Hb and Cyt Ox. Graded hypoxaemia was achieved by stepwise reduction of the fraction of inspired oxygen (FiO(2)) from 30% (baseline) to 4%, A significant decrease in hepatic arterial blood flow an d total hepatic blood flow was seen with severe hypoxaemia while there was no significant change to portal vein blood flow. Oxygen partial pressures i n the hepatic artery, portal vein and hepatic vein decreased progressively with all grades of hypoxaemia. There was an immediate reduction of hepatic HbO(2) and simultaneous increase in hepatic Hb with all grades of hypoxaemi a. Hepatic Cyt Ox was reduced significantly only with FiO(2) less than or e qual to 10%. A significant correlation (p < 0.001) was found between the ch anges in hepatic oxygenation parameters measured by NIRS and HVPO2. HVPO2 m easurement did not predict the reduction in intracellular tissue oxygenatio n demonstrated by NIRS with a decrease of Cyt Ox oxidation. In conclusion t here was a good correlation between the tissue oxygenation parameters measu red by NIRS and HVPO2. However, the reduction of intracellular oxygenation found with severe hypoxaemia was demonstrated only by NIRS. Copyright (C) 2 000 S. Karger AG, Basel.