Assessment of hepatic ischaemia reperfusion injury by measuring intracellular tissue oxygenation using near infrared spectroscopy.

AIMS/BACKGROUND: Hepatic ischaemia/reperfusion (I/R) injury is a major cause of liver damage during liver surgery and transplantation. The relationship between the severity of I/R injury and the degree of intracellular hypoxia has not been investigated. METHODS: New Zealand white rabbits were used in 4 groups (n=6 each). At laparotomy, left lobe hepatic ischaemia was produced for 30, 45, or 60 min followed by 60 min reperfusion and compared with controls. Liver function, bile flow, and flow in the hepatic microcirculation (HM) were measured. Near infrared spectroscopy (NIRS) was used to monitor hepatic oxyhaemoglobin (HbO2), deoxyhaemoglobin (Hb), and cytochrome oxidase (Cyt Ox). RESULTS: I/R injury produced deranged liver function tests, reduced bile flow, and reduced flow in the microcirculation in comparison with controls. During ischaemia, HbO2 and Cyt Ox were significantly reduced in comparison with controls. After reperfusion, a biphasic change in tissue oxygenation was observed, with an initial increase in HbO2 and Cyt Ox followed by a progressive reduction. The reduction in tissue oxygenation with ischaemia and reperfusion paralleled the ischaemia time. After I/R, the changes in Cyt Ox (intracellular oxygenation) significantly correlated with the parameters of hepatocellular injury to a higher degree than HbO2 (extracellular oxygenation). CONCLUSION: This study shows the potential of monitoring the degree of I/R injury by measuring hepatic tissue intracellular oxygenation.

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 critical level associated with irreversible hepatocellular damage is unknown. Measurement of hepatic tissue oxygenation and hepatic vein oxygen partial pressure (HVPO(2)) reflects oxygen supply and consumption. Near infrared spectroscopy (NIRS) can be used to monitor hepatic oxyhaemoglobin (HbO(2)), deoxyhaemoglobin (Hb) and cytochrome oxidase (Cyt Ox) oxidation. This study compared regional hepatic tissue oxygenation (HbO(2), Hb and Cyt Ox) using NIRS with HVPO(2). The use of tissue oxygenation measured by NIRS and HVPO(2) 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 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 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 HbO(2) and simultaneous increase in hepatic Hb with all grades of hypoxaemia. Hepatic Cyt Ox was reduced significantly only with FiO(2) < or =10%. A significant correlation (p<0.001) was found between the changes in hepatic oxygenation parameters measured by NIRS and HVPO(2). HVPO(2) 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 HVPO(2). However, the reduction of intracellular oxygenation found with severe hypoxaemia was demonstrated only by NIRS.

Effect of graded hypoxia on hepatic tissue oxygenation measured by near infrared spectroscopy.

BACKGROUND/AIMS: In liver transplantation ischaemia-reperfusion injury of the graft reduces hepatic tissue oxygenation which has prognostic value for patient survival. Near infrared spectroscopy (NIRS) can measure extracellular (haemoglobin oxygenation) and intracellular tissue oxygenation (cytochrome oxidase oxidation). However, it has not been validated for measuring hepatic tissue oxygenation in an experimental model with graded hypoxia. METHODS: New Zealand White rabbits (2.9+/-0.3 kg, n=9) underwent laparotomy for liver exposure. Heart rate, blood pressure, temperature, arterial blood pH and blood gas partial pressures were monitored during the experiments. Near infrared spectroscopy probes were placed on the liver surface to record continuously hepatic oxyhaemoglobin, deoxyhaemoglobin and cytochrome oxidase oxidation. Graded hypoxia was achieved by stepwise reduction of the inspired oxygen from 15 to 4%. During recovery from hypoxia 30% oxygen was administered. RESULTS: There was an immediate reduction of hepatic oxyhaemoglobin with hypoxia and a simultaneous increase of hepatic deoxyhaemoglobin. Hepatic oxyhaemoglobin showed a positive correlation with arterial oxygen pressure (r=0.77, p<0.001). Hepatic deoxyhaemoglobin showed a negative correlation with arterial oxygen pressure (r=-0.75, p<0.001). Hepatic cytochrome oxidase decreased significantly with an inspired oxygen of 10% or less and showed a positive correlation with arterial oxygen pressure (r= 0.90, p<0.001). CONCLUSIONS: Near infrared spectroscopy is an effective method for monitoring hepatic extracellular and intracellular tissue oxygenation.

Changes in tissue oxygenation of the porcine liver measured by near-infrared spectroscopy.

Near-infrared spectroscopy (NIRS) is a novel method for the measurement of tissue oxygenation and may have a role in monitoring liver oxygenation and viability. The aim of this study is to validate the application of NIRS for monitoring hepatic tissue oxygenation. Large Landrace pigs (n = 12) underwent laparotomy and liver exposure. Total hepatic blood flow (THBF) was measured by the Transonic Medical Flowmeter system. NIRS probes were placed on the liver surface to continuously record changes in hepatic tissue oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), and the reduction-oxidation state of cytochrome oxidase (Cyt Ox). Reduction of hepatic tissue oxygenation was achieved by hepatic vascular inflow occlusion (n = 6) or reduction of inspired oxygen (FIO2; n = 6). The THBF changes correlated significantly with hepatic HbO2 (r = 0.84; P <.001) and Cyt Ox (r = 0.88; P <.001). With reduction of FIO2, a significant correlation was found between arterial oxygen saturation and hepatic HbO2 and Hb (r = 0.99 and r = -0.99, respectively; P <.0001). NIRS measurement of liver parenchymal oxygenation correlates well with changes in liver blood flow and arterial oxygenation.