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.