Near-infrared spectroscopic assessment of mitochondrial oxygenation status—comparison during normothermic extracorporeal liver perfusion by buffer only or buffer fortified with washed red blood cells: an experimental study

Abstract

Background Use of marginal and non–heart-beating donors leads to an increased incidence of complications after clinical liver transplantation. Normothermic extracorporeal liver perfusion (NELP) may allow resuscitation and evaluation of such organs. Despite recent success in long-term liver preservation by NELP, no methods of organ evaluation have been defined. Mitochondrial cytochrome oxidase (Cyt Ox) levels reflect oxygen and substrate delivery, and hence ATP production at the cellular level. This study used near-infrared spectroscopy (NIRS) to measure Cyt Ox levels during NELP. Methods Livers retrieved from New Zealand white rabbits were immediately perfused in an extracorporeal circuit with oxygenated buffer (group A, n = 4) or red blood cell (RBC)–fortified buffer (group B, n = 4). Perfusion was continued for 3 hours at 37°C pH 7.4, and perfusate was gassed with 95%O 2/5%CO 2 at 1 liter per minute. Cyt Ox levels were monitored continuously by NIRS and bile output was measured. Results Cyt Ox was reduced at the start of perfusion in both groups, but even more rapidly in the buffer-perfused group. After initial deterioration, Cyt Ox levels improved significantly ( P < .05) with perfusion in the RBG-perfused group, but remained impaired in the buffer group 5.74 ± 1.51 Δμmol/L and −25.77 ± 21.94 Δμmol/L for groups B and A, respectively, at 180 minutes. Differences in bile output were not significant (19.33 ± 9.50 and 25.00 ± 16.81 μmol/min/100 g for groups B and A respectively). Conclusions Cyt Ox levels may offer better viability markers than bile output. NIRS is a practical method to measure tissue oxygenation, and RBC-based perfusion provided better oxygenation during NELP.