Non-invasive detection of ischemic vascular damage in a pig model of liver donation after circulatory death.

BACKGROUND AND AIMS Liver graft quality is evaluated by visual inspection prior to transplantation, a process highly dependent on surgeon's experience. We present an objective, non-invasive, quantitative way of assessing liver quality in real time using Raman spectroscopy, a laser-based tool for analysing biomolecular composition. APPROACH AND RESULTS A novel porcine model of donation after circulatory death (DCD) with normothermic regional perfusion (NRP) allowed assessment of liver quality pre-mortem, during warm ischemia (WI) and post-NRP. 10% of circulating blood volume was removed in half of experiments to simulate blood recovery for DCD heart removal. Left median lobe biopsies were obtained before circulatory arrest, after 45 min of WI and after two hours of NRP, and analysed using spontaneous Raman spectroscopy, stimulated Raman spectroscopy (SRS) and staining. Measurements were also taken in situ from the porcine liver using a handheld Raman spectrometer at these time points from left median and right lateral lobes. Raman microspectroscopy detected congestion during WI by measurement of the intrinsic Raman signal of haemoglobin in red blood cells (RBCs), eliminating the need for exogenous labels. Critically, this microvascular damage was not observed during WI when 10% of circulating blood was removed before cardiac arrest. Two hours of NRP effectively cleared RBCs from congested livers. Intact RBCs were visualised rapidly at high resolution using SRS. Optical properties of ischemic livers were significantly different to pre-ischemic and post-NRP livers as measured using a handheld Raman spectrometer. CONCLUSIONS Raman spectroscopy is an effective tool for detecting microvascular damage which could assist the decision to use marginal livers for transplantation. Reducing the volume of circulating blood before circulatory arrest in DCD may help reduce microvascular damage.