MEASUREMENTS OF TISSUE VIABILITY IN TRANSPLANTATION

Near-infrared spectroscopy has primarily been used in monitoring chang es in cerebral haemoglobin oxygenation and haemodynamics. However its use as a method for the assessment of tissue viability following trans plantation has recently been explored experimentally in our laboratory . The ability to measure changes in oxygenation and perfusion during h arvesting and following transplantation of organs or transfer of free and pedicled flaps is potentially important in reconstructive surgery. We have found that near-infrared spectroscopy is extremely useful in detecting vaso-occlusive events and can accurately and reliably distin guish between arterial, venous or total occlusions. Venous congestion indicated by raised levels of deoxygenated haemoglobin with a concomit ant increase in blood volume and the presence and magnitude of reactiv e hyperaemia are both easily recognizable features by near-infrared sp ectroscopy. We have shown that near-infrared spectroscopy measurements of venous congestion in kidneys (and other tissues) following prolong ed storage correlate with medullary vascular congestion confirmed by a ngiographical and histological analysis of intrarenal perfusion. Clini cally we have shown that flap perfusion can be improved by altering fl uid replacement regimes and the addition of ionotropes. Cerebral near- infrared spectroscopy measurements in a liver transplant model showed statistically significant differences within minutes after the anhepat ic phase in cerebral perfusion and oxygenation, between animals transp lanted with ischaemically damaged livers compared to those isografted with minimally stored livers. Similarly we have found that near-infrar ed spectroscopy can be used as a monitor to assess the adequacy of flu id or blood replacement in haemorrhagic and hypovolaemic models. We be lieve that near-infrared spectroscopy provides a sensitive and reliabl e postoperative method for the assessment of tissue viability followin g the transfer of free and pedicled flaps and organs.