ASSESSMENT OF TISSUE VIABILITY USING NEAR-INFRARED SPECTROSCOPY

Prolonged and severe tissue hypoxia results in tissue necrosis in pedi cled flaps. We demonstrate the potential of near-infrared spectroscopy for monitoring of skin flaps. This approach clearly identifies tissue regions with low oxygen supply, and also the severity of this challen ge, in a rapid and non-invasive manner, with a high degree of reproduc ibility. Tissue haemoglobin oxygen saturation and water content of pre -selected dorsal sites were monitored for 72 h prior to, and 72 h foll owing elevation of a reversed McFarlane rat dorsal skin flap (n = 9. O xygen delivery to flap tissue dropped immediately upon flap elevation. This was most pronounced in the distal half of the nap and least pron ounced in the region nearest its base. Haemoglobin oxygen saturation o f tissue proximal to the vascular base of the flap recovered, exceedin g pre-elevation saturation values, within 6 h of raising the flap. Typ ically, this higher haemoglobin oxygen saturation persisted for the fu ll 72 h post-elevation observation period. At a distance greater than 2 cm from the vascular pedicle, the tissue remained hypoxic over the p ost-elevation monitoring period. Tissues remaining below a certain hae moglobin oxygen saturation threshold (oxygen saturation index < 1) for prolonged periods (> 6 h) became increasingly dehydrated, eventually becoming visibly necrotic. Tissues above this threshold (oxygen satura tion index > 1)? despite being significantly hypoxic, relative to the pre-elevation saturation values, remained viable over the 72 h post-el evation monitoring period.