Assessment of tissue viability using near-infrared spectroscopy

Prolonged and severe tissue hypoxia results in tissue necrosis in pedicled 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 challenge, in a rapid and non-invasive manner with a high degree of reproducibility. Tissue haemoglobin oxygen saturation and water content of pre-selected dorsal sites were monitored for 72 h prior to, and 72 h following elevation of a reversed McFarlane rat dorsal skin flap (n = 9). Oxygen delivery to flap tissue dropped immediately upon flap elevation. This was most pronounced in the distal half of the flap and least pronounced in the region nearest its base. Haemoglobin oxygen saturation of tissue proximal to the vascular base of the flap recovered, exceeding pre-elevation saturation values, within 6 h of raising the flap. Typically, this higher haemoglobin oxygen saturation persisted for the full 72 h post-elevation observation period. At a distance greater than 2 cm from the vascular pedicle, the tissue remained hypoxic over the post-elevation monitoring period. Tissues remaining below a certain haemoglobin oxygen saturation threshold (oxygen saturation index < 1) for prolonged periods (> 6 h) became increasingly dehydrated, eventually becoming visibly necrotic. Tissues above this threshold (oxygen saturation index > 1), despite being significantly hypoxic, relative to the pre-elevation saturation values, remained viable over the 72 h post-elevation monitoring period.