Assessing flap perfusion after free tissue transfer using hyperspectral imaging (HSI)

Hyperspectral imaging (HSI) is a new device for monitoring microcirculation. The aim of this study is to describe hyperspectral imaging after free tissue. We assessed 22 patients from our department who underwent hyperspectral imaging monitoring. Four parameters were measured: tissue oxygenation, tissue hemoglobin index, deep tissue near-infrared perfusion index, and water distribution. Measurements were taken from normally perfused flaps, areas of locally impaired perfusion, and complete flap malperfusion daily within the first 7 days. Statistical differences were determined using Student’s t tests. Receiver operating characteristic curves were illustrating the reliability of each parameter. Ten free anterolateral thigh flaps and eight free latissimus dorsi flaps were included. One flap was subsequently lost. Of 184 total measurements, 119 were taken in normally perfused flap areas, 63 in areas of locally impaired perfusion due to partial flap necrosis, and 2 were taken of a flap without perfusion due to arterial occlusion. In the latter case, tissue oximetry and tissue hemoglobin index were 3% (normally perfused flaps 37.5±12.6% (p<0.05) and 23.7±19.4% (p<0.05), respectively), whereas for locally impaired perfusion tissue, hemoglobin index was raised to 76.8±19.9% (p<0.05) and tissue oximetry and deep tissue near-infrared perfusion index were reduced to 28.8±15.8% (p<0.05) and 24.0±16.9% (p<0.05), respectively. A tissue hemoglobin index of ≥ 53% had a sensitivity of 92% and a specificity of 93% for the detection of locally impaired perfusion. Other parameters were less reliable. HSI is a useful tool for flap monitoring after microsurgical tissue transfer. It provided accurate information which correlated with clinical assessments and guided decision-making regarding revision because it can easily detect impaired flap perfusion dueto arterial occlusion or venous stasis. It also defined locally impaired perfused tissue at theflapborder. Level of evidence: Level IV, diagnostic study.