*Article* **New Approach to the Old Challenge of Free Flap Monitoring— Hyperspectral Imaging Outperforms Clinical Assessment by Earlier Detection of Perfusion Failure**

**Daniel G. E. Thiem \*, Paul Römer, Sebastian Blatt, Bilal Al-Nawas and Peer W. Kämmerer**

Department of Oral and Maxillofacial Surgery, University Medical Centre Mainz, 55131 Mainz, Germany; paul.roemer@unimedizin-mainz.de (P.R.); sebastian.blatt@unimedizin-mainz.de (S.B.); bilal.al-nawas@unimedizin-mainz.de (B.A.-N.); peer.kaemmerer@unimedizin-mainz.de (P.W.K.) **\*** Correspondence: daniel.thiem@uni-mainz.de; Tel.: +49-(0)-613-117-5459

**Abstract:** In reconstructive surgery, free flap failure, especially in complex osteocutaneous reconstructions, represents a significant clinical burden. Therefore, the aim of the presented study was to assess hyperspectral imaging (HSI) for monitoring of free flaps compared to clinical monitoring. In a prospective, non-randomized clinical study, patients with free flap reconstruction of the oromaxillofacial-complex were included. Monitoring was assessed clinically and by using hyperspectral imaging (TIVITA™ Tissue-System, DiaspectiveVision GmbH, Pepelow, Germany) to determine tissue-oxygen-saturation [StO<sup>2</sup> ], near-infrared-perfusion-index [NPI], distribution of haemoglobin [THI] and water [TWI], and variance to an adjacent reference area (∆reference). A total of 54 primary and 11 secondary reconstructions were performed including fasciocutaneous and osteocutaneous flaps. Re-exploration was performed in 19 cases. A total of seven complete flap failures occurred, resulting in a 63% salvage rate. Mean time from flap inset to decision making for re-exploration based on clinical assessment was 23.1 ± 21.9 vs. 18.2 ± 19.4 h by the appearance of hyperspectral criteria indicating impaired perfusion (StO<sup>2</sup> ≤ 32% OR StO2∆reference > −38% OR NPI ≤ 32.9 OR NPI∆reference ≥ −13.4%) resulting in a difference of 4.8 ± 5 h (*p* < 0.001). HSI seems able to detect perfusion compromise significantly earlier than clinical monitoring. These findings provide an interpretation aid for clinicians to simplify postoperative flap monitoring.

**Keywords:** HSI; objective; hyperspectral signature; timely recognition; reconstruction; head and neck; non-invasive; non-contact
