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

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 oro-maxillofacial-complex were included. Monitoring was assessed clinically and by using hyperspectral imaging (TIVITA™ Tissue-System, DiaspectiveVision GmbH, Pepelow, Germany) to determine tissue-oxygen-saturation [StO2], near-infrared-perfusion-index [NPI], distribution of haemoglobin [THI] and water [TWI], and variance to an adjacent reference area (Dreference). 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 (StO2 ≤ 32% OR StO2Dreference > −38% OR NPI ≤ 32.9 OR NPIDreference ≥ −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.

Intramuscular Near-Infrared Spectroscopy for Muscle Flap Monitoring in a Porcine Model

Background Current near-infrared spectroscopy (NIRS)-based systems for continuous flap monitoring are limited to flaps which carry a cutaneous paddle. As such, this useful and reliable technology has not previously been applicable to muscle-only free flaps where other modalities with substantial limitations continue to be utilized. Methods We present the first NIRS probe which allows continuous monitoring of local tissue oxygen saturation (StO2) directly within the substance of muscle tissue. This probe is flexible, subcentimeter in scale, waterproof, biocompatible, and is fitted with resorbable barbs which facilitate temporary autostabilization followed by easy atraumatic removal. This novel device was compared with a ViOptix T.Ox monitor in a porcine rectus abdominus myocutaneous flap model of arterial and venous occlusions. During these experiments, the T.Ox device was affixed to the skin paddle, while the novel probe was within the muscle component of the same flap. Results The intramuscular NIRS device and skin-mounted ViOptix T.Ox devices produced very similar StO2 tracings throughout the vascular clamping events, with obvious and parallel changes occurring upon vascular clamping and release. The normalized cross-correlation at zero lag describing correspondence between the novel intramuscular NIRS and T.Ox devices was >0.99. Conclusion This novel intramuscular NIRS probe offers continuous monitoring of oxygen saturation within muscle flaps. This experiment demonstrates the potential suitability of this intramuscular NIRS probe for the task of muscle-only free flap monitoring, where NIRS has not previously been applicable. Testing in the clinical environment is necessary to assess durability and reliability.

507 Quantifying the Limitations of Clinical and Technology-Based Flap Monitoring Strategies Using A Systematic Recurrent Themes Analysis

Aim Multiple techniques exist to monitor free flap viability postoperatively, varying with practical and personal preference, yet the limitations of each technique remain unquantified. This systematic review aims to identify the most commonly reported limitations of these techniques in clinical practice. Method A systematic review was conducted according to PRISMA guidelines using MEDLINE, EMBASE and Web of Science with search criteria for postoperative free flap monitoring techniques. Search results were independently screened using defined criteria by two authors and a senior clinician. Limitations of the techniques found in the discussion section of eligible papers were recorded and categorised using recurrent theme analysis. Results A total of 4826 records were identified. 4643 articles met the eligibility criteria and were subsequently reviewed, with 195 papers included in the final analysis. The most frequently reported limitations of clinical monitoring were interpretation requiring expertise (25% of related papers), unsuitability for buried flaps (21%), and lack of quantitative/objective values (19%). For non-invasive technologies: lack of quantitative/objective values (21%), cost (16%) and interpretation requiring expertise (13%). For invasive technologies: application requiring expertise (25%), equipment design and malfunction (13%) and cost (13%). Conclusions This is the first systematic review to quantify the limitations of different flap monitoring techniques as reported in the literature. The limitations identified better inform clinicians to decide the best single or combined monitoring approach for their practice and aid development in new flap monitoring technologies.

1362 Early Experience on Flap Perfusion? Monitoring with Near-Infrared Spectroscopy Tissue Oximetry

Introduction Free flap reconstruction is a routine procedure with more than 99% success rates. Yet, vascular complications may occur leading to flap failure. Thus, early detection of vascular compromise is crucial for flap salvage. Vascular complications may be detected early using Infrared Spectroscopy Tissue Oximetry (NIRS) parameter changes. This method can distinguish changes caused by arterial and venous thrombosis before surgical re-exploration. This study aims to assess the validity or feasibility of using NIRS Oximetry in free flap monitoring and compare it to standard clinical examination and Doppler . Method A prospective cohort observational study. Flap perfusion was measured using the INVOS™ 7100 system for 24-h continuous postoperative monitoring. The data were compared to findings of clinical assessment. Results Ten patients completed the measurements after breast flap reconstruction. Age ranged from 41 to 61 years. Patients underwent immediate d eep inferior epigastric perforators (DIEP) (n = 4), delayed DIEP (n = 4), transverse upper gracilis flap (n = 1), and latissimus dorsi flap with lipofilling (n = 1). All ten flaps are successfully monitored for 24hrs post-operatively. The overall flap survival was 100%. Clinical examination, Doppler studies and surgical outcome were consistent with NIRS (need numbers). There were no false negatives. Conclusions NIRS tissue oximetry could potentially monitor flaps non-invasively. Future adequately sampled cohort study is recommended.

A Wireless Near-Infrared Spectroscopy Device for Flap Monitoring: Proof of Concept in a Porcine Musculocutaneous Flap Model

Background Current near-infrared spectroscopy (NIRS)-based systems for continuous flap monitoring are highly sensitive for detecting malperfusion. However, the clinical utility and user experience are limited by the wired connection between the sensor and bedside console. This wire leads to instability of the flap–sensor interface and may cause false alarms. Methods We present a novel wearable wireless NIRS sensor for continuous fasciocutaneous free flap monitoring. This waterproof silicone-encapsulated Bluetooth-enabled device contains two light-emitting diodes and two photodetectors in addition to a battery sufficient for 5 days of uninterrupted function. This novel device was compared with a ViOptix T.Ox monitor in a porcine rectus abdominus myocutaneous flap model of arterial and venous occlusions. Results Devices were tested in four flaps using three animals. Both devices produced very similar tissue oxygen saturation (StO2) tracings throughout the vascular clamping events, with obvious and parallel changes occurring on arterial clamping, arterial release, venous clamping, and venous release. Small interdevice variations in absolute StO2 value readings and magnitude of change were observed. The normalized cross-correlation at zero lag describing correspondence between the novel NIRS and T.Ox devices was >0.99 in each trial. Conclusion The wireless NIRS flap monitor is capable of detecting StO2 changes resultant from arterial vascular occlusive events. In this porcine flap model, the functionality of this novel sensor closely mirrored that of the T.Ox wired platform. This device is waterproof, highly adhesive, skin conforming, and has sufficient battery life to function for 5 days. Clinical testing is necessary to determine if this wireless functionality translates into fewer false-positive alarms and a better user experience.

Hyperspectral Imaging (HSI) as a new diagnostic tool in free flap monitoring for soft tissue reconstruction: a proof of concept study

Objectives Free flap surgery is an essential procedure in soft tissue reconstruction. Complications due to vascular compromise often require revision surgery or flap removal. We present hyperspectral imaging (HSI) as a new tool in flap monitoring to improve sensitivity compared to established monitoring tools. Methods We performed a prospective observational cohort study including 22 patients. Flap perfusion was assessed by standard clinical parameters, Doppler ultrasound, and HSI on t0 (0 h), t1 (16–28 h postoperatively), and t2 (39–77 h postoperatively). HSI records light spectra from 500 to 1000 nm and provides information on tissue morphology, composition, and physiology. These parameters contain tissue oxygenation (StO2), near-infrared perfusion- (NIR PI), tissue hemoglobin- (THI), and tissue water index (TWI). Results Total flap loss was seen in n = 4 and partial loss in n = 2 cases. Every patient with StO2 or NIR PI below 40 at t1 had to be revised. No single patient with StO2 or NIR PI above 40 at t1 had to be revised. Significant differences between feasable (StO2 = 49; NIR PI = 45; THI = 16; TWI = 56) and flaps with revision surgery [StO2 = 28 (p < 0.001); NIR PI = 26 (p = 0.002); THI = 56 (p = 0.002); TWI = 47 (p = 0.045)] were present in all HSI parameters at t1 and even more significant at t2 (p < 0.0001). Conclusion HSI provides valuable data in free flap monitoring. The technique seems to be superior to the gold standard of flap monitoring. StO2 and NIR PI deliver the most valuable data and 40 could be used as a future threshold in surgical decision making. Clinical Trial Register This study is registered at the German Clinical Trials Register (DRKS) under the registration number DRKS00020926.

Clinical and Radiological Safety of Retained Implantable Doppler Devices Used for Free Flap Monitoring

Introduction: Implantable Doppler devices are reliable adjuncts used for free flap monitoring. Occasionally, the probe/wire is not removed and remains in the soft tissues. The clinical safety of the retained probes and safety and compatibility with magnetic resonance imaging (MRI) have not been studied. We present a series of retained implantable Doppler probes examining clinic outcomes, safety and compatibility with MRI, and effect on MRI image quality. Methods: A retrospective review was conducted of patients who had an implantable Doppler device for free flap monitoring between July 2007 and August 2018. Routine post-operative imaging was reviewed for all patients to identify incidental findings of a retained probe. A subset of patients with retained implantable Doppler probes who underwent MRI was identified. Magnetic resonance images were reviewed to detect any degradation of image quality. Results: A total of 323 patients who had an implantable Doppler device placed were reviewed 18 (5.6%) patients were identified with a retained probe and were included in this study. Mean age was 49 years with mean follow-up of 34.4 months. One potential device-related complication occurred in 1 (5.6%) patient. A total of 32 MRI scans were performed in 8 patients with retained devices, including 6 patients who underwent a total of 21 MRIs of the surgical site. There were no complications related to the MRI scans, and we found no significant degradation of image quality. Conclusion: Retained implantable Doppler probes were not associated with substantial adverse clinical outcomes nor affected MRI image quality of the surgical site.

Free Flap Monitoring, Salvage, and Failure Timing: A Systematic Review

Background Microsurgical free tissue transfer has become a reliable technique with success rates around 99% and around 5% requiring exploration for vascular compromise. Protocols for flap monitoring between plastic surgery units vary. We aimed to elucidate the time period when monitoring is crucial for flap salvage. Methods A systematic search of literature was performed in PubMed, Cochrane Library, Medline, and Scopus databases from 1966 to July 2018 according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, identifying 3,844 studies with mention of free flap and monitoring or timing or salvage or compromise. Studies were screened for relevance according to predetermined inclusion criteria. Data was extracted from included studies relating to flap type, monitoring, timing and reason for failure, and success of salvage intervention. Results A total of 109 studies featuring 44,031 free flaps were included. A total of 2,549 (5.8%) flaps required return to theater for compromise; 926 (2.1%) were lost and 1,654 (3.7%) were salvaged. In the first 24 hours postoperatively 93.8% of explored flaps are successfully salvaged, by day 2: 83.33%, day 3: 12.1%, and beyond day 4: none were successful. Of the 355 flaps where the cause of failure was reported, 59.5% was venous, 27.9% was arterial, 2.3% was a combination of both, and 10.2% was hematoma or infection. The proportion of flap failures at various recipient sites was highest in the trunk/viscera (7%, 95% confidence interval [CI] 0.00, 0.36), followed by limbs (5%, 95% CI 0.02, 0.08), head and neck (3%, 95% CI 0.02, 0.04), and breast (<1%; 95% CI 0.00, 0.02). Conclusion Close flap monitoring is of most value in the first 48 hours postoperatively, facilitating rapid detection of vascular compromise, early salvage, and better outcomes. The location of the flap has implications on its success and certain recipient sites may need particular attention to improve chances of success.