Near-Infrared Spectroscopy (NIRS) versus Hyperspectral Imaging (HSI) to Detect Flap Failure in Reconstructive Surgery: A Systematic Review

Rapid identification of possible vascular compromise in free flap reconstruction to minimize time to reoperation improves achieving free flap salvage. Subjective clinical assessment, often complemented with handheld Doppler, is the golden standard for flap monitoring; but this lacks consistency and may be variable. Non-invasive optical methods such as near-infrared spectroscopy (NIRS) and hyperspectral imaging (HSI) could facilitate objective flap monitoring. A systematic review was conducted to compare NIRS with HSI in detecting vascular compromise in reconstructive flap surgery as compared to standard monitoring. A literature search was performed using PubMed and Embase scientific database in August 2021. Studies were selected by two independent reviewers. Sixteen NIRS and five HSI studies were included. In total, 3662 flap procedures were carried out in 1970 patients using NIRS. Simultaneously; 90 flaps were performed in 90 patients using HSI. HSI and NIRS flap survival were 92.5% (95% CI: 83.3–96.8) and 99.2% (95% CI: 97.8–99.7). Statistically significant differences were observed in flap survival (p = 0.02); flaps returned to OR (p = 0.04); salvage rate (p < 0.01) and partial flap loss rate (p < 0.01). However, no statistically significant difference was observed concerning flaps with vascular crisis (p = 0.39). NIRS and HSI have proven to be reliable; accurate and user-friendly monitoring methods. However, based on the currently available literature, no firm conclusions can be drawn concerning non-invasive monitoring technique superiority

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.

836 DIEP Flap Monitoring Adherence

Aim The popularity of Deep Epigastric Perforator (DIEP) free flaps for breast reconstruction after mastectomies have increased due to their natural aesthetic results and reliability. Free flaps require strict post-operative monitoring by nursing staff during the early post-operative period where they should notify the surgeons to anticipate vascular compromise in order to salvage the flap. To ensure success the DIEP guidelines were introduced to Morriston Hospital, Swansea. This was a first cycle closed loop re-audit. Method Interventions from initial audit were implemented in 2018. Retrospective analysis of patient notes over an 8-month period (August 2019- March 2020) and compared with DIEP checklist. Clinical notes, nursing cartex and flap observations and medication charts were reviewed. Results 100% had bear huggers, antiemetics (87% in 2018), correct thromboprophylaxis (75% in 2018) and laxatives (37% in 2018). 100% had senior reviews daily post op (75% in 2018). 100% had flap observations performed as guidelines immediately post op. Conclusions This was a successful re-audit showing significant improvements in adherence rates amongst the surgical and nursing staff in the plastic surgery department. Implementation of the DIEP operation note template may help maintain such adherence amongst staff.

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.

Significance of vesicles in flap monitoring in oral cancer surgery: Report of two cases

The success rate of vascularized free flap transplantation in head and neck oncologic surgery is high, ranging from 94% to 98.8%; however, flap necrosis sometimes occurs after surgery. When vessel-related complications occur, flap necrosis proceeds rapidly. Thus, flap monitoring after surgery is especially important. We recently treated two patients with flap-related complications. A vesicle appeared on the surface of the flap and enlarged within a short time; the flap’s color changed to purple, and a reoperation was eventually performed. While there are approaches to monitor flaps, this is the first report suggesting the assessment of vesicle formation for flap monitoring, since the vesicles occur several hours before changes in the flap color.