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

Mastectomy skin flap necrosis (MSFN) and partial DIEP (deep inferior epigastric artery perforator) flap loss represent two frequently reported complications in immediate autologous breast reconstruction. These complications could be prevented when areas of insufficient tissue perfusion are detected intraoperatively. Hyperspectral imaging (HSI) is a relatively novel, non-invasive imaging technique, which could be used to objectively assess tissue perfusion through analysis of tissue oxygenation patterns (StO₂%), near-infrared (NIR%), tissue hemoglobin (THI%), and tissue water (TWI%) perfusion indices. This prospective clinical pilot study aimed to evaluate the efficacy of HSI for tissue perfusion assessment and to identify a cut-off value for flap necrosis. Ten patients with a mean age of 55.4 years underwent immediate unilateral autologous breast reconstruction. Prior, during and up to 72 h after surgery, a total of 19 hyperspectral images per patient were acquired. MSFN was observed in 3 out of 10 patients. No DIEP flap necrosis was observed. In all MSFN cases, an increased THI% and decreased StO₂%, NIR%, and TWI% were observed when compared to the vital group. StO₂% was found to be the most sensitive parameter to detect MSFN with a statistically significant lower mean StO₂% (51% in the vital group versus 32% in the necrosis group, p < 0.0001) and a cut-off value of 36.29% for flap necrosis. HSI has the potential to accurately assess mastectomy skin flap perfusion and discriminate between vital and necrotic skin flap during the early postoperative period prior to clinical observation. Although the results should be confirmed in future studies, including DIEP flap necrosis specifically, these findings suggest that HSI can aid clinicians in postoperative mastectomy skin flap and DIEP flap monitoring.

Background. Postoperative monitoring of deep inferior epigastric perforator (DIEP) flaps for breast reconstruction using noninvasive tissue oximetry enables timely recognition of vascular compromise. This may limit ischemic tissue damage, minimizing postoperative morbidity and healthcare costs. The aim of this review was to provide an economic analysis of tissue oximetry for postoperative monitoring of DIEP flap breast reconstruction. Methods. A systematic literature search was conducted utilizing PubMed and Embase. Articles reporting costs related to tissue oximetry following DIEP flap breast reconstruction, costs directly related to DIEP flap surgical procedure, and costs associated with postoperative complications were included. Risk of bias was assessed using different tools depending on study type. Results. Six articles were included. Four studies provided an overview of total costs associated with DIEP flap breast reconstruction; two studies focused on whether tissue oximetry could facilitate a decrease in hospital costs. Average overall costs for DIEP flap procedure were estimated at $28 000, with additional costs up to $37 530 in case of total flap failure. Tissue oximetry to monitor DIEP flaps could potentially save up to $1667 per procedure. Moreover, it might eliminate the need for specialized postoperative care. Conclusion. Tissue oximetry following DIEP flap breast reconstruction can potentially facilitate a decrease in hospital costs since its readings enable physicians to intervene in an early stage of tissue malperfusion, contributing to minimizing complications. Tissue oximetry may eliminate the need for specialized postoperative care. However, based on the current literature, no firm conclusions can yet be drawn regarding cost-effectiveness of standard implementation.

Early detection of vascular compromise after autologous breast reconstruction is crucial to enable timely re-exploration for flap salvage. Several studies proposed non-invasive tissue oximetry for early identification of ischemia of deep inferior epigastric perforator (DIEP) flaps. The present study aimed to explore the utility of non-invasive tissue oximetry following DIEP flap surgery using a personalized oxygenation threshold. Methods: Patients undergoing immediate/delayed DIEP flap surgery were included in this prospective observational study. DIEP flap tissue oxygenation (StO₂) was monitored continuously using near-infrared spectroscopy. A baseline measurement was performed by positioning one sensor at the marked position of the major inferior epigastric perforator on the abdomen. A new sensor was positioned postoperatively on the transplanted tissue. In unilateral procedures, postoperative StO₂ values of the native breast were also obtained. Measurements were continued for 24 h. Results: Thirty patients (42 flaps) were included. Fourteen patients (46.7%) had an uncomplicated postoperative course. A minor complication was observed in thirteen patients; in five patients, at least one major complication occurred, requiring re-exploration. Median StO₂ readings were significantly lower in patients with major complications compared to uncomplicated cases. In fourteen unilateral DIEP flap procedures, StO₂ values of the native breast were similar to the preoperative baseline measurement (92%; p = 0.452). Conclusions: Non-invasive tissue oximetry following DIEP flap surgery could aid in early detection of vascular compromise. StO₂ values of the native breast and abdominal wall preoperatively can be used interchangeably and can serve as personalized reference value. Level of evidence: Level IV, diagnostic / prognostic study.

Background: Lower extremity free flap dangling protocols are still widely practiced, despite a paucity of evidence for their use. This pilot study investigates the use of tissue oximetry to provide further insight into the physiological effect of postoperative dangling in lower limb free flap transfer. Methods: Ten patients undergoing lower extremity free flap reconstruction were included in this study. Free flap tissue oxygen saturation (StO₂) was continuously measured using non-invasive near-infrared spectroscopy. Measurements were performed on the free flap and contralateral limb during dangling from postoperative day (POD) 7 until 11, according to the local dangling protocol. Results: StO₂ values measured in the free flap diminished to 70 ± 13.7% during dangling. This minimum StO₂ was reached significantly later, and correspondingly the area under the curve (AUC) was significantly larger on POD 11 compared to the start of the dangling protocol on POD 7, reflecting an improving free flap microvascular reactivity. The dangling slope was equal between the free flap and contralateral leg. The reperfusion slope was significantly flatter on POD 7 compared to the other PODs (p < 0.001). Thereafter, no significant differences between PODs were observed. Patients with a history of smoking had significantly lower tissue oximetry values compared to non-smokers. Conclusions: The application of tissue oximetry during dangling provides further insight into the physiological effect (i.e., changes in microcirculatory function) of the free flap of the reconstructed lower extremity. This information could potentially be useful to either revise or disrupt the use of such dangling protocols.

With great interest we read the recent article entitled “Postoperative monitoring of free DIEP flap in breast reconstruction with near-infrared spectroscopy: variables affecting the regional oxygen saturation'' by Salgarello et al in the latest issue of the Journal of Reconstructive Microsurgery.[1] The authors reported a positive linear correlation between tissue oximetry values and several free flap characteristics and thereby demonstrated that near-infrared spectroscopy is a reliable tool for free flap monitoring. Through this letter, we would like to suggest additional factors to address for optimization of postoperative outcome following “deep inferior epigastric perforator” flap (DIEP-flap) surgery. In autologous breast reconstructive surgery, the DIEP-flap method is increasingly popular given a low risk of microvascular thrombosis (3.38%) compared with other free flaps.[2] With respect to postoperative monitoring of DIEP-flaps using tissue oximetry, several practical and technical factors need to be taken into account. First, the surface area of the sensor. Spurious readings from surrounding tissues can be found in the case of a relatively large surface area compared with the surface area of the flap itself. In the latter situation, the regional tissue oxygen saturation (rSO₂) does not represent the area of interest. In the discussion, the authors elaborate on the aberrant saturation values found in flaps with skin islands less than 3 cm, indicating that interpretation of these data is challenging, which advocates for the use of smaller sensors for DIEP-flap monitoring. Next, quality of the vascular supply is one of the biggest concerns for the reconstructive surgeon.[3] To assess vascularization and the subsequent method of surgical resection of DIEP-flaps, several strategies have been described, for example, the “perfusion zones” by Holm et al.[3] To date, consensus is lacking regarding a superior resection method. Salgarello et al did not describe their resection method, which might have had an effect on both clinical outcomes and rSO₂ readings. Moreover, they performed the tissue oxygenation measurements in the “early-stained'' area and did not address the perfusion zones as earlier described.[3] [4] Standardization of tissue oximetry measurements is important to enable comparison across studies and contributes to inclusion of tissue oximetry in standard monitoring protocols. Another parameter affecting flap viability concerns the duration of the ischemia period. As shown by Lee et al, an ischemia time exceeding 99.5 minutes significantly increases the chance of fat necrosis (odds ratio = 9.449).[5] Although Salgarello et al included several crucial surgical factors in their study, such as the flap weight, flap area, perforator number, and perforator size, ischemia time was excluded, which might lead to underestimation of the role of ischemia time in the development of postoperative complications. In conclusion, a combination of various patient-related, surgical, and postoperative factors potentially influences the viability of a free flap transplant. Further clinical studies are needed to improve the knowledge on the added value of tissue oximetry following free flap surgery.