Post-operative monitoring of free flaps using a low-cost thermal camera: a pilot study

Ischemic preconditioning in arterialized venous flap: Temperature effects and monitoring

INTRODUCTION

Arterialized venous flap, like any other flap, will undergo an ischemic reperfusion injury during its transfer process. To overcome this, ischemic preconditioning can be done to provide protection and enhanced flap survival. One of the reliable parameters of flap survival is its temperature. However, there was no recorded data regarding AVF's temperature or its monitoring. This research aimed to demonstrate the temperature effect of ischemic preconditioning on arterialized venous flap.

METHOD

Male Wistar Rats were randomly divided into 4 groups, consisting of 6 negative control groups, 8 positive control group (PS) rats that underwent an anastomosis of the superficial epigastric artery to the superficial epigastric vein, 8 experimental rat group 1 (EX1) that underwent 3 cycles of 5 minutes pre-anastomosis clamping with 3 cycles of 5 minutes each, and 8 experimental rats' group 2 (EX2) with 3 cycles of 10 minutes. Flap's temperature was observed preoperatively and postoperatively from day 1 to day 7, day 14, and day 21 with an android-based thermal camera and recorded in Celsius degrees.

RESULTS

All the flaps (N= 26) were vital. The temperature drop was seen in all anastomosed flaps compared to the negative control (30.37 vs. 25.08 vs. 23.77 vs. 25.27, p<0.05). A significant increase in temperature occurred on days 4 to 6 in Ex1 (33.62±1.820, 33.62±1.820, 32.40±1.627; p<0.05). As in the temperature trend, Ex2 is shown to have a stable temperature from day 2 until 21.

CONCLUSION

This study has recorded an increase in temperature in the early days of the creation of the arterialized venous flap at various timings of ischemic preconditioning. The flap's monitoring was easily observed with a thermal camera that can be implemented in humans.

A pilot prospective study of forward-looking infrared (FLIR) camera measurements to predict postoperative wound complications in high-energy lower extremity fractures

PURPOSE

To prospectively determine if forward-looking infrared (FLIR) camera temperature measurements can predict postoperative wound complications in high-energy lower extremity fractures.

METHODS

This is a prospective cohort study from a single level 1 trauma centre. Adult patients who sustained unilateral high-energy lower extremity fractures (tibial plateau, tibial plafond, trimalleolar ankle, midfoot, or calcaneus fractures) were included in the study. Preoperative and post-induction FLIR thermographic measurements were taken using the FLIRONE ® PRO camera system. The main outcome of interest was the development of any wound related postoperative complication.

RESULTS

Forty-eight patients were included in the study. A majority of the patients were male (58%) with a mean age of 44.2 years. FLIR imaging detected temperature differences between the operative extremity and the contralateral extremity, both in the preoperative area and following induction (Pre-op: 33.0 vs 30.8, p < 0.001; Post-induction: 29.6 vs 28.5, p = 0.046). Overall, 11 (23.9%) patients experienced a wound complication. Regression analysis did not demonstrate a significant association between preoperative or post-induction FLIR measurements and the development of wound complications.

CONCLUSION

While FLIR imaging could detect temperature changes related to traumatic injury, these differences did not correlate with postoperative outcomes. Further large-scale study may be warranted.

LEVEL OF EVIDENCE

III.

Tissue perfusion in DIEP flaps using Indocyanine Green Fluorescence Angiography, Hyperspectral imaging, and Thermal imaging

Flap necrosis continues to occur in skin free flap autologous breast reconstruction. Therefore, we investigated the benefits of indocyanine green angiography (ICGA) using quantitative parameters for the objective, perioperative evaluation of flap perfusion. In addition, we investigated the feasibility of hyperspectral (HSI) and thermal imaging (TI) for postoperative flap monitoring. A single-center, prospective observational study was performed on 15 patients who underwent deep inferior epigastric perforator (DIEP) flap breast reconstruction (n=21). DIEP-flap perfusion was evaluated using ICGA, HSI, and TI using a standardized imaging protocol. The ICGA perfusion curves and derived parameters, HSI extracted oxyhemoglobin (oxyHb) and deoxyhemoglobin (deoxyHb) values, and flap temperatures from TI were analyzed and correlated to the clinical outcomes. Post-hoc quantitative analysis of intraoperatively collected data of ICGA application accurately distinguished between adequately and insufficiently perfused DIEP flaps. ICG perfusion curves identified the lack of arterial inflow (n=2) and occlusion of the venous outflow (n=1). In addition, a postoperatively detected partial flap epidermolysis could have been predicted based on intraoperative quantitative ICGA data. During postoperative monitoring, HSI was used to identify impaired perfusion areas within the DIEP flap based on deoxyHb levels. The results of this study showed a limited added value of TI. Quantitative, post-hoc analysis of ICGA data produced objective and reproducible parameters that enabled the intraoperative detection of arterial and venous congested DIEP flaps. HSI appeared to be a promising technique for postoperative flap perfusion assessment. A diagnostic accuracy study is needed to investigate ICGA and HSI parameters in real-time and demonstrate their clinical benefit.

An Experimental and Clinical Study of Flap Monitoring with an Analysis of the Clinical Course of the Flap Using an Infrared Thermal Camera

Flap surgery is a common method used to cover defects following tumor ablation, trauma, or infection. However, insufficient vascularity in the transferred flap can lead to flap necrosis and failure. Proper postoperative monitoring is essential to prevent these complications. Recently, research has explored the use of infrared thermal imaging in plastic surgery, leading to its clinical application. This study comprises two separate parts: an in vivo experimental study and a clinical study. In this study, 28 rats underwent reverse McFarlane flap surgery, and their flaps were analyzed using a FLIR thermal imaging camera seven days post-surgery. Additionally, thermal images of flaps were taken on postoperative days 0, 1, 2, 3, and 7 in 22 patients. This study focused on temperature differences between normal skin and the perforator compared to the average flap temperature. Results showed that the temperature difference was higher in the necrosis group and increased over time in cases of total necrosis. A lower perforator temperature compared to the flap's average indicated vascular compromise, potentially leading to flap failure. The FLIR camera, being contact-free and convenient, shows promise for understanding and inferring the clinical progression of flaps in postoperative monitoring.

Utility of Thermal Imaging in Predicting Superficial Infections in Transfemoral Osseointegrated Implants

Background

Superficial infection is a common minor complication of transcutaneous implants that can be challenging to predict or diagnose. Although it remains unclear whether superficial infections progress to deep infections (which may require implant removal), predicting and treating any infection in these patients is important. Given that flap thinning during stage II surgery requires compromising vascularity for stability of the skin penetration aperture, we hypothesized that early skin temperature changes predict long-term superficial infection risk.

Methods

We obtained standardized thermal imaging and recorded surface temperatures of the aperture and overlying flaps 2 weeks postoperatively for the first 34 patients (46 limbs) treated with the Osseointegrated Prosthesis for the Rehabilitation of Amputees transfemoral implant system. We used two-sided t tests to compare temperatures surrounding the aperture and adjacent soft tissues in patients with and without subsequent infection.

Results

During median follow-up of 3 years, 14 limbs (30.4%) developed 23 superficial infections. At patients' initial 2-week visit, mean skin temperature surrounding the aperture was 36.3ºC in limbs that later developed superficial infections and 36.7ºC in uninfected limbs (P = 0.35). In four patients with bilateral implants who later developed superficial infection in one limb, average temperature was 1.5ºC colder in the infected limb (P = 0.12).

Conclusions

Superficial infections remain a frequent complication of transfemoral osseointegration surgery. We did not find differences in early heat signatures between limbs subsequently complicated and those not complicated by superficial infection. Further research should explore more objective measures to predict, diagnose, and prevent infections after osseointegration surgery.

Continuous intraoperative perfusion monitoring of free microvascular anastomosed fasciocutaneous flaps using remote photoplethysmography

Flap loss through limited perfusion remains a major complication in reconstructive surgery. Continuous monitoring of perfusion will facilitate early detection of insufficient perfusion. Remote or imaging photoplethysmography (rPPG/iPPG) as a non-contact, non-ionizing, and non-invasive monitoring technique provides objective and reproducible information on physiological parameters. The aim of this study is to establish rPPG for intra- and postoperative monitoring of flap perfusion in patients undergoing reconstruction with free fasciocutaneous flaps (FFCF). We developed a monitoring algorithm for flap perfusion, which was evaluated in 15 patients. For 14 patients, ischemia of the FFCF in the forearm and successful reperfusion of the implanted FFCF was quantified based on the local signal. One FFCF showed no perfusion after reperfusion and devitalized in the course. Intraoperative monitoring of perfusion with rPPG provides objective and reproducible results. Therefore, rPPG is a promising technology for standard flap perfusion monitoring on low costs without the need for additional monitoring devices.

Camera-based assessment of cutaneous perfusion strength in a clinical setting

Objective. After skin flap transplants, perfusion strength monitoring is essential for the early detection of tissue perfusion disorders and thus to ensure the survival of skin flaps. Camera-based photoplethysmography (cbPPG) is a non-contact measurement method, using video cameras and ambient light, which provides spatially resolved information about tissue perfusion. It has not been researched yet whether the measurement depth of cbPPG, which is limited by the penetration depth of ambient light, is sufficient to reach pulsatile vessels and thus to measure the perfusion strength in regions that are relevant for skin flap transplants.Approach. We applied constant negative pressure (compared to ambient pressure) to the anterior thighs of 40 healthy subjects. Seven measurements (two before and five up to 90 minutes after the intervention) were acquired using an RGB video camera and photospectrometry simultaneously. We investigated the performance of different algorithmic approaches for perfusion strength assessment, including the signal-to-noise ratio (SNR), its logarithmic components logS and logN, amplitude maps, and the amplitude height of alternating and direct signal components.Main results. We found strong correlations of up tor=0.694 (p<0.001) between photospectrometric measurements and all cbPPG parameters except SNR when using the green color channel. The transfer of cbPPG signals to POS, CHROM, and O3C did not lead to systematic improvements. However, for direct signal components, the transformation to O3C led to correlations of up tor=0.744 (p<0.001) with photospectrometric measurements.Significance. Our results indicate that a camera-based perfusion strength assessment in tissue with deep-seated pulsatile vessels is possible.

Development and Evaluation of a Remote Patient Monitoring System in Autologous Breast Reconstruction

Flap monitoring after a deep inferior epigastric perforator flap breast reconstruction is crucial to detect complications in time. A novel and innovative wireless device has been developed and tested in a feasibility study. This study describes our experience with remote patient monitoring via this device in postoperative monitoring of deep inferior epigastric perforator flaps.