Continuous tissue oxygen tension measurement as a monitor of free-flap viability

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.

Wearable, wireless, multi-sensor device for monitoring tissue circulation after free-tissue transplantation: a multicentre clinical trial

Wearable sensors have seen remarkable recent technological developments, and their role in healthcare is expected to expand. Specifically, monitoring tissue circulation in patients who have undergone reconstructive surgery is critical because blood flow deficiencies must be rescued within hours or the transplant will fail due to thrombosis/haematoma within the artery or vein. We design a wearable, wireless, continuous, multipoint sensor to monitor tissue circulation. The system measures pulse waves, skin colour, and tissue temperature to reproduce physician assessment. Data are analysed in real time for patient risk using an algorithm. This multicentre clinical trial involved 73 patients who underwent transplant surgery and had their tissue circulation monitored until postoperative day 7. Herein, we show that the overall agreement rate between physician and sensor findings is 99.2%. In addition, the patient questionnaire results indicate that the device is easy to wear. The sensor demonstrates non-invasive, real-time, continuous, multi-point, wireless, and reliable monitoring for postoperative care. This wearable system can improve the success rate of reconstructive surgeries.

The use of sentinel skin islands for monitoring buried and semi-buried micro-vascular flaps. Part I: Summary and brief description of monitoring methods

Micro-vascular flaps have been used for the repair of challenging defects for over 45 years. The risk of failure is reported to be around 5-10% which despite medical and technical advances in recent years remains essentially unchanged. Precise, continuous, sensitive and specific monitoring together with prompt notification of vascular compromise is crucial for the success of the procedure. In this review, we provide a classification and brief description of the reported methods for monitoring the micro-vascular flap and a summary of the benefits over direct visual monitoring. Over 40 different monitoring techniques have been reported but their comparative merits are not always obvious. One looks for early detection of a flap's compromise, improved flap salvage rate and a minimal false-positive or false-negative rate. The cost-effectiveness of any method should also be considered. Direct visualisation of the flap is the method most generally used and still seems to be the simplest, cheapest and most reliable method for flap monitoring. Considering the alternatives, only implantable Doppler ultrasound probes, near infrared spectroscopy and laser Doppler flowmetry have shown any evidence of improved flap salvage rates over direct visual monitoring.

The use of sentinel skin islands for monitoring buried and semi-buried micro-vascular flaps. Part II: Clinical application

Despite the high success rate of micro-vascular flaps, anastomosis compromise occurs in 5-10% and that can lead to flap failure. Reliable monitoring of the flap is therefore of similar importance to that of the precise surgical procedure itself. Multiple methods have been reported for monitoring of the flap vitality, the first one being direct visual monitoring. In buried flaps direct visualisation is not feasible or is unreliable. In these cases we can extend the buried flap to expose a segment of it to act as a monitoring sentinel. For the purpose of this review we used our clinical experience as a starting point, and for the extended information and expertise we conducted a search of the PubMed database. Over 40 monitoring techniques have been reported to-date. Direct visual monitoring is still generally used method with a reliability of up to 100% and an overall success rate of up to 99%. Direct visualisation remains as the simplest, cheapest and yet a very reliable method of flap monitoring. In this review we provide a description of various possible techniques for externalising part of a buried flap, define the tissues that can be used for this purpose and we summarise the procedures that should be followed to achieve the best reliability and validity of monitoring the skin island.

Distinction between arterial and venous occlusion with tissue oxygen pressure in a porcine fascio-cutaneous flap model

BACKGROUND

In recent years, many devices have been developed to monitor free flaps. The Licox probe, which measures tissue oxygen pressure (PtO₂ ), is one of the available devices. Our aim was to demonstrate that PtO₂ could distinguish arterial from venous occlusion in a porcine fascio-cutaneous flap model.

MATERIALS AND METHODS

Twenty pigs (Sus scrofa domestica, Youna strain, males) were included in this study. The median weight was 87.6 kg (84.6-90.8). Bilateral fascio-cutaneous flaps based on the superficial inferior epigastric pedicle were harvested from each pig. Thirty-eight flaps were analyzed in this study and were monitored by a Licox system during vascular occlusion. The flaps were randomized into two groups according to the clamped vessel: the arterial group (n = 19) and the venous group (n = 19). After a stabilization period of almost 40 min, vascular clamping (arterial or venous) was performed using a microvascular clamp for almost 20 min. The curve profiles were compared between arterial and venous occlusion.

RESULTS

The inflection point was reached significantly faster in the arterial group: 11 min (9-16) for arterial clamping and 17 min (13-23) for venous clamping (p = .001). A total of 18/19 (95%) pigs in the arterial group and 13/19 (68%) in the venous group (p = .09) reached a level lower than 10 mmHg. The median duration for pressure to drop below 10 mmHg was 9 min (6-12) for arterial clamping and 10 min (9-16) for venous clamping (p = .06).

CONCLUSION

We showed that PtO₂ decreased faster in cases of arterial occlusion than in cases of venous occlusion in a pig model. Based on this observation, it may be possible to distinguish arterial from venous occlusion.

The Impact of Indocyanine-Green Fluorescence Angiography on Intraoperative Decision-Making and Postoperative Outcome in Free Flap Surgery

Background Reliable perfusion of the distal portions of free flaps is decisive for the reconstructive success. Indocyanine green near-infrared video angiography (ICG-NIR-VA) has been adopted for objective assessment of free flap tissue perfusion but is thus far not used on a routine basis. Therefore, we investigated its intraoperative impact on decision-making and postoperative outcome.

Methods From January 2017 to June 2019, 88 consecutive adipo- or fasciocutaneus free flaps were performed in conjunction with intraoperative ICG-NIR-VA. Free flap tissue perfusion was first assessed clinically and then compared with ICG-NIR-VA findings. Based on the results, the decision for intraoperative trimming of critically perfused flap zones was made. The way of decision-making, flap success, and failure rates as well as intra- and postoperative complication rates were analyzed.

Results The overall free flap success rate was 92.0%. Partial flap necrosis occurred in five cases (5.7%) and total flap necrosis in two cases (2.3%). ICG-NIR-VA aided decision-making and flap design in 34 cases (38.6%) and led to complication-free postoperative courses. When ICG-NIR-VA was relied on (82 out of 88 flaps; 93.2%), there was no unpredicted postoperative tissue necrosis (overestimation). When ICG-NIR-VA was not relied on (6 out of 88 flaps; 6.8%), there were five cases of postoperative partial flap necrosis and one case of uneventful healing (underestimation). The sensitivity of ICG-NIR-VA was 100% (95% confidence interval [CI]: 64.6–100) and the specificity was 98.8% (95% CI: 93.3–100) with a positive predictive value of 87.5% (95% CI: 52.9–99.4) and a negative predictive value of 100% (95% CI: 95.4–100).

Conclusion Intraoperative ICG-NIR-VA objectified free flap perfusion and thus refined surgical decision-making on flap design in all cases. It could always predict tissue necrosis and subjectively improved outcomes in free flap surgery at our institution. Furthermore, it could be easily implemented in intraoperative routine, only adding minimal additional operative time.

Monitoring of Myocutaneous Flaps by Measuring Capillary Glucose and Lactate Levels: Experimental Study

INTRODUCTION

In surgery, certain defects require reconstruction with a microsurgical flap. The free flap failure rate varies between 2% and 5%. Vascular thrombosis is the most frequent complication and represents 15% to 73% of failures. The success rate of salvage therapy is greater when salvage surgery is early. Currently, clinical monitoring is the criterion standard but many noninvasive or minimally invasive techniques have been developed to improve early diagnosis of complications of vascular thrombosis. The aim of our experimental study was to compare clinical assessments with measurements of capillary glycemia and lactatemia during the monitoring of free flaps.

MATERIALS AND METHODS

Myocutaneous latissimus dorsi flaps with skin paddles were created in pigs under general anesthesia. For each animal, 2 flaps were created (right and left) using the same technique. Four groups were made: group 1 (no flap ligation: control group), group 2 (flap with permanent ligation of the artery), group 3 (flap with permanent ligation of the two veins), group 4 (flap with transient ligation of the artery and 2 veins for 1 hour). The postoperative monitoring protocol consisted of monitoring the clinical, biological (glucose and lactate), and histological parameters.

RESULTS

Eight animals were operated on and sixteen flaps were created. Each flap was clinically and biologically tested 25 times. Clinical, biological, and histological monitoring showed significant variations between the groups. The analysis of variance of capillary glycemia and lactatemia showed statistically significant difference between control group and group 2 (P < 0,0001), group 3 (P < 0,0001), or group 4 (P < 0,0001). There were no histological abnormalities after transient ligature at different times contrary to permanent ligature.

DISCUSSION-CONCLUSION

Measuring capillary levels of lactate and glucose associated with clinical monitoring may shorten the time to diagnosis of flap failure. Ultimately, this will save lives and achieve better functional and aesthetic results.

Multipoint Tissue Circulation Monitoring with a Flexible Optical Probe

Compromised circulation is a potential complication during the postoperative period following tissue transplantation. The use of a monitoring device allows physicians to detect compromised circulation immediately. Such monitoring devices need to be continuously usable, wearable, and area-detectable. However, existing devices fail to satisfy all of these requirements simultaneously. We developed a wearable, multipoint pulse wave-monitoring device. An array of reflective optical sensors implemented on a thin film substrate was used as a lightweight and flexible probe. As a model of tissue transplantation, an inguinal flap in a Wistar rat was dissected and freed from all subcutaneous tissue. By ligating the artery or vein, ischemia or congestion was induced in the tissue. In a human study, ischemia or congestion was induced in the palm by pressing the feeding artery or cutaneous vein, respectively. The amplitude of the pulse wave was evaluated using the power spectrum of Fourier transformed signals. Pulse wave amplitude significantly decreased under compromised circulation in both animal and human models. Moreover, we accomplished 1 week of continuous wireless monitoring in healthy subjects. These results demonstrated the potential utility of the developed device in postoperative blood-flow monitoring to improve the rescue rate of transplanted tissue.

Free Flap Monitoring Using Near-Infrared Spectroscopy: A Systemic Review

BACKGROUND

Although free flaps have become a reliable technique, vascular occlusion remains a significant risk. Flap survival is closely linked to the time interval between the onset and surgical repair of a microvascular problem. The newly emerged near-infrared spectroscopy (NIRS) shows the characteristics of being noninvasive, continuous, easy to use, objective, and immediately reflective, possibly making it an ideal candidate for postoperative flap monitoring.

METHODS

A systemic review was conducted to determine the clinical value of NIRS in the early detection of vascular crisis associated with a free flap. A literature search was conducted using PubMed (MEDLINE), the Cochrane Library, and Web of Science from database inception through October 2013. Studies were selected strictly according to the inclusion/exclusion criteria by 2 independent reviews.

RESULTS

Eight studies were finally included in this review. A total of 710 free flap procedures were performed in 629 patients using NIRS for monitoring. At the same time, 433 free flaps performed in 430 patients without the use of NIRS were included as the control group. No significant differences in the rates of vascular crisis (P = 0.917) and re-exploration (P = 0.187). However, there were significant differences in the salvage rates (P < 0.001) and flap failure rates (P = 0.003). For the free flaps monitored by NIRS that were not associated with vascular crisis, no alarms were raised by NIRS, giving 100% sensitivity and specificity.

CONCLUSION

Near-infrared spectroscopy seems to be a highly suitable candidate for postoperative flap monitoring. Larger-scale, randomized, multicentric clinical trials are needed in the future.

Indocyanine Green Fluorescence for Free-Flap Perfusion Imaging Revisited: Advanced Decision Making by Virtual Perfusion Reality in Visionsense Fusion Imaging Angiography

BACKGROUND

Near-infrared indocyanine green video angiography (ICG-NIR-VA) has been introduced for free-flap surgery and may provide intraoperative flap designing as well as postoperative monitoring. Nevertheless, the technique has not been established in clinical routine because of controversy over benefits. Improved technical features of the novel Visionsense ICG-NIR-VA surgery system are promising to revisit the field of application. It features a unique real-time fusion image of simultaneous NIR and white light visualization, with highlighted perfusion, including a color-coded perfusion flow scale for optimized anatomical understanding.

METHODS

In a feasibility study, the Visionsense ICG-NIR-VA system was applied during 10 free-flap surgeries in 8 patients at our center. Indications included anterior lateral thigh (ALT) flap (n = 4), latissimus dorsi muscle flap (n = 1), tensor fascia latae flap (n = 1), and two bilateral deep inferior epigastric artery perforator flaps (n = 4). The system was used intraoperatively and postoperatively to investigate its impact on surgical decision making and to observe perfusion patterns correlated to clinical monitoring.

RESULTS

Visionsense ICG-NIR-VA aided assessing free-flap design and perfusion patterns in all cases and correlated with clinical observations. Additional interventions were performed in 2 cases (22%). One venous anastomosis was revised, and 1 flap was redesigned. Indicated by ICG-NIR-VA, 1 ALT flap developed partial flap necrosis (11%).

CONCLUSIONS

The Visionsense ICG-NIR-VA system allowed a virtual view of flap perfusion anatomy by fusion imaging in real-time. The system improved decision making for flap design and surgical decisions. Clinical and ICG-NIR-VA parameters correlated. Its future implementation may aid in improving outcomes for free-flap surgery, but additional experience is needed to define its final role.

Do adjunctive flap-monitoring technologies impact clinical decision making? An analysis of microsurgeon preferences and behavior by body region

BACKGROUND

Multiple perfusion assessment technologies exist to identify compromised microvascular free flaps. The effectiveness, operability, and cost of each technology vary. The authors investigated surgeon preference and clinical behavior with several perfusion assessment technologies.

METHODS

A questionnaire was sent to members of the American Society for Reconstructive Microsurgery concerning perceptions and frequency of use of several technologies in varied clinical situations. Demographic information was also collected. Adjusted odds ratios were calculated using multinomial logistic regression accounting for clustering of similar practices within institutions/regions.

RESULTS

The questionnaire was completed by 157 of 389 participants (40.4 percent response rate). Handheld Doppler was the most commonly preferred free flap-monitoring technology (56.1 percent), followed by implantable Doppler (22.9 percent) and cutaneous tissue oximetry (16.6 percent). Surgeons were significantly more likely to opt for immediate take-back to the operating room when presented with a concerning tissue oximetry readout compared with a concerning handheld Doppler signal (OR, 2.82; p < 0.01), whereas other technologies did not significantly alter postoperative management more than simple handheld Doppler. Clinical decision making did not significantly differ by demographics, training, or practice setup.

CONCLUSIONS

Although most surgeons still prefer to use standard handheld Doppler for free flap assessment, respondents were significantly more likely to opt for immediate return to the operating room for a concerning tissue oximetry reading than an abnormal Doppler signal. This suggests that tissue oximetry may have the greatest impact on clinical decision making in the postoperative period.

Variables affecting postoperative tissue perfusion monitoring in free flap breast reconstruction

Postoperative flap monitoring is a key component for successful free tissue transfer. Tissue oxygen saturation measurement (TOx) with near-infrared spectrophotometry (NIRS) is a method used for this purpose. The aim of this study was to identify external variables that can affect TOx. Patients who had breast reconstruction with free flaps were monitored prospectively and intra-operative details were recorded. Flap TOx was recorded with NIRS pre-extubation, postextubation, and then every four hours for 36 hours. At each of these time points, blood oxygen saturation (SO2), amount of supplemental oxygen, and blood pressure were recorded. Thirty flaps were monitored. Initially, a significant trend over time was detected such that for every increase of 24 hours, TOx decreased on average by 2.1% (P = 0.025). However, when accounting for SO2 levels, this decrease was no longer significant (P = 0.19). An increase by 1% in SO2 produced an increase in TOx reading of 0.36 (P = 0.007). The amount of supplemental O2, systolic blood pressure, and diastolic blood pressure did not have a significant impact on TOx (P > 0.05). The TOx values were highest in the free TRAM flaps and were lower in decreasing order in the muscle-sparing TRAM, DIEP, and SIEA flaps (P > 0.05). The TOx values did not significantly correlate with vessel size, perforator number, or perforator row. Postoperative flap TOx was found to correlate with SO2 and was not significantly dependent on blood pressure, supplemental O2, or surgical variables. Careful interpretation of oximetry values is essential in decision making during postoperative flap monitoring.

The Relationship between Oxygen Saturation and Color Alteration of a Compromised Skin Flap: Experimental Study on the Rabbit

Background

The aim of this study was to collect important data on the time of oxygen saturation change in relation to skin flap color alteration using non-invasive pulse oximetry to evaluate its ability to provide continuous monitoring of skin flap perfusion.

Methods

An experimental study on the monitoring of blood perfusion of 20 tube-island groin flaps of 10 male New Zealand rabbits was performed using pulse oximetry. The animals were randomly assigned to one of two groups representing a blockage of either arterial or venous blood flow. The oxygen saturation change and clinical color alteration were monitored from the beginning of vessel clamping until the saturation became undetectable. The result was analyzed by the t-test using SSPS ver. 10.0.

Results

The mean times from the vessel clamping until the saturation became undetectable were 20.19±2.13 seconds and 74.91±10.57 seconds for the artery and vein clamping groups, respectively. The mean time of the clinical alteration from the beginning of vein clamping was 34.5±11.72 minutes, while the alteration in flaps with artery clamping could not be detected until 2.5 hours after clamping.

Conclusions

The use of neonate-type reusable flex sensor-pulse oximetry is objective and effective in early detection of arterial and vein blockage. It provides real-time data on vessel occlusion, which in turn will allow for early salvaging. The detection periods of both arterial occlusion and venous congestion are much earlier than the color alteration one may encounter clinically.

Comparison of tissue oxygenation and compartment pressure following tibia fracture

OBJECTIVE

We investigated the ability of direct continuous measurement of intramuscular tissue oxygenation (PmO(2)) to detect acute ischaemia in the leg in patients at risk for acute extremity compartment syndrome. Following tibia fracture treated by intramedullary nailing, we compared the proportions of PmO(2) and compartment pressure (CP) measurements that met the warning criteria for compartment syndrome.

METHODS

Participants included 10 patients sustaining acute isolated closed tibia shaft fractures treated by intramedullary nailing. A tissue oxygenation probe and a CP probe were percutaneously placed into the anterior compartment of the leg. PmO(2) and CP in the anterior compartment were measured in the injured leg for 48 h postoperatively. Measurements meeting the warning criteria were defined as PmO(2) < 10 mmHg, CP > 30 mmHg and perfusion pressure ΔP < 30 mmHg.

RESULTS

None of the patients developed compartment syndrome. Comparison of CP and PmO(2) showed a CP > 30 mmHg in 50.39% of CP measurements in all patients and a PmO(2) < 10 mmHg in 0.75% of PmO(2) measurements in two patients (P = 0.005). Comparison of ΔP and PmO(2) showed a ΔP < 30 mmHg in 31.01% of ΔP measurements in nine patients and a PmO(2) < 10 mmHg in 0.76% of PmO(2) measurements in one patient (P = 0.01).

CONCLUSION

In the absence of compartment syndrome, pressure measurements following tibia fracture treated with intramedullary nailing often met the warning criteria, whereas PmO(2) did not, suggesting that measurement of intramuscular tissue oxygenation may represent a potential method for the identification of acute compartment syndrome that deserves continued investigation.

Transcutaneous PCO2 Measurement at Low Temperature for Reliable and Continuous Free Flap Monitoring: Experimental and Clinical Study

BACKGROUND

Measurement of transcutaneous oxygen pressure (TcPO2) and transcutaneous carbon dioxide pressure (TcPCO2) has been used for free flap monitoring. Because these values are obtained with sensor probes heated to 44°C, there is potential for low-temperature burns on skin flaps. We measured TcPO2 and TcPCO2 at 37°C in both animals and humans to determine the feasibility and safety of the procedure as a postoperative flap monitoring method.

METHODS

Twelve epigastric island flaps were elevated in rabbits, and TcPO2 and TcPCO2 were measured at 37°C before and after ligation of the pedicles. In addition, TcPO2 and TcPCO2 at 37°C were measured in healthy men. Subsequently, the method was applied to postoperative monitoring of free flaps in 49 clinical cases.

RESULTS

TcPO2 and TcPCO2 values were significantly affected by the experimental flap elevation. A rapid increase in TcPCO2 was observed with both arterial and venous occlusion. In the healthy men, TcPO2 and TcPCO2 were measurable at all skin surface sites. In the clinical cases of free flap transfer, TcPO2 values remained very low for at least 72 hours. TcPCO2 values ranged from 40 to 70 mm Hg for 72 hours in more than 80% of cases. In 2 cases, TcPCO2 values increased to more than 90 mm Hg, and exploration surgery was performed. These compromised flaps were saved by reanastomosis of the veins.

CONCLUSIONS

Continuous monitoring of TcPCO2 at 37°C can provide objective information and alert doctors and nurses to the need for checking the free flap.

Long term study into surgical re-exploration of the 'free flap in difficulty'

BACKGROUND

Free tissue transfers must survive in order to achieve their surgical goals. There is little consensus about managing the 'failing' free flap, and practice is often guided by anecdote.

MATERIAL AND METHODS

We have prospectively collected data about all free flaps performed within our department between 1985 and 2008 (2569 flaps). We identified 327 flaps which were re-explored a total of 369 times. We analysed these flaps with regard to indication for re-exploration, operative findings and outcome.

RESULTS

Thirteen percent (327) of free flaps were re-explored. Of these, 291 (83%) had a successful outcome. Successful re-explorations took place at a mean 19h post-op and unsuccessful re-explorations at a mean 56h post-op. Clinical diagnosis prior to re-exploration was confirmed operatively in 91% of cases.

CONCLUSION

We have considered the factors that allowed us to achieve the salvage rates described over a prolonged period, and identified two key areas. Firstly, we favour a model for free flap monitoring with clinical judgement at its core. Secondly, we feel the facility to recover patients post-operatively in a specialised, warmed environment, and return them to theatre quickly should the need arise, is essential. These two simple, yet institutionally determined factors are vital for maintaining excellent success rates.

Capillary blood gas: a novel means of assessing free flap perfusion in an animal model

OBJECTIVE

To demonstrate that in comparison to implantable O(2) microelectrodes, capillary blood gas measurements represent a reliable, accessible, and easy method of identifying failing free flaps.

STUDY DESIGN

Groin fasciocutaneous flaps were elevated in 10 rats and following venous occlusion, O(2) microelectrode measurements (pO(2) and flow), and capillary blood gas measurements (pO(2), pCO(2), pH, HCO(3)) were obtained at 10-minute intervals.

RESULTS

Measurements with capillary blood gas paralleled measurements with O(2) microelectrodes. Average capillary blood gas pO(2) fell from 42.71 to 31.57 mm Hg at 10 minutes and then to 28.67 mm Hg at 20 minutes. Average pH fell from 7.38 to 7.33 at 10 minutes and to 7.30 at 20 minutes. Results were statistically significant with both the paired Student's t test and the Wilcoxon signed rank test.

CONCLUSION

While providing users an ability to simultaneously monitor accepted modalities of flap surveillance, pH and pO(2), capillary blood gas is a reliable, accessible, and reproducible marker of flap health.

Experimental study on predicting skin flap necrosis by fluorescence in the FAD and NADH bands during surgery

The objective of the present study was to assess the feasibility of using endogenous fluorescence in intraoperative prediction of skin flap necrosis. The investigation was carried out in 10 Sprague-Dawley rats in which proximally based over-dimensioned random pattern skin flaps were dissected on the back and thereafter fixed into position. Immediately after surgery on each rat, synchronous fluorescence spectra (Deltalambda=90 nm) from five parts of the skin flap surface were measured. The presence of necrosis was evaluated on postoperative day 7. In flap parts designated as necrotic (n=18), a significantly lower (P<0.001) fluorescent signal from the nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) bands (360-380 and 440-460 nm, respectively) was detected in comparison with the vital parts (n=32) (for FAD:1767+/-39 versus 2579+/-65 auxiliary units [A.U]. and for NADH:11724+/-340 versus 16810+/-473 A.U.). The results suggested a close relationship between the fluorescent signals from the FAD and NADH bands on one side and flap necrosis or survival on the other side. Thus, the use of fluorescence spectroscopy may be considered as a valuable noninvasive tool for the prediction of skin flap necrosis.

The Use of Radial Vessel Stump in Free Radial Forearm Flap as Flap Monitor in Head and Neck Reconstruction

The versatile use of the free radial forearm flap for the reconstruction of pharyngoesophageal defects has been proven ideal in previous studies. However, the monitoring of flap viability when buried underneath the skin in head and neck surgery still posed technical difficulties. An innovative monitoring method for the buried free radial forearm flap by using distal radial vessel stump elevated over the skin is to be presented here. Eighteen patients received free radial forearm flap reconstruction for their pharyngoesophageal defects after tumor ablation during June 2003 to March 2005. All patients were males; ages ranged from 36 to 71 years, averaging 53.2 years old. Fourteen skin tubing and patches were designed for the defects. The pharyngoesophageal defects ranged from 6 to 12 cm in length, averaging 8.5 cm. The free radial forearm flap was designed to allow a distal radial vessel stump about 3 cm long, which was then elevated above the skin in the neck region after insetting to act as a monitor for the viability of the buried flap. The flap viability can be easily demonstrated simply by observing continuous pulsation coming from the distal radial vessel stump with naked eyes. The monitoring stump was then ligated and resected at bedside after the viability of the buried flap was insured 2 weeks postoperatively. All free flap transfers were successful. One case was found with kinking of artery during the operation and it was corrected immediately. One case with venous insufficiency was detected 13 hours after the operation and the flap was salvaged successfully by thrombectomy and venous reanastomosis. Three patients developed temporary fistula and healed spontaneously after conservative treatment. Deep neck infections were found in patients, and recovered after aggressive antibiotic treatment. Two patients had esophagocutaneous fistula and needed secondary surgical intervention. The use of distal radial vessel stump as a monitor for the buried flap is a reliable method in head and neck surgery. It not only allows easy monitoring, no further donor site morbidity, but it also eliminates the need for special monitoring device.

Continuous postoperative monitoring of cutaneous free flaps using near infrared spectroscopy

Reliable detection of circulatory compromise threatening free-flap viability is essential for prompt surgical intervention and flap salvage. Numerous techniques have been developed to address the issue of postoperative flap monitoring but none have achieved universal acceptance. Near infrared spectroscopy (NIRS) is a noninvasive technique that allows continuous monitoring of tissue oxygenation and perfusion. It is increasingly recognised to be a reliable method for flap viability assessment. This study was designed to investigate the ability of NIRS to detect and identify microvascular thrombosis endangering flap survival. To our knowledge, this is the first clinical evaluation of NIRS used for continuous monitoring of free flaps.

METHODS

Fifty flaps used for autologous breast reconstruction in 48 patients were included in this prospective clinical study. NIRS was employed for 72-h continuous postoperative monitoring. The data were compared to findings of clinical assessments.

RESULTS

Ten flaps (20%) developed 13 anastomosis thromboses (two arterial and 11 venous). NIRS detected all cases of flow failure prior to clinical observation with no false positives or negatives. Based on consistent patterns of NIRS parameter changes, it was possible to differentiate between changes caused by arterial and venous thrombosis with accuracy before surgical re-exploration. The salvage rate was 70%. Overall flap viability was 94%.

CONCLUSIONS

Continuous NIRS monitoring can reliably detect and identify early stages of arterial and venous thrombosis, and is a credible method for noninvasive postoperative flap surveillance. Based on these findings, we advocate its use for monitoring of flaps with a cutaneous component.

Detection of perfusion disturbances in digit replantation using near-infrared spectroscopy and serial quantitative fluoroscopy

PURPOSE

The postoperative monitoring of digit replants continues to be a challenge. Current objective methods of digit monitoring have not been adopted widely because of their complexity or lack of sensitivity. Because tissue oxygen tension correlates directly with vascular inflow, a device that tracks changes in tissue oxygenation may be useful to monitor the perfusion and viability of digits after revascularization. A clinical study was undertaken to evaluate noninvasive monitoring of tissue oxygenation using near-infrared spectroscopy in postoperative digit replantation.

METHODS

Forty-eight patients were enrolled and 64 digits were monitored at 1 institute. There were 43 male and 5 female patients with an average age of 41 years (range, 13-79 y). Digits were monitored by clinical examination, fluorescein, and a tissue oximeter at 1- to 2-hour intervals for 24 to 48 hours.

RESULTS

Sixty-one digits survived and 3 digits failed. In the surviving digits the fluorescein and tissue oxygen saturation (StO2) readings were similar to the control digit readings. There were no significant differences between fluorescein and StO2 or between StO2 readings for control and surviving digits. In the digits that failed to survive both fluorescein and StO2 readings were significantly lower in the failed compared with control digits. The StO2 values for failed digits were 30% to 70% lower and showed greater variation than the StO2 values for the control digits. There were no complications associated with fluorescein or tissue oxygenation measurements.

CONCLUSIONS

Near-infrared spectroscopy measurement of tissue oxygenation correlates with fluorescein monitoring and digit perfusion. This noninvasive monitoring is easy, reliable, safe, and useful in postoperative monitoring of digit replantation.

TYPE OF STUDY/LEVEL OF EVIDENCE

Diagnostic, Level I.

Prediction of flap necrosis with laser induced indocyanine green fluorescence in a rat model

Prediction of necrosis has a clinical relevance in all fields of plastic surgery. The new application of indocyanine green (ICG) fluoroscopy in plastic surgery allows an objective quantification of skin perfusion and a high topographical resolution. The aim of the present study is to determine threshold values for flap perfusion under well-defined experimental conditions. Twenty random pattern flaps with a length to width ratio of 4:1 (8 x 2 cm(2)) were dissected on the anterior abdominal wall of 20 male Sprague-Dawley rats. ICG fluoroscopy was performed at the end of the operation. The animals were sacrificed at the seventh postoperative day with a reliable necrosis of the distal part of the flaps. Postoperative ICG fluoroscopy then was analysed both in regions that will survive and undergo necrosis. At day 7 a mean area of 5.5 cm(2) (57% of the total flap area) survived and a mean of 3.8 cm(2) (43%) became necrotic. The surviving part of the flap had a mean perfusion index of 62% compared to reference skin. The distal parts of the flap that necrotised showed an average perfusion index of only 19% postoperatively. Differences were statistically highly significant (p<0.001). Indocyanine green fluoroscopy is a useful tool to evaluate perfusion topographically and predict necrosis. From a statistical point of view a perfusion index of less than 25% of the reference skin can be considered as a sign of developing flap necrosis.

The role of near-infrared angiography in the assessment of post-operative venous congestion in random pattern, pedicled island and free flaps

Indocyanine green near-infrared-video angiography (ICG-NIR-VA) was recently introduced for measuring perfusion of skin flaps. The prognostic value of this method with regards to post-transfer manipulations of the flap, and subsequently, flap survival is not adequately documented in the literature. In this paper, we report our experience with the ICG-NIR-VA in the intraoperative evaluation and post-operative follow-up of nine flaps (2 large random pattern, 4 pedicled island and 3 free flaps) used in various reconstructive procedures. Two flaps (1 random pattern and 1 free flap) showed delayed intraoperative uptake in ICG-NIR-VA. In the post-operative phase, (days 1-3) six flaps (1 random pattern, 2 axial pattern and 3 free flaps) showed a delay both in the ICG-NIR-VA uptake, as well as clearance. However, a clinical correlate was observed only in 2 of the 6 flaps demonstrating this delay: general and partial venous congestion was seen in a distally based interosseous posterior flap and a free lateral arm flap respectively. Leeches were implemented only based on the clinical signs. In one distally based perforator flap, the decision on perfusion augmentation via microanastomosis was based on the intraoperative ICG-NIR-VA finding. All flaps showed uneventful healing. Based on our observations, the question arises, not whether the ICG-NIR-VA is sensitive for the prognosis of venous congestion, upon which the flap manipulation strategy might rest-but whether it is too sensitive. Further, prospective studies are necessary.

Postoperative monitoring of free flaps in UK plastic surgery units

Monitoring free-tissue transfers in the postoperative period is valuable for detection of failing flaps. As well as conventional methods, a myriad of sophisticated techniques have been reported in the literature. Using a postal questionnaire, a survey was conducted to delineate current protocols employed in UK plastic surgery units. Data were received from 148 plastic surgeons in 51 units. All surgeons used clinical assessment, although there was significant disparity in the duration and frequency of postoperative monitoring. Adjuvant techniques such as laser Doppler flowmetry were routinely used by less than 20% of surgeons. We conclude that there is considerable variation in postoperative monitoring of free flaps, with significant clinical and resource implications. A protocol based on robust evidence is thus recommended.

Intra- und postoperatives Monitoring von Lappentransplantaten

BACKGROUND

According to Schmelzeisen et al. (1996), the failure rate for microvascular free flaps is 5%. While surface tissue oxygenation can be assessed clinically, if necessary by a puncture, the oxygen supply to deeper areas mostly cannot be checked. We therefore wished to find whether measurement of tissue pO(2) would prove to be an objective and practical technique that could be used for continuous and accurate intra- and postoperative evaluation of flap perfusion.

MATERIAL AND METHODS

A Clark-type microcatheter was used intra- and postoperatively to monitor tissue pO(2) in 5 pedicled pectoralis major flaps and 32 free revascularized flaps (9 jejunal flaps, 5 latissimus dorsi flaps, 6 radial forearm flaps and 12 scapular flaps).

RESULTS

The mean values for tissue pO(2) were significantly lower in pedicle grafts than in free revascularized flaps. Within in each flap group the pO(2) values measured did not vary significantly over an observation period of up to 77.2 h after transplantation.

CONCLUSIONS

Continuous measurement of tissue pO(2) by means of a Clark-type microcatheter combined with clinical examination constitutes a reliable method of monitoring tissue oxygenation in pedicle grafts and free revascularized flaps during the intra- and postoperative phases. Analysis of small and of wide fluctuations in pO(2) values may help in the diagnosis of early arterial and venous obstructions in flaps and may in the future result in new insights into the tissue oxygenation in surgical flaps allowing some alleviation of the problems currently experienced in clinical monitoring.

Micro-lightguide spectrophotometry as an intraoral monitoring method in free vascular soft tissue flaps

PURPOSE

The aim of this prospective study was to measure the hemoglobin oxygen saturation (HbO(2)%) and relative Hb concentration of free vascular soft tissue flaps using micro-lightguide spectrophotometry. The objective was to measure the normal range and topographic differences in HbO(2)% and rel. Hb conc. in tissue transfers before establishing this as a clinical method for monitoring perfusion and vitality.

PATIENTS AND METHODS

In 39 patients who had received free vascular soft tissue flaps (34 radial forearm flaps; 8 latissimus flaps) to cover defects after tumor surgery, the capillary HbO(2)% in transferred tissue was measured spectrophotometrically preoperatively at the donor site and postoperatively up to the third postoperative day. On average about 500 hemoglobin spectra (200 to 800 spectra) were measured over each 24-hour period. Additionally, the relative Hb concentration was determined for the individual measuring times. The measurements were carried out topographically on the flap base, flap center, and flap periphery.

RESULTS

The preoperative HbO(2) values at the donor site of free soft tissue flaps were between 20% and 40% in all topographic regions. In the case of clinically successful flaps, a normal distribution of the HbO(2) values of 20% to 80% was obtained in the immediate postoperative period, and from the second day on, a normal distribution of 45% to 60%. In the case of 2 flaps with partial necrosis, HbO(2) values of less than 10% to 15% were measured from the second postoperative day on. The relative Hb concentration had no influence on the amount of HbO(2)% measured in the transferred capillaries. In the postoperative phase, here was no topographic difference between the individual flap regions.

CONCLUSIONS

As a noninvasive method, micro-lightguide spectrophotometry permits quantitative determination of HbO(2)% and relative Hb concentration over the entire surface of soft tissue flaps. In the case of partially unsuccessful flaps, HbO(2) values of less than 10% to 15% were measured beforehand, thus indicating that these HbO(2) values are not sufficient to support the vitality of the free tissue transfer. When combined with clinical observation, application can be recommended for the vitality measurement of free soft tissue flaps and permits more information to be obtained on topographic capillary perfusion conditions.

Testing a device to replace the leech for treating venous congestion

OBJECTIVE

To test the effectiveness of a device designed to promote decongestion and tissue survival of a fasciocutaneous flap during 15 hours of complete venous obstruction.

METHODS

In a porcine model, a 9 x 7-cm fasciocutaneous flap was elevated and the associated veins were clamped, causing complete venous obstruction for 15 hours in 6 control and 6 treatment animals. Up to 3 devices were used to treat the flap in a predetermined pattern. Control flaps were not treated. Measures of treatment efficacy included blood volumes removed; changes in skin color, surface perfusion, and tissue oxygen tension; and end point histologic findings.

RESULTS

Control flaps were characterized by progressive darkening of skin color, undetectable surface perfusion, and low levels of oxygen tension. Histologic assessment showed severe congestion and extravasation of blood and distinct signs of necrosis. In contrast, treated flaps had significant improvements in skin color, surface perfusion, and subcutaneous oxygen tension. Histologic analysis showed little, if any, congestion and no signs of necrosis. Mean blood volume removed was 29.5 mL/h.

CONCLUSION

The device was effective in decongesting a large area of tissue during 15 hours of complete outflow obstruction, based on quantitative measurements of tissue health and viability.

Use of colour duplex Doppler imaging in the postoperative assessment of buried free flaps

The postoperative assessment of free flaps is essential to identify and act on signs of incipient flap failure. Where the flap is completely buried, this becomes almost impossible unless part of the flap is exteriorised or an overlying skin window is used. Alternatively, complicated and often impractical monitoring devices have been advocated, but these have failed to gain widespread acceptance. A simpler solution to this problem has been evaluated in a series of patients using colour duplex Doppler imaging. This re-appraisal of a previously reported technique has been facilitated by updated technology in diagnostic radiology. Duplex Doppler imaging was confirmed as an accurate, non-invasive, and inexpensive tool for the postoperative measurement of blood flow within the pedicles of five buried free flaps in four patients undergoing surgery in our unit.