Techniques of postoperative blood flow monitoring after free tissue transfer: an overview

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

Photoplethysmography in postoperative monitoring of deep inferior epigastric perforator (DIEP) free flaps

OBJECTIVE

Deep inferior epigastric perforator (DIEP) free flaps are widely used as a reconstruction option following mastectomy in breast cancer. During such cases partial tissue necrosis can occur due to the insufficient blood supply to the transplanted tissue site. Therefore, monitoring of flap perfusion and early detection of flap failure is a prerequisite to flap survival. There is a need to develop a non-invasive, easy to use, reproducible and inexpensive monitoring device to assess flap perfusion postoperatively.

APPROACH

A three-wavelength reflective optical sensor and processing system based on the principle of photoplethysmography (PPG) has been developed to investigate blood volumetric changes and estimate free flap blood oxygen saturation continuously and non-invasively in DIEP free flaps in the postoperative period. The system was evaluated in 15 patients undergoing breast reconstructive surgery using DIEP free flap. Main results and Significance: Good quality red, infrared and green PPG signals were obtained in the postoperative period. Initial estimation of blood oxygen saturation values estimated from the free flap PPGs seem to be in broad agreement with the commercial finger pulse oximeter used in this study. This pilot study has demonstrated that PPG has the potential to be used as a monitoring technique in assessing free flap viability.

Oxygen-Sensing Paint-On Bandage: Calibration of a Novel Approach in Tissue Perfusion Assessment

BACKGROUND

Knowledge of tissue oxygenation status is fundamental in the prevention of postoperative flap failure. Recently, the authors introduced a novel oxygen-sensing paint-on bandage that incorporated an oxygen-sensing porphyrin with a commercially available liquid bandage matrix. In this study, the authors extend validation of their oxygen-sensing bandage by comparing it to the use of near-infrared tissue oximetry in addition to Clark electrode measurements.

METHODS

The oxygen-sensing paint-on bandage was applied to the left hind limb in a rodent model. Simultaneously, a near-infrared imaging device and Clark electrode were attached to the right and left hind limbs, respectively. Tissue oxygenation was measured under normal, ischemic (aortic ligation), and reperfused conditions.

RESULTS

On average, the oxygen-sensing paint-on bandage measured a decrease in transdermal oxygenation from 85.2 mmHg to 64.1 mmHg upon aortic ligation. The oxygen-sensing dye restored at 81.2 mmHg after unclamping. Responses in both control groups demonstrated a similar trend. Physiologic changes from normal to ischemic and reperfused conditions were statistically significantly different in all three techniques (p < 0.001).

CONCLUSIONS

The authors' newly developed oxygen-sensing paint-on bandage exhibits a comparable trend in oxygenation recordings in a rat model similar to conventional oxygenation assessment techniques. This technique could potentially prove to be a valuable tool in the routine clinical management of flaps following free tissue transfer. Incorporating oxygen-sensing capabilities into a simple wound dressing material has the added benefit of providing both wound protection and constant wound oxygenation assessment.

Free flap pulse oximetry utilizing reflectance photoplethysmography

The successful salvage of a free flap is dependent on the continuous monitoring of perfusion. To date there is no widely accepted and readily available post-operative monitoring technique to reliably assess the viability of free flaps by continuously monitoring free flap blood oxygen saturation. In an attempt to overcome the limitations of the current techniques a reflectance photoplethysmographic (PPG) processing system has been developed with the capability of real-time estimation of arterial oxygen saturation (SpO2) levels implemented in LabVIEW. This system was evaluated in clinical measurements on five patients undergoing breast reconstruction using Deep Inferior Epigastric Perforator (DIEP) flap. Good quality PPG signals were obtained from the flaps and fingers simultaneously. The estimated free flap SpO2 values were in broad agreement with the oxygen saturation readings from the commercial pulse oximeter. The results suggest that reflectance free flap photoplethysmography can be used as a continuous monitoring technique to non-invasively monitor the perfusion of free flaps.

Intraoperative prediction of postoperative flap outcome using the near-infrared fluorophore methylene blue

Methylene blue (MB) is a near-infrared fluorophore that provides a stable visual map of skin perfusion after intravenous injection. We explored the capability of MB to predict submental flap postoperative outcome using a single intraoperative measurement. Submental flaps were created in N = 15 pigs and imaged using the FLARE imaging system immediately after surgery and at 72 hours. Using the first 3 pigs, optimal MB dosing was found to be 2.0 mg/kg. Training and validation sets of 6 pigs each were then used for receiver operating characteristic analysis. In the training set, a contrast-to-background ratio (CBR) threshold of 1.24 provided the highest sensitivity and specificity to predict tissue necrosis at 72 hours. In the validation set, this threshold provided a prediction sensitivity of 95.3% and a specificity of 98.0%. We demonstrate that a single intraoperative near-infrared measurement can predict submental flap outcome at 72 hours.

Impact of radiotherapy on microsurgical reconstruction of the head and neck

PURPOSE

To examine tissue oxygenation and perfusion of free microvascular grafts after primary reconstruction, regarding outcome for patients received adjuvant radiotherapy and different types of grafts.

PATIENTS AND METHODS

Free microvascular grafts (n = 48) after primary reconstruction of the head and neck were examined for tissue oxygenation and perfusion over a period of 6 months. 28 patients received adjuvant radiotherapy. Using a laser doppler flowmetry combined with tissue spectroscopy of the Oxygen-to-see(®)--equipment (LEA Medizintechnik, Giessen), we were able to determine oxygen saturation, hemoglobin concentration, blood flow and blood flow velocity in the graft in each of two tissue depths (2, 8 mm). Different types of graft were compared.

RESULT

Comparison of irradiated and non-irradiated grafts showed significant differences in tissue perfusion and oxygenation. Results for all radiated radial and fibula flaps showed no significant (p > 0.05) differences for all reviewed parameters. However, it showed no dose-volume effect with impaired functionality was found for irradiated grafts.

CONCLUSION

Mircovascular free tissue grafts show an increased perfusion and oxygenation after radiation compared to non-irradiated grafts.

A method for flap monitoring based on bioelectrical-resistance analysis

Axial pattern flaps are characterized by a single vascular pedicle that supplies the whole flap and carry the danger of flap loss. For this reason, monitoring and early identification of vascular perfusion is important for flap prognosis. The most commonly used method for flap monitoring is clinical assessment, but it has certain limitations. The bioelectrical properties of tissues can be affected by ischemic conditions, and a preliminary study showed that the bioelectrical resistance of blood was decreased under thrombotic conditions. In this controlled study, the resistance values of the axial flaps were calculated during thrombosis. A total of 28 rats were randomly divided into a control group (n = 14) and an experimental group (n = 14). Axial flaps were elevated based on the inferior epigastric pedicle. For the ischemic group, microvascular clamps were placed in the ischemic group to produce artificial thrombosis from day 1 of the experiment. Bioelectrical resistance was measured every 30 minutes for the first 6 hours and then daily after that. The resistance values from the ischemic group decreased progressively, and 150 minutes after the clamping, the difference became statistically significant (P < 0.05). The results showed that the assessment of flap resistance is a valuable tool and may allow early recognition of a compromise in the vascular system before clinical signs become obvious.

Eight-year experience of the Cook-Swartz Doppler in free-flap operations: microsurgical and reexploration results with regard to a wide spectrum of surgeries

BACKGROUND

Microvascular free flap has become an increasingly popular useful method of reconstruction over the past few decades. Minimizing failure rates in these operations is a primary goal in every microsurgical unit that can be accomplished by early recognition.

METHODS

In this retrospective study, we tracked the admission of the implantable Doppler in the microsurgical unit (2000-2007) and evaluated parameters measured from 473 consecutive patients who underwent a total of 548 microsurgical procedures (489 primary surgeries and 59 reexplorations). The effectiveness of the Cook-Swartz Doppler (Cook Medical®) was examined in juxtapose general and subspecialty's aspects: in each microsurgical subspecialty, we compared the overall success and failure rates of the group with the implantable Doppler (n = 259) with the control group monitored by clinical means (n = 289). We also examined the duration, outcomes, and the effectiveness of this device in reexploration operations.

RESULTS

Overall, success rates were improved by using the implantable Doppler contrary to clinical assessment (96.14% vs. 89.27%) with a statistical significant (P < 0.005). The device was most effective in ENT (94.6% vs. 84%), breast reconstructive surgeries (97.3% vs. 82.36%), and orthopedic oncology (97.37% vs. 83.72%), whereas with reanimation operations and trauma/orthopedics subspecialties, it showed no necessity. In neurosurgery and in other/esthetic surgeries, the study was too small to draw definite deductions.

CONCLUSIONS

We recommend the usage of the implantable Doppler probe as an effective monitoring system for free-flap surgeries, with emphasis on subspecialties where the device demonstrated better results than traditional monitoring methods.

Expression microarray identifies novel markers of free flap failure in a rat model

Clinical detection of free flap failure lacks sensitivity. Failure is likely accompanied by altered gene expression; however, a genomic approach that identifies potential biomarkers and therapeutic targets has not been described. This study identifies genetic RNA expression alterations via microarray in a free flap failure animal model. A free tissue transfer rat model based on the inferior epigastric vessels was utilized. After microscopic anastomosis, the vein was occluded and RNA extracted from flap tissue of failure and control groups. Gene expression of 3 experimental and control group samples was assessed with the Affymetrix GeneChip Rat 230 v2.0 microarray. Quantitative reverse transcription polymerase chain reaction was performed on RNA of genes identified on an additional 6 experimental and 7 control group flaps. Eight hundred ninety of 28,000 genes had greater than 2-fold expression differences between experimental and controls. Student t test and 2-way analysis of variance filtering with equal variance identified 53 genes with statistically significant differences. Hierarchical clustering by gene ontology identified 4 genes with likely involvement in failure pathogenesis: RT1 class II, locus Bb, secreted frizzled-related protein 1, platelet/endothelial cell adhesion molecule, and Claudin 5. Validation performed by quantitative reverse transcription polymerase chain reaction revealed statistically significant expression alterations in locus Bb, platelet/endothelial cell adhesion molecule, and Claudin 5 of the failure group. Utilizing expression thresholds for test positivity, venous occlusion was predicted with 100% sensitivity and 86% specificity. Three highly sensitive and specific novel genes predictive of flap failure from venous occlusion were identified with altered expression in an animal model.

Hemodynamic sensing using subcutaneous photoplethysmography

Pacemakers and implantable defibrillators presently operate without access to hemodynamic information. If available, such data would allow tailoring of delivered therapy according to perfusion status, optimization of device function, and enhancement of disease monitoring and management. A candidate method for hemodynamic sensing in these devices is photoplethysmography (PPG), which uses light to noninvasively detect changes in blood volume. The present study tested the hypotheses that PPG can function in a subcutaneous location, that the acute changes in blood volume it detects are directly proportional to changes in arterial pressure, and that optimum pacing intervals identified by it are concordant with those determined by arterial pressure. Aortic pressure and PPG were simultaneously recorded in 10 dogs under general anesthesia during changes in atrioventricular (AV) delay and bursts of rapid pacing to simulate tachyarrhythmias. Direct proportionality between transient changes in pressure and PPG waveforms was tested using regression analysis. Scatter plots had a linear appearance, with correlation coefficients of 0.95 (SD 0.03) and 0.72 (SD 0.24) for rapid-pacing and AV delay protocols, respectively. The data were well described by a directly proportional relationship. Optimum AV delays estimated from the induced changes in aortic pressure and PPG waveforms were concordant. This preliminary canine study demonstrates that PPG can function subcutaneously and that it may serve as a surrogate for acute changes in arterial pressure.

A survey of microvascular protocols for lower extremity free tissue transfer II: postoperative care

Due to the complex, and often tenuous nature of microsurgical tissue transfer, postoperative monitoring of free tissue flaps plays a vital role in the management of such patients. Some of the more challenging reconstructive problems occur in patients with lower extremity trauma, yet to date, no preferred protocol exists for the postoperative care of lower extremity free flaps. The present study sought to evaluate and assess current preferences in monitoring following lower extremity free tissue transfer. Members of the American Society of Plastic Surgeons (ASPS) were surveyed with regard to their choice for postoperative monitoring and return to dependent positioning ("dangling"). The results demonstrate that there is some agreement among surgeons regarding the optimal means for postoperative monitoring. Most rely on clinical observation in addition to conventional Doppler probe for an average of 4.8 days. Most surgeons follow their own flaps in addition to relying on the residents and nursing staff. The study also notes a wide variety in the times and frequencies at which dangling of the extremity was commenced. Most respondents initiate dangling within 2 weeks of surgery and begin with only 1 to 5 minutes per session.

Review of monitoring free muscle flap transfers in reconstructive surgery: role of 99mTc sestamibi scintigraphy

BACKGROUND

Free tissue transfer is a method of moving any tissue from a donor area of the body to a recipient site and re-attaching the arteries and veins to the blood vessels at the recipient site by microvascular surgery. Improved microsurgical techniques have resulted in a high percentage of successful free tissue transfers. Post-operative monitoring of tissue viability can detect early problems in free tissue transfer which may allow early intervention and salvage. Although many flap monitoring methods have been described, there is still no consensus on which of these techniques will become the standard accepted method for monitoring free muscle flaps.

OBJECTIVE

In present study, we investigated the use of 99mTc sestamibi scintigraphy in determining free muscle flap viability and complications, and also in directing treatment.

METHODS

Thirteen patients were examined prospectively during the post-operative period after free tissue transfer for foot defects. The cause of the defect was diabetic foot ulcer in 10 patients, dermatofibrosarcoma in one patient, squamous cell carcinoma in one patient and gunshot wound in one patient. Foot defect covering was carried out with a free latissimus dorsi muscle flap and skin graft (n=12) and a free gracilis muscle flap (n=1). All patients were examined with a monitoring system that consisted of visual inspection, hand-held Doppler ultrasonography and scintigraphic examinations. Scintigraphic imaging of all cases was performed routinely within the first 48 h post-operatively, and also on days 10 and 91 in two patients.

RESULTS

There were four flap failures during the study. One of these patients had viable findings upon visual inspection and no evidence of vascular compromise on Doppler at the first examination. In the other patient, visual inspection of the flap showed that it was ischaemic in one region, but there was no vascular compromise on Doppler examination. Scintigraphic images of each of these patients showed a partial hypoperfused area in the flap region. Later, these two flaps showed positive clinical indications of hypoperfusion (colour of muscle and appearance of skin graft) and Doppler abnormalities. The remaining two patients had non-viable scintigraphic images as well as positive clinical indicators of hypoperfusion and evidence of vascular compromise on Doppler. Nine patients each had a viable flap. In these patients, all three examination tools demonstrated that the flaps were totally viable and there were no vascular complications.

CONCLUSION

According to the results of this study, 99mTc sestamibi scintigraphy appears to be a feasible and promising method in the evaluation of free muscle flap viability and complications. On the other hand, to demonstrate any impact on management or patient outcome, further evaluation of 99mTc sestamibi imaging, including comparative studies with different established methods in a larger patient population, is highly recommended.

Functional evaluation of microvascular free flaps with positron emission tomography

BACKGROUND

The aim of this study was to assess blood flow (BF) of microvascular free flaps studied with positron emission tomography (PET) in patients with head and neck squamous cell cancer (HNSCC) undergoing major radical surgery 3-4 weeks after high-dose radiotherapy.

METHODS

Five patients underwent resection of the HNSCC of the oral cavity followed by microvascular reconstruction with a radial forearm flap. Regional BF in oral and neck tissues was measured with PET using radiolabelled water ([15O]H2O) twice (1-2 and 12-14 days, respectively) following radical surgery.

RESULTS

In the first postoperative PET study, the median BF in the cutaneous flap area was 5.1 mL/100 g/min, and in the muscle contra-lateral to the recipient site 19.9 mL/100 g/min. A low flap-to-muscle BF ratio appeared to correlate with circulatory incongruity, and thus with poorer flap success. The follow-up study on the second postoperative week supported the results of the primary PET scan.

CONCLUSIONS

This pilot study suggests that PET using [15O]H2O is a feasible method to quantitatively evaluate BF of the whole free flap in patients operated on for oral

Simultanes nichtinvasives Monitoring mit Laser-Doppler-Flussmessung und Gewebespektrometrie bei fasziokutanen Radialislappen und osteokutanen Fibulatransplantaten

AIM

In the literature currently available monitoring devices are usually divided into two major groups: those for monitoring perfusion and those for measuring tissue oxygenation. The O(2)C (oxygen to see) system combines these two ways of monitoring free flap viability. The aim of this prospective study was to determine the necessity of flap revision and when unnecessary revision can be avoided. Another point of interest was the question of whether critical values for the successful course of free flaps could be defined and in addition whether such values would differ for different flap types.

PATIENTS AND METHODS

In a prospective study 82 free flaps (61 radial forearm flaps and 21 fibula flaps) were monitored with the O(2)C monitoring unit. Measurements were carried out intraoperatively and postoperatively up to 14 days.

RESULTS

Perfusion compromise occurred in 12 (14.6%) of 82 monitored free flaps. Operative exploration was performed in seven cases, in five of them successfully. Five flaps (three radial forearm and two fibula flaps) were lost due to vascular compromise, which led to an overall success rate of 93.4%. Venous congestion was identified by a rapid increase in hemoglobin concentration of more than 30%. An abrupt decline of blood flow and hemoglobin oxygenation indicated arterial occlusion. Vascular complications were detected in all cases prior to clinical assessment with no false positive or negative results. For radial forearm flaps a hemoglobin oxygenation of 15%, a superficial flow of 10 AU, and a deep flow of 20 AU were identified as minimum values for flap viability. For fibula flaps a hemoglobin oxygenation of 10%, a superficial flow of 5 AU, and a deep flow of 15 AU were determined as minimum values.

CONCLUSION

O(2)C combines laser Doppler flowmetry and tissue spectrophotometry and for the first time allows simultaneous measurement of the microcirculatory parameters including blood flow, flow velocity, hemoglobin concentration, and hemoglobin oxygenation. We found this new noninvasive technique to be a reliable and accurate method for evaluating flap viability and improving the success rate in free flap transfer.

Intramucosal PCO2 Measurement as a New Monitoring Method of Free Jejunal Transfer following Pharyngo-laryngo-esophagectomy

The choices for practical monitoring of free jejunal transfer have been quite limited because of its own characteristics, such as buried form, lack of skin surface, and the structure of a hollow viscous tract. Physiologically, it is known that tissue hypoxia caused by compromised perfusion leads to an increase of partial pressure of carbon dioxide (PCO2). Because of its physiological properties, the diffusion of carbon dioxide is always equilibrated between the mucosa of a hollow viscous organ and its lumen. The intramucosal PCO2 (PiCO2) of the gastrointestinal tract can therefore be determined indirectly from the intraluminal PCO2, which is measured with the aid of the tonometer catheter. To develop an optimal monitoring method for free jejunal transfer, the authors proposed the application of PiCO2 measurement by a modified use of a tonometer catheter. Since May of 1999, the authors performed postoperative PiCO2 monitoring on 20 cases of reconstructed pharyngoesophageal tracts in 18 patients who underwent radical tumor resection and one-stage reconstruction at the Shizuoka Red Cross Hospital. All 20 cases were safely monitored by PiCO2 measurement without any complications associated with the use of the tonometer catheter. In the 17 cases that succeeded uneventfully, the mean values of PiCO2 were kept lower than 40 mmHg throughout the monitoring period. On the other hand, the other three cases (15 percent) needed reexploration due to development of vascular complications, which was alerted by an abrupt increase of PiCO2 in each case (229, 130, and 99.6 mmHg). Two of the patients were fortunately successfully treated by immediate reexploration, leading to a 95 percent overall success rate. No false-negative or false-positive cases were observed. The authors' experience suggests that PiCO2 measurement using a tonometer catheter can provide the surgeon with reliable information for evaluating the perfusion and viability of a free jejunal transfer. Simplified manipulation and the objectivity of the numerical data allow stable measurement of PiCO2 and prompt judgment of the adequacy of the perfusion, which could minimize the burden and anxiety of the surgeon, particularly in the early postoperative period.

Initial experience with personal digital assistant-based reflectance photoplethysmograph for free tissue transfer monitoring

Improved microsurgical technique has resulted in a high percentage of successful free tissue transfers. When a tissue transfer fails in the head and neck, however, the results are orocutaneous fistulas, carotid artery exposure, and deformity that adds morbidity, expense, and may delay adjuvant therapy. Postoperative monitoring of tissue perfusion can detect early problems in free tissue transfer that may allow for early intervention and salvage. The authors have demonstrated that reflectance photoplethysmography can detect perfusion changes in free tissue transfer within 5 minutes of a pedicle "insult" intraoperatively. Normative data for viable flaps from various donor sites have been established. The authors now report their initial experience with a newly developed reflectance photoplethysmograph based on a hand-held computer for routine clinical use. Their results are compared with a conventional surveillance protocol that included observation, bleeding to pin prick, and bedside duplex scanning of the vascular pedicle. In a series of 30 free tissue transfers (29 patients), there was one ischemic event (skin paddle loss only), which was detected by the monitor. The monitor was able to predict correctly (one flap) survival of a free tissue transfer even when duplex ultrasonic data were indicative of an absence of perfusion. Personal digital assistant-based photoplethysmography appears to be a promising device for bedside diagnosis of free tissue transfer viability or ischemia.

Laser Dopplers to determine cutaneous blood flow

BACKGROUND

Laser Dopplers can be useful in determining the relative amount of blood flowing through superficial skin. These instruments may be useful in assessing blood flow in healing wounds, flaps, and grafts.

OBJECTIVE

To review the theory and types of laser Dopplers available.

METHODS

This work includes a review of the literature.

RESULTS

Laser Dopplers potentially have a broad range of applications in dermatologic surgery and dermatology. Because laser Dopplers can quantify blood flow, the course of wound healing over time can be studied; however, for predicting viability of skin flaps and grafts, laser Dopplers have not been able to supplant clinical assessment.

CONCLUSION

Laser Dopplers provide an additional means of assessing superficial blood flow in the skin. This blood flow, which can be quantified, may be useful in studying wound and flap and graft healing.

Skin perfusion assessed by contrast ultrasound predicts tissue survival in a free flap model

The purpose of this study was to assess perfusion in a free skin flap model using contrast-enhanced ultrasound (CEU), and to determine if the extent of perfusion early after venous occlusion predicted long-term flap survival. Perfusion was assessed in an autologous abdominal skin flap and adjacent healthy skin in rats using CEU imaging before venous occlusion and following reflow. Perfusion assessment was possible in all flaps and quantitative measurements of microvascular blood volume (BV) and blood velocity were expressed as a ratio to that in the healthy skin. Proximal flap BV 18 h after venous occlusion was significantly greater in those that survived (n = 4) vs. those that became necrotic (n = 6) (BV ratio 0.8 +/- 0.1 vs. 0.2 +/- 0.1, p = 0.0001). A BV ratio of 0.5 predicted graft viability with a sensitivity and specificity of 100%. Microvascular blood velocity at 18 h was similar in grafts that survived and those that became necrotic. Qualitative assessment of perfusion by a "blinded" observer correlated well with quantitative data and predicted flap outcome in all cases. We conclude that skin perfusion can be assessed with CEU. Perfusion 18 h following a secondary ischemic insult in a free flap accurately predicts subsequent tissue survival in this model.

Evaluation of microvascular bone graft reconstruction of the head and neck with 3-D 99mTc-DPD SPECT scans

OBJECTIVE

We conducted a prospective investigation to evaluate the diagnostic accuracy of computer-aided 3-dimensional (3-D) technetium 99m dicarboxypropane methylene diphosphonate ((99m)Tc-DPD) single photon emission computed tomography (SPECT) reconstruction in the evaluation of microvascular bone flaps used for maxillofacial reconstruction.

STUDY DESIGN

Twenty patients who received 20 autogenous microvascular bone flaps for reconstruction of the mandible and maxilla were evaluated. Forty bone scans with subsequent computer-aided reconstruction were performed. Each graft could be assessed within 48 to 72 hours after surgery. The second bone scan was performed between 12 and 14 days after surgery.

RESULTS

Complications were observed in 5 grafts. SPECT investigation performed at the 2 time points after reconstruction showed a significantly higher tracer uptake in grafts with an uncomplicated further course than in those that developed complications.

CONCLUSIONS

Computer-aided 3D (99m)Tc-DPD SPECT reconstruction serves as a useful prognostic tool and helps in the very early recognition of complications. This technique adds significantly to the value of planar bone scintigraphy and conventional SPECT images.

The use of the photoplethysmograph to monitor the training of a cross-leg free flap prior to division

The cross-leg free flap is an important, although rarely used, option in the reconstruction of lower limb trauma. We report the use of photoplethysmography in the assessment of such a flap's training and the time of pedicle division.

Magnetic resonance imaging detection of vascular occlusion of a pedicled muscle flap

Contrast-enhanced magnetic resonance imaging (MRI) can be a highly sensitive monitor of tissue blood perfusion. This technique has been used to assess blood flow through liver, kidney, and certain tumors, but has not been widely applied to the study of skeletal muscle circulation. In our study, we used a novel scanning software to obtain contrast-enhanced T2*-weighted gradient echo MRI images of pedicled quadriceps muscle flaps in rabbits in order to study images of arterial, venous, and arterio-venous occlusion. We administered an intravenous bolus of gadoteridol contrast agent at the initiation of scanning, which produces a decrease in T2*-signal and improves the sensitivity of measuring blood perfusion. Within 30 seconds of MRI scanning, control flaps with intact pedicles exhibited a rapid decrease in T2*-signal intensity, indicating adequate perfusion of blood through muscle tissue; however, occluded pedicled flaps showed no significant change in signal intensity, indicating lack of blood perfusion. Differences in signal intensities as measured by MRI between occluded and control flaps were statistically significant (P < 0.05). Selective vascular occlusion of either artery alone, or both artery and vein were detected within 15 minutes, whereas selective venous occlusion could be detected after 2 hours. We conclude that MRI has the ability to assess skeletal muscle perfusion, and is capable of noninvasively evaluating a cross-section of tissue in both superficial and buried flaps. MRI, therefore, may have the potential for evaluating perfusion in muscle flaps (including buried flaps), and other disorders of muscle circulation such as compartment syndrome.

Monitoring free flaps using the laser Doppler flowmeter: five-year experience

Over a 5-year period, 232 microvascular composite-tissue transfers to the head and neck, trunk, and extremities were monitored using the laser Doppler flowmeter. Thirteen free flaps (5.6 percent) developed vascular complications, all within 4 days after surgery. The laser Doppler flowmeter detected vascular compromise in all cases with no false positives or negatives. Failure to monitor the flap according to protocol by nursing staff occurred in one patient, which led to a delay in detection of venous compromise and subsequent flap loss. The salvage rate was 69.2 percent, leading to an overall flap viability of 98.3 percent. Our series of free-flap monitoring using the laser Doppler flowmeter is the largest reported to date. Review of the English literature shows consistent support by numerous clinical series for the use of the laser Doppler as a valuable postoperative monitor after free-flap transfers.

Spectral analysis of photoplethysmograms from radial forearm free flaps

OBJECTIVE

Photoplethysmography utilizes a green-light-emitting diode to transmit light into a tissue. Reflected light from hemoglobin in dermal capillary red blood cells is received by a photo detector and is analyzed as light intensity along a frequency spectrum. This method of analysis allows for the removal of "noise" above (stray light and alternating current [AC]) and below (room vibrations and respiratory motion) the peak signal (1 to 2 Hz) and results in a means to distinguish between perfused and nonperfused tissues.

METHODS

Twenty-two of 30 consecutive radial forearm free flap (RFFF) patients were enrolled in an approved human studies protocol to collect descriptive data for RFFFs that were perfused, arterial occluded, and venous occluded. The protocol was performed following completion of flap elevation and prior to pedicle ligation, flap inset, and microvascular anastomoses. Six 90-second measurements per flap were obtained (n = 132), processed by fast Fourier transform (FFT), and analyzed by blinded reviewers to determine their state of perfusion. Signal was collected 5 minutes after the onset or release of individual vessel occlusion.

RESULTS

The reviewers' interpretations were compared with the status of the pedicle and analyzed for sensitivity (0.96), specificity (0.95), and positive predictive value (0.98).

CONCLUSIONS

FFT analysis of photoplethysmograms from RFFF patients provides an accurate and rapid means for determining RFFF pedicle vessel patency. Photoplethysmography may provide a clinically useful tool for postoperative perfusion monitoring of free flaps in the future.

Microvascular free tissue transfer: results in 57 consecutive cases

OBJECTIVE

To evaluate the outcomes and complications in a consecutive series of animals undergoing microvascular reconstructive procedures at two veterinary institutions.

STUDY DESIGN

Retrospective study.

ANIMALS OR SAMPLE POPULATION

A total of 44 client-owned dogs and one red-necked wallaby.

METHODS

The medical records of all animals undergoing reconstructive microsurgical procedures at the Western College of Veterinary Medicine and Michigan State University were reviewed. Microvascular flap survival and related complications were described. Statistical analysis was performed to determine the significance of relationships between operative factors and outcome.

RESULTS

A total of 57 microvascular procedures were performed on 55 animals. Reconstruction was required after trauma in 42 animals, after ablative cancer surgery in 11 animals and for correction of congenital tissue aplasia in I animal. Donor tissues included the superficial cervical cutaneous, medial saphenous fasciocutaneous or musculofasciocutaneous, caudal superficial epigastric cutaneous, trapezius muscle or musculocutaneous, caudal sartorius muscle, latissimus dorsi muscle or musculocutaneous, cranial abdominal myoperitoneal, carpal footpad, digital footpad, and vascularized ulnar bone flaps. A total of 53 of 57 flaps (93%) survived. There was a significant relationship between flap failure and level of assistant surgeon experience (P < .05). Latissimus dorsi flaps were significantly more likely to fail when compared with pooled data from all other flap types (P < .01).

CONCLUSIONS

The success of microvascular tissue transfer in this case series compares favorably with those reported in human reconstructive microsurgery. Both the primary and assistant surgeon should be practiced in microsurgical technique. Failure of latissimus dorsi flaps was not likely caused by an inherently deficient flap design, but was more likely attributed to the location and severity of trauma at the recipient site, the difficulty in isolating suitable recipient vessels for anastomosis or the absence of a trained assistant surgeon during these procedures. Clinical Relevance-This retrospective study documents the successful application of microvascular technique in a series of clinical cases requiring tissue reconstruction.

Persistence of pedicle blood flow up to 10 years after free musculocutaneous tissue transfer

The hypothesis of whether or not flap perfusion remains persistent through its vascular pedicle up to 10 years after free tissue transfer was tested. Since 1982, more than 1,000 free tissue transfers have been performed at this institution. Of these, 40 patients were selected with comparable posttraumatic soft-tissue defects of the lower leg and surgical repair by a latissimus dorsi myocutaneous free flap. All patients had a postoperative course free of complications. Measurements of flap perfusion were started in groups 1 through 4 (each 10 patients) 3 to 5 weeks, 5 to 7 months, 4 to 6 years, and 8 to 10 years after free tissue transfer, respectively. Quantitative measurements of local flap perfusion were performed by means of the hydrogen clearance technique (Ameda, Switzerland) at definite sites intracutaneously and subcutaneously within the flap's skin paddle as well as in the adjacent intracutaneous and subcutaneous skin of the surrounding soft tissue. Simultaneously, the vascular pedicle of the flap was visualized by a duplex scanner (Toshiba, Japan). In each group nine measurements were performed before (phase A), during (phase B), and after closing the pedicle (phase C) by manual compression. Each measurement took about 10 minutes. Statistical evaluation of the obtained values was achieved by the Mann-Whitney U test and the Wilcoxon signed rank test. Local flap perfusion showed no statistical differences for phase A and C in all four groups of patients. In phase B, however, a statistically highly significant (p < 0.01) absence of local flap perfusion was registered in all four groups at the site of the flap's skin paddle. No statistically significant alterations of intracutaneous and subcutaneous blood flow was found in the surrounding soft tissue. In our clinical-experimental setting, flap perfusion persisted by means of its vascular pedicle even 10 years after free tissue transfer. Our findings support the importance of an intact vascular pedicle for permanent flap survival after free tissue transfer.

Postoperative blood flow monitoring after free-tissue transfer by means of the hydrogen clearance technique

The hydrogen clearance technique was introduced for monitoring postoperative blood flow after free-tissue transfer in this prospective clinical study. This technique allows unlimited repeatable quantitative measurements of tissue blood flow in milliliters per minute per 100 gm of tissue at any site including buried flaps. In this study a real-time blood flow measuring system (Ameflow, Ameda, Switzerland) was employed. Two thousand eight hundred and twenty-three blood flow measurements were carried out on 72 free-tissue transfers, which were performed on 71 patients. Nine of these 72 flaps showed vascular complications (12.5 percent), including arterial thrombosis in 6.9 percent (n = 5), hematoma in 4.2 percent (n = 3), and venous thrombosis in 1.4 percent (n = 1). Complications as well as uneventful postoperative cases were monitored correctly by the hydrogen clearance technique in all cases, reaching sensitivity and specificity values of 1.0 for this technique in our study. Furthermore, all complications could be detected earlier by the hydrogen clearance technique than by clinical monitoring alone, which allowed flap salvation in 7 of 9 cases and a resulting permanent failure rate of free-tissue transfer of 2.8 percent (n = 2). From our data we conclude that the hydrogen clearance technique is a promising tool for postoperative blood flow monitoring after free-tissue transfer. For experimental pathophysiologic and pharmacologic studies of tissue blood flow in flaps, further evaluation of our measuring device including comparative studies with other established techniques is highly recommended.

Value of a dynamic MR scan in predicting vascular ingrowth from free vascularized scapular transplant used for treatment of avascular femoral head necrosis

We have treated three patients with avascular osteonecrosis using vascularized scapular bone graft. To predict blood perfusion in both the diseased femoral head and the transferred bone, all the hips were followed up using dynamic magnetic resonance (MR) scans, performed 1 and 7 months after surgery. In the present cases, it was shown that conventional enhanced MR imaging sometimes depicts increased intensity in bone marrow without blood perfusion due to the leakage of gadolinium-DTPA (Gd-DTPA) from the capillaries surrounding the avascular tissue. It was found that Gd-DTPA remaining in the dead bone marrow resulted in a false-positive image. By contrast, the dynamic MR scan evaluated only those images taken before the leakage. This is one of the advantages of the dynamic study, which reflects actual blood flow in the bone. The fast rise in the time-intensity curve following bolus injection of Gd-DTPA indicates that there is fast blood perfusion in the bone. The dynamic MR scan has demonstrated that there is little blood perfusion in the diseased bone 1 month after the operation and that vascular ingrowth from the transferred bone flap proceeds gradually between 1 and 7 months after surgery. These findings indicate that the dynamic MR scan is very useful in demonstrating vascular ingrowth after surgery in avascular necrosis of the femoral head and can be a reliable monitoring technique for anastomotic patency of the vascularized bone flap.

Measurements of tissue blood flow by the hydrogen clearance technique (HCT): a comparative study including laser Doppler flowmetry (LDF) and the Erlangen micro-lightguide spectrophotometer (EMPHO)

The purpose of this study was to compare the hydrogen clearance technique (HCT) with two different, well-established techniques, i.e., the laser Doppler flowmetry (LDF) and the Erlangen micro-lightguide spectrophotometer (EMPHO), for tissue blood flow measurements in an experimental setting. For the animal experiments, we chose a rat model for arterial and venous flap thrombosis, using the epigastric groin flap. Forty male dark Aguty rats were included in the study. The animals were divided into eight groups, each with a different vascular thrombotic model. HCT was used to collect 1,467 measurements, and 2,934 graphs were recorded; 27 measurements (54 graphs) had to be discarded due to faulty electrode placements and electronic noise. In 19 of the 27 discarded measurements the cause of failure was moving of the awaking animal with disruption of the decay signal. The LDF and EMPHO measurements were performed continuously during each measuring phase. Simple and multiple linear regression and paired t-tests were used to compare the three techniques. The reproducibility of registered blood flow values in phases 1, 3, 6 and 7 varied between 7.8% and 13.6% which is in about the same range as LDF and EMPHO. We could not find a significant difference between the three techniques in this regard. The correlation coefficient for HCT and LDF was r = 0.89. For HCT and EMPHO we found r = 0.67. Sensitivity and specificity values for HCT were both 1.0 in detecting arterial and venous flap thrombosis; for LDF we found values of 0.89 and 0.92, respectively. Sensitivity and specificity values for EMPHO were 0.92 and 0.95, respectively. After careful evaluation of three different techniques (HCT, LDF, and EMPHO) for measurements of local tissue blood flow we came to the conclusion that HCT must be favoured as a reliable tool for quantitative measurement of local tissue blood flow and early diagnosis of arterial and venous flap thrombosis.