Transcutaneous PO2 monitoring for assessing viability and predicting survival of skin flaps: experimental and clinical correlations

Improving the ischemia-reperfusion injury in vascularized composite allotransplantation: Clinical experience and experimental implications

Long-time ischemia worsening transplant outcomes in vascularized composite allotransplantation (VCA) is often neglected. Ischemia-reperfusion injury (IRI) is an inevitable event that follows reperfusion after a period of cold static storage. The pathophysiological mechanism activates local inflammation, which is a barrier to allograft long-term immune tolerance. The previous publications have not clearly described the relationship between the tissue damage and ischemia time, nor the rejection grade. In this review, we found that the rejection episodes and rejection grade are usually related to the ischemia time, both in clinical and experimental aspects. Moreover, we summarized the potential therapeutic measures to mitigate the ischemia-reperfusion injury. Compare to static preservation, machine perfusion is a promising method that can keep VCA tissue viability and extend preservation time, which is especially beneficial for the expansion of the donor pool and better MHC-matching.

[Postoperative monitoring of free muscle flaps using perforator-based adipocutaneous skin paddles: economy, quality of care and aesthetics]

INTRODUCTION

Besides fasciocutaneous workhorse flaps, free muscle flaps for the reconstruction of large soft tissue defects are well-established standard microsurgical procedures. Random-pattern adipocutaneous skin paddles are often included for postoperative perfusion monitoring of the muscle flap. At our institution, both conventional broad-based and perforator-based adipocutaneous skin paddles are used. While conventional skin paddles have to be removed during a second operation, perforator-based skin paddles can be removed at the bedside by ligature. The present study aims to compare economic aspects, quality of care and aesthetic results of perforator-based versus conventional adipocutaneous skin paddles after free muscle flap transfer.

METHODS

102 patients treated between August 2014 and July 2016 were identified and included in a retrospective data analysis. Patients with perforator-based skin paddles (group A) were compared with a population of patients with conventional skin paddles (group B). Patient characteristics, procedural characteristics, economic data and aesthetic results were compared between both groups.

RESULTS

Perforator-based skin paddles were raised in 72 patients (group A, 71 %), and conventional skin paddles were raised in the remaining 30 patients (group B, 29 %). Patient, defect, and flap characteristics were comparable in both groups. Operating times tended to be shorter in group B. Skin paddle removal was performed significantly earlier in group A (p < 0.01). Both overall and post-reconstructive length of hospital stay were significantly shorter in group A (p = 0.03; p < 0.01). Also, personnel and material resources were saved and more satisfactory aesthetic results were achieved in group A.

CONCLUSION

Perforator-based monitor islands can help avoid secondary operations that would otherwise be necessary to remove monitoring skin paddles. Thus, the inpatient length of stay can be reduced while sparing material and human resources.

Intraflap Vascular Catheterization Method for Monitoring, Prevention, and Intervention of Thrombogenesis in Free-Flap Surgery

BACKGROUND

Thrombosis at the anastomotic site is a significant problem in free tissue transfer with microvascular anastomosis. We report a newly developed intraflap vascular catheterization (IFVC) technique for monitoring hemodynamics, prevention of thrombogenesis, and transcatheter intervention of free-flap thrombosis.

METHODS

We performed a hospital-based, prospective study. Ninety-three patients underwent free tissue transfer by a single surgeon in a single hospital. In the IFVC group (n = 40), catheters were inserted into the arterial and venous branches of the flap main pedicle vessels near the anastomoses. The catheters were connected to the pressure monitor. A bolus injection of urokinase was administered every hour to the artery, and a continuous infusion of saline was initiated to the vein. The bolus injection of urokinase solution reached the arterial anastomosis by the retrograde flow. During the postoperative period, rapid injection of urokinase or saline was performed according to the pressure monitor. Intraflap vascular catheterization monitoring was performed postoperatively for 72 hours.

RESULTS

The overall flap survival rate in the IFVC group was 100% (40 of 40), whereas the overall flap survival rate in the non-IFVC group was 96% (51 of 53). In a subgroup analysis of lower extremity reconstruction, the flap survival rate was 100% (22 of 22) with no cases of reanastomosis requiring a return to the operation room in the IFVC group. By contrast, the flap survival rate was 92% (22 of 24), with 6 cases of reanastomosis requiring a return to the operation room in the non-IFVC group (P = 0.04).

CONCLUSIONS

The IFVC method enables monitoring, prevention, and intervention of thrombi at anastomotic sites of the free flap. Intraflap vascular catheterization may increase free tissue transfer success rate, especially in high-risk cases, such as free-flap reconstruction after the lower extremity trauma or venous leg ulcer.

Flap Monitoring Using Transcutaneous Oxygen or Carbon Dioxide Measurements

Free tissue transfer is a cornerstone of complex reconstruction. In many cases, it represents the last option available for a patient and their reconstruction. At high-volume centers, the risk of free flap failure is low but its occurrence can be devastating. Currently, the mainstay for flap monitoring is the clinical examination. Though reliable when performed by experienced clinicians, the flap exam is largely subjective, is performed discontinuously, and often results in significant time delay between detection of flap compromise and intervention. Among emerging flap monitoring technologies, the most promising appear to be those that rely on noninvasive transcutaneous oxygen and carbon dioxide measurements, which provide information regarding flap perfusion. In this article, we review and summarize the literature on various techniques but primarily emphasizing those technologies that rely on transcutaneous gas measurements. We also define characteristics for the ideal flap monitoring tool and discuss critical barriers, predominantly cost, preventing more widespread utilization of adjunct monitoring technologies, and their implications.

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.

A paintable phosphorescent bandage for postoperative tissue oxygen assessment in DIEP flap reconstruction

Flaps are common in plastic surgery to reconstruct large tissue defects in cases such as trauma or cancer. However, most tissue oximeters used for monitoring ischemia in postoperative flaps are bulky, wired devices, which hinder direct flap observation. Here, we present the results of a clinical trial using a previously untried paintable transparent phosphorescent bandage to assess the tissue's partial pressure of oxygen (pO2). Statistical analysis revealed a strong relationship (P < 0.0001) between the rates of change of tissue oxygenation measured by the bandage and blood oxygen saturation (%stO2) readings from a standard-of-care ViOptix near-infrared spectroscopy oximeter. In addition, the oxygen-sensing bandage showed no adverse effects, proved easy handling, and yielded bright images across all skin tones with a digital single-lens reflex (DSLR) camera. This demonstrates the feasibility of using phosphorescent materials to monitor flaps postoperatively and lays the groundwork for future exploration in other tissue oxygen sensing applications.

Random-pattern versus perforator-based adipocutaneous skin paddles for postoperative monitoring of free muscle flaps-a comparative retrospective cohort study

INTRODUCTION

Free microvascular muscle flaps represent well-established reconstructive options for complex soft tissue defects. However, due to their lack of cutaneous capillary beds, they are difficult to monitor postoperatively. To this end, random and axial-pattern adipocutaneous skin paddles are often included. The objective of the study was to compare the impact of random-pattern versus perforator-based adipocutaneous skin paddles on operative efficacy and muscle flap safety.

METHODS

Between August 2014 and July 2016, a total of 120 free muscle flaps were included in this retrospective monocentric cohort study. Based on their skin-paddle type, they were either grouped into a 'perforator-based' (group Pb) or 'random-pattern' (group Rp) cohort. The electronic medical records and operative reports of all patients were subsequently reviewed and patient, defect, and flap characteristics of both groups were compared. The effect of the competing skin paddle types on the overall operative time, incidences of flap loss or microvascular complications, and total length of hospital stay were then assessed.

RESULTS

Group Pb comprised 72 flaps, whereas 48 flaps constituted group Rp. Patient, defect, and flap characteristics were similar between both groups. Groups Pb and Rp were comparable regarding patient age (group Pb: 61 (10-90) vs. Rp: 59 (13-81), p = 0.556), ASA (American Society of Anesthesiologists) class (group Pb: 3 (1-4) vs. Rp 3 (1-3), p = 0.977), and comorbidities, summarized by the Charlson comorbidity index (CCI; group Pb: 1 (0-4 vs. Rp: 1 (0-5), p = 0.295). Both types of monitoring skin paddles were equally reliable. There was no significant difference in the mean operation time between both groups (group Pb: 373 ± 122 min vs. Rp: 342 ± 84 min, p = 0.124). In-patient treatment after flap surgery and total length of hospital stay were significantly shorter in group Pb (group Pb: 24 ± 10 days vs. Rp: 32 ± 17 days, p = 0.002 and group Pb: 39 ± 15 vs. Rp: 48 ± 24, p = 0.022).

CONCLUSION

Perforator-based skin paddles are a reliable tool for postoperative perfusion monitoring of free muscle flaps and help avoid additional surgical interventions as opposed to their random-pattern counterparts. Thus, the overall and postoperative length of hospital stay is significantly reduced.

Remote ischemic conditioning in a rat model of testicular torsion: does it offer testicular protection?

BACKGROUND

Testicular torsion is a surgical emergency mainly affecting adolescent boys, with a relatively high rate of missed torsion and testicular loss secondary to delay in prompt diagnosis and surgical intervention. With ischemic reperfusion injury as its underlying culprit, testicular torsion may respond favorably to remote ischemic conditioning (RIC) where a non-privileged site (e.g. limb) is concurrently rendered ischemic to divert the cascade of reperfusion injury from the privileged organ (e.g. testicle), thus offering a protective effect in improving salvage. This mechanism is established for other organs, whereas it has not been evaluated for testis.

AIM

It was aimed to evaluate RIC in a rat model of testicular torsion as a proof of principle that, similar to what has been demonstrated in other organs, RIC does offer testicular protection.

STUDY DESIGN

This is an animal experimental study. Thirty Sprague-Dawley male rats were divided into control group (n = 15) and experimental group (n = 15). Non-survival surgeries of right-sided spermatic cord torsion (720° counter-clockwise twist) were performed for both the groups (45 min) followed by detorsion and reperfusion (5 min) and then orchiectomy. For the experiment group, an intervention of tail clamping to create RIC was applied 5 min after torsion, then unclamping 5 min before detorsion, followed by detorsion and reperfusion for 5 min and then orchiectomy. The testicles were histologically and immunologically examined using a hypoxia inducible factor (HIF-1α) ELISA Kit. The histological findings on ischemic changes, vascular congestion, and immunohistochemistry were quantified using previously described, validated grading systems.

RESULTS

DISCUSSION: This is the first study to demonstrate the concept of RIC in an animal model of testicular torsion. It is limited by the non-availability of similar studies to compare outcomes and by the caution of extrapolating animal studies on humans. It does lay grounds, however, to subsequent studies to further elaborate on this concept and its clinical applicability.

CONCLUSION

When RIC is applied in the experimental setting of testicular torsion, there is less evidence of hypoxic injury by histology and immunohistochemistry.

Implantable Doppler flow system: Experience with 24 microvascular free-flap operations

Objective

Microvascular reconstruction requires postoperative monitoring to prevent vascular occlusion and flap failure. These methods require skilled personnel and can delay diagnosis and treatment of threatened flap failures. The Cook-Swartz implantable Doppler flow system provides continual feedback on vascular pedicle status, which in turn provides rapid assessment of minute-to-minute changes in flap vasculature that may allow intervention before total vascular occlusion and expeditious reexploration for threatened flap failure, possibly improving flap salvage.

Study Design and Setting

Charts of 24 patients with microvascular free-flap reconstruction and implantation of Doppler flow system at Mayo Clinic Rochester were retrospectively reviewed. Surgical technique and flap outcomes were evaluated.

Results

Microvascular reconstruction and implantation of Doppler flow system were successful in all patients. Complications were minimal, and postoperative monitoring system facilitated rapid reexploration when necessary. Flap viability was 96%.

Conclusion

Doppler flow system is reliable for monitoring minute-to-minute changes in microvascular flap vascular status postoperatively, and allows rapid recognition of complications and facilitating reexploration. This is a valuable, easily mastered tool for microvascular reconstructive surgery.

Significance

May alter postoperative monitoring techniques of microvascular surgeons.

Correction of Hypoxia, a Critical Element for Wound Bed Preparation Guidelines: TIMEO2 Principle of Wound Bed Preparation

Wound bed preparation is an organized approach to create an optimal environment for wound healing by the use of the most cost-effective therapeutic options. It has become an essential part of wound management and seeks to use the latest findings from molecular and cellular research to maximize the benefits of today's advanced wound care products. The international advisory panel on wound bed preparation met in 2002 to develop a systemic approach to wound management. These principles of this approach are referred to by the mnemonic TIME, which stands for the management of nonviable or deficient tissue (T), infection or inflammation (I), prolonged moisture imbalance (M), and nonadvancing or undermined epidermal edge (E). One critical element of pathophysiology, understanding of the hypoxic nature of the wound and correction of hypoxia as a critical element of wound bed preparation, is not covered. This article proposes to add correction of hypoxia to the TIME principle (TIMEO2 principle) based on the evidence. The evidence that will support the reason and the need for modification of the wound bed preparation protocol is discussed.

A review of the clinical significance of tissue hypoxia measurements in lower extremity wound management

The aim of this paper is to review techniques that are currently available to measure tissue hypoxia in order to benefit the management of wounds. Direct measurement of tissue partial oxygen pressure (PO(2)) is invasive and therefore unappealing in clinical practice. Several techniques (PET scans, MRI derived techniques) are primarily applicable to research rather than clinical applications. Imaging techniques (duplex ultrasonography, arteriography, MRI techniques) are recommended only as part of the workup for revascularisation. Techniques that assess local perfusion include clearance methods, transcutaneous O(2) and CO( 2) pressure measurement, and laser Doppler flowmetry and imaging. These techniques permit interpretation of altered perfusion states. Each technique offers subtly different information concerning microvascular function. All these techniques require strict protocols to derive reliable data. The potential of the promising near infrared reflectance spectroscopy (NIRS) technique is yet to be determined.

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.

Free flap monitoring using an implantable Doppler probe

Although clinical observation is the gold standard, the ideal free flap monitoring device has not been identified. The purpose of the present study was to review the first 14 months of experience using an implantable 20-MHz ultrasonic Doppler probe to monitor the microvascular anastamoses of free tissue transfers. Twenty-five flaps in 23 patients, with an average age of 51 years (age range 18 to 81 years), were performed. Probes were secured downstream of the venous anastamosis using a silicone-poly fluorotetraethylene sleeve. Doppler sounds were transduced before the flap was inset. Monitoring by nursing staff included conventional techniques (temperature, colour, capillary refill) and continuous Doppler flow monitoring. Dynamic diagnostic testing for anastomotic patency was facilitated by applying manual pressure on the flap to increase venous flow (the audible ‘whoosh’ sign) and valsalva manoeuvre to impede venous return momentarily (the ‘heave’ sign). Intraoperative vessel kinking, hematoma formation occluding venous outflow, and venous thrombosis were detected in four cases before concluding the procedure and corrected. Rapid, immediate cessation of audible flow was detected postoperatively in three of 25 flaps. Re-exploration (re-exploration rate 12%) led to salvage of all three flaps (salvage rate 100%). It was concluded from this study that flap re-exploration was prevented in four cases (16%) because of intraoperative use of the implantable Doppler probe. Earlier detection of flap compromise perioperatively is thought to have contributed to the 100% salvage rate and to the 100% flap survival rate in the first 25 cases in which the implantable Doppler probe was used.

Measurement of blood flow and oxygen tension in adjacent tissues in pedicled and free flap head and neck reconstruction

The purpose of this study was to evaluate blood flow and transcutaneous partial oxygen pressure (TcPO(2)) in adjacent tissues to free and pedicled flaps following reconstructive procedures used in conjunction with radical surgery for head and neck cancers. Fifty patients were included. Fourteen patients had reconstruction with pedicled flaps and 36 with free flaps. For each patient, TcPO(2) and laser Doppler flow measurements were taken at the center of the flap, in adjacent tissue, and in a corresponding contralateral site. Three laser Doppler measurements were performed at each site and a mean value recorded. All patients had undergone reconstruction up to 6 months prior to the time of the measurements. The collected data were analyzed using a Wilcoxon signed rank test. There were no statistically significant differences in partial oxygen tension or laser Doppler values between tissues adjacent to free compared to pedicled flaps. Although there is strong evidence to support that free flaps have improved blood flow and partial oxygen tension over pedicled flaps, further study is required to evaluate adjacent tissues. Flap choice may assist with alteration in blood flow in less favorable defects such as those in previously irradiated fields and those resulting from burn scars or chronic infections.

Continuous tissue oxygenation assessment during bloodflow alterations in an isolated hindlimb model of the pig

A continuous intramuscular oxygen tension sensor was compared, with transcutaneous oximetry and laser Doppler flowmetry, during periods of arterial flow alterations in an isolated hindlimb model in the pig. The intramuscular oxygen tension sensor correlated well with bloodflow and was superior to the other two methods.

Monitoring techniques for the detection of flow failure in the postoperative period

Free tissue transfer is now a commonly used reconstructive tool. Vascular compromise is still a common complication and salvage rates of compromised flaps have been in the region of 50%. Numerous monitoring techniques have been tried but there is yet no single technique which has enjoyed universal acceptance. This paper reviews the available techniques and indicates where current trends are leading.

Impedance monitoring for subcutaneous free flap transfers

The assessment of thoracic blood flow by electrical impedance is a well-established technique. In an application of this a small electrode array has been developed in which an alternating electric current is passed through a subcutaneous free flap and the induced voltage across a small volume measured. A graphical display of this changing voltage illustrates the pulsatile flow through the flap, allowing continuous assessment of perfusion on a beat by beat basis. The electrode array is such that it can be placed in close contact with muscle without interface problems and can assess its viability. It is non-invasive and easily removed. We have found this accurate, easily interpreted by inexperienced staff, and a considerable reassurance in the postoperative period.

Postoperative monitoring of microsurgical free tissue transfers for head and neck reconstruction

Approximately 10% of free tissue transfers fail because of thrombosis of the arterial or venous anastomoses. Postoperative monitoring to allow early detection of impaired flap perfusion is crucial, especially in head and neck reconstruction, in which failure of a free flap may be associated with significant morbidity. Furthermore, the increasing use of "buried" free tissue transfers in the head and neck precludes direct clinical observation. The various techniques that have been advocated for clinical monitoring of free tissue transfers are reviewed, and their potential applications in head and neck reconstruction are discussed with specific emphasis on the use of low-frequency continuous-wave Doppler surface monitoring and implantable high-frequency pulsed ultrasonic Doppler monitoring.

Magnetic resonance imaging for detection of arterial and venous occlusion in canine muscle flaps and bowel segments

Magnetic resonance imaging (MRI) was performed on 16 muscle flaps and eight jejunal segments in dogs to assess its usefulness in detecting vascular occlusion. Arterial or venous occlusion was carried out in 11 muscles and six bowel segments, with the remaining sham flaps serving as controls. Imaging was performed over 2 hours using a spin echo pulse sequence with T2 weighting. Arterial occlusions in muscles resulted in T2 values 15-30% higher than controls, while venous occlusion produced T2 values 55-75% higher than controls. Differences became significant (p less than 0.05) at 10 minutes after venous occlusion and at 35 minutes after arterial occlusion. Differences between occluded and control bowel segments, although demonstrating a similar trend, failed to reach statistical significance in this preliminary study. The authors conclude that magnetic resonance imaging may be a valuable method for early detection of venous and arterial occlusion in muscle flaps. Further study may also demonstrate this technique to be useful in the diagnosis of ischemic bowel.

Effects of lidocaine concentration on distal capillary blood flow in a rabbit ear model

The laser pulse doppler provides a noninvasive, reproducible method to measure the flux in distal capillary blood flow in a rabbit ear model. The distal capillary blood flow responds proportionally to changes in periarterial lidocaine concentration. The response is biphasic. Flow initially decreased from the baseline in all lidocaine concentrations between 0.5% and 10.0%. Proportional increases in distal blood flow above baseline are noted as the buffered lidocaine concentrations increase from 1.0% to 10.0%. Lidocaine concentration of 0.5% dose not increase distal blood flow above baseline.

Pulse oximetry for vascular monitoring in upper extremity replantation surgery

Pulse oximetry as a postoperative monitor for replanted or revascularized digits was evaluated experimentally and clinically. The accuracy of detection of vascular occlusion was 100%, and arterial and venous occlusion could be differentiated by changes in pulse inflow and oxygen saturation. Digits demonstrating O2 saturations above 95% remained viable, those below 85% were associated with venous occlusions, and those with no saturation represented arterial occlusions. This method is simple, noninvasive, continuous, and accurate, and it reliably assesses revascularized digits and replanted parts.

End-to-end and end-to-side microvascular anastomoses: a comparative study

The decision to use an end-to-end versus end-to-side anastomosis remains a controversial issue in microvascular surgery, although it is generally accepted that certain clinical situations require skills in both techniques (eg, vessel size discrepancy or the need to preserve donor vessel distal flow). Using rats, this investigation presents a unique free flap model comparing not only arterial end-to-end and end-to-side anastomoses, but venous anastomoses as well. There were 15 animals in each anastomosis group with a greater than 80% flap survival rate in each group. This supports findings of earlier studies that suggested no difference in survival when these two anastomosis types were compared. Equally important was the assessment of dermofluorometry as an immediate postoperative perfusion monitoring device. In this model, fluorometry was not found to be useful for predicting flap viability in an early period after completion of the anastomoses.

Significance of deep body thermometer for assessing haemodynamics of free flaps

A deep body thermometer was used in 13 cases of microvascular tissue transfer in order to assess the post-operative haemodynamics of the flaps. Nine of 10 cases involving free skin flaps demonstrated good blood flow by the temperature recovery curves in cooling and rewarming (CR) tests conducted immediately and 6 to 12 hours after operation but in the tenth, anastomotic problems were predicted by the tests. None of the three musculocutaneous flap cases demonstrated good blood flow patterns initially but two were good at 6 hours and did well. The third had a poor pattern at 6 hours and suffered partial necrosis. This study confirmed that it is possible to assess the state of circulation in a flap by the CR test after free flap transfer.

Noninvasive tissue oxygen monitoring in surgical and critical care medicine

Noninvasive tissue oxygen monitoring techniques are becoming increasingly important as a means for assessing perfusion and oxygenation in clinical and experimental medicine. Applications of several oxygen monitoring modalities in surgical and critical care medicine are described.

Experience with transplantation of composite tissues by means of microsurgical vascular anastomoses. I. Indications, techniques and early results

The clinical experience with 65 transplantations of composite tissues by means of microsurgical vascular anastomoses is reported with emphasis on indications, operative techniques, vascular complications and soft tissue healing. Donor tissues, comprising 28 latissimus dorsi flaps, 20 groin flaps, 2 saphenous flaps, 4 fibular flaps, 9 dorsalis pedis artery flaps and 2 second toes, were transplanted to recipient sites in the head and neck area (18), upper extremity (8), torso (2) and lower extremity (37) in sixty-two patients with defects caused by traumata (45), tumor excisions (16) or congenital malformations (1) in which on average 3 therapeutic attempts had been unsuccessful. The reconstruction failed in 3/65 (5%) cases due to vascular thrombosis at the anastomotic sites. Early circulatory impairment (less than 1 week postoperatively) in the transplanted tissues was seen in 16/65 (25%) cases, thirteen of which were successfully managed by evacuation of a haematoma (9) and/or by resection of the anastomotic site and reconstruction of vascular continuity (5). Late circulatory impairment (greater than 1 week postoperatively) secondary to local infection was seen on 2 occasions and resulted in total loss of one flap. In one case persistent posttraumatic ostitis resulted in partial loss of a flap necessitating further reconstructive attempts. Altogether the reconstructive attempt failed in the early postoperative period (less than 3 months) in 5 cases (8%). It is concluded, that difficult reconstructive problems may be solved in a single stage using microsurgical composite tissue transplantation in patients who otherwise would have faced prolonged multistaged reconstructions and/or major limb amputations. Microsurgical composite tissue transplantation has widened the possibilities of reconstructive surgery and seems to be a reliable method, at least as safe as conventional reconstructive flap procedures.

Continuous subcutaneous tissue pH measurement as a monitor of blood flow in skin flaps: an experimental study

A miniaturised glass pH probe that makes possible the continuous measurement of subcutaneous tissue pH is described. This instrument has been evaluated as a monitor of blood flow in experimental skin flaps. A rapid fall in tissue pH in response to either arterial or venous occlusion was observed. The results suggest that this technique may be a useful method of monitoring microvascular free flaps.

Late patency of clinical microvascular anastomoses to free composite tissue transplants. II. Hemodynamical aspects

In a series of 37 free composite tissue transplantations performed to the lower extremity in 34 patients, skin islands were included in 35 cases, as a cutaneous island flap (3), as a musculocutaneous island flap (19), and as an osteocutaneous island flap (13). In a follow-up study which included 26 patients with 29 flaps 6-48 months postoperatively an estimate was made of the importance of the blood supply through the vascular pedicle relative to the collateral blood supply through the recipient bed. Using transcutaneous oxygen tension measurements a significant reduction in calculated relative skin blood flow averaging 70% (p much less than 0.01) was seen after digital occlusion of the vascular stalk, suggesting that patent microvascular anastomoses are important for the vascularity of the transplanted tissues, not only for immediate postoperative survival, but also on the longer view.

Clinical application of transcutaneous oxygen measurements in replantation surgery and free tissue transfer

In 65 replantations and 18 free tissue transfers (6 toe-to-thumb and 12 free flaps) transcutaneous oxygen levels were used as a postoperative monitoring system of the microcirculation. In successful replants and successful free tissue transfers an identical pattern of oxygen levels was observed. In failing replants or free tissue transfer, PO2 levels react immediately to changes in microcirculation and these changes in PO2 appear several hours earlier than the clinical symptoms or changes in temperature. This enables salvage operations after circulatory failure caused by thrombosis to be performed before irreversible tissue damage occurs.

Critical comparison of transcutaneous PO2 and tissue pH as indices of perfusion

A critical laboratory evaluation of transcutaneous PO2 monitoring and tissue pH monitoring in lower abdominal island flaps based on the superficial inferior epigastric vessels in rabbits revealed that transcutaneous PO2 values correlate poorly with tissue survival under circumstances of decreased arterial inflow. The inability of the transcutaneous PO2 monitor to accurately predict viability of the flaps in this study is attributed to physiologic changes in the microcirculation and not to instrument error. Tissue pH was, in all instances, a reliable index of the perfusion status of the flaps.

Direct microvascular monitoring with implantable ultrasonic Doppler probes

A method for constructing high-frequency pulsed Doppler ultrasonic microprobes is described. Such probes were constructed and implanted on the femoral arteries of 14 rats. All of the probes gave excellent signals during the early postoperative period and all probes were found to be functional when retrieved one month after implantation. We feel that high-frequency pulsed Doppler microprobes have important advantages for microvascular monitoring.