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  • Introduction Microvascular free flap surgery is one of the m

    2018-11-06

    Introduction Microvascular free flap surgery is one of the most important operations in reconstructive surgery especially in dealing with large or complex defects. Because of the advancement of the microsurgical technique, the success rate of free flap pedicle anastomosis is currently >90%. An even higher (95–97%) success rate has been reported by some medical centers with large case numbers. The key to enhance the free flap success rate is early detection of vascular thrombosis and salvaging of the failing flap with early intervention. The gold standard of postoperative free flap monitoring is clinical observation of flap color and capillary refill. With experienced staff early detection of pedicle thrombosis is possible, but the standard is subjective and observer-dependent. Even well-trained medical staff may not all be alert enough to find the pedicle thrombosis early enough to salvage all failing flaps. There are many objective methods for detecting free flap pedicle thrombosis such as a handheld Doppler, surface temperature, implantable Doppler system, and near infrared (IR) spectroscopy. Recent advances in these flap monitoring methods are reviewed in this SAR 405 article.
    Implantable Doppler system The implantable Doppler system was first introduced in 1988. A 20-MHz ultrasonic probe with 1-mm piezoelectric crystal embedded in a soft silicone sleeve was sutured directly to the blood vessel distal to the vascular anastomosis. It was left in place for 7 days for postoperative detection of vascular thrombosis. Then the probe was removed directly at the bedside from the wound. In a recent report by Smit and colleagues on 327 flaps monitored by the implantable Doppler system, 35 flaps needed revision, and the salvage rate was 69% and was not significantly different from that in the conventional method group (60%). By contrast, in another report from Paydar and colleagues on 169 head and neck free flap reconstructions monitored by the implantable Doppler system, 19 failing flaps due to pedicle problems were all detected and 18 of them were successfully salvaged (salvage rate, 94.7%). Another large retrospective study from Schmulder and colleagues included a wide spectrum of microvascular free flap surgeries. With 259 free flaps monitored by the implantable Doppler system, 33 flaps needed reexploration, and the successful salvage rate was 88% (29 cases), which was significantly higher than that in the control group assessed by clinical observation, with a salvage rate of 46% (12/26). From their studies, the most significant difference was observed in head and neck reconstruction followed by breast reconstruction. The implantable Doppler system is a unique method because of its direct and continuous monitoring ability. It is especially valuable in buried flaps. However, with controversial results from these retrospective studies, it remains inconclusive as to whether the device ultimately improves outcomes in free tissue transfers. The implantable Doppler system can be used to monitor the pedicle artery or vein, but reports of the system exclusively used in the vein showed a better positive predictive rate. The possible explanation is that venous thrombosis is more common than arterial thrombosis, and the artery will be patent for a certain period after venous thrombosis.
    Flap temperature monitoring Surface temperature is a conventional method for postoperative free flap monitoring. Khouri and Shaw retrospectively reviewed 600 consecutive free flaps, where surface-temperature recording was the main method of monitoring used and a detailed temperature record was kept. They defined a value CΔT, which represents the change in temperature difference between the flap and control sites over a specified period, and found a difference of more than 1.8°C to be significant in representing flap circulation compromise. Papillion and colleagues reported the postoperative measurement of surface temperature in 47 microvascular free flaps. Temperatures of the flap failure group during the past 24 hours yielded a mean difference of 2°C compared with surviving flaps (p < 0.05), and the flap failure group had a 3.7°C difference between its temperature and the adjacent skin control temperature compared with a 1.5°C difference in the surviving flaps and their adjacent skin control. Although surface temperature measurement is regarded as a sensitive tool in monitoring venous congestion of digital replantation, some authors reported that surface temperature monitoring failed to detect any changes prior to complete or partial flap failure or reoperation in any case of deep inferior epigastric perforator (DIEP) breast reconstruction.