The Role of Optical, Acoustic, and Human Dependent Technologies In Monitoring Vascular Perfusion After Free Flap Tissue Transfers in Reconstructive Surgery
Introduction. Free tissue transfer flaps, or commonly referred to as free flaps, are portions of tissue that can be dissected away from its anatomical location, due to its own unique arterial and venous blood supply,and transplanted into its non anatomical position in the case of injury1. The free flap tissue transfer complication rate has been reported to be around 30%, with the caveat that complete flap loss represents nearly 4% of all free flap transfer operations.1 Of the roughly 30% of free flap surgeries with complications, approximately 10% of these are able to be re-explored as the majority of them present within 72 hours of surgery, the remaining flaps are vascularly compromised and display the “non-reflow” phenomenon, leading to total flap loss.4,5 Focusing on vascular compromise as the main pathology: arterial inflow and venous outflow are the basic principles on which flaps transfers insure their viability. When these tenets are violated by pedicle geometry problems or disruption of the anastomotic integrity, flap failure occurs. Pathologicaly this manifest as a venous thrombosis, secondary to poor pedicle geometry and anastomotic disruption.2 These findings suggest an alternative solution to monitoring perfusion to free flap tissue operations, given the efficacy of the standard of care. Methods. Studies various emerging technologies and translational medical imaging devices were examined in depth and factors such as number of flaps salvaged, positive predictive value, cost, and number of total flap failures were considered against the current standard of care. Results. Technologically, the Doppler signal/ultrasound is used in order to measure flow in real time and in some rare cases an implantable doppler is placed on the wound. Other proxies of vascular compromise include: surface temperature, electrical impedance, microdialysis and tissue pH.3,6 When examining two free flap monitoring methods for success and salvage rate compared to the current clinical standards of care. It was found that among 5 total studies consisting of 571 operations, The Cook – Swartz Doppler may be more effective in monitoring free flaps compared to that of the clinical standard of care; however there exists some limitations due to the propensity for false positives. In reviewing the literature, a Self-Calibrated Tissue Viability Sensor for Free Flap Monitoring was found in which it measures StO2 ( tissue oxygen saturation) as a potential assessment tool for flap monitoring, regardless of a patient’s predisposition to risk factors. This predisposition can at times hamper the care provider’s ability to check for capillary refill, especially in larger patients.3 This skin type and provide flap failure was tested. This was done through creating 9 free flaps, creating ischemic circumstances, and taking StO2 measurements as well as qualitative measurements made by microvascular surgeons. 6 Near Infrared Spectroscopy (NIRS) has been used by cardiovascular surgeons and anesthesia providers to measure cerebral perfusion to the brain during open heart surgery when the great vessels are clamped. This same monitoring setup can be applied to free flaps in order to assess their perfusion level as well.3,6 In 57 cases, the NIRS was able to detect one case of arterial insufficiency and 3 cases of venous insufficiency through regional oxygen saturation decrease, before the flap color itself shifted to a pale or “venous congested” hue. This allowed for all four flaps to be revised through re-exploration rather than progress to free flap morbidity.6 Conclusions. Early signs of vascular compromise have not been noted to allow for feasible warning of ischemic onset. Furthermore, standard of care relies upon a nurse to check the wound on a schedule whose protocol may not involve using doppler to ascertain vascular integrity. Some buried flaps may only present with visual symptoms days after surgery, by which time flap revascularization is not feasible. The need for a continuous monitoring system, regardless of flap type exists.
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