Flaps, Free Tissue Transfer

Definition

Free tissue transfer is defined as the vascular detachment of an isolated and specific region of the body (eg, skin, fat, muscle, bone) followed by transfer of that tissue to another region of the body with reattachment of the divided artery and vein to separate artery and vein. This ability to transplant living tissue from one region of the body to another has greatly facilitated the reconstruction of complex defects.

Free tissue transfer has become commonplace in many centers around the world. The numerous advantages include stable wound coverage, improved aesthetic and functional outcomes, and minimal donor site morbidity. Since the introduction of free tissue transfer in the 1960s, the success rate has improved substantially and is currently 95-99% among experienced surgeons. This article provides a framework to facilitate the planning, execution, and monitoring of free flaps.

For more information on various flap procedures, see the Flaps section of eMedicine’s Plastic Surgery journal.

Indications

Free tissue transfer currently is used for the reconstruction of complex defects and disorders throughout the body. As with all techniques in plastic surgery, adherence to the basic principles and concepts of reconstruction is essential. The "reconstructive ladder" that all plastic surgeons learn is based on performing the simplest procedure to correct a particular condition. Although these principles are valuable and almost always justified, aesthetic and functional considerations occasionally warrant performing more complicated procedures. These considerations are most evident following ablative procedures for cancer, for restoration of function, and for aesthetic appearance.

Numerous clinical situations exist in which the use of a free flap is justified and beneficial. Refinements in mandibular reconstructions have led to the use of the free fibular flap, which results in improved appearance and function of the neomandible. The use of the muscle-sparing free transverse rectus abdominis myocutaneous (TRAM) and deep inferior epigastric (DIEP) artery and vein flaps in breast reconstruction allows for excellent shape and contour of the breast mound while minimizing donor site morbidities related to abdominal strength and contour.

Innervated free muscle flaps have successfully restored upper extremity and hand function and the ability to generate facial animation in incidents of nerve and muscular dysfunction. The use of numerous perforator flaps such as the DIEP flap, superficial inferior epigastric artery (SIEA) flap, thoracodorsal artery perforator (TAP) flap, and superior or inferior gluteal (SGAP, IGAP) flaps have served to further increase the surgeon's options and further decrease donor site morbidity.¹

Preoperative Considerations

Preoperative preparation is an essential component of the successful free tissue transfer. Preoperative evaluation includes analysis of the recipient site, consideration of available donor sites, and the clinical status of the patient. Proper patient selection is of utmost importance when analyzing outcomes. The specific factors are reviewed below.

Analysis of recipient and donor sites

Factors related to the recipient site include the size, depth, and location of the defect; quality of the surrounding tissue; exposure of vital structures or hardware; zone of injury; presence of bacterial colonization or infection; previous irradiation; and functional and aesthetic considerations. Factors related to the donor site include appropriate tissue match; length of the vascular pedicle; caliber of recipient vessels; surface area, volume, and thickness of the flap; and donor site morbidities. Flaps with a short vascular pedicle requiring a vein graft and flaps with a bone component are associated with an increased rate of flap loss in some clinical series.² Some sites, such as the head and neck, have various recipient vessel options; therefore, a thorough understanding of the anatomy is essential.³

Clinical status of the patient

The clinical status of the patient depends on a variety of factors that also may impact the free flap. These include advanced age, nutritional status, tobacco usage, and presence of underlying comorbidities (eg, diabetes mellitus, cardiopulmonary disease, peripheral vascular disease). Although advanced age and tobacco use are not contraindications to free-flap operations, poor nutritional status can impede wound healing and recovery. Patients with poorly controlled diabetes mellitus and peripheral vascular disease require adequate glucose control and may require revascularization procedures prior to free tissue transfer. Surgical clearance by a medical physician is recommended for patients with multiple medical problems.

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Donor tissues

Specific donor tissues are variable, and donor sites are chosen based on recipient site requirements. Available tissues include muscle, musculocutaneous, fasciocutaneous, osteocutaneous, and bone flaps. In general, free muscle flaps are indicated for soft tissue coverage of bone and synthetic materials and to obliterate a large dead space.

• Innervated muscle flaps are useful for facial reanimation operations and for upper extremity reconstruction.
• Musculocutaneous free flaps are useful for large defects requiring aesthetic contouring.
• Fasciocutaneous flaps permit tendon gliding in the extremities and provide excellent contouring of the head and neck.
• Osseous and osteocutaneous free flaps are useful for segmental bone defects involving the mandible and extremities.
• Adipocutaneous or perforator flaps are especially useful to minimize donor site morbidity.
• For the irradiated wound, free tissue transfer is recommended and has been demonstrated to be safe and well tolerated, with no increased rate of partial or total free flap loss.

Timing

In the trauma patient, the timing of free-flap reconstruction is of prime importance. Free tissue transfer within 3-7 days allows time for adequate debridement, declaration of the zone of injury, and prevention of chronic bacterial colonization. Immediate free-flap reconstruction is often preferred for the acquired operative wound, especially in the presence of vital structures and hardware and for aesthetic and functional considerations. Consider delayed free-flap reconstruction when oncologic concerns are present.

Other considerations

Other factors that require consideration include choice of anesthesia and patient position for the operation. Anesthetic options include general, spinal, or epidural and depend on the nature and location of the reconstruction. General anesthesia is preferred for most patients and can be administered via oral, nasal, or tracheal routes. Oral intubation is preferred for trunk and extremity reconstructions; however, nasal and tracheal intubations are preferred for most reconstructions involving the head and neck. Spinal anesthesia occasionally is used for lower extremity free flaps and has the advantage of providing a transient sympathectomy that promotes vascular dilation. Epidural anesthesia is primarily used for postoperative pain management.

Patient positioning may require an inflatable beanbag, Wilson frame, or Mayfield headrest. The inflatable beanbag is useful in placing the patient in the lateral decubitus position (eg, when harvesting a latissimus dorsi flap). The Wilson frame or chest rolls benefits patients in the prone position, allowing chest expansion during general anesthesia.

Intraoperative Considerations

The operative portion of the free tissue transfer requires absolute attention to detail. Numerous factors must be considered to predictably obtain a successful outcome. These include use of appropriate medications and solutions, properly functioning equipment and instruments, anastomotic issues, and flap insetting.

Intraoperative medications

Required medications include intravenous antibiotics, antibiotic solution for wound irrigation, intravenous heparin administered 5 minutes prior to free flap harvest, 4% Xylocaine for topical vasodilatation, and heparin solution (100 U/cm³) for luminal irrigation. Studies evaluating the effects of various intraoperative anticoagulants have demonstrated that the flap loss rate is lower in patients receiving a heparin bolus of 5000 U only or a heparin bolus of 2000-3000 U followed by postoperative infusion. Low-dose heparin does not increase the risk of hematoma or postoperative bleeding. Other medications that may be used include Decadron 4-8 mg to reduce edema and swelling (especially for reconstructions of the head), papaverine as an alternate vasodilator, and streptokinase or urokinase for lysis of intraluminal thrombus.

Anastomoses issues

Various issues are related to the anastomoses. Factors contributing to a difficult anastomosis include trauma to the zone of injury, radiation, scar, and infection. Success can be amplified by adhering to the some basic principles.

• The nursing staff and primary surgeon must inspect the micro-instruments and microscope to ensure proper function.
• The diameter of the artery and vein, both for the flap and recipient site, should be 1-3 mm to permit adequate inflow and outflow.
• Blood vessels must be free of all loose adventitia, and the vascular approximation must be tension free. Acland clamps should facilitate vascular exposure and manipulation.
• Complete the anastomosis using either a vascular coupler or sew it by hand. The author prefers to hand sew; however, the coupler has demonstrated its usefulness, especially for venous anastomoses, in improving patency and decreasing operative time.
• Complete the hand-sewn anastomosis using 8-0, 9-0, or 10-0 nylon sutures placed in an interrupted fashion. In general, anastomose larger caliber vessels (2-3 mm) using 8-0 or 9-0 sutures and smaller caliber vessels (1-2 mm) using 9-0 or 10-0 sutures.
• Using operative loupes rather than a microscope has been reported; a minimum of 3.5-power magnification is recommended.
• The tolerated flap ischemia times depend upon the composition of the tissues being transferred. In general, perforator flaps tolerate longer periods of ischemia because no muscle is involved. Ischemia times of up to 4 hours for a perforator flap may be well tolerated. Musculocutaneous flaps, on the other hand, do not tolerate prolonged ischemia times because of the metabolic requirements of the muscle. In general, 2-3 hours of ischemia is the maximum time tolerated.⁴
• Following completion of the anastomoses, the flap must be properly inset. Inspect the vascular pedicle for kinks, twists, compression, and to ensure that no tension is present across the anastomosis. Inspect the distal aspect of the flap for arterial and venous bleeding. Use a Doppler unit to assess arterial and venous flow through the pedicle and in the flap. Finally, recheck the vascular pedicle to ensure a gentle, nontwisting course of the vessels before completing the final suturing of the flap, especially if the patient's position has been changed.
• Place a closed suction drain under the flap away from the anastomoses and suture the flap in position.

Postoperative medications

Using postoperative medications to inhibit clot formation at the anastomosis is controversial. Studies evaluating the efficacy of heparin, dextran, and aspirin have demonstrated that none is absolutely necessary for an uncomplicated anastomosis. However, the author prefers to run intravenous dextran-40 at 30 cm³/h for the first 12-24 hours, followed by oral Ecotrin 325 mg daily for 2-4 weeks.

Postoperative Monitoring

Techniques to monitor the free flap depend on the tissue composition and location of the flap. Specific monitoring techniques include evaluation of color, capillary refill, turgor, surface temperature, presence of bleeding, skin graft adherence, and auditory assessment of blood flow. Use of these techniques depends on whether the flap has a fasciocutaneous component, is covered with a skin graft, or is buried and inaccessible to visual assessment.

Surface characteristics

For the fasciocutaneous, adipocutaneous, musculocutaneous, and osteocutaneous flaps, surface characteristics are important. Normal flap color is similar to that of the recipient site. Normal capillary refill is 1-2 seconds. Surface temperature of the flap can be monitored using adhesive strips (for an accurate number) or the back of the hand (to provide a comparative assessment with the surrounding skin). Problems with arterial inflow are suggested when the flap is pale relative to the donor site, cool to the touch, and when capillary refill is slow or absent. Problems with venous outflow are suggested when the flap is congested, edematous, and when capillary refill is brisk and rapid. Color and appearance of congested flaps can vary depending on whether the congestion is mild or severe and ranges from a prominent pinkish hue to a dark bluish purple color.

Surface Doppler assessment for flaps with a fasciocutaneous component may yield a false positive result by picking up signals from surrounding or deep blood vessels. Characteristics of blood from the flap following pinprick also can provide clues. Dark venous blood suggests venous occlusion, and absence of bleeding suggests arterial occlusion.

Muscle flaps with skin grafts

The muscle flap covered with a skin graft often is easier to monitor. Surface temperature and capillary refill generally are not used in these situations; however, color, turgor, skin graft adherence, and Doppler signals are useful. Signs of venous outflow obstruction include flap congestion and edema, dark blood on pinprick, and loss of the venous Doppler signal. Signs of arterial occlusion include a flat and pale flap, poor skin graft adherence to the flap, no bleeding on pinprick, and loss of the arterial signal.

Deep or buried flap

The most difficult flap to monitor is the deep or buried flap (eg, fibula flap without a skin paddle). Surface Doppler signals often are unreliable. In these situations, placing the temporary implantable Doppler probe adjacent to the artery and vein at the time of operation is useful.

Salvage Procedures for the Failing Flap

Monitoring the free flap during the postoperative phase is critical to ensure flap survival. When recognized early and managed promptly (<6>

• Following recognition of flap compromise, immediately transport the patient to the operating room for exploration.
• Administer intravenous heparin.
• Inspect the vascular pedicle for kinks and compression and assess the patency of the anastomosis.
• Identification of thrombus requires separation of the vessels at the anastomosis.
• Perform embolectomy, proximally and distally, using a number 2 or 3 Fogarty catheter.
• Administer intraarterial streptokinase or urokinase at a dose of 50,000-100,000 U as necessary.
• Following restoration of adequate circulation, inset the flap again and maintain the patient on intravenous heparin or dextran.
• Failure to restore adequate circulation requires flap removal.
• The use of medicinal leeches, Hirudo medicinalis, has demonstrated value in the treatment of venous congestion.⁵ This option is indicated when arterial inflow is adequate but venous outflow is poor. The mechanism of action depends on the active agent, hirudin, which is a selective thrombin inhibitor. Apply the leech to the surface of the flap and surround it with a corral of moistened gauze to prevent leech migration. Prophylactic antibiotics are recommended to prevent infection with Aeromonas hydrophila.

Keywords

free flap, flap, skin flap, transplantation, free flaps, tissue transfer, tissue transplantation, soft tissue defect, microvascular free flap, DIEP free flap, free flap surgery, muscle-sparing free transverse rectus abdominis myocutaneous flaps, TRAM flaps, deep inferior epigastric artery flap, DIEP vein flaps, DIEP flaps, breast reconstruction