Introduction
It is something of a dent to personal pride to be singled out among so many internationally distinguished contributors to write a chapter on complications in microsurgery. How did the editors know we were so experienced in complications? We would like to be able to make the same boast as an esteemed surgical mentor who, when asked to speak on complications, warmed to the subject by stating that, “ I am an authority on complications – I saw one once. ” Sadly, good judgment comes from experience and experience comes from bad judgment. We at least qualify from the experience side of the equation.
Free flap failure is a traumatic experience for patient and surgeon alike and sharply brings into focus a self-appraisal of the wisdom of the operation in the first instance. Not only has the reconstruction failed but now a donor site scar is present – two holes instead of one. Perhaps also the telltale limb scars of vein grafts, salvage trails of the desperate surgeon, and hematomas from rashly considered anticoagulation. Incredulity from inquiring relatives, the shattered confidence and bitter disappointment of the patient. Self-doubt, recriminations: “What more could I have done to make this work? Was it bad tissues, the assistant, the anesthetist, the nursing, monitoring, or just a good surgeon out of luck?” “Why am I doing microsurgery? Do I need this? How did I get into this mess? Who can I share it with? Where is the caustic soda? Which way to the river?”
The answers to these questions can be analyzed under three headings:
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Failure of planning
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Failure of execution
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Failure of postoperative care
Failure of Planning
For a brief summary of failure of planning, see Box 27.1 .
Fitness for Anesthesia
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Age, coagulopathy, general health, prolonged positioning
Poor Choice of Donor Flap
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Inappropriate characteristics: size, color, texture, thickness
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Access: prevents simultaneous resection and recipient site preparation and donor site dissection
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Pedicle length too short
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Predisposes to postoperative complications, eg, tight chest closure (LD flap) → respiratory problems, tight abdomen and pelvic dissection (DIEP) → DVT
Recipient Vessels
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Access: too deep, too far away, needing vein grafts
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Damage: scar, edema, trauma, infection, radiation
Timing of Surgery
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Too early: inadequate planning and/or patient preparation
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Too late: excessive waiting prior to wound coverage
In hindsight, flaps that do well are those that proceed with comfortable familiarity; no change of plan; no unanticipated need for vein grafts; access for microvascular repair is easy; recipient vessels are large; and the artery has good forward flow. The anastomotic site can be closed without tension. The patient is warm, fluid filled, and relaxed postoperatively. The flap can be well visualized, kept warm, and monitored by experienced staff. Conversely, where there is indecision, too many cooks giving advice, and general lack of purpose, results will be proportionately unpredictable.
The Patient
Many complications can be avoided by ensuring that each patient undergoes a thorough clinical evaluation prior to formulation of the management plan. Today, successful outcomes in free tissue transfer and replantation are achieved consistently in the presence of patient factors once considered to present a high risk for treatment failure, provided that these factors are identified at the planning phase and appropriate measures taken to reduce their effect. In a historic, multicenter prospective survey of free flaps performed over a 6-month period involving 493 flaps from 23 units, including our own, several factors emerged as important to outcome. Overall, there was a failure rate of 4.1% and the only factors adversely influencing survival were irradiated field and the use of muscle flaps with skin grafts. Postoperative thrombosis rate requiring reexploration was 10% and more likely in chronic wound areas and if vein grafts were used. The paper by Khouri et al., from 1998, remains as one of the highest level evidence papers that has been published on microsurgical outcomes.
Fitness for Anesthesia
As with all major surgery, cardiac and respiratory fitness should be appropriate before electing a microsurgical case. Prolonged awkward postures need to be tolerated, which may temper the choice of donor flap and extent of operation. A personal or family history of thrombosis should be especially sought in the preoperative screening and consideration given to preoperative anticoagulation in routine cases.
Age
Age per se is not a contraindication to microvascular surgery. A number of studies have shown no difference in free flap survival when extremes of age are evaluated. Pediatric patients have excellent free flap survival rates, with very few nonsurgical complications and no apparent growth-related complications noted at donor or recipient sites, although research indicates exposure to anesthesia before 3 years of age may result in cognitive deficits. Prospective studies on this are still ongoing. Although excellent flap survival rates are observed in patients of advanced age, 75% of patients older than 70 years have more than one medical issue contributing to complications such as myocardial infarction, pulmonary embolism, and prolonged intubation. In one series, mortality was as high as 5.4% in the age group 60–69 years with significant preoperative medical. In other reports, although medical complications were very high, mortality was much lower.
Systemic Disease
Diabetic patients do not seem to experience a higher incidence of free flap thrombosis and/or failure. Most of the robust research on diabetic free flaps has been reported in the lower extremity with success rates around 92%. Numerous reports show the importance of tight glucose control pre- and postoperatively to minimize surgical morbidities in diabetic patients. Data from our institution show poor long-term glycemic control in patients with an HbA 1c >6.5% leads to increase in wound dehiscence. Hypercoagulable patients should be managed in conjunction with hematology, as these patients have a much higher rate of thrombosis and a lower rate of free flap salvage. It is important to take a thorough history of previous deep venous thrombosis (DVT), multiple miscarriages, or a family history of blood clotting abnormalities. Obesity alone does not appear to be associated with increased free flap failure rates, although the incidence of hematoma or hemorrhage appears to be higher. A recent meta-analysis of free autologous breast reconstruction showed that patients with a BMI >40 had a much higher prevalence of complications compared with non-obese patients.
Tobacco Smoking
The influence of smoking on the outcome of microvascular surgery is a contentious issue. The detrimental effect of nicotine on cutaneous blood flow and wound healing is accepted. Chang and Buncke reported an extraordinarily detrimental effect of smoking on replantation surgery outcomes, stating that 80% of patients who smoke in the period between 2 months before and 2 months after surgery can be expected to lose their replants. Our experience does not support this low survival rate.
The effect of smoking on free tissue transfer outcomes is less clear. Although numerous experimental studies have linked cigarette smoking with delayed microvascular anastomotic healing and free flap failure, we demonstrated significant reductions in blood flow without reductions in microvascular anastomotic patency in animal models following nicotine administration. Furthermore, a number of large clinical studies have demonstrated no significant difference in vessel patency, flap survival, or reoperation rates in smokers compared with non-smokers. Of interest, perforator free flaps may differ from traditional free tissue transfers in that reoperation rates, and anastomotic complications appear to be higher in smokers than non-smokers. It is our practice to recommend that smokers undergoing elective reconstruction cease smoking at least 2 weeks before the procedure, and refrain from smoking for at least 2 months postoperatively. We have several anecdotal cases of both digits and flaps undergoing irreversible arterial spasm as a direct consequence of smoking.
Defect
Site and Cause
The site of the defect for reconstruction has not been shown to significantly predict survival or microvascular complications in free flap surgery. In particular, free tissue transfer to defects of the lower extremity does not seem to have a higher incidence of complications than to other sites. Similarly, outcomes do not seem to be predicted by the condition requiring reconstruction, whether it be trauma, chronic wound, osteomyelitis, congenital anomaly, burns, cancer, or other condition. With respect to trauma, this is inconsistent with the reports of Godina and Byrd et al., who convincingly showed that complications were higher and flap survival less when free flaps were transferred to compound lower-leg wounds after the first week of injury. Empirically, if there is poor vascularity of the defect bed, irradiation damage, infection, or residual tumor, even though the microvascular component of the procedure may be heralded as a success, the likelihood of non-microvascular complications and hence failure to achieve the purpose of the procedure, is higher.
Dimensions
The surgeon must anticipate likely alterations in defect dimensions: for example, after wound contractures have been released, adjacent joints positioned in extremes of functional range of motion, residual pathology, or anticipated die-back of surrounding skin margins are excised. When resurfacing defects on convex surfaces, such as the scalp, heel, or limb, or when myocutaneous flaps are employed and the underlying muscle has to be accommodated, a larger area of skin needs to be included to account for the increased circumference. Skin size can become critically deficient once postoperative swelling occurs. Having to release tight sutures postoperatively from a free flap can lead to non-graftable bed exposure and an embarrassing, surviving, islanded monument to incompetent design and the need for further flap coverage. Especially in lower extremity cases, planning must ensure coverage of the pedicle, which may be farther from the defect. Tension surrounding the pedicle must be minimized to ensure that there is no external pressure. It may be preferable to intentionally accept a second-stage reduction of redundant tissue once swelling has resolved. Additionally, the surgeon should ensure that the chosen flap is of adequate volume to obliterate dead space and not merely be of sufficient area to permit wound closure. In breast reconstruction, the flap size may be deliberately smaller than the opposite side, in anticipation of a secondary reduction on that side.
Donor Flap
Site
Choice of flap donor site is determined primarily by the defect with respect to size, contour, thickness, color, function, etc., but is tempered by the significance of the secondary defect and positioning of the patient to allow simultaneous recipient and donor surgery. The donor choice may influence outcome, in terms of flap failure rates and anastomotic thrombosis. Free groin flaps seem to have higher failure rates than other cutaneous free flaps raised on larger-caliber pedicles. Similarly, rectus and TRAM flaps have been observed to be associated with reduced incidences of take-back and failure when compared with flaps from other donor sites, although this association does not appear to be significant. The anterolateral thigh flap has surpassed all others in popularity no doubt because of its multiple attributes, size, thickness, long, large diameter vessels, ease of access away from the site of primary surgery, and usually direct closure.
Composition
The composition of free tissue transfers influences outcome in certain situations. Khouri et al. identified the use of a skin-grafted muscle flap as a significant predictor of free flap failure. Higher flap failure for these transfers appears to be secondary to an impaired ability to detect postoperative thrombosis, rather than a higher vascular thrombosis rate per se . Muscle and musculocutaneous flaps have traditionally been favored over fasciocutaneous flaps for coverage of chronically infected wounds. Traditionally, musculocutaneous flaps were shown to be associated with improved oxygenation into the contaminated wound space and subsequent greater reductions in bacterial counts over time, when compared with fasciocutaneous flaps. However, recent osteomyelitis models demonstrate there are no convincing data that muscle is superior to fascia following adequate debridement.
Machens et al. examined the vascular connections to the recipient bed 10 years after muscle flap transfer to the lower limb using Doppler and hydrogen gas washout. They noted that only in those cases where there had been a salvageable vascular complication at the time of transfer, in other words an added angiogenic stimulus, did significant ingrowth occur into the recipient bed to allow vascular independence from the pedicle.
Pedicle Length and Caliber
Free flap failures are higher when flaps with smaller-diameter pedicles are utilized. Indeed, the increase in free flap success rates observed over the past 25 years can be attributed in large part to the development of free tissue transfers with pedicles of greater diameter and length than those of the first free flaps described, such as the free groin flap. It could be argued that microvascular free flap surgery would not have had a long-term future if it were not for the discovery of the latissimus dorsi and radial artery flaps, which took anastomotic success from the preserve of the professional gambler to the common man. However, with the advent of supermicrosurgery and perforator-to-perforator techniques, in some hands-free tissue transfer is not dependent on size. Pedicle length is important to facilitate proper access and orientation of clamps so that microvascular anastomosis can be performed accurately. Extra pedicle length will permit elevation of the clamped vessels out of cavities and permit orientation of the clamps to best suit the operator.
Donor Morbidity
All flap surgery “robs Peter to pay Paul” and the art is to strike the appropriate balance. The risk of donor site complications varies with patient factors and site and composition of the flap to be raised. Complications are heightened when flaps are dissected with the patient in an unconventional position: for example, harvest of a latissimus dorsi flap with the patient supine or an anterolateral thigh flap with the patient on their side. Here the landmarks for perforators and connective tissue septae can markedly change, and greater caution must be exercised in planning flaps and anticipating pedicles. Unfamiliarity easily leads to errors. Individual free flaps are associated with their own specific complications and are not discussed here.
Recipient Vessels
Successful free flap surgery is surgery of the recipient vessels. The majority of factors known to predict outcome in microvascular surgery relate to the recipient vessels.
Access
Recipient vessels may be normal and of good caliber, but unless they are accessible for microvascular anastomosis, the stage is set for a cascade of technical errors that account for most free flap failures. The choice of recipient vessels must factor in access: not too deeply placed and in proximity to the defect to avoid vein grafts.
Damaged Vessels
Irradiated, avulsed, edematous, scarred vessels or those in an inflamed field have higher incidences of anastomotic thrombosis and free flap failure. Microanastomosis to vessels within irradiated fields has been shown experimentally to be associated with poor patency rates and a high incidence of flap complications. Khouri et al. showed clinically that reconstruction of an irradiated recipient site is a significant predictor of free flap failure. Inflamed, scarred, and avulsed vessels similarly have poorer patency. Mitchell et al. demonstrated histologically, in a rabbit avulsion model, that significant arterial pathology extended up to 4 cm from the rupture point, despite no detectable abnormality under the operating microscope. By contrast, the venous injury did not extend significantly beyond the site of rupture. In avulsed human and monkey arteries, significant circumferential intimal and medial skip lesions were also observed to extend many centimeters from the rupture site.
Where damaged or irradiated vessels must be used, it is important to minimize mobilization and dissection of recipient vessels, employ careful debridement of vessel ends, and microsuture from inside to outside, to prevent intimal separation. This is especially important for calcified vessels. Calcified vessels must be handled with care, as intimal separation and intimal flaps can occur very easily if the calcified wall is damaged. We routinely administer topical heparin (10,000 units in 100 mL of normal saline) and a one-time systemic dose of heparin (5000 units IV) during the clamping and anastomotic phase to prevent thrombosis in such circumstances. In some cases, vein grafts will be needed to anastomose the flap vessels to recipients outside the zone of injury but vein grafting brings its own risks and inherent complications.
Number of Venous Anastomoses
Ideally, two venous anastomoses should be considered for tissue transfer and at least two for digital replants whenever possible, in an attempt to reduce flap loss, but for flaps this is usually impractical. This is supported by Khouri, who observed a significantly higher failure rate when only a single vein was repaired (4.3%) versus two veins (0%) when flaps requiring vein grafts were excluded from the study. Rarely, however, is it practical to have two recipient veins close together; similarly, two flap veins may not be available.
Timing
Flap complications such as thrombosis and failure, as well as osteomyelitis and hospitalization times are significantly increased when flap coverage is delayed in cases of lower extremity trauma. Godina showed improved outcomes when early, stable soft tissue coverage of open tibial fractures was achieved with free tissue transfers. Similarly, Byrd et al. showed that complications worsened when open tibial fracture cover was delayed until the subacute phase of wound healing and contamination. These adverse outcomes are likely to be a result of pathologic recipient vessels during this unfavorable time period.
Failure of Execution
For a brief summary of failure of execution, see Box 27.2 .
Surgeon
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Disciplined, methodical
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Experience
Anesthetic
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Warm: theater temperature, warming blankets
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Wet: fluid-filled; CVP; hematocrit
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Happy: anxiolytics
Vessels
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Recipient
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Traumatic dissection
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Inadequate access
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Poor forward flow
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Size mismatch
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Donor
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Too short
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Tension
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Twists and kinks
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Anastomotic Technique
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Vascular access too deep
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Orientation of clamps preventing visualization of lumens
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Damaged vessel resection
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Suture damage and catching back wall
Vein Graft
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To be avoided where possible because of increased failure rate
Thrombosis
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Arterial
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Venous
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