TITLE: THE BASICS OF MICROVASCULAR SURGERY
SOURCE: UTMB Dept. of Otolaryngology Grand Rounds
DATE: February 26, 1997
RESIDENT PHYSICIAN: Christopher Thompson, M.D.
FACULTY PHYSICIAN: Karen Calhoun M.D.
SERIES EDITOR: Francis B. Quinn, Jr., M.D.

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"This material was prepared by resident physicians in partial fulfillment of educational requirements established for the Postgraduate Training Program of the UTMB Department of Otolaryngology/Head and Neck Surgery and was not intended for clinical use in its present form. It was prepared for the purpose of stimulating group discussion in a conference setting. No warranties, either express or implied, are made with respect to its accuracy, completeness, or timeliness. The material does not necessarily reflect the current or past opinions of members of the UTMB faculty and should not be used for purposes of diagnosis or treatment without consulting appropriate literature sources and informed professional opinion."

HISTORY

The origins of microvascular surgery can be traced back to Alexis Carrel in the early 1900s. His work illustrated reproducible methods of suturing vessels together with excellent patency rates. Modern microvascular techniques are credited to Jacobsen and Suarez who borrowed the use of the operating microscope from their otologic colleagues, in the 1950s. Human tissue transfer was accomplished as early as 1957 when Som and Seidenberg reconstructed an esophagus with a free jejunal segment. However, this was also the time that regional flaps were coming into use and further microvascular advances were delayed until the 1970s. Multiple reports of free fasciocutaneous flaps entered the literature in 1972, and in 1979 Taylor introduced the composite osteocutaneous groin flap. The late 1980s saw an explosion in free flap reconstruction of mandibular and soft tissue defects, and the use of osseointegrated implants was introduced. From the late 1980s until present, free tissue transfer techniques have become an accepted tool in the reconstruction of head and neck defects.

ADVANTAGES AND DISADVANTAGES OF FREE TISSUE TRANSFER

Free flap reconstruction has several advantages over other methods, particularly in the head and neck. Free tissue transfers are usually designed as a single-stage procedure, as opposed to many of the pedicled reconstructions. Pedicled flaps require a less efficient use of tissue as entire muscles are defunctionalized in order to safely transfer enough tissue to fill the defect. Free transfers allow the harvest of exactly tailored grafts, minimizing donor morbidity. Similarly, free tissue transfers are usually associated with less postoperative atrophy, eliminating the need to overcorrect.

Head and neck defects are often inhospitable, requiring contact with saliva, nasal secretions, and tissues previously exposed to radiation and surgery. Well perfused free flaps are suited to these conditions. Pedicled flaps frequently have less perfusion at the margins, which may be very distant from the blood supply. Skull base defects may require a water-tight closure to prevent CSF leakage. Again, excellent perfusion at the wound edges make the free tissue transfers more likely to live up to these expectations.

Bony reconstruction is now virtually synonymous with free tissue transfer. Resorption, which plagued non-viable bony transfers is eliminated. Unlike other reconstructive techniques, primary osseointigration is now possible. Transferring well perfused tissues incites a strong union with the surrounding bone in as little as 1 to 2 months, eliminating the long term use of reconstruction plates.

Both functional and aesthetic advantages are abundant with free tissue transfers. Flap transfers capable of sensation are plausible with the use of neurofasciocutaneous free tissue transfers, unlike any of the pedicled flap transfers. Pedicle flaps are often less than perfect when the defect requires the extremes of massive bulk or thin, pliable tissue. Free flaps are not limited by these constraints. Along the same lines, pedicled flaps often transfer skin of a poor match to the host site. Free transfers provide a much wider range of skin characteristics.

The principal disadvantage in free tissue transfer is the technical demands required by the technique. A great deal of additional expertise and equipment is required intraoperatively, as well as perioperatively. This drives the costs of the patient’s care up significantly. Although the technique is usually performed with a two-team approach, an average of 4 hours are added to an already lengthy surgical procedure. Even in the most experienced hands, one can expect a 5 to 10 percent flap failure rate, usually due to thrombosis. Flap failure necessitates a second operative procedure as well as additional donor site morbidity if a second flap is required. This problem is encountered less frequently with pedicled flap reconstructions.

PREOPERATIVE CONSIDERATIONS

Because of the great technical demand involved in this technique, preoperative planning is a major undertaking that significantly impacts on the success of the procedure. Patient selection, anesthetic planning, donor site selection, and timing of the procedures are all additional concerns in the work-up of a patient who is already preparing to undergo a major head and neck procedure. The viability of the transferred tissue is generally attributed to the technical aspects of microvascular anastomosis; however, errors in patient selection, donor selection, flap transfer timing, and the geometry of flap inset can all result in flap failure.

There are no absolute indications for free flap reconstruction, and for virtually every instance in which free transfer is used, an argument for a pedicled graft can be made. However, certain defects have proved to be better indications for free transfer. Reconstruction of mandibular defects seem particularly suited to free tissue transfers as do reconstructions that require a thin, pliable consistency such as in the floor-of-mouth. Massive skull base defects present problems that free flaps seem to solve better than pedicled flaps. Also, because of the potential for neural anastomosis, facial reanimation has recently seen the application of this technology.

Concerning contraindications, there are a number of patient factors that severely limit the likelihood of successful free tissue transfer. Age in and of itself may not be important; however, many of the following patient factors are more often found in patients of advanced age. Severe cardiovascular disease and atherosclerosis obviously compromise the flap vascularity and strongly advise against such a procedure.

Diabetes is also a detriment to vascularity and often impairs wound healing. Connective tissue disorders may compromise the cardiovascular system and should be strongly considered. One must also consider the requirements for surgical and nursing personnel; because not only will they be required for the initial procedure, they must be available in the early postoperative period in the event of flap failure.

PRINCIPLES OF MICROVASCULAR SURGERY

The techniques used in microvascular surgery are unlike those of conventional surgery. The development of these techniques comes from prior repetition. This experience is usually obtained in the microsurgical laboratory on rat vessels.

As in all microsurgical situations, maneuvers must be delicate and accurate. The vascular intima is easily damaged or sent into spasm with excessive traction. Attention to vessel drying is necessary to avoid spasm and thrombosis. Vessels should be constantly bathed in 37 degree centigrade normal saline or Ringer's solution. Excessive vessel cooling will also induce spasm, as will contact with fresh blood.

Great care is needed when lining the vessels up for anastomosis. The vessels should be adequately mobilized with as long a pedicle as possible. The greater the mobilization, the easier the anastomosis. Obviously, one wants to avoid any tension at the anastomotic site. But just as important is care in avoiding redundancy in vessel length. This will encourage kinking or twisting of vessels and ultimately thrombosis. Insetting the flap must be considered before the anastomosis. Flap geometry is often sited as a common cause of thrombosis postoperatively.

The process of microvascular suture is considered to be the most important determinant of vessel patency. Accurate alignment of the intima is of utmost importance. Suture placement must always be symmetrical. Knots must lie flat, and cannot be placed with excessive tension, as intimal damage will result.

The technical and time requirements necessitate a team approach. The resection team does some identification of suitable vasculature, but the reconstruction team will prepare the recipient area. Ideally, this is done while another team is harvesting the donor flap. Although such an approach requires up to 6 surgeons, the procedure moves efficiently and quickly.

END-TO-END ANASTOMOSIS

This technique is used for both arterial and venous anastomosis. The technique is more difficult for veins as the venous walls are thinner and more collapsible. Arterial anastomosis usually require more sutures due to the high pressures.

End to end anastomosis is the simplest, most reliable, and most-widely used method. To prepare the vessels, 2-3mm of adventitia is stripped from the end of each vessel. This is done with the jeweler's forceps and microscissors under 10 - 16x magnification. This prevents adventitia from being caught in the lumen during anastomoses. The framed approximator clamp is then applied, bringing the two ends of the vessels close enough so that there is little tension during the anastomosis. It is important to remember that the clamps will be flipped after the anterior anastomosis is complete. Blood in the vessel lumen should be flushed, using heparinized saline via a #22 angiocath. Vessel spasm can be reversed with topical lidocaine or gentle dilation.

The needle is grasped using a two-handed technique by grasping the suture with one hand and the needle with the other. The needle is held just beyond its midpoint, 1-2 mm back from the end of the needle holder. Three guide sutures are placed 120 degrees apart, two on the anterior, and one in the posterior wall. . The tails are left long. It is imperative that these be accurately place, as guide sutures not exactly 120 degrees will result in twisting at the anastomoses. With the guides in place, equal number of interrupted sutures are placed between each suture. Enough sutures are placed so that there is no anastomotic leak. Usually a total of 9 sutures are necessary.

Needle placement must be accurate and symmetric. The needle entry point should be twice the thickness of the vessel wall away from the edge. Symmetrical entry should be taken on the opposite edge. Uneven placement leads to vessels overlapping and thrombus. Needle placement should utilize a two-handed action under 20x to 30x magnification. The needle lumen is cannulated with microforceps (in larger vessels the adventitia is grasped) to provide counter pressure as the needle is placed between. After the needle penetrates the wall, the needle is pulled along its arch. A two-pass technique is usually used, unless the edges are approximated.

Tying the suture correctly also impacts on the likelihood of vascular patency. Knots are generally tied under 16x magnification. They need to lie flat. The proper amount of tension must be applied each time. Excessive tension damages the vascular intima, inadequate tension hampers the vessel approximation. Surgeons knots are thrown first, followed by a simple square knot. After the anterior wall is sutured, the clamp is flipped, and the process is repeated.

CLAMP RELEASE

Releasing the clamps should be done in the same order each time. Once both anastomoses are completed, the clamp release is begun. The anastomoses are irrigated with a 1% lidocaine solution. The arterial clamp is released first, then the venous. This eliminates misinterpreting venous backflow for adequate arterial inflow. Some leakage will occur, and usually stops with pressure. Brisk bleeding will occasionally occur and requires additional sutures.

VESSEL MISMATCH

Careful placement of sutures can accommodate mismatches of up to a 2:1 lumen. The technique involves placing interrupted sutures farther apart on the larger vessel. When vessel differences between 2:1 to 3:1 occur, beveling or spatulation needed. When beveling an edge, the oblique cut should not be more than 30 degrees. Spatulation involves a longitudinal incision in the cut end of the smaller vessel. When the discrepancy exceeds 3:1, end to side anastomoses is required.

END TO SIDE ANASTOMOSIS

As stated above, this method is useful for large vessel mismatches. In order to minimize turbulent flow, the angle of union between donor and recipient should be as small as possible. Angles less than 60 degrees are usually acceptable. The angle of anastomosis can be decreased by spatulating or beveling. To prepare the recipient vessel, an elliptical excision in the wall is made. Unlike the end to end technique, there are only two guide sutures, each placed 180 degrees apart. The intervening sutures are placed as usual.

CONTINUOUS SUTURE TECHNIQUE

The major advantage of this technique is that it is faster and associated with less anastomotic leakage (50% faster). However, it significantly narrows the vessel lumen. As a result, vessels less than 2.5mm in diameter respond poorly to this method. The main application is for end to side anastomoses on large veins.

INTERPOSITIONAL VEIN GRAFTS

This adjunctive technique is required when the vascular pedicles do not approximate without tension. The most common choice of donor veins are the saphenous. When aligning the vessels for arterial anastomoses, the vein grafts must be reversed so that valves do not obstruct flow. This is not necessary for the venous system. Placement of a free suture through the distal end of the vein serves to orient the vessels.

MECHANICAL AIDS

Several different techniques exist for making the anastomoses simpler or quicker; and, until recently, none have been proven to be better or safer in humans. Lasers-assisted anastomosis has been demonstrated to weld vessels in less time than traditional techniques. The decrease in suture also produces less foreign body reaction. However, to date, only animal studies support these conclusions. Stapling devices have existed for some time, but the first commercially available device became available less than 10 years ago. This device, the 3M Coupler, has been examined recently in two publications and has received favorable reviews. The device reduced anastomotic time in the range of 50 - 75%, and had patency rates similar to the suture techniques. The device performed well on thin-walled vessels of similar size, but had problems with intimal damage on thick-walled arteries. Some familiarity with the device is necessary, but the technique can be learned quickly in the microvascular lab.

PATENCY AND PREVENTING THROMBOSIS

Patency of an anastomosis can be tested in a variety of ways. Venous patency is easily evident when the vessel is translucent. Direct observation of expansive pulsation is a reliable indicator of patency, whereas longitudinal pulsation usually portends partial or complete obstruction. The most reliable test is the intraoperative Doppler Ultrasound Flowmeter.

As stated previously, the chance of thromboses is greatest at the site of anastomoses 15 to 20 minutes following the closure. It is therefore customary to observe the anastomosis and test its patency during this period of time. If partial obstruction occurs, gently squeezing the vessel with forceps, or massaging the vessel may break up the thrombus. A complete thromboses necessitates resection of the damaged area, and repeat anastomoses.

Vascular thrombosis is most commonly due to technical error in suture placement, or the use of a vessel with damaged intima. Venous rather than arterial thrombosis is the most common cause of flap failure. The thinner venous wall makes the anastomosis more fragile, more compressible, and more likely to twist and kink. After the first 20 minutes, the next critical period is postoperative days 1 - 3. In most cases, a flap that is successful at day 5, will not thrombose. However, the vascular pedicle cannot be safely divided for at least 8 days.

CONSIDERATIONS IN FLAP INSETTING

In head and reconstruction, the best recipient vessels are probably the transverse cervical artery and the external jugular vein. Other good choices include the superior thyroid artery, facial artery, and any of the branches of the external carotid artery End to side anastomosis into the internal jugular vein or transverse cervical veins are good for venous drainage. The common or internal carotid arteries are used as a last resort, and probably should not be used.

Flap geometry has been demonstrated in some studies to be an important determinant of flap survival. In retrospective reviews, experienced surgeons have noted problems with flap circulation due exclusively to poor choice of flap geometry. Before the anastomosis is begun, one must visualize how the flap will be inset to ensure an ideal path for the pedicle. Lack of attention here may result in vessel kinking and subsequent thrombosis. The most favorable geometry allows for the vessels to lie longitudinally in the neck without tension, yet without excessive pedicle length.

POSTOPERATIVE CARE

Proper care after the surgery requires personnel who understand the basic principles of free flap reconstruction. With this knowledge, it becomes common sense to avoid any pressure in the vicinity of the pedicle. Such pressure may come in the form of tracheotomy ties or dressings. It must also be pointed out that supplemental oxygen, or humidified air will cool a superficial flap and inhibit its blood flow. Strict orders to keep the head in a neutral position will limit the tension placed on the anastomosis.

Hemodynamics and blood volume must be monitored closely. Although scant scientific evidence exists to support an ideal hematocrit in postoperative free flap patients, the consensus among experienced surgeons is somewhere between 27 and 29. It is important to inform the ICU personnel to avoid transfusing these patients without notifying the surgeon. Close surveillance for hematoma formation is necessary to avoid the deadly consequences of vascular compression. Blood pressure should be maintained appropriately.

Pharmacotherapy has become a routine is free tissue transfers, and much of the basis is borrowed from organ transplantation data. Aspirin therapy is initiated after the surgery using 5 - 10 grains daily for 2 to 3 weeks in order to inhibit platelet and endothelial cyclooxygenase. Dextran 40 is also part of most protocols with its viscosity lowering properties and inhibition of rouleaux formation. Antibiotics are given as usual for head and neck procedures. Delerium tremens prophylaxis is often necessary in this patient population.

POSTOPERATIVE MONITORING

Although many different methods exist, the current standard is clinical evaluation. This is accomplished by visually inspecting flap color, turgor and capillary refill; dopplering the pedicle frequently during the first 3 days; and performing the prick test daily. A healthy flap will be pink, warm, minimally edematous, and will have a capillary refill time of 1 - 3 seconds. The prick test will produce 1 to 3 drops of bright red blood. Venous occlusion is indicated by bluish, edematous flap and brisk, dark bleeding on the prick test. Arterial problems produce a pale, cold, flap with no bleeding after pricking.

It is self-explanatory that early detection of flap compromise allows for earlier intervention, and improved survival. It is with this in mind, that we have the development of so many different methods of monitoring. Temperature measurements have demonstrated reliability, and a recent review of 600 free flaps indicated a sensitivity of 98% and a predictive value of 75% using this technique. They continue to be plagued by interference from ambient temperatures when used in the oral cavity. A more recently introduced technique uses near infra-red spectroscopy to non- invasively monitor the concentrations of oxy and deoxyhemoglobin. Animal studies indicate accurate measurements through as much as 10cm of tissue. The device has yet to be used in humans. Transcutaneous and intravascular devices which measure oxygen tension have seen some enthusiasm, but expense continues to be an obstacle. The laser doppler flowmeter also holds promise, but is not applicable to deep flaps or those in the oral cavity. As in many cases in medicine, multiple different solutions to a problem indicate lack of a good solution. Clinical assessment will remain the standard until the expense and reliability problems of the others improve.

TREATMENT OF VASCULAR COMPROMISE

The above section leads into this discussion because early detection remains the key to successful salvage. As stated, the second critical period occurs during postoperative days 1 - 3. Venous thrombosis is the most common etiology of flap failure. Most studies indicate that exploration within the first 1 - 2 hours of detection yield the best salvage rates. Success rates fall off dramatically after 8 hours of occlusion. Aggressive exploration can increase the survival rates by up to 10%.

Once the patient is returned to the operating room, the flap is quickly dismantled and the anastomosis examined. Extrinsic pressure from hematoma formation, kinking, or twisting is logically performed first. Unless successful, the next step is takedown of the anastomosis. Once this is accomplished, the flap vessels are irrigated with heparinized saline, and the anastomosis is repeated. Failure of free irrigation indicates a long standing thrombosis in the microvasculature. Plasminogen activators such as strepto and urokinase, and recombinant tissue plasminogen activator (TPA) have been used successfully in such instances. These are applied with the venous drainage from the flap disconnected, to avoid systemic doses. This allows high concentrations of the drug. Once free irrigation is accomplished, the anastomosis are redone in the usual manner.

SPECIFIC FLAPS

  1. MUSCULAR:
    1. -Pectoralis Minor
      1. Blood supply: Pectoral Branch of Thoracoacromial artery
      2. Nerve: Medial pectoral nerve.
      3. Anatomy: A flat triangular muscle lying just under pec major that attaches to ribs 2-5 and coracoid process
      4. Advantages:
        1. Minimal to no post-operative disability
        2. Size, shape, lack of bulk good for facial soft-tissue and reanimation procedures
        3. Good reinnervation potential
        4. Can be used as a composite graft when includes underlying rib
      5. Disadvantages:
        1. Short vascular pedicle (usually < 3 cm)
        2. Sometimes not enough bulk
  2. OSTEOCUTANEOUS
    1. -Iliac Crest
      1. Blood supply: Deep circumflex iliac artery (DCIA) and vein
      2. Nerve: None
      3. Anatomy: Osteocutaneous flap utilizing the iliac crest and overlying skin
      4. Advantages:
        1. Reliable flap
        2. Good for large bony defects
        3. Minimal donor deformities
        4. Defect closed primarily
      5. Disadvantages:
        1. Risk of damage to femoral nerve, iliac vessels, peritoneum and bowel
        2. Difficult to elevate and find vessels
        3. Painful site of healing and long scar
    2. -Fibula
      1. Blood Supply: Endosteal and periosteal branches of the peroneal artery and vein
      2. Nerve: None
      3. Anatomy: Up to 25 cm of fibular bone accompanied by overlying skin
      4. Advantages:
        1. Minimal donor site morbidity
        2. Excellent periosteal supply allows the use of osteotomies to shape the graft
        3. Two-team approach possible
      5. Disadvantages:
        1. Variability of the septocutaneous perforators to the skin may limit viability
        2. Questionable osseointegration
    3. -Scapula Flap
      1. Blood supply: Subscapular artery and subsequent circumflex scapular branch with the venous drainage being the vena comitantes.
      2. Nerve: none
      3. Anatomy: Thin pliable flap mostly skin and subcutaneous tissue (with bone if desired) 6 x 8 cm width by 10 to 18 cm length
      4. Advantages:
        1. Long vascular pedicle (6-8 cm)
        2. Large, thin, pliable fasciocutaneous flap
        3. Two bone segments available with independent pedicles by harvesting the angular branch of the thoracodorsal artery
        4. Composite flap with each component having an independent vascular supply
        5. Can include lat. dorsi muscle in flap
        6. Very reliable
        7. Donor site closes primarily
      5. Disadvantages:
        1. Patient must be in the lateral decubitus
        2. The shoulder must be immobilized for 4-5 days
        3. Some potential for post-operative shoulder dysfunction
  3. FASCIOCUTANEOUS
    1. -Radial Forearm Flap
      1. Blood supply: Radial artery and vena comitantes
      2. Nerve: Medial and lateral cutaneous sensory nerves
      3. Anatomy: Fairly thin flap along anterior forearm, can include bone
      4. Advantages:
        1. Ease of pre-operative evaluation
        2. Easy to harvest
        3. Reliable blood supply
        4. Good source for mandible when bone is taken
        5. Preop tissue expansion for larger
      5. Disadvantages:
        1. Vascular supply to hand at
        2. Postoperative dysfunction from tendinous
        3. Usually requires skin graft for closure
        4. Significant risk of pathologic fractures with bone
    2. -Lateral Thigh
      1. Blood Supply: Septocutaneous branches of the 3rd perforator of the profunda femoris system and associated vena comitantes
      2. Nerve: Lateral femoral cutaneous nerve
      3. Anatomy: Fasciocutaneous tissues of the lateral thigh
      4. Advantages:
        1. Thin pliable flap for intraoral and pharyngeal reconstructions
        2. Reinnervation possible for sensate flaps
        3. Two-team approach
        4. Primary closure
      5. Disadvantages: Anomalous vasculature may require intraoperative modifications
  4. MUSCULOCUTANEOUS
    1. -Latissimus Dorsi
      1. Blood supply: Two major branches off the thoracodorsal, the interior longitudinal and posterior transverse branch (the posterior transverse branch is vital to flap survival)
      2. Nerve: Thoracodorsal nerve (runs in neurovascular bundle)
      3. Anatomy: Very large triangular muscle
      4. Advantages:
        1. Large amount of tissue (25 x 35 cm) available
        2. Easily closed donor defect with minimal morbidity
        3. Long vascular pedicle possible
        4. Very reliable flap
      5. Disadvantages:
        1. Requires patient in lateral decubitus position.
        2. Sometimes flap too bulky
    2. -Inferior Rectus Abdominis
      1. Blood supply: Inferior epigastric artery.
      2. Nerve: none
      3. Anatomy: Large flat musculocutaneous flap
      4. Advantages:
        1. Large flaps
        2. Long, reliable vascular pedicle
        3. Can be closed primarily with minimal donor defect
      5. Disadvantages:
        1. Often bulky
        2. Possible hernia formation
  5. HOLLOW VISCUS
    1. Jejunum
      1. Blood supply: Vascular arcade based on the superior mesenteric artery and vein
      2. Nerve: None
      3. Anatomy: Second loop of jejunum most reliable (1.5 to 2 feet beyond ligament of Treitz)
      4. Advantages:
        1. Minimal donor defect (often none noticeable).
        2. Most physiologic choice for pharyngoesophageal reconstruction.
      5. Disadvantages:
        1. Bowel or pharynx fistulas.
        2. Need for abdominal procedure

CONCLUSION

Free tissue transfer has advanced to the point of becoming a routine method of head and neck reconstruction. The advantages enumerated above allow wonderful functional and cosmetic rehabilitation of complex defects. Only the great technical demands of the technique limit it from widespread use. Advances in anastomotic techniques, monitoring devices, and new donor sites will ultimately reduce such technical demands.

BIBLIOGRAPHY

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3. Sullivan M.J., Carroll W.R. The Free Scapular Flap for Head and Neck Reconstruction. Am J. Otolaryngol 11:318-327, 1990.

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10 Delacure MD. Clinical Experience with a Microvascular Anastomotic Device in Head and Neck Reconstruction. Am J Surgery, 1995;170:521.

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15. Schusterman MA. A Single Center’s Experience with 308 Free Flaps for Repair of Head and Neck Cancer Defects. Plastic and Reconstructive Surgery, 1994;93(3):472.