Although free flap transfer is now a routinely performed operation with high success rates, a size discrepancy between the donor and the recipient vessels is a common issue, which increases the procedural complexity and the risk for anastomotic failure.1 For example, in microsurgical reconstruction of head and neck, the recipient vessels are often of smaller diameter than vessels of the donor flap, whereas in lower limb reconstruction, the recipient vessels are generally of greater caliber than the donor ones. This situation can also be encountered in microsurgical replantation procedures, when the vascular tree of the affected organ or tissue is lost.
Numerous anastomotic methods have been described for overcoming this situation, but each one is accompanied by limitations, and none of them perfectly works in all kinds of discrepancy. A microsurgeon should choose the most suitable technique for every different anatomic and functional condition. An ideal technique should be simple and safe, which means that it should be easy to learn, less time-consuming, and at the same time provide the best long-term patency rate.
Conventional end-to-end (ETE) micranastomosis is acknowledged as the standard method for equal-sized vessels but not for vessels with size discrepancy.2,3 Here, the authors propose 3 techniques including mechanical dilation, single-mattress suture, and wedge resection, for ETE anastomosis of vessels with mild-to-large size discrepancy. The data of 103 microvascular cases (112 flaps) with 364 anastomoses are presented. The clinical applications, indications, advantages, and considerations of the techniques are discussed.
PATIENTS AND METHODS
Since June 2015 to May 2018, consecutive free tissue transfers or replantations were performed in Shanghai Ninth People's Hospital Affiliated to Shanghai Jiao Tong University School of Medicine. The clinical courses of 183 arterial and 181 venous anastomoses performed by one senior surgeon (H.X.) were reviewed. The distribution of patient profiles, tissue transfers, surgical type, and clinical endpoints were summarized as means with standard deviations for continuous variables and as numbers with valid percentages for categorical variables. An anastomotic failure was defined whenever operative reintervention was performed for vascular compromise secondary to thrombosis or compression, regardless of the outcome of the flap. Results of a reanastomosis for flap salvage were recorded as data of a separate case of anastomosis, as long as the ETE techniques were reapplied. All data were processed using the statistical package SPSS 17.0 (SPSS Inc, Chicago).
Anastomoses were performed under operating microscope (10× magnification); heparinized saline (50 U/mL) was used for topical irrigation. Overlapping adventitia was trimmed, and the internal size of the vessels was measured; 9-0 to 11-0 nylon was used depending on the size and thickness of the vessels. After sufficient gentle dilatation of the smaller vessel caliber, 3 different ETE anastomosis techniques were applied according to the caliber ratio (CR).
Group I (CR, ≤1–1.5)
Caliber disparity was eliminated by mechanical dilation of the smaller vessel using forceps (Fig. 1B). Usually, 8 to 12 simple interrupted sutures are necessary for the anastomosis (Fig. 1C).
Group II (CR, 1.5–2)
Caliber disparity was eliminated by performing a single-mattress suture technique on the larger vessel, as described hereafter.
The first stay suture is placed where it is comfortable. The second stay suture is taken 180 degrees apart on the smaller vessel's circumference, and lies at equal distance (half of the smaller vessel's circumference) from the first suture on the larger vessel (Fig. 2A). Simple interrupted sutures are placed in with equal spacing between the 2 stay sutures (Fig. 2B). The vessels are then turned over 180 degrees, and interrupted simple sutures are placed on the other lateral side in the same manner (Fig. 2C) except the last stitch, which is in a horizontal mattress way. The entry and the exit points of the mattress suture on the larger vessel are placed adjacent to the last interrupted stitch and the stay suture (Fig. 2D). The anastomosis is completed when the in and out suture ends are tied in a transverse way on the small lumen side (Fig. 2E).
Group III (CR, 2–3)
Caliber disparity was eliminated by narrowing the wider lumen with a wedge resection, as described hereafter.
A 30-degree triangular resection is performed on the larger vessel to equal the dilated lumen of the smaller vessel (Figs. 3A, B), and the incision is closed by simple interrupted stitches (Fig. 3C). After knot tying of the last stitch is completed, the suture threads are used to wrap and tie the margin tissue to close the distal incision (Fig. 3D). Simple interrupted sutures are also performed for the anastomosis of the 2 vessels, except the last stitch which is a mattress suture placed at the cross point of 3 walls, and then the anastomosis is complete (Figs. 3E, F).
Postoperative Flap Protocols
Postoperative flap monitoring included clinical observations for capillary refill, warmth, color, and tissue turgor. Decision of reexploration surgery was made by the senior surgeon (H.X.). Heparin was routinely administered for 48 hours after anastomosis and for 72 hours after reanastomosis for flap salvage.
One hundred three patients undergoing free microvascular transfer or replantation (112 flaps, 364 anastomoses) were recruited in this study, 31 were males and 72 were females, mean age was 42.3 years (6–72 years) (Table 1). Flaps included 53 deep inferior epigastric perforator flaps, 27 latissimus dorsi flaps, 6 superficial temporal artery flap, 6 scapular flaps, 7 anterolateral thigh flaps, 3 dorsum pedis flaps, 8 replanted scalps, and 2 replanted ears (Table 2). Indications for the free flap surgeries included breast reconstruction, lip reconstruction, extremity reconstruction, scalp reconstruction, nasal reconstruction, and scalp or ear replantation (Table 3). The average ± SD anastomosis time for group I (n = 214) was 22.3 ± 4.5 minutes, for group II (n = 111) was 24.8 ± 6.4 minutes, and for group III (n = 39) was 28.2 ± 5.7 minutes. The overall incidence of anastomotic failure was 3.0% (11/364), and the overall flap failure rate was 3.6% (4/112) (Table 4). Reexploration surgery revealed 10 cases of anastomotic thrombosis, and the flap salvage rate was 60% (6/10) (Table 5). The flap failure cases included 2 replanted scalps and 1 replanted ear, all of which suffered severe avulsion injury, and included 1 superficial temporal artery flap for nasal reconstruction.
Theoretically, ETE anastomosis offers the most dynamically efficient way to get blood flow through the anastomotic site. However, in cases of moderate-large vessel caliber discrepancy, a conventional ETE anastomosis is not suitable. Fish mouth incision and oblique incision are 2 useful modifications that increase the circumference of the smaller vessel for severe mismatch. Nevertheless, these 2 techniques add to the surgical time and result in the presence of either an angle that produces turbulence or excessive suture material at the anastomosis, both of which increase the risk of thrombosis.4–7 A novel V-plasty technique was introduced to increase the smaller circumference for its advantage of creating a smooth transition of the diameters, and maintaining a linear axis between the 2 vessels of size discrepancy (1.5:1 to 4:1). Nevertheless, the operation requires precise calculation in design, advanced microsurgical technique, and experience for operator.8 There are modifications of ETE technique that decrease the circumference of the larger vessel, including application of a ligaclip and wedge resection.9,10 The former method is operatively convenient but lacks precision and might create kinking and result in vessel twisting, whereas the latter one is operational reliable but time-consuming in practice, especially when the discrepancy is large.
End-to-side (ETS) microanastomosis is another valid solution for significant vessel-size discrepancy.11 Nevertheless, debate exists concerning its efficiency and long-term patency.12 There is concern that ETS anastomosis is hemodynamically inefficient, owing to the angulation between the vessels, the sudden deflection of flow at the bifurcation, and the turbulence it brings at the anastomosis, which might increase the risk of obstruction under adverse condition. In contrast, other literatures suggested that, even in a low pressured venous system, the intravascular flow disturbances will not translate into risk of anastomotic failure in clinical microsurgery.13 Nevertheless, convincing evidence from large-scale clinical trials is absent.
Our results depicted operational convenience and reliability of 3 ETE techniques to overcome mismatch of vessel size. Mechanical dilation alone is sufficient and preferred in addressing discrepancy within a factor of 1 to l.5. It is important to exercise caution and gentleness during the vessel expansion, which should not be repeated over 3 times to not injure the vascular endothelium. The single-mattress suture technique was performed after vessel expansion to address discrepancy within a factor of 1.5 to 2. Despite dealing with a larger discrepancy, this technique showed no significant difference in either patency rate or anastomosis time, as compared with mechanical dilation alone. Wedge resection was used to address discrepancy within a factor of 2 to 3. The technique showed similar reliability but required longer anastomosis time, as compared with the former two ones. Thus, it is not recommended when vessel discrepancy exists at more than a 3 ratio, for its prolonged operative time and the excessive suture material at the anastomosis.
In 1998, Boeckx et al14 first described use of a series of interrupted mattress sutures for reduction of the larger vessel caliber in an ETE anastomosis, with a 96% survival rate in 25 consecutive clinical transplantations. This technique is reliable but operatively complex and time-consuming. In 2005, a technique modification was introduced that replaced the micro-mattress sutures with simple interrupted sutures on posterior wall of the anastomosis.15 The modified technique was as reliable but faster and more convenient than the old one. In the present approach, a single-mattress suture rather than multiple mattress stitches was used to “gather” the larger vessel to address moderate vessel size discrepancy. We achieved 97.3% patency rate in anastomosing either mismatched vessels of great caliber, such as deep inferior epigastic perforator vessels (1.8–3.7 mm) with internal mammary vessels (1.1–2.4 mm), or mismatched vessels of small caliber, such as superficial temporal vessels (1.5–2.0 mm) with angular vessels (0.8–1.1 mm). This technique caused no significant increase in anastomosis time over that of mechanical dilation performed alone. No severe leakage occurred in either arteries or venous anastomosis. One concern of this technique is that the uneven distribution of the excess tissue on the larger lumen side and the abrupt change it brings in caliber may cause turbulence and predispose to platelet aggregation along the suture line with subsequent thrombosis.16 However, our results depicted low rate of either arteries or venous thrombosis. It may be explained by the characteristic advantages of mattress suture, including adequate eversion of the vessel walls and a minimum of foreign material (sutures) in the lumen, which reduce the chance of thrombosis.
Factors influencing the decision of microvascular anastomosis include preference of surgeon, operative experience, and the anatomy of the recipient and donor pedicle vessels. The 3 techniques we recommended enable the surgeon to overcome vessel size discrepancy while still permitting ETE anastomosis with convenience and reliability. However, no microvascular technique can be used in all clinical situations, and the choice of technique is best decided on a case-by-case basis. For example, an ETS microanastomosis is preferred when vessel discrepancy exists at more than a 3 ratio or when no end artery is available in the recipient site; a vein graft with a larger diameter for one side and a smaller diameter for the other side is preferred when the length of the donor pedicle is not long enough to reach the desired location.17 Thus, it is wise for a microsurgeon to train various precise microsurgical techniques and master 1 or 2 of them for routine anastomosis.
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