Principles and techniques of microvascular surgery

Types

Two types of loupe are used in surgery: the compound (Galilean) and prismatic loupe. In contrast to single-lens off-the-shelf magnifying reading glasses, compound loupes have significantly superior optics. These consist of two magnifying lenses separated by air, achieving higher magnification, greater depth of field, and better working distance. However, image quality tends to become distorted at magnifications above 2.5× and all such lenses create a “halo” effect at the periphery of the visual field which may disturb the surgeon. These drawbacks are counterbalanced by their relatively low cost and light weight and they are widely used and available from most manufacturers.

Prismatic loupes provide higher optical quality because of a Schmidt prism, which lengthens the path of light through a series of mirror reflections inside the loupe. They can provide improved magnification, wider fields of view, and longer depths of field or working distance, but are 30–40% heavier, more expensive than compound loupes, and more easily damaged.

Choosing loupes

While choice of magnification is largely dependent on the surgeon's preference, as a rough guide, a 2.5× magnification is often sufficient for hand surgery and flap harvesting. If the loupes are to be used for perforator dissection, including thin flaps or anastomoses, 3.5–4.5× magnifications may be more suitable although 2.5× is sufficient for standard perforator dissection. It is important to note that both the field of view and depth of field decrease with increasing magnification, while the weight of the loupes increases. Loupes with a magnification higher than 4.5× tend to be cumbersome and too heavy for daily use (especially if they are prismatic), resulting in neck tension and increased fatigue. In such instances, opting for the microscope might be a better option. It is worth reporting, however, that with accumulation of experience and familiarity with flap donor site, some surgeons have the prowess to perform standard perforator dissections without any magnification.

Once the magnification has been chosen, other features such as lens design, working angle, and distances need to be considered. Some might choose to have the loupes mounted on glasses or headbands, while others might prefer through-the-lens (loupes mounted to the lenses of the frames) over the flip-up or snap-fit type. The latter permits cheaper changing of the magnification and the ability to change the lens prescription more conveniently. Some manufacturers can also supply headlights for use where additional lighting may be required – particularly useful with the use of higher magnifications.

Types

Microsutures

Buncke described making his first microneedle by drilling a hole in a 75 mm stainless steel wire. This needle held a single strand of silk and was used to replant a rabbit's ear by anastomosis of 1 mm vessels. Soon a commercially available needle was developed by Acland, working with the Springler–Tritt company.

Since then, microsurgical sutures have been available in combinations of different materials, suture sizes (8-0 to 12-0), tensile strengths, and needle configurations. The microsuture is considered to be the standard means of vascular anastomosis. The most widely used sutures are 9-0 monofilament nylon on a 100 µm curved needle, and 10-0 nylon on 70–100 µm curved needles and 11-0 nylon on a 50–75 µm curved needle, and 12-0 on a 50 µm curved needle. The choice is usually made based on the vessel wall thickness and diameter, with 9-0 sutures used for vessels of 2 mm or more in diameter and 10-0 for those between 1 and 2 mm in diameter, and 11-0 to 12-0 for smaller vessels. Another consideration is the length of the needle, 3.6 mm vs. 5.1 mm, with our preference being the longer needle (5.1 mm) for 9-0 and 10-0 and the shorter (3.6 mm) for 11–0 and 12-0. Microneedles are typically shaped as three-eighths of a circle but are also available as a half-circle or straight (rarely used now), with round, tapered (commonly used), or spatula-shaped tips to prevent damage to the fragile vessel wall. The commonest suture used in microsurgery is non-resorbable nylon which has low tissue reactivity and knot-holding ability, although polypropylene is preferred by some as it slides and handles better within the tissue.

Anastomotic devices

Despite the fact that microsutures are nowadays relatively inexpensive, reliable, and readily available, they do not fully meet the criteria of an “ideal” anastomosis. Many non-suture techniques have been developed in the search for faster and less traumatic anastomosis.

In 1962, Nakayama et al . introduced an anastomotic device consisting of two metallic rings and interlocking pins that remain in situ as a permanent implant. Östrup and Berggren developed the UNILINK system in 1986; the 3 M and ACE coupling devices that were adaptations of this ring–pin device are currently marketed under the name Microvascular Anastomotic COUPLER System (Synovis Micro Companies Alliance, Inc., Birmingham, AL). This system consists of two disposable rings made of high-density polyethylene with a series of six to eight evenly spaced 0.16 mm diameter stainless-steel pins that are implanted with a reusable anastomotic instrument.

The ring–pin device is a simple and fast technique of anastomosis and has the added advantage of not disturbing the intima in the anastomosis. It is the most successful and commonly used coaptation device. It has yielded excellent patency rates of up to 100%, even in fields that have been previously irradiated. The rings come in a variety of sizes from 1 to 4 mm in diameter, allowing the coaptation of vessels ranging from 0.8–4.3 mm with a maximal wall thickness of 0.5 mm, and the device is suitable for both end-to-end and end-to-side anastomosis. It is contraindicated in peripheral vascular disease, areas with ongoing radiation therapy, active infection, concurrent diabetes, and corticosteroid therapy.

In an experimental comparison of venous anastomosis with use of this device, the sleeve technique, and the standard end-to-end technique, patency rates were 100%, 80%, and 95%, respectively. In an analysis of 1000 consecutive venous anastomoses with this method in breast reconstruction, Jandali et al . reported an anastomotic time of 2–6 minutes with a 99.4% patency rate. No total flap losses were encountered. It has also been used effectively in end-to-side anastomosis of veins in head and neck free flap reconstruction, with 99–100% patency. To resolve the problems of a permanent rigid ring, an absorbable anastomotic coupler was developed and has been used experimentally and clinically, achieving patency rates of 92.9–100% and 95%, respectively. The ring was completely absorbed at 70 days to 30 weeks after anastomosis. Although used mainly for venous anastomoses, the mechanical coupling device has been also used successfully in performing arterial anastomoses, with up to 100% patency rate, proving to be expeditious, safe, and reliable. Contraindications of using this device on arterial anastomosis include thick-walled vessels that do not adequately evert, diameter discrepancies of more than 1.5 : 1 ratio, non-pliable vessels stiffened by prior radiotherapy or calcification, and any artery less than 1.5 mm in diameter.

Another form of coupler devices exists and is known as vacuum-assisted microvascular anasto-coupler, which uses negative pressure as an a traumatic force to fix vessels walls instead of the pins. This design, however, was only tested on rats, with no clinical applications to date.

The nonpenetrating microvascular stapler, available as a disposable device (VCS clip applier system), reported by Kirsch et al ., uses nonpenetrating titanium clips applied in an interrupted, everting fashion. The clips come in four sizes, ranging from 0.9 to 3.0 mm, and demonstrate a reduced anastomotic time and higher patency rate. In an end-to-end anastomosis, two stay sutures are first placed at 180° to facilitate the eversion of vessel walls during clip placement and a special everting forceps and experienced assistant are needed. In an end-to-side anastomosis, four sutures are recommended with sutures at the heel and toe and two stay sutures at the 3 and 9 o’clock positions. Yamamoto et al . reported clinical use of these staples with a mean anastomosis time of 12 minutes and Cope et al . reported a 100% patency rate of 153 anastomoses of both veins and arteries. A comparative scanning electron microscopic study demonstrated no major differences between sutured and stapled anastomoses.

All anastomotic devices are essentially for use on healthy vessels only; the veins should be pliable, the arteries soft to allow eversion, and the vessel ends should be minimally size-discrepant.

Other non-suture methods

Methods to glue or to weld a union of two vessels seem attractive and have been intensively studied experimentally.

Two adhesives have been studied for use in anastomoses: fibrin glues, and cyanoacrylate glues. To prevent the glue entering the vessel lumen, it was essential first to approximate the vessel walls with conventional sutures, thereby reducing the total number of sutures required for an adequate seal. Fibrin glue is now commercially available as two components, one with fibrinogen, factor XIII, and plasma proteins and a second with thrombin, aprotinin, and calcium chloride. When mixed together, it imitates the final pathway in coagulation. Fibrin glue has been used to seal anastomoses, both experimentally and clinically. In a comparative study of fibrin glue in free flaps, the application of fibrin glue reduced the number of sutures required to complete the anastomosis and significantly reduced the anastomotic, but not ischemic, times with a slightly lower survival rate in the suture-only group. Although these demonstrate a faster union without compromising patency rate, fibrin has not achieved clinical popularity, partly because of concerns that glue might inadvertently enter the vessel lumen, and the potential for allergic reactions and anaphylaxis. Cyanoacrylates have been used experimentally, but have been plagued by findings of histotoxicity, marked foreign-body granulomatous response, extreme thinning of the vessel wall, splitting of the elastic lamina, and calcification of the media. 2-Octyl-cyanoacrylate, however, might be less toxic.

Welding with thermal or laser energy has long been advocated but, despite intensive experimental investigation, its clinical application remains scarce. Different laser types (neodymium : yttrium-aluminum-garnet, carbon dioxide, argon and, most recently, diode lasers ) have been used, showing up to 100% patency rates and better blood flow in veins when compared to conventional suturing techniques. Laser-activated protein solders have been introduced to achieve more strength. In an experimental setting, a diode laser-assisted carotid artery end-to-end microanastomosis provided an equal survival rate as a contralateral suture anastomosis, with a shorter anastomosis time, and scanning electron microscopy showed faster healing on the laser side. Although later studies have shown promising results on tensile strength, the fear of possible weakening at the site of the anastomosis with consequent pseudoaneurysm formation has so far limited the clinical use of laser welding. In a study of 27 patients with laser-assisted microvascular anastomosis, there was a 96.6% overall success rate with one rupture of the arterial anastomosis and three hematomas requiring surgical evacuation.

Other experimentally studied methods of anastomosis have included cylindrical or T-shaped intravascular stents. An external metallic ring has been suggested to keep the cylindrical form of a sutured anastomosis and to avoid through-stitching.

Magnets were first tested by Obora in 1978, then the idea was further tested on large animal models as side-to-side AV or in vein grafts anastomoses. A deployment device was used to insert the magnets at both sides and when triggered the magnets attracted and compressed the arterial wall forming a two-magnet vascular port.