Vascular and Microsurgical Instrumentation and Equipment

Operating Microscope

The microscope serves two main functions—magnification and illumination—permitting smaller exposures, improved visibility for dissection of delicate tissues, and safer hemostasis when working through narrow and deep surgical corridors. ¹^, ²

Halogen or xenon lamps provide high-intensity illumination along the line of sight. Illumination can be so strong as to cause thermal injury to the tissues, and thus full strength should generally be avoided. Newer generation microscopes tackle this problem by self-adjusting the light intensity.

Surgical microscopes consist of several joints to allow for pan-directional mobility. A key component of the surgical microscope is the mouthpiece switch. This electromagnetic device disengages all the joints along the arm of the microscope with a low-pressure bite, allowing it to float, easily tracing the movements of the head (Video 1.1). Mobility along the x-, y-, and z-axes is permitted while maintaining static pitch, yaw, and roll of the microscope head. This allows the surgeon to scan the surgical field, adjust or maintain focus on a target, or focus on a new target while continuing ongoing manual maneuvers. There are many other functions that can be programmed into the various buttons on the microscope hand grips and foot pedal, including neuroimaging for stereotactic guidance, video and still photography, and automatic balancing. Microscope light filters, in conjunction with oral or intravenous dyes, serve as adjuncts in oncologic and vascular neurosurgery. Probably, the most widely used vascular neurosurgery dye is indocyanine green (ICG). ICG video angiography allows visualization of vessels at submillimeter levels and can thus reveal an incompletely clipped aneurysm or an inadvertently stenosed or occluded vessel. ³

1.2 Operating Microscope Chair

Microsurgery can be lengthy, and muscle fatigue, coupled with mental fatigue, affects even the fittest, most experienced surgeons (Video 1.1). The operating chair serves to reduce isometric large muscle activation while operating. In addition to gluteal and lumbar support, proper arm support is particularly crucial. In the starting position, the forearms rest on the distal aspects of the forearm platforms (so that the platforms do not inadvertently strike the table or retractor arms when moving), in a mildly supinated position, such that the hands rest upon the patient on the dorsal aspects of the fifth metacarpal bones. In this manner, the instrument rests on its balance point upon the second proximal phalanx, rather than having the surgeon lift his/her hands and instruments while manipulating the instruments. Hand and arm position is then adjusted according to what the procedure requires.

The height and width of the forearm platforms should be adjusted such that the shoulders and elbows are entirely relaxed, with the elbow joints as close to 90° as the operative field will allow. By neutralizing muscles and joints proximal to the elbows, individual surgical maneuvers are restricted to the wrists and fingers, thereby improving accuracy and endurance.

1.3 Bipolar Electrocautery

Bipolar electrocautery was developed by Malis in the late 1950s by combining a spark-gap transmitter with surgical forceps, the evolution of two-point coagulation as described by Greenwood. ⁴^, ⁵ The bipolar coagulation device allows current to pass between the tips of the forceps, coagulating the tissues in between (albeit with a small degree of lateral thermal spread). ⁶^, ⁷ Should the tips of the bipolar forceps touch, a short circuit is created, and no coagulation occurs. Bipolar cautery is very effective on small blood vessels and around nervous tissue because less current is needed to achieve the same cauterizing effect as with monopolar cautery.

Use of the bipolar forceps on dry tissue can cause char formation and reduce coagulation efficacy, and tissue can stick to the tips of the instrument. In 1972, King and Worpole observed that coagulation could occur even if the tips of the forceps were immersed in irrigation fluid or cerebrospinal fluid (CSF), so they attached an irrigating tube to the bipolar forceps. ⁸ Though normal saline is the common irrigation solution used, mannitol appears to offer some advantages, since it is nonconductive and the current passes only through the tissue between the forces tips. ⁹ Bipolar forceps tips coated with Teflon or other materials are available, intended to avoid sticking. Should charring occur, the tips need to be gently cleaned with a wet sponge and not be scraped with sharp instruments, such as scratch pads or scalpels, in order to protect the coating. In addition, the best way to prevent char and sticking is to coagulate in short bursts, constantly opening and closing slightly the tips, without any metal-to-metal contact.

1.4 Bayonetted Instruments and Instrument Length

Bayonetted forceps and angled suction tips are commonly used and are peculiar in that the shafts of the instrument are offset with respect to the axis of the handles, in order to allow the surgeon to look down the barrel without his/her hands blocking the view of the operative field.

The handles of bayonetted instruments are designed to sit between the thumb and the second and third phalanges, and the tips should approximate with gentle pressure. The recoil (opening) force varies according to material and length of the instrument. Forceps with greater recoil force are ideal for tissue dissection and definition of surgical planes. The ideal bayonetted bipolar forceps thus acts as a dual instrument: coagulator and dissector (Video 1.2).

When varying lengths of the same instrument are available, the principle of using the shortest possible instrument is rooted in two concepts. The first is to allow the surgeon’s hands to rest on the skull. The second is that longer instruments magnify movements (and thus errors) at their tips, proportional to their length. When working on the surface of the brain, for example, for a superficial bypass procedure, short, nonbayonetted instruments are suitable. As dissection is carried deeper, instrument length is increased to allow for the ideal hand position, adding the bayonette configuration after about 6 inches length.

The tips of forceps are designed with variable width and shape. The tips are most commonly straight; however, instruments with curved tips are available, for when the surgeon needs to work around tight corners. When a bipolar forceps is used for electrocautery, usually thinner tips with a smooth inner surface are preferred for more accurate point coagulation. For tissue dissection and grasping, forceps with serrated, toothed, ringed, and/or cupped ends can be used.

Microscissors are available with straight or curved tips that are either sharp or blunt. The length, shape, and directionality of the instrument vary depending on the working surface. Longer, bayonetted microscissors allow for working at a depth (Video 1.2). Curved microscissors allow for visualization of the cutting tips with cutting in-line with respect to the surgeon’s fingers, and for lifting and cutting simultaneously. Microscissors with straight tips are more easily visualized when cutting in a direction orthogonal to the line of sight.

1.5 Suction Tubes

The appropriate use of the suction tube is crucial for maintaining adequate visualization in two ways. Directed suction is used to maintain an operative field clear from blood, CSF irrigation, and other fluids. At the same time, the appropriately positioned suction shaft, often placed over a patty, provides dynamic brain retraction, thereby minimizing the risk of ischemic injury caused by edges of rigid retractor blades. Neurosurgical suction tubes are available ranging in bore from 3 to 12 French (F), where 3F = 1 mm ( ▶ Fig. 1.1). The shafts may be rigid or malleable. All microsurgical suction tubes should be connected to flexible in-line extension tubing, rather than directly to the suction vacuum tubing, which is heavy enough to torque the suction in the surgeon’s hand inadvertently.

Fig. 1.1 Suction tubes used in cerebrovascular microsurgery. Rhoton-Merz design and PMT MacroVac suction tubes offer a radiused, cylindrical dilation at the tip meant to minimize trauma to adjacent brain when used to retract tissue. The tip of the Fukushima design tapers to a sharp end, and thus is ideal for use where only a slight amount of retraction distal is needed, such as near the basilar apex. The Fukushima suction tube offers a clever tapered design, where the inner diameter is smallest at the tip, such that tissue plugs that can enter the suction tube will not block the suction more proximally. Variable suction intensity on the Fukushima and PMT MacroVac suction tubes is permitted by employing a teardrop-shaped finger vent.

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