Intersting facts about the microcannulas used in cosmetic surgery

Microcannulas, the Tumescent Technique, and Hemostasis

The tumescent technique developed by Klein involves the infiltration of a highly dilute lidocaine solution with epinephrine into the subcutaneous tissue prior to lipoaspiration. The concentration of the lidocaine usually falls in the range 0.05–0.1%, while the concentration of epinephrine is usually in the 1:2,000,000– 1:1,000,000 range. Tumescent infiltration of a dilute lidocaine–epinephrine combination into the fat confers two major advantages. First, in part owing to vasoconstriction and in part owing to lidocaine’s lipophilic action, much higher doses of lidocaine can be used compared with the traditional 7 mg/kg that is considered to be the upper limit when 1% lidocaine is directly infiltrated in the skin. In the tumescent technique, there is a slowly absorbed depot effect from the subcutaneous tissue that allows up to 35–55 mg/kg lidocaine to be used. Slow absorption ensures that toxic serum levels of lidocaine are not attained. Second, because of the vasoconstrictive effects of epinephrine, profound hemostasis is achieved. This enables the use of microcannulas, which are potentially more traumatic to vascular structures than larger cannulas.

While large macrocannulas generally produce more overall trauma to the subcutaneous tissue and fibrous septa compared with microcannulas, the smaller cannulas have the potential to produce more vascular trauma and hemorrhage. This is because for any given volume of fat removed, the surface area of the wound is larger with microcannulas. However, the tumescent fluid’s vasoconstrictive effects provide significant hemostasis such that microcannulas can be safely used.

Microcannula: Definition

Microcannulas are defined by Klein as having an inside diameter of less than 2.2 mm. This equates to the inside diameter of a 12-gauge needle. However, 10- gauge cannulas with an inner diameter of 2.7 mm are also manufactured and many practitioners consider cannulas less than 3 mm to represent “microcannulas.” These microcannulas are made of hypodermic stainless steel and typically have a thinner wall than standard liposuction cannulas. This thin wall creates a delicate cannula such that manipulation and utilization of the cannula is different than with typical macrocannula liposuction. Structural limitations impact the aperture shape and size. In contrast to Klein’s definition, many cosmetic surgeons clinically define microcannulas as 3 mm in size or smaller. Many 3-mm inside diameter cannulas have a somewhat thicker wall typical of more standard cannulas. This results in a proportionately larger outside diameter with a stronger wall that allows for a longer cannula and thereby fewer incision sites for aspiration ports.

Microcannula Clinical Aspects: Advantages and Disadvantages

Microcannula liposuction has been tested and applied as part of the tumescent technique for liposuction under local anesthesia. Use of microcannulas in the “wet” or “superwet” methods of liposuction or for liposuction under general anesthesia has not been evaluated, although presumably microcannulas would be effective. Microcannulas typically remove less fat with each pass, resulting in a technique that requires some adjustment on the part of cosmetic surgeons who may otherwise anticipate removal of large volumes quickly. However, removing small volumes with each pass confers significant overall controlled access to the fat compartment. Use of microcannulas allows both deep and superficial layers to be addressed with a reduced risk of skin deformity compared with use of larger cannulas. Removing fat from the superficial layers ultimately results in a greater amount of fat removal overall because larger cannulas cannot safely access superficial areas adjacent to skin without risk of contour irregularities. Microcannulas also have the advantage of less disruption of fibrous attachments that connect skin to underlying muscle, reducing the potential for loose skin. For cosmetic surgeons, microcannulas offer easier penetration into fibrous areas with reduced force. Less muscle strength is required, diminishing elbow and shoulder stress and potentially decreasing repetitive injury problems for the cosmetic surgeon.

In areas where arm position or posture may be suboptimal, the ease of moving microcannulas through the tissue reduces surgical effort and minimizes physician exhaustion on longer or larger procedures. While microcannula liposuction requires more time, the physical component is considerably less tiresome overall, reducing fatigue at the completion of even challenging cases. Furthermore, the multiple ports utilized allow for positional comfort for the cosmetic surgeon since he or she spends less time working with aspiration ports that may be in an uncomfortable position or that require liposuction with the non-dominant hand. Even cosmetic surgeons who do not regularly utilize microcannulas may in fact find them useful. As noted previously, certain areas such as the neck and cheek are treated with lowest risk utilizing microcannulas, removing minimal fat deposits to achieve a sculpting effect. The periumbilical area is another preferred spot. This region is often quite uncomfortable even with complete tumescence. Application of microcannulas in this area is highly effective in minimizing discomfort. Areas such as the inner thighs often require minimal fat removal and at are at risk for contour irregularities without the use of microcannulas. The medial knee fat pad is also best sculpted with the microcannula technique. Another major advantage of the use of microcannulas is the reduced risk of scarring at cannula entry sites. Often, more entry points are utilized but these incision sites are very small and the amount of additional scarring is minimized.

In practice, these 1–2- mm wounds heal promptly without sutures and with excellent cosmesis. Disadvantages of microcannula liposuction include the potential for overaggressive liposuction resulting in skin depressions. Although it is true that small amounts of fat are removed per stroke, with improper surgical technique, large amounts of fat may ultimately be aspirated, resulting in depressions. This risk is less, however, than with the use of larger cannulas. The microcannulas are fragile and more easily damaged during liposuction surgery or cleaning, resulting in greater expense for replacements. As noted already, more incisions are required, which can result in noticeable marks or dyschromia in prone individuals. Surgical procedures require more time with the microcannula technique in tumescent liposuction. Finally, nursing staff must be more attentive in cleaning as microfragments of fat can clog the small apertures. Importantly, the cosmetic surgeon must constantly be attentive to the relationship of the aperture and the underside of the skin when working superficially. Since microcannulas are often directed superficially, it is imperative that the cosmetic surgeon be aware of the particular aperture utilized since some of these cannulas have apertures on all sides. The apertures must always be pointed away from the overlying skin to avoid damaging the underside of the dermis and if cannulas with apertures on all sides are being used, the cannulas must not contact the underside of the dermis. Cutaneous necrosis can result from excessive injury to the dermis.

Cannula Nomenclature and Design

Microcannulas smaller than 3 mm are manufactured from hypodermic needle tubing. Both the size and the tip design are important in these cannulas. Because of the small internal diameter, microcannulas smaller than 3 mm are referred to in “gauge” rather than millimeters. Smaller “gauge” refers to larger diameters. For instance, a 12-gauge cannula is larger than a 14-gauge cannula. However, there appears to be some variance in the actual internal diameter measured in millimeters depending on the reference. For accuracy, it would be best if the internal diameter size is specifically and consistently defined among practitioners and manufacturers. Klein notes two different sizes for 12-gauge cannulas, 2.2 and 2.15 mm. Furthermore, in jewelry manufacturing, 12 gauge has an internal diameter of 2.05 mm.

In the medical industry, the established standard for 12-gauge hypodermic cannulas is an inside diameter of 0.088 in. (or 2.23 mm) manufactured from type 304 stainless steel (KMI Kolster Methods, Corona, CA, USA, personal communication). While clinically the actual size may not impact outcome, there is a 15% difference in surface area of the 12-gauge cannulas between the upper and lower diameter sizes as determined in the aforementioned references. This size variation begins to blur the difference between different gauge sizes and therefore blunts the clinical accuracy in the operative report and between each physician practicing the procedure. In clinical practice, many physicians and vendors consider a 10-gauge cannula to be similar to a 3-mm cannula although the surface area difference between the cannula is almost 20%. Aperture is the next important aspect of microcannulas.

One common design features multiple small apertures along the cannula near the distal tip. These apertures are circumferential and care must be therefore be taken when working directly adjacent to skin. Commonly these are referred to as “Capistrano” cannulas. Another cannula type demonstrates apertures directly along only one side of the cannula and is designed so the cosmetic surgeon is always knowledgeable about aperture location. The common nomenclature for this type is the “Finesse” cannula. In the cosmetic surgeons’ experience, cannulas designed with multiple circumferential apertures are surprisingly effective at removing a considerable volume of fat. Cannulas with apertures only along one side are less efficient in fat removal, but safer when working near the skin and in areas where conservative liposuction is required. All microcannulas are blunt bereft of aggressive tips common in larger cannulas. A few manufacturers produce the bulk of cannulas for many of the better recognized brands.