Mouth diameter
Bag manufacturers often differentiate bag sizes by indicating “volume” in milliliters. Bag volume, however, offers little clinical value to surgeons, as pelvic mass dimensions are usually measured in centimeters on imaging. Rather, an important characteristic for bag selection is the diameter of the rim of the bag when it is fully opened—the so-called bag mouth diameter. For a specimen to fit, the 2 dimensions of the specimen must be smaller than the dimensions of the bag entrance.
Notably, the number often linked to the specimen bag—as, for example, in the 10-mm Endo Catch bag (Covidien/Medtronic)— describes the width of the shaft of the bag before it is opened rather than the mouth diameter of the opened bag. The number actually correlates with the trocar size necessary for bag insertion rather than with the specimen size that can fit into the bag. Therefore, a 10-mm Endo Catch bag cannot fit a 10-cm mass, but rather requires a trocar size of 10 mm or greater for insertion of the bag. Fully opened, the mouth diameters of the 10-mm Endo Catch bag are roughly 6 cm x 7 cm, which allows for delivery of a 6-cm mass.
Because 2 bags that use the same trocar size for insertion may have vastly differing bag dimensions, the surgeon must know the bag mouth diameters when selecting a bag to remove the presenting pathology. For example, the Inzii 12 (Applied Medical) laparoscopic bag has mouth diameters of 9.7 cm × 13.0 cm, whereas the Anchor TRSROBO-12 (ConMed) has mouth diameters of 6.7 cm × 7.6 cm (TABLE). Although both bags can be inserted through a 12-mm trocar, both bags cannot fit the same size mass for removal.
Shape and taper
Laparoscopic bags come in various shapes (curved, cone, or square shaped), with varying levels of bag taper (steep, gradual, or no taper) (FIGURES 2 and 3). While taper has little impact on long and skinny specimens, taper may hinder successful bagging of bulky or spherical specimens.
Each bag has different grades of taper regardless of mouth diameter or trocar size. For round masses, the steeper the taper, the smaller the mass that can comfortably fit within the bag. This concept is connected to the idea of “ball fit,” explained below.
In addition, bag shape may affect what mass size can fit into the bag. An irregularly shaped curved bag or a bag with a steep taper may be well suited for removal of multiple specimens of varying sizes or soft masses that are malleable enough to conform to the bag’s shape (such as a ruptured ovarian cyst). Alternatively, a square-shaped bag or a bag with minimal taper would better accommodate a round mass.
Ball fit
When thinking about large circular masses, such as myomas or ovarian cysts, one must consider the ball fit. This refers to the maximum spherical size of the specimen that fits completely within a bag while allowing the bag to cinch closed. Generally, this is an estimation that factors in the bag shape, extent of the bag taper, bag mouth diameter, and specimen shape and tissue type. At times, although a mass can fit through the bag’s mouth diameter, a steep taper may prevent the mass from being fully bagged and limit closure of the bag (FIGURE 4).
Curved bags like the Anchor TRSVATS-15 (ConMed), which have a very narrow bottom, are prone to a limited ball fit, and thus the bag mouth diameter will not correlate with the largest mass size that can be fitted within the bag. Therefore, if using a steeply tapered bag for removal of large round masses, do not rely on the bag’s mouth diameter for bag selection. The surgeon must visualize the ball fit within the bag, taking into account the specimen size and shape, bag shape, and bag taper. In these scenarios, using the diameter of the midportion of the opened bag may better reflect the mass size that can fit into that bag.
Bag strength
Bag strength depends on the material used for bag construction. Most laparoscopic bags in the United States are made of 3 different materials: polyurethane, polypropylene, and ripstop nylon.
Polyurethane and polypropylene are synthetic plastic polymers; in bag form they are stretchy and, under extreme force, may tear. They are best used for bagging fluid-filled cysts or soft pliable masses that will not require extensive bag or tissue handling, such as extraction of large leiomyomas. Polyurethane and polypropylene bags are more susceptible to puncture with sharp laparoscopic instruments or scalpels, and care must be taken to avoid accidentally cutting the bag during tissue extraction.
Alternatively, bags made of ripstop nylon are favored for their bag strength. Ripstop nylon is a synthetic fabric that is woven together in a crosshatch pattern that makes it resistant to tearing and ripping. It was developed originally during World War II as a replacement for silk parachutes. Modern applications include its use in sails, kites, and high-quality camping equipment. This material has a favorable strength-to-weight ratio, and, in case of a tear, it is less prone to extension of the tear. For surgical applications, these bags are best used for bagging specimens that will require a lot of bag manipulation and tissue extraction. However, the ripstop fabric takes up more space in the incision than polyurethane or polypropylene, leaving the surgeon with less space for tissue extraction. Thus, as a tradeoff for bag strength, the surgeon may need to extend the incision a little, and a small self-retracting wound retractor may be necessary to allow visibility for safe tissue extraction when using a ripstop nylon bag compared with others.
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