Microwave Ablation
Microwave ablation (MWA) uses electromagnetic methods to induce the destruction of tumors via thermal energy at frequencies ≥ 900 MHz [33]. A generator emits an electromagnetic wave through an antenna resulting in the application of heat to tissues. It has several advantages over radiofrequency ablation, including consistently higher intratumoral temperatures leading to larger ablation zones and shorter treatment times; it has an active heating mechanism that allows for more uniform tumor necrosis even in close proximity to large blood vessels; it can be effective in tissues with high impedance such as lung or charred, desiccated tissue; and multiple tumors can be treated simultaneously with an additional antenna [34, 35].
The most common generators include EmprintTM (Medtronic, Boulder, CO) and NeuwaveTM (NeuWave Medical, Madison, WI). The Medtronic antennas come in three different shaft lengths, 15, 20, and 30 cm, but the radiating (green) section of the probe that becomes hot with use is 2.8 cm on all probes. The NeuWave probes vary in size from 13to17 gauge and lengths of 15, 20, and 25 cm. Power and time settings are recommended by the manufacturer depending on the tissue type, size of the lesion, and number of probes used.
In people, MWA has been described via an open approach, percutaneously via image guidance and with laparoscopy and thoracoscopy. There is limited published information on MWA in veterinary medicine and even more limited information on its use with laparoscopy and thoracoscopy. Yang et al. [36] described the use of MWA with an open approach for the treatment of hepatic neoplasia in five dogs. More recently, Oramas et al. [37] described the feasibility of laparoscopic access to the liver lobes in cadaveric dogs and then detailed the use of MWA with laparoscopy in two clinical cases of hepatic neoplasia. Video‐assisted MWA of pulmonary metastasis has also been reported in a dog [38].
Clip and Staple Applicators
Hemostatic clips have been adapted for endoscopic use. These are C‐shaped clips, in which the tip of the clip closes first, preventing tissue from slipping out of the tip as the clip is closed. Endoclips (Medtronic, Minneapolis, MN) are made in both a 5‐ and a 10‐mm shaft diameter (Figure 5.12). The 10‐mm clips have three sizes: medium, medium/large, and large. The 5‐mm clip is available in medium/large sizes. Ethicon also manufactures hemostatic clips for endoscopic use (LigaMax; Ethicon Endo‐Surgery, Cincinnati, OH), which are available in 5, 10, and 12mm shaft diameters. Locking clip designs with the intent to provide superior clip stability are also available (Reflex ELC 530, Utica, NY). All devices have an indicator on the instrument that details the number of clips left in the device. Complications with clip application include placing too much tissue within the jaws of the clip and clip slippage. Importantly, clips should not be applied to tissue under tension because this can result in changes in diameter of the tissues and clip slippage when the tension is released.
Figure 5.12 Endoclips come in different shaft diameters and clip sizes. They apply C‐shaped clips that close from the tip first. (A) Endoclip applicator. (B) The instrument provides instruments on number of clips left. (C) Tip of clip applier.
Source: From Huhn [3].
Figure 5.13 Endoscopic gastrointestinal anastomosis staplers have a 10‐mm‐diameter shaft that has three different length staplers with four different staple sizes. The largest staple leg length (5 mm, black) requires a 15‐mm port because of the larger diameter of the stapler.
Source: Image courtesy of Medtronic (Minneapolis, MN).
Endoscopic staplers are commonly used in MIS. The most commonly used device is the Endo GIA stapler (Medtronic, Minneapolis, MN) (Figure 5.13), but the Endo TA (Medtronic, Minneapolis, MN) stapler is also available. These are sold as multi‐fire handpieces with disposable cartridges. The Endo GIA comes in three different lengths (30, 45, and 60 mm) and four different staple height sizes (Table 5.3). This stapler fires six rows of staples and then cuts in between, leaving three rows of staples behind. The new tri‐staple technology allows for graduated compression improving perfusion to the staple line. The Endo GIA is also available reticulated, which allows a more precise placement of the cartridge of staples. The Endo TA stapler is available in a 30‐mm length. It fires a triple staggered row of staples in either 2.5 or 3.5mm leg length. These staples are composed of titanium and are B shaped when compressed, which allows for microvascular perfusion to the staple line, preventing necrosis, which could lead to delayed hemorrhage or leakage.
A study comparing two Endo GIA 30 vascular staple cartridges in a porcine model found both the 2.0 and the 2.5mm staple height to be equivalent for hemostasis of large blood vessels (renal artery and vein, caudal vena cava, and aorta). Both achieved vessel sealing greater than 310 mmHg and were able to seal arteries up to 17 mm and veins up to 22 mm [39]. Lansdowne et al. [40] reported thoracoscopic lung lobectomy in nine dogs. They recommended using the 3.5mm staple height and longer staple cartridges because the 30mm length alone often was not long enough to span the hilus of the lung lobe. Imhoff and Monnet evaluated the Tri‐stapleTM technology in an ex vivo model for lung biopsy and found leakage at lower pressures when compared to standard staples with a nongraduated compression [41]. Despite these ex vivo results, the Tri‐stapleTM technology is commonly used during thoracoscopic lung lobectomy.
Table 5.3 Internal stapling heights for medtronic Tri‐Staple technology for Endo GIA.
Source: Adapted from Medtronic (Minneapolis, MN).
| Tri‐StapleTM technology for ENDO GIA – laparoscopic and open procedures | |||
|---|---|---|---|
| Cartridge color | Open staple height | Closed staple height | Tissue type |
| Grey | 2, 2, 2 mm | 0.75, 0.75, 0.75 mm | Vascular |
| Tan | 2, 2.5, 3 mm | 0.75, 1, 1.25 mm | Vascular/medium |
| Purple | 3, 3.5, 4 mm | 1.25, 1.5, 1.75 mm | Medium/thick |
| Black (15 mm Port) | 4, 4.5, 5 mm | 1.75, 2, 2.25 mm | Extra‐thick |
References
1 1 Dubiel, B., Shires, P.K., Korvick, D., and Chekan, E.G. (2010). Electromagnetic energy sources in surgery. Vet. Surg. 39 (8): 913.
2 2