Ultrasonic cutting is accomplished mechanically using a blade that oscillates back and forth in a linear fashion (Fig. 23.15, center). The oscillation is achieved using an element located in a handle that vibrates the blade, hook, or one arm of the clamp 55,000 times per second (55 kHz). The distance of the oscillation can be varied and determines the efficiency of the cutting process. The tip of the device cuts mechanically, but there is a degree of collateral thermal tissue coagulation injury that can be used for hemostasis. In low-density tissue, the process of mechanical cutting is augmented by the process of cavitation, in which reduction of local atmospheric pressure allows vaporization of intracellular water at lower temperatures than those required for laser or electrosurgical vaporization.
Because of the visual, tactile, and mechanical limitations of laparoscopy, prevention of bleeding is important for efficient, effective, and safe procedures. Radiofrequency electricity is the least expensive and most versatile method for achieving hemostasis during laparoscopy and can be applied with either monopolar or bipolar instruments. Regardless of the type of system, the process of electrical desiccation and coagulation is best achieved by contacting the tissue with the activated electrode using continuous low-voltage or “cutting” current. With adequate power, typically 20 to 30 watts (depending, in part, on the surface area of the electrodes), tissue will be heated, desiccated, and coagulated. Blood vessels should be compressed with the blades of the forceps before the electrode is activated so that the “heat sink” effect of ﬂowing blood is eliminated. This allows the opposing walls of the vessel to bond, forming a strong tissue seal in a process called coaptive coagulation. Bipolar devices can be fitted with a serial ammeter that measures the current ﬂowing through the system. When the tissue between the blades of the forceps is completely desiccated, the device is no longer able to conduct electricity, which can trigger a visual or auditory cue for the surgeon. Alternatively, the generator can be designed to stop automatically when current is no longer being conducted by the tissue between the blades of the forceps. The surgeon can reduce lateral thermal spread of radiofrequency energy by manually pulsing delivery or by simultaneously running irrigation ﬂuid over the pedicle. Automated generators that pulse energy automatically are available, and such bipolar systems can include mechanical blades to cut tissues following coagulation of the tissue (Fig. 23.16).
Control of superficial bleeding can be achieved with fulguration, the near-contact spraying of tissue with a unipolar instrument using modulated, high-voltage radiofrequency waveforms from the “coagulation” side of the electrosurgical generator. Care must be taken to safely perform laparoscopic fulguration, ensuring that the entire shaft of the laparoscopic instrument is well away from the bowel.
Ultrasonic instruments can be used for hemostasis as well. Those with a forceps-like end effector disperse the mechanical energy in a way that allows the tissue to be heated and coagulated. These
Figure 23.16 Displayed are two devices that cut and coagulate or seal tissue. Top (A–C) are the ligating cutting shears (LCS) that are based on the same technology as the harmonic scalpel displayed in Figure 23.13. The bottom blade oscillates (C), while the top blade is opened to grasp the tissue and used by the surgeon to slowly transect and seal the blood vessels in the tissue being transected. The PlasmaKinetic (D–F) is a bipolar radiofrequency device that, using electrical impedance, tells the surgeon when the tissue is coagulated. Then the orange trigger (top) is pushed deploying the blade (F), thereby cutting the coagulated tissue.