Small Animal Laparoscopy and Thoracoscopy. Группа авторов
Meticulous hemostasis, one of Halsted's seven principles, is important for any surgery, but particularly for minimally invasive procedures, in which a small amount of hemorrhage can compromise visualization. Numerous devices are available for hemostasis with laparoscopy and thoracoscopy, including hemostatic clips, endostapling equipment, and energy devices.
Energy has been used in surgery for thousands of years. The first form of energy used in surgery was thermal cautery, or the application of energy as heat to tissues. Although this was invaluable for controlling hemorrhage, lateral thermal damage to normal tissues was extensive. This technology evolved as William T. Bovie developed the first electrosurgical unit (ESU) that provided both cutting and coagulation settings. Rather than electrocautery, which relies on the transfer of heat directly to tissues, this new technology created an electrical current that was applied to the tissues and, in turn, created heat. Almost 100 years later, we are still using monopolar and bipolar electrosurgical devices similar to the “Bovie,” but advances in technology have created safer units with more consistent tissue effects. More recently, vessel sealant technology has gained popularity in minimally invasive procedures. These bipolar electrosurgical devices have been used in numerous types of minimally invasive procedures, including surgeries of the reproductive tract, splenectomies, adrenalectomies, nephrectomies, lung biopsies, and pericardial surgery.
All surgeons should have a basic understanding of electrosurgical devices to allow for appropriate use of this equipment and to prevent unnecessary injury related to their use. Energy devices have their advantages and disadvantages for a given procedure, and it is up to the surgeon to understand the shortcomings of a particular device and decide which is the most appropriate for a given situation.
Electrosurgical Theory
Electricity is the movement or flow of electrically charged particles from one electrode to another. Electrosurgery instruments apply an electrical current to tissue, enabling cutting, coagulating, desiccating, or fulgurating by generating heat. There are three properties of electricity that affect the rise in temperature of the tissue: Voltage, current, and resistance, or impedance. The interaction of these three properties is explained by Ohm's law, which describes the flow of electricity along a circuit:
Whereas current is a measure of electron movement through tissue in a given time, voltage is the driving force that moves the electrons against the tissue resistance or impedance within the circuit. Tissue resistance or impedance is a function of both the composition of the tissues and blood supply. As voltage drives electrons through the circuit against impedance, heat is generated. This tissue resistance or impedance produces heat rather than the active electrode. Therefore, tissues with greater impedance will result in the generation of more heat. Tissue impedance constantly changes as an electrical current is applied and the tissues become desiccated. The degree of heat leads to varying tissue effects (Table 5.1).
Table 5.1 Tissue effect in relation to temperature.
Source: Modified from Dubiel et al. [1].
| Temperature (°C) | Tissue effect |
|---|---|
| 250 | Tissue carbonized from dehydration |
| 100 | Cell wall rupture |
| 90 | Tissue desiccation |
| 70 | Protein denaturing |
| 50 | Enzymatic activity inactivated |
| 40 | Inflammation and edema |
Another important concept in understanding electrosurgery is the concept of power. Power is a measure of work per unit time. It is a function of voltage and current and is measured in watts. Power tells you the rate at which the energy works. Power rises exponentially with increases in voltage and decreases inversely with increases in resistance or impedance. However, voltage is the main determinant of tissue effect and is a function of the waveform that the generator delivers (see waveform section below).
An ESU is composed of four basic components: A generator, an active electrode, the patient, and the return electrode. The ESU uses low‐frequency alternating current (AC) from a wall outlet and converts it to a higher voltage radiofrequency (RF) output. The current can be used to induce diathermy but also stimulates muscle and nerve cells. Stimulation of muscle and nerve cells can lead to pain, muscle spasm, and even cardiac arrest. The sensitivity of nerves and muscles cells to electrical stimulation decreases and the excitability threshold increases with increasing frequency, meaning that nerve and muscle cell stimulation is refractory to electrical stimulation above 100‐kHz [2]. Therefore, electrosurgical devices use frequencies in the range of 350–500 kHz. This range is referred to as the medium RF electromagnetic spectrum (Figure 5.1).
Waveforms
There are three basic types of waveforms generated in electrosurgery: Cutting waveform, coagulation waveform, and blended waveforms (Figure 5.2). Cutting waveforms are continuous waveforms, and coagulation and blended are intermittent waveforms.
The continuous cutting waveform uses less peak voltage at a similar power setting to the intermittent waveform, resulting in less lateral thermal tissue damage. With pure cut, the amplitude of the continuous waveform is the same. This induces a localized effect on the tissues, creating high tissue temperatures (>100 °C), vaporization of the interstitial fluid, and tissue separation with little hemostasis. Heat is absorbed by water released from the cells, which minimizes thermal damage and provides minimal coagulation. Power settings for the cut waveform are often between 50 and 80 W [4].
The intermittent waveform of the coagulation waveform produces a high current density delivered in pulses. This waveform has a higher voltage than the continuous waveforms and delivers the electrical charge deeper into the tissues. The pauses between the pulses lead to decreased tissue heating, resulting in coagulation rather than cutting. Coagulation is achieved with a power setting between 30 and 50 W [4]. Coagulation can either be performed using desiccation or fulguration. Whereas fulguration uses a noncontact technique to control diffuse hemorrhage, desiccation is a contact technique used for local bleeding. Fulguration uses an intermittent waveform, which allows for proteins to melt and recongeal, forming a coagulum. Some ESUs also contain a spray mode, which is useful for oozing capillary beds. Spray mode does not penetrate as deeply into tissues and can be used in more delicate tissues. Desiccation or a contact technique leads to less heat production than fulguration. A coagulum is formed by tissues drying out and proteins melting.
A blended waveform results in simultaneous coagulation and cutting. Whereas blend 1 is more effective at cutting with minimal hemostasis, blend 3 results in better hemostasis and decreased cutting (see Figure 5.2). Many surgeons prefer to use the blend waveform because it provides a trade‐off between thermal tissue damage and hemostasis.
Despite its name, the cutting waveform can be used for coagulation, and in some scenarios, it is recommended over the coagulation waveform. An example is when applying electrosurgery to the hemostat or forceps in what is referred to as coaptive coagulation. In this scenario, cutting energy is recommended because this produces deeper hemostasis and less thermal spread compared with coagulation energy. Coagulation results in rapid increase in impedance from char at the electrode.