Surgical Modalities

Laser, Radiofrequency, Ultrasonic, and Electrosurgery

Energy is a fundamental tool of modern surgery. Transduction of energy can take many forms; however, most energy-based surgical tools rely on electrons, photons, and sound waves to transfer energy to tissue. The use of controlled application of energy to tissue has expanded greatly in surgery. It is used for coagulating blood vessels; welding, dissecting, and ablating tissue; and facilitating the stimulation of vascularization and healing.

Surgeons expect specific and repeatable results from energy-based tools. An understanding of the basic underpinnings of energy transfer and its effect on tissue is necessary before one can adapt technology to specific surgical applications. As an example, spatial control of energy distribution is very difficult to predict and control. This chapter discusses the energy transduction devices most commonly used in surgery today. Many are indispensable and have well established clinical data; others are relatively new and have limited data supporting their application in a wide range of tissues.

Radiofrequency Technology

In the 1920s, neurosurgeon Harvey Cushing, working with physicist William Bovie, developed a device that delivered high-frequency alternating electrical current that could be used to incise or coagulate tissue to obtain hemostasis.3,10 This device, commonly known as the “Bovie,” allowed Cushing to operate on patients that had been previously inoperable because of risk of hemorrhage. The Bovie has since become a cornerstone of modern surgery.

Over the past nearly 100 years since its introduction, the Bovie has gone through many advances. Generators have evolved from bulky unreliable units to compact devices run by sophisticated computer-controlled units. The delivery of radiofrequency energy has also advanced significantly. Devices today include radiofrequency energy–delivering endovascular catheters, laparoscopic tools, and percutaneous instruments capable of reaching almost any part of the body. Recently, feedback controls have been developed to optimize electrosurgical vessel sealing and minimize surrounding tissue damage.

Electrosurgery should not be confused with electrocautery. Electrocautery is the use of electrical current to heat an instrument, which is then used to cauterize tissue in the same manner as a branding iron affects tissues. Electrosurgery is a form of energy transfer via electrons from the instrument to tissues.3,10 All matter is formed of atoms with a nucleus of positively charged protons and neutral neutrons orbited by negatively charged electrons. Atoms become charged by gaining or losing electrons, creating a charged state. When positive and negative ions are placed in opposition, a gradient or voltage is created. A conductor provides a path so that electrons can flow along the gradient, creating a current. A current is proportional to the voltage and inversely proportional to the resistance of the conductor.^6,10 Current always flows along the path of least resistance and heads toward the electron sink. Although commonly known as the ground in a circuit, for electrosurgery, the flow is actually toward the electron sink (patient return electrode, or dispersive pad) and not the earth ground; thus the generator is actually isolated from the earth ground (Figure 16-1). Living tissue is an excellent conductor because of its high electrolyte content.⁶

Figure 16-1 The electrosurgical generator is isolated from the ground. Electrical current flows between the electrode (handpiece) to the patient and the return electrode (dispersive pad) to the generator because this is the path of least resistance. (From Massarweh NN, Cosgriff N, Slakey DP: Electrosurgery: history, principles, and current and future uses. J Am Coll Surg 202:520, 2006.)

The mode of application of electrocautery energy may be monopolar or bipolar. Monopolar radiofrequency, which uses a current applied through a hand-held active electrode, travels back to the generator through an inactive electrode attached to the patient (the grounding pad), so that the patient is part of the electrical circuit (Figure 16-2).^6,9,10 Monopolar electrocautery is also known as unipolar. Bipolar electrocautery consists of active and return electrodes incorporated into a single hand-held instrument, so that the current passes between the tips of the two electrodes and affects only a small amount of tissue (Figure 16-3).¹⁰ Because no flow of current occurs with electrocautery, a return electrode (grounding or dispersive pad) is not necessary.

Figure 16-2 Alternating current flows from the generator to the handpiece. High current density occurs at the electrode (handpiece) tip, through the patient, to the dispersive pad. The lower density current is then returned to the generator, thus completing the circuit. ESU, Electrosurgical unit (generator). (From Smith TL, Smith JM: Electrosurgery in otolaryngology—head and neck surgery: principles, advances, and complications. Laryngoscope 40:769, 2001.)

Figure 16-3 In bipolar electrocautery, the electrode “pencil” is replaced by forceps. The active electrode is on one prong, and the dispersive electrode is on the other. Current passes between the active electrode and the dispersive electrode, and then returns to the generator. Because the target tissue is between prongs of the forceps, application of current is more precise, and stimulation of adjacent tissues (muscle twitching) and collateral damage are lessened. (From Smith TL, Smith JM: Electrosurgery in otolaryngology—head and neck surgery: principles, advances, and complications. Laryngoscope 40:769, 2001.)

Tissue Effects of radiofrequency Energy

The thermal effect of radiofrequency energy on tissues is dependent on the level of energy, the duration of application, and the nature of the tissues. In addition, electrode type (monopolar versus bipolar), size, and shape can each have an effect on the tissue.

Although radiofrequency devices and lasers differ fundamentally in the way they generate heat within a tissue, both classes of devices are capable of producing temperatures within the range considered necessary for collagen denaturation and subsequent tissue shrinkage (65° to 75° C).¹⁰ When collagen is heated to 65° C, its heat-labile, intramolecular cross-links are broken, and the protein undergoes a transition from a highly organized crystalline structure to a random, gel-like state (denaturation).¹⁰ Collagen shrinkage occurs through the cumulative effect of the “unwinding” of the triple helix due to destruction of the heat-labile intramolecular cross-links and the residual tension of the heat-stable intermolecular cross-links.^3,10 However, it must be remembered that when it comes to cell viability and tissue response, heat is heat. Once critical temperatures are reached, cells will die (45° C) and collagen will become denatured (65° C), no matter what the source of energy.

Monopolar versus Bipolar

Typical radiofrequency surgical generators operate as monopolar or bipolar units.⁹ A monopolar electrosurgical unit is used both in surgical dissection and for hemostasis. When undamped high-frequency electrical current (Figure 16-4) is passed through tissue, the active electrode, or tip, acts like a bloodless knife, and the tissue at the wound edges disintegrates.⁹ Thermal injury also occurs peripheral to the plane of cutting, resulting in thrombosis of tissue-associated blood vessels. When the current flow is intermittent, or the oscillations in the current are dampened, hemostasis is accomplished without cutting (Figure 16-5).⁶ Monopolar cautery causes cells to rapidly dehydrate and vessels to coagulate. Damage to tissue can be extensive, and the unit power setting should be the lowest possible to achieve the desired tissue effect (Figure 16-6). Frequently, precise application of energy to the tip of divided blood vessels is all that is needed.