ELECTROSURGERY UNITS PREPARED BY: DR NINA KORLINA MADZHI
INTRODUCTION •
Electrosurgical units are used in surgical procedures for cutting and coagulating tissue. There are many applications from small units used in dermatology to remove skin lesions, to more powerful units that may be used during procedures such as open heart surgery
•
The concept of cautery as a medical practice has been around for hundreds of years. In ancient times, rocks heated in a fire were used to seal off wounds. Modern medical electorsurgery uses this principle of cautery, but uses heat generated by electric current rather than hot stones. The first electrosurgical unit (ESU) was invented in the early 1900s by William Bovie. The name Bovie remains widely popular in the electrosurgical industry today, and many people still refer to ESUs as Bovies.
INTRODUCTION • The term electrosurgery (radiofrequency surgery) refers to the passage of a high-frequency (radiofrequency) electrical current through the tissue in order to achieve a specific surgical effect such as cutting or coagulation. Each electrosurgical device consists of a high frequency electrical generator and two electrodes (Figure 1). Adjacent to the active electrode, tissue resistance to the passage of alternating current converts electrical energy to heat, resulting in thermal tissue damage. The large return electrode disperses the current, reducing the current density to levels where tissue heating is minimal.
Figure 1. An electrosurgery circuit in monopolar biterminal mode (image from Taheri A et al. Electrosurgery; basics and principles. Journal of American Academy of Dermatology. In press.)
MODES OF ESU • There are two primary modes used in electrosurgery: cut and coagulation. • Cut uses electrical current passed through an active electrode, also referred to as a hand piece, to cut through tissue. There are two types of cut modes: blended cut and pure cut. In pure cut mode, the surgeon achieves a clean cut, very similar to an incision produced by a scalpel. In pure cut mode, there is no process to stop bleeding, also known as hemostasis.
• Coag, short for coagulation, is a technique used to control bleeding. In coag mode, the tissue is cauterized between contact with the hand piece. Both cut and coag may be performed at the same time using a blend setting.
• Blend refers to the ability to both cut tissue and simultaneously coagulate at the surgical site.
PRINCIPLE OF ELECTROSURGERY IN THE OR •
The electrosurgical generator is the source of the electron flow and voltage.
•
The circuit is composed of the generator, active electrode, patient and patient return electrode.
•
Pathways to ground are numerous but may include the OR tablem staff members and equipments.
•
The patient’s tissue provides the impedance, producing heat as the electrons oversome the impedance.
FREQUENCY SPECTRUM •
Standard electrical current alternates at a frequency of 60 cycles per second (Hz).
•
ESU could function at this frequency, but because current would be transmitted through body tissue at 60 cycles, excessive neuromuscular stimulation and perhaps electroculation would result.
•
An electrosurgical generator takes 60 cycle current and increases the frequency to over 200,--- cycles per second.
BIPOLAR ELECTROSURGERY • Both active and return electrode functions are performed at the site of surgery.
• Two tines of the forceps perform the active and return electrode functions. • Only the tissue grasped is included in the electrical circuit. • Because the return function is performed by one tine of the forceps, no patient return electrode is needed.
BIPOLAR CIRCUIT • Active output and patient return functions are both accomplished at the site of surgery
• Current path is confined to tissue grasped between forceps tines.
• Patient return electrode should not be applied for bipolar only procedures.
MONOPOLAR ELECTROSURGERY • Commonly used due to its versatility and clinical effectiveness. • Active electrode is in the surgical site. • The patient return electrode is somewhere else on the patient’s body. • The current passes through the patient as it completes the circuit from the active electrode to the patient return electrode
MONOPOLAR CIRCUIT • Consists of : Generator, active electrode, patient and patient return electrode
TISSUE EFFECTS CHANGE AS THE WAVEFORM MODIFIED
• Electrosurgical generators are able to produce a variety of electrical waveforms. As waveforms change, so will the corresponding tissue effects.
• “Cut” - a constant waveform - the surgeon is able to vaporize or cut tissue. This waveform produces heat very rapidly.
• “Coagulation”- causes the generator to modify the waveform so that the duty cycle (“on” time is reduced. This waveform will produce less heat. Instead of tissue vaporization, a coagulum is produced.
• • • •
“Blended current”- a modification of the duty cycle.
“Blend 1”- able to vaporize tissue with minimal hemostasis. “Blend 3”- less effective at cutting but has maximum hemostasis. As we go from Blend 1 to Blend 3 the duty cycle is progressively reduced. Lower duty cycle produces less heat.