Lec Rec 1.1 - Electrosurgery Basic Electrical Principles
Lec Rec 1.1 - Electrosurgery Basic Electrical Principles
Lec Rec 1.1 - Electrosurgery Basic Electrical Principles
Department of Surgery, University of Missouri—Kansas City, Kansas City, Missouri, and Department of
Medical Education, Saint Luke’s Hospital of Kansas City, Kansas City, Missouri
INTRODUCTION
The safe use of electrosurgery in the operating room requires a
basic understanding of the principles of electricity and how they
apply to electrosurgery. In this, the second article in a series, we
will examine these principles. In future issues we will address
topics such as radio-frequency tumor ablation, laparoscopic
electrosurgery, and the argon beam coagulator. In this article we
focus on what the surgeon should know about electricity and its
application to electrosurgery.
BASIC ELECTRICITY
Electrical current is defined as the flow of electrons through a
FIGURE 1. Direct vs alternating current. (Courtesy of Valleylab Inc, Pfizer
circuit in response to an applied electromotive force. Electrons Hospital Products Group, 5920 Longbow Drive, Boulder, CO 80301.)
orbit the nuclei of atoms. In the atoms of some substances,
known as conductors, the atoms are loosely held, and can flow
from one atom to the next. This flow of electrons through a current through a conductor, or a human body, is known as
conductor constitutes current. resistance and is measured in ohms. These elements— current,
Current flows from positive to negative. Now, electrons are voltage, and resistance—combine to create a circuit.
negatively charged. That means that electrons flow from the A circuit is a continuous pathway for the flow of electrons.
negative pole of a battery to its positive pole. This doesn’t make There must be a continuous circuit for electrons to flow. The
a great deal of sense, but it all goes back to the 18th century. components are a voltage source, resistive element, and current
They could have set up the conventions so that electrons would path. This electrical system is analogous to the human cardio-
have turned out to be positive, and then current flow would vascular system. Current can be seen as blood flow, the voltage
follow electron flow. They didn’t. Blame it all on Ben Franklin, source as the heart, the resistive element as the small vessels and
who had at least something to do with it. So we have to live with capillaries, and the current path as the blood vessels.
the convention that current flows positive to negative, when The flow of current through a conductor is governed by
what is really going on is that electrons are flowing from nega- Ohm’s Law, which ties together current (I), voltage (V), and
tive to positive. resistance (R):
Fortunately, electrosurgery is not direct current, but alternat-
ing current. Radio-frequency alternating current, in fact. The V
positive-to-negative convention has little effect on understand- I⫽
ing electrosurgery (Fig. 1). R
Current—alternating or direct—is measured in amperes or,
It states that current is equal to voltage divided by resistance. In
for smaller current flows, milliamperes. The electromotive
other words, current increases as voltage increases and current
force, which pushes electrons from atom to atom, is also called
decreases as resistance increases.
voltage, and is measured in volts. The effort required to push
Current passing through a circuit can do work. If one turns
on a light, current through the light bulb makes light (and
heat). The amount of work done by the current is called power.
Correspondence: Inquiries to Charles W. Van Way III, MD, Department of Medical Edu-
cation, St. Luke’s Hospital, 4401 Wornall Road, Kansas City, MO 64111; fax: (816) Power is defined as the rate at which work is done in the circuit
932-5179; e-mail: cvanway@saint-lukes.org and is represented by
CURRENT SURGERY • © 2000 by the Association of Program Directors in Surgery 0149-7944/00/$20.00 261
Published by Elsevier Science Inc. PII S0149-7944(00)00234-8
FIGURE 3. The radio-frequency spectrum extends from the type of alter-
FIGURE 2. The electrosurgical circuit contains the generator, the elec- nating current used in homes to the high frequencies used in radio and
trosurgical instrument, the patient, and the return electrode. (Courtesy of television broadcasting. Electrosurgery is at the low end of the radio
Valleylab Inc, Pfizer Hospital Products Group, 5920 Longbow Drive, broadcast band of frequencies. (Courtesy of Valleylab Inc, Pfizer Hospital
Boulder, CO 80301.) Products Group, 5920 Longbow Drive, Boulder, CO 80301.)
to 50 W for coagulation, and at least 60 W for blended cutting. where patients were touching grounded operating room tables
The amount of “blend” has some influence. The less blend, the or other equipment. The legal profession did not ignore these,
less drag. less common though they might have been. The more enter-
Because coagulation current is more effective at lower power, prising lawyers sued not only the hospital, but also the manu-
many surgeons habitually use coagulation current for cutting. facturers of the equipment. Ah, the American legal system is the
Although this can be useful in some circumstances, such as wonder of the world.
going across muscle, it is generally poor technique. Cutting The electrosurgical manufacturers have, over the past 20
current, even with a blend level of 2 or 3, produces much less years, gone to great lengths to prevent return site burns and
collateral damage and charring of the tissue than does coagula- burns caused by unintentional grounding of patients. Today, all
tion current. electrosurgical equipment is isolated (Fig. 5). That means that
Actually, electrosurgery is usually quite safe. Unintended in- the circuit composed of the generator, the patient, and the
juries produced by the surgeon are relatively uncommon. Of return electrode is isolated from any other electrical circuit. In
course, no technology can help the surgeon if he or she cuts the particular, the circuit is isolated from ground. So putting the
wrong structure, or unintentionally applies current to a struc- patient in contact with a grounded piece of equipment cannot
ture adjacent to the intended target. But most of us use electro- cause a burn. Furthermore, the old ground pad has become a
surgery every day and have little trouble with it. Lasers, by highly sophisticated return electrode. The return electrode can
comparison, are considerably more dangerous to use. But elec-
trosurgery has its definite hazards.
The most common site of electrosurgical injury is at the
return electrode. Conversion of current to heat occurs at the
active site, where the current is concentrated into a small area.
The return electrode is supposed to be low resistance large
enough to disperse the current, and to produce no heat. But if
the patient return electrode has dried out or come loose, then
there may be only a small area of contact with the patient’s skin.
The current exiting the body at that point may have a high
enough current density to heat the skin, which may result in an
unintended burn. The same problem can be produced by an
electrode that has a poor quality (high resistance) contact with
the skin.
Electrosurgical burns at the return site (“ground pad burns”)
were a serious problem for many years. In fact, more lawsuits FIGURE 5. All electrosurgical systems used today are isolated from the
were filed against hospitals for this cause than for any other power line, and from ground, so that the generator and the patient form a
closed system. Notice also that the return electrode is monitored by an
operating room injury. There are lawyers who have lived well interrogation circuit. (Courtesy of Valleylab Inc, Pfizer Hospital Products
and retired rich on ground pad burns. Burns were also seen Group, 5920 Longbow Drive, Boulder, CO 80301.)