Electrosurigical Units

Electrosurgery has been in clinical use since 1926 or 1927, depending upon the source of information you use. Harvey Cushing, M.D., a neurosurgeon in Boston is generally credited with its invention. W.T. Bovie, Ph.D. ,a physicist at Harvard University, did some engineering of Dr. Cushing’s idea along with Henry Liebel and Ed Flarsheim to produce the final product. Bovie — a trade name — became a genetic name over the years for electrosurgical devices.

Electrosurgery generators supply radio-frequency (RF) energy at a frequency between 400KHz and 1.2MHz, depending upon the type. Generally, the higher frequencies are spark gap/tube generators and the lower frequencies are solid-state generator designs. The power output can range from a few watts to more than 400, depending on generator design and power settings. The RF output generally is frequency modulated (FM) and pulsed and/or modulated to provide the level of hemostasis that the surgeon needs for the procedure being performed.

Electrosurgery 101
Regardless of the manufacturer of the generator, electrosurgery is a simple technology. The principle of operation is simple: A high-frequency current is applied to a cell, the cell heats up and the cell wall bursts open, drying out the cell. With electrosurgery one electrode is large, more than 25 square centimeters, and is called the ground, inactive, dispersive or return electrode; the other, active electrode or pencil, is small, often about 2 millimeters or less in diameter or width, and is handled by the physician doing the procedure. This is called monopolar electrosurgery. The surgeon controls the output of the generator via a foot switch or hand switch on the active electrode. When the switch is activated, the output of the generator is applied to the patient. The energy dries out the cells that are touched by the active electrode, and the excess energy is returned to the generator via the ground electrode. Diathermy also uses a high-frequency current to heat cells but not to the point of bursting. The reason for the cells not bursting is the size of the electrodes coupled to the skin. Diathermy units use two large electrodes so the energy is spread over a large area

The ground electrode should not be placed over scar tissue, damaged tissue or hair. Contact between the ground electrode and the patient must be secure to avoid burns. Most generators have a built-in system for checking the ground electrode impedance and will not allow the generator to be activated if that impedance is too high. The ground electrode should not be placed on a patient’s pressure point as that can lead to uneven impedance of the electrode and increase the potential for a burn. The long side of the electrode should be positioned towards the surgery site to reduce heat build up on the electrode. As with any RF work, the majority of the energy is concentrated on the leading edges of the electrodes. The longer the leading edge, the better the heat distribution on the electrode. Some ground electrodes are capacitive-coupled to the patient, other use conductive adhesive, as the traditional gelled electrode is no longer commonly used.

Red, white and round: burns
Electrosurgical burns are not as common as they once were because of the improved ground electrodes and impedance monitoring circuits — plus better training of the users. Electrosurgery burns are generally round, red and with a white or black dot in the center. They may appear small on the surface but the typical burn is like an inverted cone; it gets wider the deeper it goes. The cause is generally current division, as the RF finds another conduction to ground besides the dispersive electrode.

Bipolar electrosurgery is commonly called bipolar coagulation. Many current generators have both mono and bipolar outputs. Basically, the frequency is the same, but the maximum power is considerably lower. Also, with bipolar there is no dispersive/ground electrode applied to the patient. It is often used in laparoscopic surgery, where small “bleeders” — veins — have to be sealed, in ENT (ear, nose, throat) procedures and neuro work. The hand-piece is often similar to a large tweezers. One tip is the active electrode, and the other is the return. These electrodes may only be 2 millimeters to 5 millimeters in size while the rest of the hand-piece is insulated. The physician locates the tissue that needs to be sealed or cut, slowly squeezes the tweezers, and as the electrodes get close to each other, the RF will jump the gap, either sealing or cutting the tissue.

Unfortunately RF burns are becoming more common with the bipolar applications as pinholes develop in the insulation of the tweezers creating an alternate path to ground for the RF energy. Hospitals should test the reusable hand-pieces after each use to determine if there are problems with the insulation.

Some of the common problems that will be reported on electrosurgical units (ESU) are as follows:

• No output. This usually cannot be duplicated, as the users did not have a good dispersive plate contact to the patient. The unit worked as designed. If you find that there is no output, check the power transistors first, as they probably are the problem. Many biomeds will replace both output transistors.

• Erratic output. This could be heat-related or user problems. On spark gap units, it could be that the gaps are not set correctly. An old trick is to use a dollar bill folded in half as the gauge between the contacts of the spark gaps. It’s also possible that the plates may need to be filed down if peaks are present on them. Use a fine file.

• Need to increase power during the operation. This is generally a user problem where the surgeon allows the surgical field to become too wet; not enough suctioning of the site. Excess fluid will reduce the effectiveness of the RF energy.

A couple of questions:

1. The output power of an ESU ranges up to …

A. 10 watts
B. 25 watts
C. 100 watts
D. 400 watts

2. Dispersive electrode is the same as …

A. active electrode
B. ground electrode
C. return electrode
D. B and C

Kevin Earl, a staff biomed for Technology in Medicine at MetroWest Medical Center (Framingham and Natick Mass.), contributed to this article.

Please direct questions to Dave Harrington at dharrington@techmed.com.