With the introduction of the surgical microscope over ten years ago, many surgical procedures became more refined; microsurgery became possible. All microsurgeons use special microsurgical instruments and suture material, but confusion still exists about the use of electrosurgical equipment and accessories. This frequently leads to unnecessary complications. Parameters of using electrosurgical generators and accessories for microsurgery are discussed in the following.

CONVENTIONAL MACRO SURGERY

From its inception, almost a century ago, electrosurgery has been associated with burning and charring of tissue. As a result, many surgeons use electrosurgical techniques either in a limited way, or not at all.

It is generally believed that all electrosurgical generators have similar output and performance characteristics and that, by selecting special electrodes, the desired effects are accomplished. This is a misconception. The output characteristics of a generator, the shape of its waveform, its output impedance and peak voltages all are important and, to a great extent, determine the surgical performance of an electrosurgical generator.

CUTTING AND BLENDING CURRENT

For MACRO surgery, such as laparotomy, the surgeon needs a "cutting current" with peak voltages to 1,200 volts, or a "blending current" with peak-to-peak voltage of up to 2,000 volts. Using a lancet or knife electrode, the surgeon obtains good cutting with capillary hemostasis. Additional bleeding of vessels up to four millimeters in diameter can be controlled by "spray coagulation" or, preferably, "contact coagulation". Table 1 defines the various currents.

A blended current is a modulated current of up to 2,000 volts, peak-to-peak. When this type of current is used, a significant amount of sparking results.

COAGULATION CURRENT

For coagulation, most surgeons prefer coagulation current, using cutting electrodes. Coagulation current is a modulated current with peak-to-peak voltages of up to 6,000 volts, with solid-state generators; spark-gap generators can go up to 15,000 volts. The relatively low current and extremely high voltages cause intensive sparking between the active electrode and the tissue.

A less traumatic and much more reliable hemostasis is produced by contact coagulation. Coagulation electrodes, such as a ball, the side of a blade, forceps or hemostats, are employed. In contrast to general belief, a cutting current, not a coagulation current should be used here.

Contact coagulation can be carried out with a cutting current at less than 500 volts. When using a coagulation current, the process of coagulation requires over 2,000 volts. Laparoscopists know that contact coagulation, either unipolar or bipolar, should be carried out with non-modulated current.

The reason for misconception over which type of current to use lies in the incorrect and greatly antiquated terminology for cutting current and coagulation current. It would be much better to use the correct terminology: modulated current and nonmodulated current. Many accidents originate out of this misconception

Non-modulated current (Figure 1) is a continuous sinusoidal current with a nonchanging voltage pattern. In contrast to the modulated current which is interrupted providing enormous voltage variations which clinically produce no cuts, but excessive arcing (Figure 2).

Most conventional electrosurgical units found in operating rooms throughout the country are suitable for conventional MACRO surgical interventions but not for microsurgery.

Table 1 -- Electrosurgery Terminology

Blended Current -- In the true sense it is a mixture of cutting (non-modulated) and spray coagulation (modulated currents). It permits cut with predetermined tissue destruction (relatively high voltage current for cutting) -- up to 2,000 volts.

Coagulation Current -- Modulated current for spray coagulation; high voltage/low current; 6,000 volts with solid-state generator; to 15,000 volts with spark-gap generator, peak to peak voltages.

Modulated Current -- Same as spray coagulation current -- high voltage, low current -- must draw arc between active electrode without direct contact.

Non-Modulated Current -- Ideally suitable for scalpel-like cutting utilizing needle, lancet, and blade electrodes and contact coagulation with cutting electrodes such as balls, blades, hemostats, forceps, suction cannulae, ect.

Bipolar Coagulation -- Both electrodes, generally forceps, must be of equal size, and isolated from each other, energized with low voltage, non-modulated RF current in an isolated (floating) - earthflow circuit. Since current flows only between the two electrodes, no trauma will be created elsewhere.



Figure 1. Non-Modulated Waveform is suited for scalpel-like cutting

Figure 2. Modulated Waveform, or spray coagulation waveform, has high-voltage low-current

ELECTRO-MICROSURGERY

To reduce surgical trauma as much as possible, the electrosurgical generator, its accessories, and the surgical techniques must all be considered.

A true microsurgical generator must provide a relatively low power output of less than 70 watts, precisely controllable over a large scale. The output impedance must be tailored to the impedance of the microfine needles for cutting, and for the micro needles for coagulation. If all factors are not taken into consideration, a fine needle electrode may burn up before actual contact with the tissue is made, or shortly thereafter, leading to undesirable tissue trauma.

The electrosurgical handle should be light in weight and, when hand switching is desirable, the switching mechanism must be activated by a very light touch.

The active electrodes consist of extremely fine needles for cutting, and heavier gauge needles or ball electrodes for coagulation.

For coagulation, the unipolar contact and sometimes even the micro-spray technique is suitable. However, when possible, bipolar coagulation with special bipolar micro forceps should be employed. With bipolar technique, the sealing of blood vessels is more reliable and much less traumatic.

It is mandatory that a microsurgical system provide a separate bipolar generator. Such a generator must have an output range which permits precise dosage, and a low output impedance, not to exceed 100 ohms.

ELECTROSURGICAL ACCESSORIES

Electrosurgical accessories, such as patient return plate, cables, forceps, handles and active electrodes, are an integral part of the electrosurgical system or circuit. With respect to the patient return plates (neutral electrode), fear and confusion exists about the different types available. No type of plate, whether reusable or disposable, pre-gelled or capacitively applied, is safe - if the plate is put on the patient carelessly There is no substitution for careful application of the neutral electrode. Permanent plates, if they are free from bends and warps, are just as safe as the relatively expensive disposable ones. Practically all plates that are on the market are safe when carefully applied to the patient. It is important to inspect the plate frequently, particularly when the patient has been repositioned.

Cables are subject to corrosion, and thus should be discarded after six months or one year of use. Cables and other accessories should be inspected carefully each time before use to assure safety and troublefree operation. Active accessories, such as handles, electrodes and forceps, must always be free from coagulum.

THE MICRO/MACRO CIRCUIT

Gynecological and neurological surgeons, in particular, require a unit which performs during the MACRO surgical intervention and also permits microsurgical use i.e., an electrosurgical unit which has dual performance characteristics, simply selected by a changeover switch.

If such a MICRO/MACRO unit is not available, two separate units may be used -- a conventional electrosurgical unit for laparotomy or suction coagulation, and a separate microsurgical generator. This is a solution when economics permits, but extreme care must be taken to insure that all patient return plates and circuits are on common electrical levels. The biomedical department should be consulted and the operating-room nurse must carefully check that the cables are properly connected and in place, at all times. Poor performance often results when performing microsurgery with a macrosurgical unit by adapting special microsurgical accessories. We strongly advise against this practice because it subverts the purpose of microsurgery.

Electrosurgical instrumentation compares favorably with the surgical laser. The advantage of the electrosurgical application is that the surgeon can mechanically control the activity on the tissue, which is not possible with the laser beam.

THE AUTHOR

KARL HAUSNER has been President of Elmed Incorporated since 1969. Prior to this. he was Division Mannager of Siemens Medical of America, Incorporated. He holds degrees in natural science and engineering, and has over 25 years experience in biomedical technology He may be contacted at Elmed, 60 West Fay Ave., Addison IL 60101, 630/543-2792.

JUNE. 1985

GO TO ELMED

GO TO ELECTROSURGERY