ALL ELECTROSURGICAL UNITS ARE NOT CREATED EQUAL
By Karl Hausner
Since the "Star Wars" glamour of laser surgery has subsided and the majority of surgeons are putting laser surgery in its proper perspective, renewed interest is being shown in electrosurgery.
Laparoscopic cholecystectomy and gynecological pelviscopy are rapidly gaining clinical acceptance, and with it the use of the electrosurgical generator in place of the laser, which was initially promoted for these newer procedures. This, however, invites renewed risks of accidents when the improper electrosurgical equipment and techniques are employed, as was the case when laparoscopic tubal sterilization gained popularity in the early 1970s.
With this presentation surgeons and nurses are to be alerted to the risks of injury when a unit, which was designed for general surgery, is utilized for endoscopic procedures.
THE MISLEADING WATTAGE METER
It seems that we, as a society, are always looking for an easy way out of our responsibilities. The incorporation of wattage indicators on electrosurgical equipment is gaining rapid popularity under the misguided belief that such indicators will significantly eliminate improper power output selections. This is a misconception, as the following simple examples will show:
A Watt is technically known as a Volt-Ampere (VA). Wattage is a measurement of the power obtained when Voltage (V) is multiplied by Amperage (A). Let us Itake the Wattage measurement of 20 Watts as an example:
20 V x 1 A = 20 Watts
200 V x 0.1 A = 20 Watts
2000 V x 0.01 A = 20 Watts
10,000 V x 0.002 A = 20 Watts
So, if you as surgeons are convinced that you need 20 Watts, as an example, for a given application, you could be utilizing insufficient voltage, or excessively high voltage. For example, 20 Watts from a low voltage bipolar generator could contain 200 Volts, or if you have an improperly designed bipolar unit, it could energize the bipolar forceps at 10,000 Volts, or even higher; a dangerous situation. Such bipolar generators are in use in hospitals today!
'The situation can be equally misleading for unipolar generators. 20 Watts of non-modulated, "cutting" current may energize the electrode at 400 - 1,200 Volts. If the output is switched to the modulated "blended" or "coagulation" currents, if you have the same 20 Watts displayed, the electrode will begin discharging a high voltage arc of between 1,500 - 3,000 Volts.
Such high voltage arcing can be both more destructive, and particularly in the endoscopic environment, more hazardous
Another consideration regarding Wattage indicators is that they only show the power delivered to the generator's output socket under a given impedance load. When the electrosurgical current leaves the unit through the attached RFconnection cable, many factors take effect, such as varying impedance and/or capacitance levels, which may be determined by the length, diameter and configuration of the RF-cable (coaxial style cables are known to create more capacitance in the circuit) or by the environment of the surgical procedure performed. The long, insulated instruments and the associated instrument cannulae used in endoscopic surgery, create a significant amount of capacitance in the electrosurgical circuit, making the higher voltage current extremely hazardous, both to patient and personnel. This also renders the Wattage indicator less useful.
Different generators also have substantially different output Voltage characteristics, even within one manufacturer's line, by a factor of +/- 20%. Therefore, the 20 Watt output level indicated on the digital meter is useless and/or misleading information, unless the output Voltage level is also known and taken into account.
Also, RF-output wattage meters are known to be inaccurate, particularly at lower power settings. This problem is intensified in surgical interventions which require low output power, such as ophthalmic, microsurgical and certain endoscopic procedures. For example, the service manual for the Valleylab Force 4 generator, on page 15 under "Power Readouts" states; "Power readouts agree with actual power into a rated load to within +/- 10%, or 5 Watts, whichever is greater." This means if you select 10 Watts output for an ophthalmic or microsurgical procedure, you may actually be delivering between 5 and 15 Watts, which is +/- 50%. This variation can be even higher at lower settings.
Voltage is an extremely important consideration to factor in. It has a dramatic effect on the electrosurgical electrode and its performance. The higher the peak-to-peak voltage, the greater the likelihood of capacitive discharge through the RF-cable or electrode insulation. It is for this reason that the American Association of Gynecological Laparoscopists (AAGL), as a consequence of numerous injuries during laparoscopic procedures, developed voluntary standards which were submitted to the Bureau of Devices of the FDA. The FDA accepted and published these standards in the Federal Register on February 26, 1980 (45:12701).2
Contained within this standard is the recommendation for electrosurgical equipment to be used in laparoscopy, which limits the recommended unipolar output power to 1,200 Volts peak-to-peak, ;and 100 Watts at maximum generator output.
Soderstrom has elaborated on this proposal in the interest of reducing risks and burn injuries. Hausner has not only participated in this standard development, but actually proposed these standards based on the absolutely objective characteristics of radio frequency current behavior, as documented in text books on electro-physics.
'The voltage also determines the temperature at which tissue coagulation is effected. Modulated currents ("blended" and "coagulation" currents), due to their higher peak-to-peak voltage potentials, will generate considerable arcing, prociucing tissue carbonization. In contrast to this, the smooth, non-modulated current can either cut, or when used with a larger surface area electrode, produce contact coagulation, resulting in tissue dehydration. All of this can happen at the same wattage level.
It is regrettable that many surgeons and nurses simply pay no attention to these characteristics and risk unnecessary injuries to patients and operating room personnel.
Electrosurgical generators operate between 500 KHz (500,000 cycles per second) and 3 MHz (3,000,000 cycles per second).
The capacitive effect, defined as power loss through an insulator, is significantly greater at 3 MHz than at 500 Khz. Thus, electrosurgical generators which operate at extremely high frequencies will have much more RF-current leakage tlnrough RF-cables, insulated instruments and cannulae than their lower frequency counterparts. To illustrate this capacitive effect consider the following; a 10' AC line cable conducting current energized at 50 Hz (European line frequency) will have about 10 uA of leakage. If the same line cord is energized at 60 Hz (U.S. line current) you will measure 12 uA, an increase of 20%. When frequency is increased to 2-3 MHz, the RF-leakage can be significant, and again will distort the reliability of the wattage meter on the electrosurgical unit when it is used as a scientific basis for output selection.
The output impedance, at which most unipolar generators operate, is 500 Ohms. For laparoscopy or for bipolar coagulation you may want 50 or 100 Ohms. Accordingly, whether the generator output is functioning at 50 Ohms, 500 Ohms or 2,000 Ohms makes a major difference with respect to the clinical performance of an electrosurgical unit at a given wattage meter reading. We, at ELMED, have continuously collaborated with surgeons to develop equipment which provides the ultimate in safety, refraining from the panacea solutions which some manufacturers seem to promote. For a number of years, many electrosurgical unit manufacturers have promoted the isolated, rather than the ground referenced output, declaring "ultimate safety". Now, many have reversed their philosophy. Next came the misconceived notion of the insulated trocar sleeve, which only increased the capacitance in the electrosurgical circuit. Again, due to an extraordinary number of burn injuries, the published FDA standard of February 26, 1980 recommends the use of only conductive trocar sleeves and cannulae for diameters above 7 mm. At that point, every instrument manufacturer returned to metal, conductive trocar sleeves. Now, some members of the industry seem to be reversing science again, in the name of convenience, by promoting disposable, X-ray permeable 8, 10 and 11 mm nonconductive trocar sleeves!
Another dilemma is created when general purpose electrosurgical equipment is used for microsurgery, It is a fallacy to believe that to perform microsurgery you simply get a fine, hair-thin electrode and connect it to any electrosurgical generator and just turn the power down to a low level on the Watt meter.
Of course, the results depend upon the criteria with which a surgeon judges microsurgery. Hausner has elaborated on the subject of micro vs. macro electrosurgery in detail.
It is a dangerous misconception that all forms of coagulation have to be performed with a "coagulation current". Endoscopic procedures, particularly coagulation, should be performed by the non-modulated current ("cutting current") utilizing a larger surface electrode, for contact coagulation at a lower voltage with reduced arcing. By utilizing specially shaped coagulation electrodes, such as a spatula for unipolar, or whenever possible with special bipolar instruments, a more safe, effective and reproducible technique is employed.
Gadgetry and convenience are often appealing, but do not always provide valuable features and rarely do they contribute to safety. The Wattage meter is a convenient, but expensive feature. More importantly, it must never be used exclusively as the criteria for output selection.
More important than such flashy meters is the realization that surgery during the last decade has become enormously sophisticated. Therefore, a specially designed electrosurgical unit should be utilized for surgical procedures such as endoscopic polypectomy and laparoscopic/pelviscopic procedures. The general surgeon, who has been using electrosurgical equipment empirically for a long time, will have to retrain himself with respect to the selection and use of electrosurgical equipment for laparoscopy, just as he must learn the new technique and coordination of performing surgery while looking at a video screen.
1. ECRI, Health Devices, Electrosurgery and Laparoscopy, 1973; 2:222
2. U.S. Food and Drug Administration, Classifications and Guidelines, Subcommittee on Endoscopy, Federal Register, 1980; 45:12701
3. Soderstrom, R., Refinements in Laparoscopic Equipment, Contemporary OB/GYN, 1980; 16:121
4. Soderstrom, R., Electrosurgery- Advantages and Disadvantages, Contemporary OB/GYN, 1990; TECHNOLOGY 1991, page 35
5. Hausner, K., Electrosurgery, Elmed Incorporated, 1985
6. Hausner, K., Electrosurgery - Micro Vs. Macro, Medical Electronics, June 1985
LIST No, 52-5775 ELMED ESU 100 L has all the important features pertaining to safety and performance. Our most basic laparoscopic unit should be considered when cost is a factor.
Elmed Incorporated can be contacted at: 60 W. Fay Avenue, Addison, Illinois 60101, USA, or PHONE: (630) 543-2792 FAX: (630) 543-2102
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