Electrosurgery Units ELECTROSURGICAL UNITS (ESUs) Jclemens (2009), electrosurgery [photograph]. Retrieved from https://commons.wikimedia.org/wiki/File:Electrosurgery.jpg

Electrosurgery: Overview Electrical arc used in surgery (≈3000C) Usually 1Mhz, 300W max. Modes Cut Coagulation Blend Probes: Monopolar Bipolar

ESU Summary Modern ESUs have great flexibility, control, and feedback measurements to control cutting and stop bleeding (coag). Additional functions include fulguration and dessication BMET Tests include power measurements by simple devices such as EWH tester, or sophisticated tests by ESU Analyzers All testing is on fixed loads that don’t resemble actively changing tissue resistance, so surgeons may still complain Failure modes are most likely “traumatized” parts such as power cords, leads, and output power stages (or power supplies)

General Surgery The electrosurgical unit (ESU) is generally used in surgery. The laser is less efficient, less powerful, more costly, more bulky in the operating room The skill of the surgeon is a major factor in the selection of any surgical “knife.” (metal, ESU, or laser)

ELECTROSURGICAL UNITS The Electro Surgical Unit (ESU) cuts tissue by heat, created from radio frequency (RF) currents in the range of 100 kilohertz to 5 megahertz. Surgical Functions: Incisions (cutting deep into tissue) Excisions (removing surface growths) Coagulation (stopping blood flow) Desiccation (drying tissues) Fulguration (charring tissues)

Efficient, Powerful, Economical ESU is the most efficient, powerful, and economical of the thermal knives presently available. It is most widely used in general surgery and in cutaneous surgery. It is capable of fast cutting through massive tissue and of effective hemostasis (stability). Adverse side effect is thermal tissue damage.

Bovie Operation 1 Transformer steps up the line voltage, which is then applied across a spark-gap gas tube. High-voltage AC peaks ionize gas in the spark-gap, making low resistance and high current. This drops the voltage and extinguishes the gas, which now has high resistance again, so cycle starts over. This “limit cycle” repeats at RF frequencies, where oscillation frequency is set by series capacitor and primary coil.

Bovie Operation 2 When a return plate is used in surgery, the voltage is taken off the primary coil shown in the figure. The Oudin coil is a secondary coil that increases the voltage by transformer action, so that fulguration can be done without the return electrode. For other surgical procedures (cutting) the patient return plate is used.

Bovie Operation 3 During surgery, the RF current exits the relative sharp electrode, dissipating between 50 and 400 W of power into the tissue to make an incision. The cutting electrode is about 0.1 mm thick and contacts several millimeters of the tissue. Voltage of several thousand volts sets up a line of small sparks and raises the tissue temperature, such that the tissue separates as the cells vaporize.

Bovie Operation 4 The electrode—tissue interface is illustrated below.

Tissue Vaporizing The cells themselves form capacitors with a conductive electrolyte inside separated by a nonconductive membrane from the interstitial fluid (fluid between cells) That membrane passes the RF currents into the cell, causing it to vaporize.

Optimal Cutting Currents 1 If the voltage is high enough and is passed quickly enough through the tissue, the thermal damage is almost imperceptible. However, if one goes slowly or if the voltage is too low, thermal tissue damage will result. Surgeons might tell a BMET the cut isn’t “smooth” – they operate by feel, and there are several “mixes” of AC current This could mean the ESU RF power output stage has damage

Optimal Cutting Currents 2 To achieve hemostasis, a certain amount of damage is desirable seals the wound, or “cauterizes” The control of this factor is key to good surgical technique using the ESU. Modern ESU’s have complex RF modulation controls

Modern ESU RF Generators An RF oscillator still forms the basis for a modern ESU, but the AC waveform is modulated to give more control: Cut mode — Pure sine wave, for cutting with the least coagulation (allows bleeding) Coag mode — Pulsed sine wave, low-duty cycle, for coagulation of bleeding tissue (stops bleeding) Blend 1 mode — Modulated sine wave, for coagulating as the tissue is cut. Blend 2 mode — Modulated sine wave, for coagulating as the tissue is cut.

Modulated RF Modes Coag mode—Pulsed sine wave, low-duty cycle, for coagulating bleeding tissue. Blend 1 mode—Modulated sine wave, for coagulating with cut, moderate duty cycle Blend 2 mode—Modulated sine wave, for coagulating with cut, higher duty cycle Cut mode—Pure sine wave, for cutting with the least coagulation.

Cut Mode To cut tissue, the switch is usually set to the cut position This connects the RF voltage to the amplifier, which then delivers to the active electrode 1,000 to 8,000 volts peak-to-peak AC at from 100 kHz to about 2 megahertz. High-density currents emerge from the active electrode to do the cutting.

Return Current Dispersion 1 A blade electrode is moved through the tissue like a knife to do the cutting. Knife high-density currents disperse throughout the conductive fluids of the body and return at a low-current density to the patient return electrode to complete the circuit back to the ESU. Return electrode has uniform contact to avoid burns due to current concentrations

Return Current Dispersion 2 The return electrode is large in area and gelled to keep the skin resistance low and the region cool.

Ground Isolation to Avoid Burns The RF circuit is isolated from ground in newer ESUs So if the patient’s body comes in contact with ground (through a metal operating table, for example), there should be no current flow (or burns) In some older machines, there is no ground isolation, so a patient touching grounded table could mean burns But stray capacitance can still lead to some ground current even in modern equipment A tingle can result from touching active ESU patient

Cut Mode is Smoothest In the cut mode, the ESU continuously delivers its highest average power. Thus, at every instant as the blade is moved along, the tissue receives the same treatment. This results in a smooth cut with no jagged edges. Complaints that cut isn’t smooth could mean modulation or power output problems (or operator error in setting)

Coag Mode is Slower, Ragged In the coag mode, the average power delivered to the tissue is reduced from cut mode, as AC pulses are “on” for only 15% to 20% of the time instead of 100% A blunt (ball-tipped) electrode may also be touched to the tissue The larger surface gives less-dense current and doesn’t vaporize cells

Coag Mode Automatically pulsing the AC voltage on 20% and off 80% slows the cutting process, and allows the heat to propagate into the tissue to form the coagulum. The depth of coagulation also depends on how long the electrode contacts the tissue, because tissue damage is caused by heat propagating into the tissue. The edge of the cut will tend to be ragged, and some browning of the tissue will be visible

Blend Modes 1 and 2 Blend modes 1 and 2 are used to cut and seal “bleeders” simultaneously. Blend 1: The pulsed AC ON time to OFF time ratio is 25/75 (25% duty cycle) so cuts more than Coag, but seals blood better. Blend 2: The pulsed AC ON time to OFF time ratio is 50/50 (50% duty cycle), so cuts half the time with less “blood sealing” than Blend 1, but smoother cut.

Fulguration This word means “lightning,” and this is exactly what the fulguration spark is. The air between the body and a sharp ESU pencil ionizes when the electric field intensity exceeds 3000 kV/m, like lightning This ionized “plasma” chars the unwanted tissue A return electrode is not needed at the high voltage, but does improve current flow

Dessication If the ESU needle electrode is introduced into a mass, such as a vascular tumor, the currents will inject power that raises the fluids to above 100 C, vaporizing and dehydrating the lesion. Since lipids and proteins require more than 500 C to decompose, the surgeon has a mechanism to control dehydration. He or she keeps the temperature below 500 C so as to not decompose the tissue while dehydrating it.

Minimum Testing: Lights & alarms Electrode monitoring Arc on wet soap Coagulation, Cut & Blend modes Footswitch and handpiece operation

Surgical Techniques, Problems The use of an ESU is very dependent on the surgeon preferences, so one surgeon may see an ESU “fault” where another doesn’t. The use of the ESU is a refined surgical skill, developed by practice. ESU machines from different manufacturers have different waveform shaping, amplitudes, duty cycles, and crest factors A new surgeon or new ESU machine may see a machine problem that really just requires re-training to the new machine (new settings) The BMET must have an ESU tester to prove all modes are OK

ESU Performance Testing 1 Also, calibration of the power levels is done into a test load of fixed resistance, even with sophisticated testers But the actual tissue resistance depends upon its type as well as the electrode contact area pressure against the tissue. Some high-end ESU machines use active feedback to measure resistance and adapt power output All of these factors influence how much power actually gets into the tissue.

ESU Performance Testing 2 The energy then getting into the tissue depends on the duration of contact, which is his “fine control” The effect of the RF current on the tissue cannot be controlled completely from the ESU machine It is controlled by the surgeon who has experience in the procedures required and with the specific ESU being used

Patient Lead Classifications Monoterminal — An ESU with one wire for patient contact. Bi-terminal — An ESU with two wires for patient contact. Active electrode — The electrode that delivers treatment to the surgical field. Patient electrode — The large surface area return electrode. Monopolar electrode — An active electrode that uses a patient electrode to complete the circuit. Bipolar electrode—Two electrodes in close proximity and of approximately the same size that are arranged so that the current tends to be confined to a small region between the two electrodes (used for precise coagulation, such as removing skin growths).

Lead Resistance-to-Ground Check The resistance of both leads to ground should exceed several megohms, as a check for ground isolation. This will insure that any alternative path from the patient to ground would not complete the circuit, to prevent burn injuries at the point of patient-to-ground contact. Someone may set the return plate on a radiator, or it may make contact with a grounded bed or operating table.

Split Return Pad with Monitor Serious burns can result from Patient Return Electrodes which make poor body contact, or none at all. One solution is to use two “split” return pads, and monitor the resistance between the pads. The ESU will show a fault and not deliver current If the resistance doesn’t match the expected skin resistance – due to poor contact of either pad (or shorted pads on a radiator!) The Cost: Every instrument failure. safety “interlock” gives another mode of

Common Problems: Patient Burns Broken cables Faulty foot switch or hand piece Blown power transistors Adjustments (REM etc.) Fires

Safety: Safety is extremely important; High power spark in O2 rich environment Possible high current density for patient Improper use

Electrical safety methods: Electrical Isolation Return electrode resistance REM electrode