ENTC 4350

1. ENTC 4350 ELECTROSURGICAL UNITS (ESUs)

2. 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 and less understood due to a smaller case history data base work to discourage its use in many cases. • So much depends upon the skill of the surgeon in the use of any surgical knife, that the selection is often a professional judgement.

3. ELECTROSURGICAL UNITS • To do surgery, the electrosurgical unit (ESU) delivers, through an electrode, radio frequency (RF) currents in the range of 100 kilohertz to several megahertz. • It is capable of • Making incisions and excisions and • Performing • coagulation, • desiccation, and • fulguration.

4. It 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. • Its primary adverse side effect is thermal tissue damage.

5. The original ESU was invented by William Bovie.

6. The transformer, connected to the 60-cycle power mains, steps up the voltage, which is then applied across a gas tube.

7. The high voltage during the peak parts of the cycle ionizes the gas, lowering its resistance and thus drawing a current. • This, in turn, drops the voltage and extinguishes the gas, which then rises again in resistance. • This oscillation occurs at RF frequencies. • That oscillation is selected by the series capacitor and primary coil.

8. 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 the patient return plate is used.

9. 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. • The voltage, ranging from 1,000 to several thousand volts, sets up a line of small sparks and raises the tissue temperature such that the tissue parts as the cells vaporize.

10. The electrode—tissue interface is illustrated below.

11. The cells themselves form capacitors with a conductive electrolyte inside separated by a nonconductive membrane from the interstitial fluid. • That membrane passes the RF currents into the cell, causing itto vaporize.

12. 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.

13. To achieve hemostasis, a certain amount of damage is desirable. • The control of this factor is key to good surgical technique using the ESU.

14. An RF oscillator forms the basis for a modern ESU.

15. The device has several modes: • Cut mode—Pure sine wave, for cutting with the least coagulation. • Coag mode—Pulsed sine wave, low-duty cycle, for coagulating bleeding tissue. • 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.

16. The device has several modes: • Cut mode—Pure sine wave, for cutting with the least coagulation. • Coag mode—Pulsed sine wave, low-duty cycle, for coagulating bleeding tissue. • 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.

17. Front panel switches enable the operator to select the mode desired.

18. 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.

19. A blade electrode is moved through the tissue like a knife to do the cutting. • The 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.

20. The return electrode is large in area and gelled to keep the skin resistance low and the region cool.

21. The RF circuit is usually isolated from ground; so if the patient’s body comes in contact with ground (through a metal operating table, for example), an alternative path for the return current would not be established.

22. In some machines, especially older models, the return electrode is grounded. • In this case, if the patient’s finger would also become grounded, an alternative path would be established, which could cause a burn on the finger.

23. In any case, at these frequencies, there is always some stray capacity that could connect the return lead to ground. • With proper design and careful operating procedure, this can be reduced to insignificance. • Because of this effect, one sometimes feels a tingle when touching a person who is receiving ESU treatment.

24. 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.

25. Coag Mode • In the coag mode, the average power delivered to the tissue is reduced from that delivered in the cut mode. • A blunt electrode may be touched to the tissue to produce a coagulum that establishes hemostasis.

26. The power per unit area at the tissue surface is lower than that from the blade in this case. • Therefore, the tissue is raised enough to produce coagulum without vaporizing it.

27. The coag mode may also be established by delivering pulsed energy at a low duty cycle (the ratio between the on time and the period between the starting times of successive pulses) of between 15 and 20 percent. • Automatically turning the voltage on and off like this slows the cutting process, and allows the heat to propagate into the tissue to form the coagulum.

28. The depth of coagulation 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. • There are low resistance paths for the electrical current and the heat, such as along a blood vessel or a nerve going through fat, which can cause deep coagulation.

29. Blend Modes • The blend modes are used when one desires to cut and seal bleeders simultaneously. • The lower average power delivered reduces the cutting and increases the propagation of heat into the tissue to coagulate the blood.

30. In this mode, bursts of voltages high enough to establish a cutting spark are delivered at a duty cycle above about 25 percent. • In this case, cutting would occur about one fourth of the time; and the rest of the time, the heat generated would propagate into the tissue, creating a layer of coagulum along the incision to control bleeding. • The degree of coagulation can be monitored by observing the browning of the tissue.

31. The incision cut may be less smooth than in the cut mode. • The sloughing of the tissue under the cut may not be visible from the surface.

32. Less coagulation and faster cutting may be achieved by selecting the blend 2 mode, which may have a duty cycle of about 50 percent. • This would increase the time the cutting spark is activated and leave less time for coagulation to occur.

33. Fulguration • The Latin word fulgur means “lightning,” and this is exactly what the fulguration spark is. • The air between the body and a sharp ESU electrode ionizes when the electric field intensity exceeds 3,000 kV/m.

34. When lightning strikes the earth, the bolt occurs when a charge on a cloud differs sufficiently from that in the earth. • With respect to an ESU needle electrode, the body is a charged mass of ionic fluid separated by an insulating layer of skin and air. • The inside of the body is the ground, just as the earth is ground for lightning.

35. It is not necessary to have a return electrode to the instrument any more than one would need a return path to the cloud during lightning. • The currents travel in and out of the body at the radio frequency of the ESU unit.

36. However, if one does use a return electrode, this adds another path for the current and increases the current in the spark. • Likewise, stray capacity affects the size of the spark.

37. 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.

38. Sealing Bleeders • Bleeders up to 2 mm in diameter can be stopped if they are clamped with a metal hemostat. • To make instantaneous coagulation, the hemostat is touched with the ESU blade.

39. This process is also done with an electrocautery hemostat. • This device consists of a conductive forceps that serves as the active electrode. • The forceps is clamped over the bleeder, and the current is applied to seal it.

40. The current returns to the ESU through a large-area patient electrode.

41. Surgical Techniques • The surgeon has control of the cutting and coagulation by the stroke he or she uses. • One surgeon may prefer to use a coag-blend mode throughout the procedure and control the cutting and coagulation by the force exerted on the blade, the depth of the blade in the tissue, and the duration of contact. • The use of the ESU is a refined surgical skill, developed by practice.

42. The different ESUs from different manufacturers produce different waveforms. • The waveforms have different amplitudes, pulse duty cycles, and crest factors (the ratio between coag and cut waveform amplitudes). • Thus, a surgeon trained on one machine may have to be retrained to use another machine.

43. The practical consequence of this for attendants is that they should not change the ESU without informing the surgeon. • Even different machines from the same manufacturer can differ in subtle ways.

44. Also, calibration of the power levels is done into a test load of fixed resistance. • But, in practice, the tissue resistance depends upon its type as well as the electrode contact area pressure against the tissue. • All of these factors influence how much power actually gets into the tissue.

45. The energy then getting into the tissue depends on the duration of contact. • The effect of the RF current on the tissue cannot be controlled completely from the machine; • It must be controlled by the surgeon who has experience both in the procedures required and with the specific ESU being used.

46. Patient Leads • Traditionally, the leads have been classified as either monoterminal or biterminal. • This is because some ESUs have only one lead and are used exclusively for fulguration.

47. The lead classifications are as follows: • Monoterminal—AnESU with one wire for patient contact. • Bitermmal—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.

48. Each electrode is connected to a separate insulated wire but may be packaged in one cable. • This type of electrode is used for precise coagulation.

49. The arrangement of the patient leads on most modern ESUs is illustrated in (a). • The patient leads are usually isolated so that any leakage currents at power line frequencies would be suppressed.

50. The resistance of both leads to ground should exceed several megohms. • The effect of this would be that any alternative path from the patient to ground would not complete the circuit so as to cause burn injuries at the point of patient-to-ground contact.