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Biomed 101: Infusion device basics

Dr. William T. Bovie and Dr. Harvey Williams Cushing developed the first ESUs in the 1920s. Early ESU units used spark gaps to control RF energy. ESUs now allow for surgeries with more preci- sion and less blood loss...

Tue Sep 04 2012By TechNation Magazine

An electrosurgical unit (ESU) uses high radio frequency (RF) electric currents to cut, coagulate, dehydrate or fulgurate tissues. This device is used in almost all surgical procedures and is especially useful in procedures such as minimally invasive surgery (MIS), where mechanical cutting is difficult. In order to avoid or reduce blood loss during surgery, an ESU can be used as an alternative to a conventional steel scalpel.

Electrosurgical equipment uses a high RF voltage and current to cut and coagu- late the tissue at the same time. When the electrical current is passed through the tissue, it heats up, resulting in evapo- ration of the water, which ultimately destroys the cells. Thus, the process of cutting, clotting and dehydrating the blood cells and tissues is achieved with minimal blood loss.

Dr. William T. Bovie and Dr. Harvey Williams Cushing developed the first ESUs in the 1920s. Early ESU units used spark gaps to control RF energy. ESUs now allow for surgeries with more preci- sion and less blood loss.

Electrosurgery Terms

Electrosurgery – RF current is used to heat the tissue, ultimately achieving dehydration of the tissue. The current must pass through the tissue to produce the desired effect.

Electrocautery – Uses electricity to heat an object that is then used to burn or sear the tissue to stop bleeding. An electrocautery unit is a low voltage device in which electrical current heats the electrode, which is used to cauterize the tissue.

Bovie – A registered trademark name of one of the first ESU models manufacutred. It has become a trade name of electrosurgical units.

Current Density – The intensity of the cur- rent as it passes through the tissue. The current concentration/density is high at the cutting site and low at the return electrode site.

Duty Cycle – The percentage of time in which the ESU current is on versus one complete cycle of time. ESUs range from 25 percent to 100 percent duty cycle.

Active Electrode- The active electrode, or hand piece, is where the power is dissipated to the tissue of the patient. Has a high current density due to the small surface area.

Return Electrode- Also called the dispersive electrode, this is the electrode placed on the patient to return the cur- rent back to the ESU. Has a low current density due to the large surface area.

Eschar – Thermal charring of the tissue.

Patient Impedance – The total opposition (resistance, inductance, and capacitance) that the ESU current passes through.

• Normal range for an ESU: 100 – 1000 ohms
• Average range (used for calibration): 300 ohms
• If the impedance gets too high, the unit will not work.

Surgical Smoke – Created when tissue is heated and the cellular fluid is vaporized by the thermal action of an energy source. Surgical plume is created by lasers. Surgical smoke and plume can contain toxic gases and vapors, such as benzene, hydrogen cyanide and formal- dehyde, bioaresols, and dead and living cellular material and viruses.

Types of electrosurgical units

Hyfrecator Unit - A low powered ESU used in an office setting for minor skin surgeries, including wart removal, sebaceous gland disorder surgery, destruction of superficial veins, certain types of plastic surgeries and destruction of skin cancers, such as basal cell carcinoma.

Grounded ESU Generator – The current passes through the patient and returns to the generator, which is linked to ground. The problem is the current can go to any grounded object other than the pad (electrocardiograph (ECG) electrodes, surgical table, any metal objects) and cause alternate site burns. If the return pad is not placed on the patient, or is not in contact with the patient’s skin, a ground referenced generator will still send current through the active electrode and into the patient. If the patient is grounded by any other means, the current goes wherever it finds a path, this may again result in patient burns at alternate sites if current densities are high. Ground referenced generators are considered to be outdated technology but are occasionally found in some ORs.

Isolated Power ESU Generator – These devices isolate the current from ground and do not allow significant current to seek alternate paths to ground. The current must return through the return pad to the generator. Although isolated ESU generators are a great improvement over ground-referenced ESU generators, improperly placed return pads may still cause burns to the patient.

Argon Beam ESU - The Argon Beam ESU was invented in the late 1980s. A stream of argon gas is used to couple RF energy from ESU to improve the surgical effectiveness of the electrosurgical current. This creates a more uniform surface coagulation, without damage to lower tissues. Gas and current are controlled by the surgeon at the hand piece. Argon- enhanced electrosurgery is used in some of the more “bloody” surgeries to effectively cauterize large areas quickly.

Modes of Operation

Monopolar Output – In this traditional mode, current flows from the surgical site, back to the ESU unit through the use of a return electrode.

Bipolar Output – In this mode, the active and return electrodes are on the same instrument. NO return electrode is used in this mode, which is used at low power for delicate procedures. Not all ESUs have this option. The bipolar output is a separate plug than the monopolar output. This is a safety feature to prevent the bipolar instruments (which are low power) from being plugged into the higher powered monopolar plug.

Cut Pure – The cut waveform has 100 percent duty cycle. A higher power setting provides very clean and deep cuts, with very little coagulation and thermal charring.

Blend – A cut waveform, with intermittent bursts of coagulation to achieve cutting and coagulation simultaneously. Blend 1 provides deep cut, with some coagulation. Blend 3 provides cut with increased coagulation. Blend 3 provides cut with full coagulation and very deep thermal charring.

Coag – This mode provides full coagulation with no cut and very deep thermal charring. Pin-point is a specialty coag mode, available on some ESUs, where small amounts of tissue are dried out from the active electrode in contact with the tissue. Spray is a specialty coag mode, available on some ESUs, in which small amounts of tissue are dried out from the active electrode in contact with the tissue.

Tissue Effects-The versatility of waveforms available with modern generators allow surgeons the opportunity to create a multitude of tissue responses and results.

Cut – Cut creates a separation of tissue, similar to the effects of a traditional steel scalpel. There is very little eschar. The higher the power settings, the deeper and wider the cuts.

Desiccate – A form of coagulation, in which direct energy application slowly drives water out of the cells, dehydrating the cells and causing necrosis to the tissue. The active electrode must remain in good contact with the tissue. The probe tip heats cell tissue past the temperature at which cells can survive.

Fulgurate – A form of coagulation, where arcing or sparking of energy above the tissue is used to create a surface char- ring. The active electrode is not in con- tact with the tissue. The surgeon dabs at the tissue to stop the bleeding. There is a deep eschar of the tissue. Sparks result in far higher temperatures at the point of contact, causing very high temperatures and carbonization of the tissue immediately at the spark-contact point and below it.

ESU Accessories

Active Electrode (Hand Piece) – Delivers the RF current from the generator to the surgical site. The hand piece has both cut and coag settings.

Return Electrode (or Dispersive Electrode) – Provides a path for current to return safely to the ESU.

Foot Switch – Allows the surgeon to activate the Cut and Coag features from a switch that they control with their foot.

Safety

ESUs produce very high current that can cause patient and operator injury if not properly used and maintained. Many problems have been associated with the use of ESUs, such as burns at the return electrode site. Surgical fires can be caused by ignition of flammable materials used in the operating room. Interference to the ESU from devices such as pacemakers and ECG monitoring systems has been a problem in some cases. There is also risk of a gas embolism when using argon beam ESU. Some of these problems can be avoided by following simple safety procedures and precautions, which are described below.

Return Electrode Monitor (REM) – A circuit that measures the impedance of the return electrode. If the impedance is greater than 30 ohms, an alarm will activate and the ESU will not operate. A REM monitor uses a special type of return electrode, which has two separated surface areas.

Return Fault Monitor – A a circuit that measures the RF current leaving and returning from the ESU. If all the current leaving does not return, the alarm activates and the ESU will not operate. It functions like a ground fault circuit interrupter (GFCI).

When handling ESUs, keep the following safety tips in mind:

• ESUs should not be used in the presence of flammable agents or in oxygen enriched environments.
• The hand piece should always be placed in the nonconductive holster when not in use.
• Rubber catheters or other materials should not be used as a sheath on active electrode tips.
• Use caution, as radio frequency is not always confined by insulation.
• Cords should never be wrapped around metal instruments, as RF cur- rent can pass into the metal instrument, causing burns.
• Cords should never be bundled together.

Preventative Maintenance

PM should include a visual inspection of:
1. Chassis/Housing
2. Mount
3. Casters/Brakes
4. ACPlug/Receptacles
5. LineCord
6. StrainReliefs
7. Circuit Breakers/Fuse
8. Cables
9. Fittings/Connectors
10. Dispersive Electrodes
11. Filters
12. Controls/Switches
13. Indicators/Displays
14. Dispersive Cable Continuity Monitor 15. Audible Signals
• Activation indicator
• Dispersive cable continuity monitor

The following electrical safety tests should be performed:

1. Grounding Resistance: ≤ 0.5 Ω
• Chassis:≤0.5Ω
• Footswitch:≤0.5Ω
• Return electrode:>20MΩ
2. Chassis Leakage Current: ≤ 100 A 3. Output Isolation: Manufacturer’s Specification or ≥ 80%

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