Principles of Electrosurgery

Module

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Objectives

• Explain the fundamentals of electricity
• Describe various modalities of electrical energy used in surgery
• Choose an appropriate energy modality for a given clinical situation
• Demonstrate patient safety protocol when using electrosurgery

Principles of Electrosurgery

• Employs the use of high frequency electric current (~350 kilohertz)
• Requires a complete closed circuit for the flow of electricity
• Transfer of kinetic energy to heat tissue and achieve a desired effect
• Effects defined by tissue characteristics, and parameters of electron flow

Check Your Knowledge

Which statement best describes the use of electrosurgery in modern medicine?

1. It rarely is associated with adverse patient outcomes
2. It cannot be used in patients with a BMI > 50 due to increased resistance
3. It requires general anesthesia
4. It is a complex technology that is not well understood by many surgeons

What is the proper name for what’s conveyed in the image?

1. Electrocautery
2. Bovie surgery
3. Cautery
4. Electrosurgery

Important Distinction

Note that in the OR, we use ELECTROSURGERY, and NOT electrocautery – an electrocautery hand-held instrument shown below. (used in dermatology frequently – for example, to drain an infected toenail)

Electrocautery or Electrosurgery?

• Electrocautery is a direct current that comes from a power source (usually a battery) that heats an instrument. The heat, but not any current, is then transferred to patient

• Electrosurgery is an alternating current that heats tissue by conduction of electric current. The patient is part of the electrical current.

Electricity Basics: Fundamentals of Electricity

• Electricity must complete circuit or it will not flow
• Electricity always returns to ground
• Electricity follows the path of least resistance
• W(power or watts)=V(electromotive force or voltage) x I (electron flow or current)
• I = V/R(resistance)
• Substitution: W=V2/R

As resistance increases, in order to maintain the power to perform a function, the electromotive force or voltage increases exponentially.

In electrosurgery, resistance is a function of tissue characteristics (eg, water content).

Key Point

• Electrosurgical units (ESU) used in operating rooms convert standard electrical frequencies from the wall outlet, which are 50 to 60 Hz, to much higher frequencies, 500,000 to 3,000,000 Hz
• This is important to minimize nerve and muscle stimulation, which occurs at electrical currents below 10,000 Hz

Alternating Current Frequency Spectra

Generator Current

So now that you know about current, what can we do with the current from the electrosurgery generator?

• Cut tissue
• Coagulate tissue
• Desiccate tissue
• Fulgurate tissue

Requirements for Electrosurgery

Basic Principles of Electrosurgery: Bipolar

Monopolar Electrosurgery

Bipolar Electrosurgery

Monopolar Versus Bipolar

Monopolar

• Handpiece is active electrode and ground pad is return electrode
• Need ground pad to have full contact with patient
• Heat conduction is higher
• Good for dissection
• Greater tissue penetration
• Greater area of coagulation
• Coag and cutting options
• Blunt dissection with instrument 

Bipolar

• Active and return electrodes are on same instrument
• Do not need ground pad
• Lower voltages can be used
• Less thermal spread
• Cannot use for cutting tissue
• Not good for dissecting
• Less tissue damage at application site
• No chance of capacative coupling
• Less smoke
• Less interference with pacemakers

Check Your Knowledge

Do you need a grounding pad with bipolar waveform?

1. Yes
2. No 

Bipolar Energy

Bipolar Circuit

• Instrument contains both the active and the return electrode
• Does not require a patient return electrode pad
• Electrosurgical effect confined to tissue between the instrument electrodes
• Adjacent tissue is subject to thermal effects of heat generated

Common Bipolar Energy Devices

• Kleppinger forceps for tubal cauterization or bleeders at laparoscopy

• Bipolar energy examples used to ligate large pedicles in laparoscopic cases (TLH, oophorectomies, etc.)

Bipolar Example

Monopolar Energy

Monopolar Circuit

• Instrument contains an active electrode
• Current disperses and passes through patient’s body to the return electrode that carries electrical energy back to generator
• Tissue effect concentrated at active electrode tip (area of greatest current density)
• Adjacent tissue may be affected by unintended energy paths

Waveforms

What’s the difference between cut and Coag current waveform?

What color on the pencil (foot pedal) is CUT?

Cut Versus Coag

• Cutting waveform
  • Continuous, unmodulated and undampened

• Coagulation waveform
  • Interrupted and dampened
  • Current is on only 5% of the time and off 94% of the time during a duty cycle
• The electrosurgery generator has both cutting and coagulation capabilities, which the surgeon can select by adjusting voltage and waveform

Electrosurgical Modes

• Generator delivers different waveforms
• Cut (continuous)
  • Continuous sinusoidal waveform
  • Lowest voltage

• Coagulation (interuppted)
  • Interrupted sinusoidal waveform
  • Active "on" current < 10% of time

• Blend
  • Shorter off cycles than coagulation

• Here’s what the current looks like when you choose “COAG”

And here’s “CUT”

Monopolar Tissue Effects

	No Contact	Contact
Cut (continuous)	Vaporization	Desiccation
Coagulation (interrupted)	Fulguration	Desiccation

 

• Vaporization
  • Cellular temperature rises rapidly above 100℃ causing cell rupture and release of steam
  • Low voltage
• Dessication
  • A form of coagulation by drying out the cell under 100℃ leading to cell dehydration and shrinkage
  • Cut waveform preferred to keep voltage lower
• Fulguration
  • Form of coagulation from arcing sparks to tissue surface causing charring and carbonization of superficial tissue
  • High resistance, high voltage

Cutting Waveform

• A high current, low voltage continuous waveform
• Divides tissue with least amount of lateral thermal spread
• Minimal depth of necrosis
• Non-contact
• Lowest possible voltage is used
• Uses: incisions, dissection, adhesiolysis, salpingostomy, LEEP, etc.
• Bipolar cautery uses only a cutting waveform

Cutting Mode in More Detail

• In cutting mode electrode touches the tissue, and sufficiently high power density is applied to vaporize its water content. Since water vapor is not conductive under normal circumstances, electric current cannot flow through the vapor layer. Energy delivery beyond the vaporization threshold can continue if sufficiently high voltage is applied (> +/-200 V) to ionize vapor and convert it into a conductive plasma. Vapor and fragments of the overheated tissue are ejected, forming a crater
• Electrode surfaces intended to be used for cutting often feature a finer wire or loop

Examples of Cutting Current in Use in Gynecology

• Laparoscopy: divide tissue

• Hysteroscopic myomectomy

Coag Waveform

• Coagulation is performed using waveforms with lower average power, generating heat insufficient for explosive vaporization but producing a thermal coagulum instead
• Electrode “footprint” or shape is wider than a cutting needle, so electrons are placed on a a larger surface and do not condensate at the end as with a monopolar needle
• Dessication
  • Deep coagulation (note that any waveform can cause this)
• Fulgaration
  • Non-contact of electrode while pressing coag
  • Sparks “ spray ” to tissue and cause a superficial eschar with minimal necrosis
  • Good for oozing capillary beds as on muscle

Dessication

• The electrode touches tissue open to air and amount of heat is lower than that required for cutting. The tissue surface and some of the tissue more deep to the probe dries out and forms a coagulum. Used to treat nodules under the skin where minimal damage to the skin surface is nodules under the skin where minimal damage to skin surface is desired
• Sort of like a hard boiled egg

Dessication Example on Toe Lesion

Mostly used in dermatology

Fulguration Mode

• Electrode is held away from the tissue, so that when the air gap between the electrode and the tissue is ionized, an electric arc discharge develops
• With this approach, the burning to the tissue is more superficial, because the current is spread over the tissue area larger than the tip of electrode
• Under these conditions, superficial skin charring or carbonization is seen over a wider area than when operating in contact with the probe, and this technique is therefore used for very superficial or protrusive lesions such as skin tags

What is Blend?

• We are not actually blending the current
• Combines the cut and coag tissue effects
• Variation of time current is on during a duty cycle
  • Blend 1 is 80% on and 20% off
  • Blend 2 is 60% on and 40% off
  • Blend 3 is 50% on and 50% off
• As duty cycle (the amount of time current is on) decreases, the voltage must increase as long as power remains constant

Waveform

Controlled Factors During Electrosurgery

During electrosurgery, the surgeon can control:

1. Waveform
   • Cutting or coag or blend
2. Electrode Size
   1. footprint of your instrument = bovie tip
3. Power setting on generator
4. Time that you hold electrode to tissue
5. Surgical technique

The surgeon controls waveform, that is, cut versus coag versus blend

Electrosurgical Tissue Effects

Electrode Size

The surgeon controls electrode size, or the tip of the bovie.

Power Setting Controlled

Power Setting Examples

• Laparotomy: Typically 30-35 for bovie handpiece
• Laparoscopy: Use lower currents: 15–25 is usually fine
• LEEP: use higher currents so less thermal spread (80 cut is good for the LEEP and 50 coag is good for the ball electrode for hemostasis)
• Hysteroscopic myomectomy with monopolar loop electrode – need high power since working in fluid, ~100–120 cutting waveform

Time and Surgical Technique Controlled

Complications of Monopolar Energy

Unintended Energy Paths

• Direct coupling - when two conductive materials touch during electrical activation passing current from one to the other
• Insulation failure - a crack, tear, or break of the insulting layer around an electrosurgical instrument allowing an alternative path of electrical circuit completion
• Capacitive coupling - when two conductors are separated by an insulator a charge can build up in the coupled conductor and discharge to ground causing unintended energy release

Direct Coupling

Direct coupling can occur if the tip of the active electrode comes in direct contact with another metal instrument or conductor within the surgical field.

Direct Coupling at Laparoscopy

• If the active electrode accidentally touches or arcs to the laparoscope, the entire laparoscope becomes electrified. If the laparoscope is placed through a metal cannula, the current on the laparoscope will simply flow to the metal cannula and then harmlessly to the patient's abdominal wall and return electrode.
• If, however, the laparoscope has been placed in a nonconductive or plastic cannula, the current transferred from the active electrode to the laparoscope will not flow to the patient's abdominal wall; instead, again out of the field of view, the current will be transferred to the bowel or other internal tissue touching the electrified laparoscope. If the density of current is high enough, it will result in significant thermal injury

Direct Coupling: Touches Laparoscope

Direct Coupling: Insulation Failure

Direct Coupling

Capacitive Coupling 

• Capacitive coupling is the induction of stray current to a surrounding conductor through the intact insulation of an active electrode (e.g., active electrode—insulation—metal trocar sheath). The magnitude of the coupled charge is proportional to the amount of voltage and trocar diameter.
• In simpler terms: Current transferred from an active electrode through intact insulation and into adjacent conductive matter such as bowel.
• Almost always occurs with coag: noncontinuous, so a higher voltage

Risk Factors for Capacative Coupling

• Longer instruments
• Thinner insulation
• Increased voltage
• Narrow trocars (5 mm)
• Hybrid sleeves
• Do not activate the current until your instrument is touching the tissue

Complications: Capacitive Coupling

Capacative Coupling

Patient Safety

• Active electrode
  • Keep in cradle when not in use
• Return electrode
  • Place as close to operative site as possible
  • Place on large muscle mass
  • Ensure good contact with skin (increased surface area, decreased tissue effect)

Patient Safety

• Do not secure power cord for active electrode using metal instrument
  • Creates opportunity for capacitive coupling
  • Potential for patient burn or drape fire
• Use short intervals of energy application
  • Allows for dissipation of coupled electrons
  • Minimizes adverse effects of capacitive coupling

Know How it Works, and Use It Carefully

• Never activate your current until it is touching tissue
• Keep active electrode away from the tip of your scope or other instruments
• Keep active electrode in view at all times
• Avoid coag when possible at laparoscopy

Conclusions

• Don’t be afraid of using electrosurgery – it is safe, versatile, and low cost
• It’s up to you to know how it works and maintains patient safety

Developed in association with The Association of Professors of Gynecology and Obstetrics.

Last updated March, 2019