Electrosurgery Units (ESU’s)
2016-01-16 rev
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2016-01-16 added key points page
Electrosurgery Units (ESU’s)
and their variants
© D. J. McMahon 150107
rev cewood 2016-01-16
Key Points
Electrosurgical Units:
- typical output frequency of modern ESU’s
- difference in return circuit between of monopolar and bipolar modes
- difference in waveforms between Cut, Coag, and blend modes
- principle of Return Electrode Monitoring
- fulguration, desiccation, ablation, ligature
- know what the “crest factor” is
- Argon beam coagulators
- hazards of return electrodes
- know the principle of the harmonic scalpel
- four essentials of maintenance of ESU’s
A little history:
Dr Harvey Cushing
Wm. Bovie, PhD
Electrosurgical Theory A few terms:
Electrosurgery: application of a high-frequency electrical current to
tissue to stop bleeding or to cut tissue.
Ablation: removal of a layer of tissue
Cautery: any application of heat to seal bleeding tissue
Coagulation: formation of clot to seal bleeding tissue
Desiccation: to dry-up (in the sense of removing fluid & blood)
Eschar: dead, charred tissue
Fulguration: use of sparking electrosurgery to desiccate tissue
Ligature: tying or binding something tightly; sealing a vessel with ESU
Electrosurgical units are
radio frequency (RF) generators:
Typically 450-500 kHz, but may be as high as 5 MHz (plastic surgery)
higher frequency → finer cut & less ancillary damage
The basic idea: ESU’s are RF generators
“ESUs are little radio stations”
Modulation of the RF for electrosurgical uses:
Most usage is either ‘Cut’ or ‘Coag’
Typical power range:
0 - 300 watts
Typical power range:
0 - 120 watts
Cutting action 100% duty cycle
Fulguration - highest voltage, lowest duty cycle.
Higher voltage creates more heat, causing hemostasis.
‘Crest Factor’ or ‘Peak-to-Average Ratio’:
Vpeak
Crest Factor =
VRMS
( eg, for a sine wave, CF = 1.41
pure DC would be 1.0)
Crest Factor indicates the ‘quality’ of a waveform.
A high CF indicates a less efficient or noisier waveform.
Different tissues offer different impedances to RF:
newer
automatic
ESU
typical
older
ESU
Basic Monopolar Electrosurgery:
Bipolar mode cautery - (typical for neuro)
(No need for a return pad)
Current flows thru
insulated forceps
Typical power range:
0 - 70 watts
RF Ablation:
removal of a layer of tissue
by use of localized RF
(typical for heart, liver)
Safety Issues in ESU’s:
> External “second site” RF burns
> Internal “second site” RF burns
> RF interference on adjacent devices
> Smoke plume
> Fire
Effective distribution of RF energy to the return pad
Tissue is burned where desired, but not on exit
Faulty contact of the return pad
Tissue is burned where desired, and at the pad.
BAD: Alternate Site Burns in a Basic Monopolar System
BETTER: The Isolated Electrosurgical System
Isolated system is deactivated if the return path is opened,
but burns can still occur if there is a path to ground.
BEST: the Return Electrode Monitoring (REM) system:
Typical REM signal is
80 kHz @ ~10µA
Return pad has two conductive plates, which are
monitored by the ESU for continuity.
aka ‘Contact Quality Monitoring’
Internal “second site” burns during endoscopy:
Hazardous practices to be aware of:
> “Buzzing” the hemostat: touching the active
electrode to a hemostat (or several hemostats)
clamped to tissue in order to save time. Can result in
shocks or burns.
> Wrapping the active lead wire around metallic
instruments.
> Stacking other medical electronics on or under the
ESU. RF from the ESU can trigger or alter the function
of other equipment.
ESUs are the primary source of ignition
for O.R. fires.
O.R. personnel are expected to take appropriate precautions:
- Eliminate the use of alcohol-based prep solutions
- Minimize “fuel loading” (flammable materials on & near the site)
- Minimize oxygen flooding around the surgical site.
- Have a fire extinguisher within ready access.
Smoke plume
Smoke plume from electrosurgery is just as much a
hazard to staff as is plume from lasers.
- Gases and particulates are toxic and carcinogenic.
OSHA and the AORN both encourage the routine use of
smoke evacuators, high-filtration masks, and eye
protection when using electrosurgical units.
- Compliance has not been universal.
Smoke-evacuation for ESU’s:
older Valleylab
current Valleylab
Buffalo ‘ViroVac’
Megadyne ‘Vac Plus’
Variations on
Electrosurgery:
Argon Beam Coagulators
- Essentially an enhanced ESU -
still has cut, coag, bipolar
- Use high voltage from the ESU to ionize a
stream of Argon gas
- Resulting plasma acts to provide a cleaner,
wider coagulating effect
Conmed’s Argon Beam Coagulator model 7500
Valleylab’s ‘Force Argon’
argon beam coagulator
used with their Force-FX
Variants on the ESU:
Valleylab’s ‘Ligasure’ vessel-sealing system
Proprietary Variants on
Electrosurgery
> Specific to a surgical procedure
> Often use a higher frequency
> 500kHz
> Usually a surgeon’s preference
> Usually use a unique disposable
Arthrocare Corp: ‘Coblator II’ for ENT surgery
Elmed 50-P: for Gynecological surgery
Medtronic Corp: ‘Cardioblate’ for ablation of heart tissue
Hologic Corp: ‘NovaSure’ for thermal ablation of the uterus
http://www.novasure.com/info/novasure-and-heavy-periods/novasure-patient-animation.cfm
Somnus: Somnoplasty (for snoring)
Conmed’s “Hyfrecator” Low energy cautery, without a grounding pad
Hyfrecator output modes:
Bipolar mode
Monopolar with return pad
Monopolar without pad
Variants on the ESU:
The Harmonic Scalpel
(Ethicon / Johnson & Johnson)
-- NOT an electrosurgical unit
-- Uses piezoelectric component to create an axial
vibration (at ~56 KHz) at the surgical tip
-- Use a variety of surgical probes and extensions
specific to the surgical procedure
-- Technically elegant; calibration pretty simple
Testing ESU’s:
(usually 500 Ω)
Generic ESU tester –
> Derives a small DC voltage from the RF from the ESU
> DC value is proportional to the output power
Functional Check:
1) Return Electrode Monitor
- Measure the resistance from the REM connector
to ground: should be >20M Ω.
- For single conductor return electrodes, verify that
the unit alarms and does not deliver power if the
resistance across the REM leads is >10 Ω.
- For “split pad” return electrodes, verify that the unit
alarms and does not deliver power if the resistance
across the REM leads is < 5 Ω or >150 Ω.
(Depends on the model - check the manual!)
Functional Check: 2) RF Power Output
- Use your analyzer or external non-inductive
resistors as appropriate load impedances for
Bipolar, Cut and Coag modes,
(typically 100Ω, 300Ω, and 500Ω).
- Test the unit in the Cut, Coag, and Bipolar modes,
at a low power and at maximum power.
- 5 watts for the low end
- maximums typically 300W for Cut,
120W for Coag
70W for Bipolar
- Power readings should be ±5W or ±15%
Functional Check:
3) RF Leakage (not 60 Hz current)
- Configure the analyzer for RF Leakage
- For any monopolar output, with appropriate load,
RF leakage should be < 100mA (not µA!)
- For the bipolar output,
RF leakage should be < 60 mA.
(Check the manual - some models allow 150mA)
Thorough testing an ESU includes power
output tests at a variety of load impedances,
in order to simulate the variable loads in the
different types of tissue encountered by the
active electrode during surgery.
Current ESU analyzers enable the user to
test in each mode and power setting at
several impedances sequentially.
Functional Check:
4) Electrical Safety Check
- per your department protocol
and finally, Document !
- the ESU control number is entered in the
surgical record by nursing staff for each surgery.
If there is any “sentinel event”, your maintenance
record can be used in a legal action.
ESU Test Equipment -
Fluke 454A (legacy)
ESU Test Equipment -
Fluke QA-ES
ESU Test Equipment BC Group’s ESU-2300
Test setup with load resistors
Typical Troubleshooting - Surgeons complain about poor output
- Active lead wires increase resistance with age
- Foot pedals fail from abuse
- ESU signals cause interference on video displays
- REM pad connectors break and become intermittent
Major Players in:
General Electrosurgery:
- Valleylab
- Conmed
- Erbe
Argon Beam Coags:
- Valleylab
- Conmed
Harmonic Scalpels:
- Ethicon
- Olympus
Valleylab Force 2
(legacy)
Valleylab Force FX
Valleylab switch for simple or split return pad
Valleylab’s “Force Triad”:
combines a Force FX with a Ligasure
Valleylab Surgistat II
Atmos RS 221
2.2MHz, 100W
Entermed ESG -01-01-21:
4.0 MHz, 130W
Conmed
More information:
Non-Valleylab ESU service website:
www.servicingvalleylabgenerators.lefora.com
Valleylab tech reference site:
http://energysolutions.covidien.com/content/biomedconnect
Nice history of electrosurgery:
http://www.electrotherapymuseum.com/Museum.htm
Very nice review of electrosurgery principles, safety issues,
and surgical video:
http://www.youtube.com/watch?v=ZeHNJSyrLPk