What is a Watt? Everything you ever wanted to know about Electrosurgery. Fahad bamehriz, MD

History Beer 1910: First endoscopic use of electrosurgery Benjamin Franklin: 18th Century-first experiments Arsene D'Arsonval: first to experiment with alternating currents in the late 19th century first to study clinical effects with modulated and non-modulated current Beer 1910: First endoscopic use of electrosurgery Fulguration of bladder tumours using the cystoscope Bovie and Cushing 1928: first electrosurgical generator with continuous sinewave current

Fundamentals of Electricity Electricity is electrons freed from atoms Current <I> is electrons flowing in the same direction (measured in amperes) flow from negative to positive terminal Voltage <V> is the electromotive force to drive the current through the conductor difference in potential between the poles Current that is one-way is direct current <DC>

Fundamentals of Electricity Current that reverses direction is alternating <AC> The movement of electrons reverses direction at regular intervals <cycles per second=hertz> Resistance <R> is the difficulty that a material presents to the flow of electricity <ohms> WATER IS THE KEY FOR TISSUES More water less resistance

Fundamentals of Electricity High School Physics: Ohm’s Law: V=I X R Power is the rate of doing work <watts> W=I X V W=I2 X R W=V2/R Total quantity of electrons moved and the pressure gradient against which the movement occurred

Alternating Current Household power: 60 cycles/s AM Radio: 550-1600 kHz Electrosurgical generators: 500-3000 kHz

Current Waveforms Modulated current is just interrupted current this is the COAG button highest peak to peak voltage Non-modulated current is a continuous sinewave this is the CUT button low peak to peak voltage

Current Waveforms

Cellular Effects Vaporization (cutting): Dessication/Coagulation: rapid oscillation of cell positive and negative ions causing high temperatures (600 °c) and converting mechanical energy to thermal energy. Cell expansion and steam formation lead to cell explosion Dessication/Coagulation: slower process with temperatures at 70-100 °c and evaporation of intracellular water and protein denaturation

Cellular Effects

Cellular Effects Fulguration: Superficial coagulation of broad tissue surface using electrical arcs of high voltage of modulated current rapid desiccation and tissue resistance limits current flow the only really good reason to use modulated current

Cellular Effects Cautery: destruction of tissue by the application of heat or a caustic substance ie: grasping tissue with pickups and touching pickups with active electrode

Capacitance Property of an electrical circuit to store energy Capacitor=any device that can create capacitance exists when two conductors with different potentials are separated by an insulator the difference between them creates an electrostatic force capacitance is directly proportional to voltage

OR Capacitors Surgeons Pts’ jewelry OR table IV pole idle electrode surgical instruments induced currents may lead to alternate current pathways back to ground surface area key…small is bad

Grounding A form of conductive connection between a circuit and earth earth can absorb infinite electrical charges equalization occurs Risk of alternate site burns (EKG electrode) eliminated by dispersive return electrode (blue pad) low impedance route back home remember hair, scar and fat free

Dispersive (return) Electrode Injury

Return Electrode Modern generators have alarms place in a non-dependent area area with good blood flow (water concept) *****if the generator doesn’t work: check return electrode********** DO NOT TURN UP THE GENERATOR!!!

Direct Coupling Activated electrode unintentionally touches another metal object may be out of the field of view may be undetected avoided by staying aware of location of all instruments

Direct Coupling

Capacitive Coupling Induction of stray current to surrounding capacitor through insulation of active electrode active monopolar electrode, insulation, metal cannula worse with higher voltage, smaller cannulas, longer electrodes Minimize by using a Non-modulated (cutting) current Avoid hybrid (metal and plastic cannulas)

Capacitative Coupling

Insulation Failure Insulation can be damaged by very high currents Breaks and holes can be caused by cannula valves or cleaning If defective spot on active electrode touches tissue, damage may occur inspect instruments for damage

Current Density Electrons congregate on edges determined by shape and size of electrode same device may be multifunctional i.e. flat vs. sharp edge of spatula electrode important for loop excisions, hysteroscopy and of course laparoscopy

Bipolar Electrosurgery Active and return electrode are on the instrument together eliminates risk of capacitive coupling and alternate current pathways lower power requirements needed secondary to high concentration of current between the poles So…..use unmodulated current with low peak to peak voltage Therefore, only dessication and coagulation possible

Bipolar Electrosurgery Able to grasp and compress blood vessels Able to dessicate tissue that is immersed in fluid Limited to small “bites of tissue”, large pedicles not ideal May have increased thermal spread than monopolar

Bipolar Current

Conclusions Keep active electrode clean, carbon impedes current flow Know your instruments!!! Remember Ohm’s law Think :-)