and utility . 10-12 Despite this contribution , Bovie was defunded by Harvard in 1927 and moved through positions at several different institutions before settling at Colby College in 1939 . He sold his patent for $ 1 and lived as a pauper in Maine until his death in 1958 . 1
Electrosurgery vs . Electrocautery
Electrosurgery is a technique that uses electromagnetic energy to cut and coagulate tissue .
As its high frequency current contacts tissue that has a high resistance and poor electrical conduction , the spark between the probe and the surgical site creates localized heat . This heat produces both cutting and coagulating effects . Below 45oC , these thermal changes are reversible . 1 At roughly 60-90oC , proteins denature and lose their structural integrity . 1 At 100oC , water molecules vaporize , causing tissue desiccation . 1
Electrosurgery includes the patient within the electrical circuit . An Electrical Surgical Unit ( ESU ), often called a “ generator ,” sends current to the active electrode which transmits to the tissue . Current exits the tissue through a return electrode , often placed on the patient ’ s thigh , thus completing the electrical circuit . Electrosurgery operates at a frequency 300 kHz – 1 MHz , 13 which is too high to affect cardiac conduction . This frequency allows for local heating of tissue at the entry point , 9 which then flows through the body to the return electrode without causing muscle contractions or producing pain , spasms or burns elsewhere . 5
A common mistake is interchanging the definitions of electrosurgery and electrocautery . Electrosurgery involves high frequency alternating current ( AC ), whereas electrocautery involves the passive transfer of heat via direct current ( DC ) through an object ( e . g ., metal wire ) that resists the flow of electricity and becomes hot , which can then cause a thermal effect via direct contact with tissue .
Duty Cycles
The resultant tissue effect of electrosurgery is dependent on several factors including the waveform of the current applied , the current density ( related to the size of the electrode ), the period of contact and surgical technique . The waveform itself is most related to the different duty cycle ( i . e ., the ratio of time when the circuit is on versus off ), which can be changed on the ESU .
A “ cut ” waveform is a pure sinusoidal at a single frequency within the radiofrequency range ( Figure 1 ). The current in this setting is undamped , passing through the tissue and causing vaporization of tissue . Because the amperage in this setting is lower relative to other settings , thermal spread to adjacent tissue is limited . The cut setting is most useful for incising tissue . Though the coagulate setting is the more intuitive choice , the cut setting creates a more homogenous seal since the voltage is lower and the waveform is continuous . The coagulate setting with this technique creates a heterogenous seal that is weaker .
Figure 1 : Cut ( left ), blend ( middle ) and coagulate ( right ) waveforms .
Figure 2 : Monopolar electrosurgery : including the Electrosurgical Unit ( ESU or ‘ generator ’), the monopolar device , the patient , and the grounding electrode .
Figure 3 : Bipolar electrosurgery : including the Electrosurgical Unit ( ESU or “ generator ”), the bipolar device , and patient ( note no grounding pad is needed , as the current travels through the tissue between the tips of the electrodes and not through the patient ).
“ Coagulation ,” on the other hand , involves a modulated , interrupted burst of higher voltage radiofrequency waveform with a low duty cycle range ( Figure 1 ). This means the current is active for a short period of time ( approximately 6 % of the time relative to continuous mode in the cut setting 1 ) followed by a long rest . This setting produces the thermal effect . Tissues do not reach temperatures adequate for vaporization , but instead coagulate . This setting is used with a pinpoint technique , where the electrode makes physical contact with the tissue to provide hemostasis and stop localized bleeding . 14
Lastly , the “ blend ” setting is a modulated ( around 25 kHz ) sinusoidal waveform with a duty cycle of 50-80 % ( Figure 1 ). Essentially a mix of the previous two waveforms , this setting allows for simultaneous cutting with some degree of hemostasis . This setting is used for sealing small bleeders or resecting masses of tissue . 14
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