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Diathermy
- definition
The use of high frequency AC current (>100Khz) to create heat on patients tissues, to produce dissection or coagulation.
- B/G science
Heat is generated when current travels through resistor
Heat = Current^2/Area
Current density around diathermy electrode can be 10A/Cm2 - producing 200W of heat.
High frequency current has low tissue penetration = doesnt cause cardiac defib
Components
Diathermy electrode
Patients neutral or passive plate
Diathermy case which modifys freq and voltage
Isolating capacitor between patients plate and earth or floating/isolated diathermy circuit
How does it work
Patient pad - large area = low heat
Isolating capacitor - low impedence to high frequency, high impedence to low frequency (cardiac shock protective)
Cutting - continuous sine waveform
Coagulation - modulating waveform pattern
How is bipolar diathermy different
No patient plate
Current flows through one tip, into tissue then out another.
Bipolar is weaker and is ok for coagulation but less effective for cutting.
Frequently used for neurosurgery or ophthalmic surgery
Safety issues
Patient plate area reduced = extra heat and potential for burns. If detached completely may travel between patient and earth (ie ECG leads)
Electrical interference with monitoring equipment
Interference with pacemakers
Can cause ignition of OT fires.
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