Dr. David Lyness
MONOPOLAR & BIPOLAR
Surgical diathermy equipment uses the heating effects of high frequency (kHz–MHz) Electrical current coagulates and cut tissues.
There are two basic types – monopolar and bipolar
- Generates electrical energy at 200 kHz to 6 MHz.
- The energy is applied between two electrodes (neutral and active).
- The neutral electrode has a large conductive surface area producing a low current with no measurable heat effect.
- The active electrode has a very small contact area resulting in a very high current density.
- The heating effect beneath the active electrode is considerable producing deliberate tissue damage.
- Cutting diathermy employs a sine waveform whilst coagulation uses a modulated waveform.
- In basic terms, is usually a 'wand' with a patch/plate attached to the patient
- Not good with pacemakers! Can interfere.
- Underneath the patient plate should be checked after all procedures.
- There is an earth wire inside the diathermy machine
- Bipolar diathermy operates with a much lower power output (15-20w for example)
- The output is applied between the points of a pair of forceps producing high local current density.
- No current passes throughout the rest of the body.
- NO PATIENT PLATE
- This is the only diathermy that should be used with pacemakers
Modern ECG’s also contain floating or isolated circuits to avoid providing a route to earth for any stray currents.
- The patient plate is attached within the diathermy machine to an isolating capacitor.
- The diathermy current which is of high frequency flows easily across the capacitor
- Impedance decreases with increasing frequency of current
- The lower mains frequency is subject to a much higher impedance.
- The patient plate is prevented from becoming a route to earth via which currents from faulty equipment may be conducted.
- Fires and explosions may be caused by sparks igniting flammable materials, e.g. skin cleaning solutions, bowel gas.
- Burns to the patient if the monopolar plate isn't connected properly and the patient comes in contact with a conductor
- Inadvertent firing is avoided by using a quiver for the diathermy device and avoiding hitting the pedals