Andy Falconer. Principles of surgical diathermy

Transcription

1 Andy Falconer Principles of surgical diathermy 1

2 Andy Falconer Principles of surgical diathermy From an Engineer s perspective 2

3 Surgical Diathermy Uses RF Current to cut tissue or cause coagulation

4 Modes of Operation Monopolar Bipolar Cut Blend 1 Blend 2 Blend 3 Coagulation Micro Macro

5 Principles of use Monopolar electrosurgery Diathermy unit Active electrode Return cable Neutral plate

6 Monopolar application RF current used to cut or coagulate Active electrode small in area high heat RF returns via plate larger area (150 cm2) negligible heat Lower power outputs for coagulation High voltage arcs spray coagulation or fulguration

7 Principles of use Bipolar operation Tissue Insulator Leads Forceps

8 Bipolar operation Suitable for delicate work Lower power outputs No neutral plate required Microbipolar for very fine work

9 Frequency considerations I(mA) f(hz) Current at which neuro-muscular stimulation is produced depends on frequency

10 Frequency considerations > 100 khz to avoid neuro-muscular stimulation At high frequencies (MHz), stray capacitances become more problematic Most electrosurgery today between 300 khz and 4 MHz

11 Output power Application Typical maximum output power Cutting tissue 400 W maximum Coagulation Bipolar Microbipolar 120 W 50 W 15 W

12 Output waveforms Unmodulated sinusoid good for cutting Burst fired damped sinusoid good for coagulation Typical modern coagulation - 20μs bursts at 17 khz Blend waveforms intermediate between cut and coagulation

13 Example output waveforms

14 Active electrodes Effect of RF depends on electrode geometry Small surface area (e.g. needle or loop) for cutting Larger surface area (e.g. ball or spatula) for coagulation Bipolar forceps mainly for coagulation

15 Return Electrode plates/pads Return path to diathermy unit for RF Should produce no localised heating effects Aluminium foil dry plates used today Self adhesive, single use plates also used Plate and connection to diathermy unit should be in good condition

16 Return Electrode plates/pads An early one

17 Return Electrode plates/pads Single use plates

18 Return Electrode plates/pads Single plate / Split plate Single Plate Cable Split Plate Cable

19 Plate to patient contact monitoring Good contact essential for patient safety Various methods used Monitor RF voltage on plate Check for imbalance between active and neutral leads Monitor resistance of plate in two halves For example REM NESSY ARM

20 Hazards of surgical diathermy Electrical interference

21 Hazards of surgical diathermy Interference to implanted devices Low frequency patient leakage current Fire or explosion RF burns

22 Causes of RF burns Poor plate continuity Poor plate to patient contact Accidental contact with active electrode Unintentionally high outputs Coagulation of internal current path

23 Testing surgical diathermy units Tests should include:- Power calibration checks Output modulation checks Alarm function checks Electrical safety inspection and tests Includes RF leakage currents

24 Power output & waveform checks Check for all modes Power outputs Output waveforms

25 Alarm function checks Alarms include :- Plate/Pad continuity Plate to patient contact Various monitoring methods & techniques Any other Alarms which are equipment specific

26 Testing surgical diathermy units ElectroSurgical Analysers (ESA s)

27 Electrical safety checks Visual inspections Careful inspection of all leads and foot-switches Check patient leakage with output inactive You do what you can RF Leakage outputs

28 Summary Hi Frequencies & High temperatures + the usual Electrical hazards Learn to Drive Equipment & Test equipment All functions, modes & test loads Operating & Testing environments 28

29 Summary Standards & Manufacturers Information It is yet another piece of Medical (Electrical) Equipment But stay safe! 29

30 And Finally Thank You! & Any Questions? 30