HF Leakage of Electrosurgical Unit

http://ultramedic.com/contact/contact.htm

Please provide a reference to this requirement. (link)

Basically an ESU is a very high frequency current generator, where the generated frequency is high enough beyond the threshold that will cause the muscle twitching sensation on the patient. It is use for cutting tissues, coagulating blood and/or a combination thereof. Being a high frequency generator, it behaves like any other HF or VHF transmitter that if an AM radio receiver is close by, its reception will be over-ridden by the ESU generated current!

I believe what you may be looking for is how well and effective the designed current return path of that ESU unit? Normally the output of the generator beside being measured, calibrated and monitored, it also imperative that whatever that power was outputted, it should return back to the generator to complete that circuit.

An ESU unit if properly designed and functioning, monitors and measures the current that leaves and comes or collected back to the unit. This approach not only ensures system effectiveness, and by monitoring the return path it also ensures that any stray currents are minimized thus enhancing electrical safety. Any imbalance monitored triggers corresponding alarm parameters!

That means, by doing HF leakage test, we are monitoring the leakage of power, right ?

Or are are monitoring the leakage current ?

When you do that HF leakage test, basically you are trying to verify that whatever monitored power that comes out (delivered to the surgical site), effectively returned and find its direct path back to the machine to complete its circuit!

Bear in mind that power is a combination of current and voltage! One is a function of the other and therefore cannot be separated!

Cont'd

On some ESU models, an alarm feature called REM, (return electrode monitoring), are employed. This measures the continuity and skin impedance of the return electrode circuitry. It helps guide the proper placement of the grounding or return electrode close to the surgical site, insuring the shortest current return path that also enhances the expected cutting results using the least or minimum power setting!

Good luck

Check the link given above for Ultramedic. That device monitors 30hz - 2.5Mhz under load, but since outputs below 100hz are filtered out, those outputs should be zero.

So basically the intent of the device is:

1. monitor the intended RF output

2. monitor the 50 or 60 hz current which should be filtered out

3. monitor all the harmonics of that 50 or 60hz current.

NEC requires an alarm to sound for total hazard currents above 5mA.

For Patient Safety;

There are two types of current leakages that are present, being minimized and continuously monitored in this particular type of medical device!

1) Regular low frequency or power line leakage current (either 50 or 60 Hz) derived from or based on power source. This determines the micro-shock hazard threshold of the unit.

2) High frequency current leakages developed from the generator cutting/coagulating currents. This determine the amount of stray current that can cause un-intended damage to the surrounding tissues or organs in the patient's body!