Importance of testing for leakage currents in ESU’s

Leakage currents in ESU's

As with anything in the medical device industry, there are a lot of technical requirements and regulations that a developer or maintenance technician of electrical medical equipment must follow. Electrical safety and the overall safety and efficacy of the product is obviously the ultimate goal, but often people get a bit confused by the IEC series of standards. But not ERD! We get it! We are certified biomedical solution providers who perform routine maintenance for industrial and electrical measurement instruments to validate that they work correctly and can follow the AAMI/IEC 60601-2-2 standards.

What does an ESU do?

Electrosurgery is the application of a high-frequency electrical current to biological tissue as a means to cut, coagulate, desiccate, or fulgurate tissue. Electrosurgical units (ESU) are frequently used during surgical procedures because they help to prevent blood loss by sealing the tissue and blood vessels during the cutting of the tissue. Electrosurgery can be used to achieve either the mass destruction of large volumes of tissue as in endometrial ablation, fine incision as required by the reconstructive microsurgeon, or tasks requiring both cutting and coagulation, such as incision of the skin and subcutaneous tissue with hemostasis.

How do you test for High Frequency(HF) leakage currents?

Testing for an HF leakage current in electrosurgical units (ESU) is one of the many solutions ERD provides healthcare facilities. Electorsurgery uses the principle of alternating current to directly heat the tissue, generated by electric current. William Bovie invented the first electrosurgical unit in the early 1900s and the name Bovie remains widely popular in the electrosurgical industry today. In fact many people still refer to ESUs as Bovies.

The measurement of leakage currents that Biomedical Technicians perform everyday is created from the 60 Hz a.c. that provides power to medical devices. The HF leakage current in ESU’s is a result of the 300 to 500 KHz output waveform that performs the actual work of the ESU. Leakage current occurs when the electro-magnetic energy(EMF) capacitively couples with certain metals in the surgical field. If the leakage is above the limit, the leakage can cause interference in displays or other electronic circuits within the operation rooms. Unintended current flow to the patient and the staff creates the greatest danger. This danger occurs when unintended capacitive coupling of the HF current transfers to metal objects near the surgical site. The heat generated is from the tissue’s impedance (resistance to current flow), but the majority of heat stems from the rapid vibration of molecules within the tissue. Unintended capacitive coupling in the surgical field occurs when a ferrous object absorbs the EMF of the ESU active electrode. If that ferrous object comes in contact with the patient or staff, a wound will result that is proportional to the thermal density of the contact point. The correct operation of electrosurgical units is essential to ensure patient’s safety and management of the risks associated with the use of high and low frequency electrical currents on the human body.

What is the Testing Specifications for HF leakage?

AAMI/IEC 60601-2-2 specifies requirements for the safety of high frequency surgical equipment and HF surgical accessories used in medical practice. Some low-powered high frequency surgical equipment (for example for micro-coagulation, or for use in dentistry or ophthalmology) are exempt from certain requirements of this particular standard. Please refer to the copyrighted material in 60601-2-2. When tested as described in 60601-2-2, the HF leakage current flowing from the active or neutral electrode through a non-inductive 200-Ω resistor to earth shall not exceed 150 mA. Here is a diagram of coupling when the RF energy induces a secondary, non-intended current path through a conductive surface:

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