ECRI Update: Between-Use Electrical Leakage Testing of TEE Probes

The Importance of Leakage Current Testing

Although TEE probes do not come into direct contact with the heart, the probe tip will be positioned near the heart during the imaging procedure. The risk is that electrical current leaked from the probe could cause potentially fatal ventricular fibrillation. Current can leak from a TEE probe if, during the course of handling and use, the probe sustains cuts or punctures in any of its outer protective components. Such defects can allow fluid to leak into the probe’s interior, thus producing a path for electrical current to the outside of the probe.

In addition to an electrical hazard, fluid ingress via cuts and punctures can lead to other problems. For example:

• Pathogens can enter parts of the probe that cannot be properly disinfected, potentially infecting staff or patients.
• The probe’s electronic components can be damaged by saline, body fluids, and disinfection fluids, all of which are corrosive.

If disinfection fluid leaks into an area of the probe that is impossible to rinse properly, it can cause an injury to a patient’s mouth, tongue or esophagus.

“Visual inspection of the TEE probe shaft can identify obvious damage,” explains Ismael Cordero, senior project engineer in ECRI’s Device Evaluation group, “but it isn’t enough.” Small punctures may not be visually detectable and can lead to harm. That’s why an electrical leak test, which will help detect damage from any puncture, is needed between each use.

Between-Use Testing

Between-use testing should be performed after cleaning and reprocessing and before the next use. It also should be performed if the probe has not been used for an extended period after its last leakage test, or if you suspect that the probe may have been damaged by being dropped or struck against another object.

Between-use testing can be performed by most technicians without assistance from health technology management personnel. Additionally, it can be performed without having the TEE probe attached to an ultrasound unit, and without the use of a standard electrical safety analyzer. Typically, a less expensive specialized TEE probe leakage tester can be used.

Selecting a TEE probe leakage tester – Generally, ultrasound manufacturers consider the use of a TEE probe leakage tester an acceptable compromise to avoid the inconvenience of performing the full electrical safety test between every use, particularly for higher-volume hospitals. The model of leakage tester should be selected based on the TEE probe manufacturer’s recommendations. Some manufacturers provide customers with a tester when they purchase their TEE probes.

Some leakage testers display the measured leaked current in microamperes (µA), some have simple PASS and FAIL indicators, and others may both display a value and have a PASS/FAIL indication. Display of a measured current value allows observation of trends in probe deterioration.

Leakage testers also test the conductivity of the bath solution where the probe leakage is being measured. A minimum conductivity level ensures that there is a conductive path for leaked current so that the leakage test can be considered valid.

The probe’s pass/fail current leakage limits, as well as the conductivity thresholds of the bath solution, are provided by the probe manufacturer and are commonly programmed into the tester. Some testers can store manufacturer thresholds for multiple probe models.

Generic between-use testing procedure – The methods and steps that should be followed for between-use leakage testing are indicated in the probe manufacturer’s instructions for use (IFU). Testing methods vary among manufacturers, but there are some common steps and considerations:

• After the TEE procedure, the TEE probe is disconnected from the ultrasound system and undergoes high-level disinfection. Leakage current testing is then conducted with a portion of the probe immersed in the disinfectant solution.
• The technician connects the TEE probe to the tester via an ultrasound transducer adapter unique to the probe being tested. Note that only the model of tester recommended in the probe manufacturer’s IFU should be used.
• The portion of the probe that is inserted into the patient is immersed in a basin or soak tray with disinfectant. Alternatively, if the facility is using a dedicated probe disinfecting system, the probe may be tested while it is in the system, immediately following high-level disinfection. (These test setups are illustrated in the figure.)
• The leakage tester probes are immersed in the disinfection solution.
• To ensure that the electrical leakage test will be accurate, the conductivity of the cleaning solution is tested. Note that cleaning solutions with very low conductivity can yield false readings with some leakage testers. (See the full ECRI article referenced below for details.) Use only the solutions recommended in the probe manufacturer’s IFU.
• The leakage current is tested. Pass/fail status and measurements are displayed on the tester. Results are logged for documentation as per facility policy.

If a TEE probe fails the between-use leakage test it should be immediately tested again. If it fails a second time, it should be tested by health technology management personnel or by a manufacturer service representative. Such testing may require following the standard electrical leakage current testing protocol outlined below. “Anytime there’s doubt about the between-use test result, do a full test,” advises ECRI’s Cordero.

Testing during IPM and after Repairs

Standard electrical leakage current testing of a TEE probe is much more extensive than the between-use tests. It is performed by health technology management personnel, or by manufacturer service representatives, using an IEC 60601-1-compliant electrical safety analyzer. This testing is done after repairs, periodically at a frequency recommended by the manufacturer, or as specified in a formal alternative equipment maintenance (AEM) program. Testing is also done after users report electrical safety concerns.

These tests are described by each manufacturer in their IFU and generally consist of:

• Submerging the TEE probe in a conductive solution while connected to the ultrasound system, which has protective and isolation circuitry that reduces the amount of leakage current transmitted to the probe.
• Testing the probe as an applied part with permissible single-fault leakage current of 500 μA or less for a Type BF device and 50 μA or less for a Type CF device. (“Applied parts” are parts of medical devices that come into physical contact with the patient. They have differing electrical safety requirements depending on their classification – i.e., BF or CF.)

To Learn More

This article is adapted from ECRI’s “Between-Use Electrical Leakage Testing of Transesophageal Echocardiography (TEE) Probes” (Device Evaluation 2021 Nov 3). The complete article is available to members of ECRI’s Capital Guide, Device Evaluation, and associated programs. To learn more about membership, visit www.ecri.org/solutions/evaluation-and-comparison, or contact ECRI by telephone at (610) 825-6000, ext. 5891, or by e-mail at clientservices@ecri.org.