The high-power electrosurgical and radio-frequency (RF) ablation devices that apply a high level of RF current to the patient for extended periods can increase the risk of patient skin burns at the grounding pad’s attachment site. Safety measures that have been proven effective using traditional electrosurgical procedures may not be sufficient to prevent grounding pad burns when used in procedures that require any combination of high current, long activation times and the use of conductive fluids (e.g., saline) for irrigation or distention. 1

The problem is that some of the new electrosurgical devices and surgical techniques can produce higher current levels than an AAMI-HF-18 compliant grounding pad can safely withstand, significantly increasing the risk of a burn at the grounding pad site. According to the AAMI HF-18 standard, an adult grounding pad should be designed to safely carry a current load of 500 mA for continuous period of 60 seconds. In order to pass the AAMI HF-18 performance test, an adult grounding pad must safely carry twice this amount of power, i.e., 700 mA for continuous period of 60 seconds (note: 700 mA double the power of 500 mA according to the power equation P=I2*R). However, some of the newer radio-frequency devices can deliver current levels of 1000–2000 mA for few minutes or up to 20 minutes and longer. Under these conditions, an AAMI HF-18 compliant grounding pad may not safely and effectively disperse the current, resulting in a patient burn at the site of the grounding pad.

A grounding pad must not heat the patient’s skin in excess of 6 °C during the tissue ablation or electrosurgical procedure according to AAMI HF-18 standard. The RF current return is usually concentrated around the edges of grounding pad (edge effect), causing excessive heating at the highest current densities. A temperature of 45 °C will burn the skin. Since human skin is usually 30–33 °C, a burn will not occur until the pad causes a temperature rise of 12 °C. In order to provide a thermal safety margin, the skin under the pad should remain much cooler than this during electrosurgery.2 Second- or third-degree patient burns from grounding pads are not uncommon. The Cool Grounding pad technology described here will ultimately eliminate the skin burn complication at any RF power level and will work with existing RF generators and grounding pads in the market.

The concept is based on the design idea published June 2011 on the Tech Briefs Create the Future design contest site.3 Unlike standard grounding pad in use today, it regulates the patient’s body temperature precisely at the grounding attachment site to a safe level, as well as monitoring the grounding pad’s RF current return for safety and contact quality. It consists of a specially designed grounding plate with integrated heat removal components such as thermoelectric cooling devices (TEC), which can transfer heat from one side of the device to the other. A matrix of temperature sensors such as medical-grade thermocouples are equally spaced and embedded into the grounding pad or assembled on a separate thin plate. The image shown depicts the conceptual design and a working prototype of the Cool Grounding Pad.

Controlling Mechanism

Conceptual (above) and working prototype (below) of the Cool Grounding Pad. (Credit: ScientificRFA)

An FPGA temperature controlling mechanism with mathematical algorithm such as PID (proportional integral derivative) was developed to control and regulate the grounding pad’s surface temperature precisely within AAMI HF-18 standard. The modular design of the controlling system can be integrated into the new RF generator design or can operate as a standalone system working with existing RF generators in the market.

The controller can support multiple grounding pads simultaneously and monitors the grounding contact quality as well. Figure 1 shows the test result data chart collected at 50 °C heat applied to the edges of the grounding pad with a target temperature setting of 20 °C in a half-hour time period. Benefits of the device include the following:

  • Solves the excessive heating problem causing patient severe skin burns, especially with higher power RF generators and electrosurgical units.

  • Works with existing RFA generators and electrosurgical units in the market.

  • Works with existing grounding pads in the market.

  • Offers modularity and flexible programmability that allow for many possible scenarios, including customized mathematical algorithms developed by the doctors and specialists.

  • Provides data logging and saving with analysis capabilities.

  • Communicates with the RF generator through serial or I2C port, e.g., emergency shutdown of the generator because of malfunction, open ground, or excessive temperature of the pad, etc.

References

  1. Reducing Grounding Pad Burns During High Current Electrosurgical Procedures,” 3M Technical Bulletin, 2007.
  2. 3M Universal Electrosurgical Pad (Electrical and Thermographic Performance),” 3M.
  3. Cool Grounding Pad,” Create the Future Design Contest entry, 2011.

This article was written by Mike Nasab, ScientificRFA. For information about licensing the technology, contact. This email address is being protected from spambots. You need JavaScript enabled to view it.. For more information, visit here . A video of the technology is available here .


Medical Design Briefs Magazine

This article first appeared in the November, 2020 issue of Medical Design Briefs Magazine.

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