In recent years, surgical energy devices are widely used during thyroid and parathyroid surgery. In addition to hemostasis, they are also used for cutting, grasping, and dividing tissue. However, the heat generated from the device may cause thermal injury to the recurrent laryngeal nerve.
Therefore, it's necessary to qualify and quantify the possible thermal effect of this device that commonly used first during surgery. It's not recommended to verify safety parameters through trial and error repeatedly on humans with the newly developed surgical energy devices. In comparison, animal experiments have a significant advantage.
The surgical situations to apply a surgical energy device are diverse, and the safety parameters developed for scenario simulation in animal studies have reversed value for clinical use. As technology advances, newly developed devices will continue to emerge. The experimental methods can assess the advantages and restrictions of the devices before their first clinical applications by surgeons.
Therefore, we propose this protocol to provide the researchers with a structural design, specialized materials, and the standardized procedures to make it feasible to reproduce parameters in their own laboratory. To begin, select Duroc-Landrace pigs of age three to four months and weight 18 to 30 kilograms. After anesthesia, make a 15 cm centimeter long transverse cervical incision on the skin, one centimeter above the sternum.
Separate the strap muscles by the midline approach and retract laterally to visualize the thyroid cartilage, cricoid cartilage, tracheal rings, and thyroid gland. Then, dissect the sternocleidomastoid muscles bilaterally. Expose and dissect along the recurrent laryngeal nerves and vagus nerves bilaterally.
First, install the ground electrodes outside the surgical incision wound. Then, install a 2.0 mm automatic periodic stimulation, or APS electrode, on one side of the vagus nerve. Connect all electrodes through the interconnection box to the monitoring system, and ensure that electrodes are connected correctly.
Find the Vagus APS Stim"column and set the current of stimulation at 1.0 milliamperes. Click on baseline. A new window named Establishing APS Baseline"will appear on the right side of the screen.
Input the session title and session comments. Select the channel to be tested, upon which the system automatically starts to measure 20 times. The baseline amplitude and latency are automatically calculated and shown.
Click on accept"if the baseline is correct. Click on the fast forward icon in Vagus APS Stim"column to start a test. After each electrophysiology experiment, click on the pulse icon to stop recordings.
Select the Reports"page and set the report output format to save the file. Next, apply the surgical device, or SED, to the soft tissue at a distance of 5 mm from the RLN, and activate the device. Observe the change in EMG, and operate at the same activation distance thrice, unless a substantial change in EMG amplitude occurs.
Then, apply the SED to the soft tissue at a 2 mm distance from the RLN and activate the SED. Repeat this step, with the SED placed at a distance of 1 mm from the RLN. If a substantial decrease in EMG amplitude is observed during these steps, stop the experiment and record the realtime EMG continuously for 20 to 60 minutes to determine whether the injury is reversible, and record the results as a table.
For cooling time tests, apply single SED activation to the SCM muscle. Touch the RLN with the tip of the SED. After five seconds of waiting and cooling, observe the EMG change.
Repeat the test for a cooling time of two seconds, while observing the change in EMG amplitude. Proceed with the MTM test by applying single SED activation to the SCM muscle, only for one second. Quickly touch the activated surface of the SED with another position of the SCM.
Immediately after MTM, touch the RLN with the tip of the SED. Again, apply single SED activation to the SCM muscle. Immediately, touch the RLN with the tip of the SED without MTM.
If a substantial decrease of EMG amplitude is observed, stop the RLN experiment, and continuously monitor the realtime EMG response for at least 20 minutes to determine whether the RLN injury is reversible. Place the camera at a distance of 50 cm from the target tissue, at an angle of 60 degrees from the experimental table. Use 5 mm as the standard strap muscle thickness for SED activation.
Wipe the surface of porcine strap muscles with dry gauze. Grasp the strap muscle at the full length of the blade using SED. After a single activation, observe the maximum temperature as displayed on the screen during measurement.
Measure the blade length and lateral thermal spread of the 60 degree Celsius isothermal line after a single activation. When the highest temperature on the screen exceeds 60 degrees Celsius, record any smoke and splash on the screen, and repeat five measurements in different areas. Repeat these steps after grasping the strap muscle with an anterior one-third length of the blade using SED, and perform five measurements in different areas.
For wet environment tasks, soak the porcine strap muscles in sterile water for three seconds just before SED activation. For different areas, evaluate the lateral thermal spread, smoke, and splashing, by grasping the strap muscle for full length and anterior one-third length of the blade using SED. After single SED activation with the whole blade on the strap muscle, start recording the cooling time until the highest temperature on the screen is less than 60 degrees Celsius.
Repeat five measurements in different areas. After a single activation of the SED with the whole blade on the strap muscle, quickly touch the activated surface of the SED with another position of the strap muscle. Record its temperature immediately after leaving the SED from the strap muscle with the blade open.
After this step, start recording the cooling time until the highest temperature on the screen is less than 60 degrees Celsius. Present the electrophysiological and thermographic safety parameters in table form, with smoke and splashing marked. Using this protocol, electrophysiological activation tests were performed on the RLN, from the proximal to the distal segments, at different distances, and the EMG signal was monitored during the study.
An electrophysiological cooling study was also performed on the RLN. Whole blade thermographic activation tests in a dry environment showed that the maximum activation temperature was more than 60 degrees Celsius during the activation. During one-third blade tests in a dry environment, splashing was observed after activation.
Whole blade tests in the wet environment showed a more obvious lateral thermal spread compared to the dry environment. Whereas in one-third blade tests, smoke is more obvious compared to the dry environment. Electrophysiological and thermographic safety parameters were evaluated in this study and presented as a table.
Electrophysiological study established a critical parameter for nerve injury, and thermographic study established a preventive parameter for risk of thermal injury. Through the interpretation of parameters, surgeons can preserve sufficient safety distance and cooling time in the routine surgical steps. On the other hand, thermographic study can be applied in diverse activated environments such as thermal spread, smoke, or wave spray, that the energy device generated.
This study can also help to evaluate the risk corresponding to different clamping lengths from the blade of the energy device. We expect that this proposal and the model will provide the researchers, manufacturers, and the surgeons the best opportunity to investigate the thermal effects and define the safety parameters of each newly developed energy device to avoid the recurrent laryngeal nerve thermal injury during thyroid and the parathyroid surgeries.
