The new article describes in detail the approach to be followed when evaluating medical devices impacting, intentionally or unintentionally, the temperature of human tissues.
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The Food and Drug Administration (FDA or the Agency), the US regulating authority in healthcare products, has published a draft guidance document dedicated to evaluating the thermal effects of medical devices that produce tissue heating and/or cooling.
Once finalized, the guidance will provide an overview of the applicable regulatory requirements, as well as additional clarifications and recommendations to be taken into consideration by medical device manufacturers and other parties involved to ensure compliance with it.
At the same time, it is essential to mention that provisions of the guidance are non-binding in their legal nature, nor are they intended to introduce new rules or impose new obligations.
Moreover, the authority explicitly states that an alternative approach could be applied, provided such an approach is in line with the existing legal framework. It has been agreed with the authority in advance.
Verification of Device Parameters
First, the FDA emphasizes the importance of bench testing to confirm that medical devices meet their specified parameters, including energy-related ones, across their full operational range. Such testing should be guided by pre-defined acceptance criteria reflecting actual use conditions.
Deviations from these criteria necessitate a scientific rationale to affirm device safety and effectiveness.
This verification serves as a critical element to ensure that subsequent assessments of tissue effects and thermal energy dispersion accurately represent the device’s performance in its final form.
Furthermore, early verification of device parameters is expected to precede evaluations of tissue effects and thermal energy spread.
Experimental Assessment of Tissue Effects and Thermal Energy Spread
The document further describes in detail various approaches to be followed by the parties responsible for medical devices when evaluating the thermal effect the products might have.
Experimental Models
The guidance outlines phantoms, ex vivo animal tissue models, and in vivo animal testing as viable methods to assess tissue effects and thermal energy spread tailored to the device’s intended application.
The selection of an appropriate method hinges on the extent and nature of the thermal effects produced by the device, with considerations for the feasibility of creating suitable models, especially for devices causing regional or systemic temperature changes.
Phantom Testing
Phantom models, simulating minimal localized temperature increases, are ideal for characterizing tissue effects and thermal energy spread for specific devices.
These models are particularly relevant for low-impact devices and specific cryotherapy applications, where they can aid in demonstrating comparable ice-ball dimensions or safe energy output levels.
The choice of phantom should be representative of the clinical conditions the device is intended for, with thorough justification provided in premarket submissions regarding the model’s relevance and its translatability to in vivo conditions.
Ex Vivo Animal Tissue Testing
For devices expected to cause significant local temperature rises or when phantom testing is inadequate, ex vivo animal tissue testing becomes pertinent.
This method should replicate the in vivo environment to a considerable extent, with submissions required to justify the model’s appropriateness for the device’s specific indications.
Ex vivo testing may reach its limits when the spatial extent of thermal effects approaches critical anatomical structures, necessitating further in vivo or clinical evaluations.
In Vivo Animal Tissue Testing
In cases where phantom and ex vivo assessments cannot provide information, in vivo testing in clinically relevant animal models is essential.
This approach is indispensable for devices affecting tissue temperature over prolonged periods or on a regional/systemic level.
The in vivo model must mimic clinical use conditions closely, with submissions needing to detail the model’s applicability to the intended human applications and its alignment with patient safety objectives.
The use of anaesthetics and its potential impact on the assessment should also be addressed.
Conclusion
The present draft guidance developed by the FDA provides an in-depth overview of the approach to be followed when it comes to the evaluation medical devices should undergo in the context of the effect they cause on tissue temperature when used for the intended purpose. The document highlights the key points to be considered by medical device manufacturers and other parties involved to ensure the testing duly addresses all the critical points and provides sufficient and reliable information about the device in question, its safety and performance.
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