ISO 18562-4:2017 ヘルスケアアプリケーションにおける呼吸ガス経路の生体適合性評価 — Part 4: 凝縮液中の浸出物のテスト | ページ 10

A.2 Rationale for particular clauses and subclauses

5.2 — Test method

a) 3)

Typically, the extraction ratio will be 3 cm² of inner gas pathway surface per ml of water.

Care should be taken if the bulk material of the walls of the gas pathway are non-homogeneous. For example, a tube with a coating or a co-extruded tube could have different materials on the inner gas contact surfaces from the materials forming the outer surfaces. In this case, grinding up the bulk material to perform the extraction will not give results representative of an intact tube.

Also, be aware that with some materials, fresh cut surfaces can have different properties from the surfaces resulting from the actual manufacturing process. For example, extruded foamed materials typically have a closed film surface, while the inner bulk material has a foam structure with a much greater surface area. These two different physical forms of the same material may well give different results when a typical extraction is performed.

Some authorities having jurisdiction recommend exhaustive extraction for prolonged and permanent duration medical devices.

b) and c)

In any assessment, the most important consideration is the actual dose-to-patient, which is calculated by taking the concentrations multiplied by the volume the patient inhales or ingests per day.

The experts on the committee discussed at length the amount of liquid condensate that might reach the patient per day. The committee noted that it is established clinical practice to have methods in place to prevent liquid water as condensate from reaching the patient. These methods include heated breathing hoses and water traps. The committee concluded that having condensed water reaching the patient was bad clinical practice and was an anomalous event, not a regular occurrence.

The committee decided that as ISO 14971 requires them to consider intended and reasonably foreseeable misuse, the daily permitted volume of water entering a patient should be set at 1 ml. This value of 1 ml should be used in the calculations to derive the dose to the patient. The condensate enters the lungs. The dose is therefore compared with derived limits for inhalation, not oral ingestion.

d) and e)

Historically, a medical device with a breathing gas pathway, which exposed a patienttoleachable substances in condensate, was evaluated as externally communicating with contact to tissue/bone/dentin according to ISO 10993-1. As such, the medical device was evaluated for a range of biological effects, including local and systemic endpoints. The tolerable intake and threshold of toxicological concern methodologies principally address systematic effects (e.g. carcinogenicity), but are also adequately protective for many local effects (e.g. irritation).

Cytotoxicity testing has been retained, as these tests are very sensitive and serve as a screening test for local effects.

Sensitization testing (in-vivo) has been retained as the ti and ttc methodologies are not adequately predictive, and no in-vitro methods are known to be adequate.

Annex B

Reference to the essential principles

This document has been prepared to support the essential principles of safety and performance of gas pathways as components of medical devices according to ISO 16142-1 ^[16]. This document is intended to be acceptable for conformity assessment purposes.

Compliance with this document provides one means of demonstrating conformance with the specific essential principles of ISO 16142-1 ^[16]. Other means are possible. Table B.1 maps the clauses and subclauses of this document with the essential principles of ISO 16142-1.

Annex C

Terminology — Alphabetized index of defined terms

Bibliography