Categories of Medical Devices

ISO 10993-7:2008 classified medical devices into several categories based generally on allowable limit of EtO residues.

First three general categories are;

1. Limited Exposure Devices.

     These are devices which is used or applied to patients with contact up to 24 hours either in single or multiple use.

     The average daily exposure limit for ethylene oxide (EtO) is 4 mg while average daily exposure limit for ethylene chlorohydrin (ECH) is 9 mg.

2. Prolonged Exposure Devices

     These are devices used on a patient or have patient contact of more than 24 hours but not exceeding 30 days either in single or multiple uses.

     The allowable limit for ethylene oxide is 4 mg for first 24 hours and 60 mg for up to 30 days of patient contact. It is also required that the average daily dose to a patient should not exceed 2 mg/day

     The allowable limit for ethylene chlorohydrin is 9 mg for first 24 hours and 60 mg for 30 days of patient contact.

3. Permanent Contact Devices

     These is devices use on a long term on a patient which exceed 30 days either in a single or multiple use.

     The allowable limits for ethylene oxide consisted of 

           i) Average Daily Dose of 0.1 mg/day

          ii) First 24 hrs limit of 4 mg/device

         iii) First 30 days limit of 60 mg/device

         iv) Lifetime exposure limit of 2.5 g

     The allowable limits for ethylene chlorohydrin consisted of  

           i) Average Daily Dose of 0.4 mg/day

          ii) First 24 hrs limit of 9 mg/device

         iii) First 30 days limit of 60 mg/device

         iv) Lifetime exposure limit of 10 g

 

Beside these 3 categories, there are medical devices which will not or difficult to comply with the set allowable limit.  These devices are placed under special categories including;

Intraocular Lens which normally contain chlorine (they are kept in saline solution) will have high ECH level. In fact it was estimated that the resulting ECH toxicity was four times greater than the EtO corresponding level.   The EO limit in intraocular lenses was set as not to exceed 0.5 ug/lens/day or 1.25 ug per lens. However, suggestion by several sources that the limit for ECH in intraocular lenses to be 4 times that of corresponding EtO level is WRONG! The statement in ISO 10993-7 is ...

     "The acceptability of ECH levels in intraocular devices made from viscoelastic materials that contain chlorine may need to be evaluated, as the level of ECH that results in ocular toxicity is about four times greater than the corresponding EO level"

The statement clearly says that ECH limit in intraocular lenses need to be evaluated and no limit has been set for ECH in intraocular lenses. Probably, the revision of ISO 10993-7 will address this issue.

Blood cell separator: For blood cell separators used in patient and donor blood collection, the maximum allowable dose of EO is
10 mg and the maximum allowable dose of ECH shall not exceed 22 mg.


Blood Oxygenators: For blood oxygenators and blood separators, the maximum allowable dose of EO to patient is 60 mg and the
maximum allowable dose of ECH shall not exceed 45 mg.

Devices used in Cardiopulmonary bypass: Any medical devices used in cardiopulmonary bypass procedures should contain maximum allowable limit of 20 mg for EtO and 9 mg for ECH.

Extracorporeal Blood Purification Devices: These devices should should contain at most 4.6 mg/device for both EtO and ECH.

Drapes, Gowns,OT Table Clothes: For these large surface areas devices which are meant to have skin contact only, tolerable contact limit (TCL) may be applied. TCL is expressed as total amount of residues per centimeter squares of contact surface area of devices.  Manufacturers will have to determine the contact surface areas of their devices and should verify that the contact surfaces would exhibit negligible irritation as specified in ISO 10993-10. The allowable TCL for drapes, gowns and table cloths are 10 ug/cm2 for EtO and 5 mg/cm2 for ECH.

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