The classification concept is based on a general risk-analysis approach that estimates
potential hazards related to the use of the device under normal conditions or during failures.
The classification criteria consider whether a device comes into contact with the
human body, whether it is invasive, duration of use, whether it is in contact with vital
organs, and whether it is activated by an energy source. According to this system, medical
devices are placed in one of four classes as follows:
● Class I: Lowest level/responsibility for compliance under the manufacturer
● Class IIa: Mainly control of production
● Class IIb: Both design and production control
● Class III: Highest level/pre market approval
Since the adoption of council directive 93/42/EEC (CD, 1993), the responsibility of classification
of medical devices rests with the manufacturers, who must group their products
into the previously mentioned four classes in accordance with rules stated in annex IX of
the MDD. The Commission of the European Union has issued guidelines for the classification
of medical devices into one of the four risk classes using a decision tree.
The rules are based on criteria related to duration of contact between the device and the
patient, the degree of invasiveness, and the anatomy affected by the use of the device. The
duration of use is divided into three periods: transient use (less than 1 hour), short term
use (from 1 hour to 30 days), and long-term use (more than 30 days). A medical device
is classified as invasive if it penetrates inside the body, either through the surface of the
body or through a body orifice. For the noninvasive devices, contact with blood is an
important classification criterion. Modification of the biological or chemical composition
of blood increases the risk associated with a device. Active medical devices are defined
as those that are driven by electrical energy and differentiated in terms of the amount of
energy that they exchange with the body.
According to the MDD and the guidelines, the classification rules apply accordance
with the intended use of the device, not its technical characteristics. It is possible that two
manufacturers would produce similar devices and assign them two different uses.
Therefore, the intended, not accidental, use of a device factors into the classification of it.
If a user uses a device in a manner not intended by the manufacturer, he or she does so
under his or her own ‘responsibility and does not change the class assigned for the conformity-
assessment procedure.
Whenever there is a doubt as to classification based on the MDD, the manufacturer
should ask an NB. If the manufacturer and the NB responsible for the conformityassessment
dispute the classification, the manufacturer should refer the matter to the competent
authority, which decides the classification according to Article 9 of the directive.
In addition, the directive states that the medical device committee is the final decisionmaker
in an extreme case.
Conformity assessment procedures, as previously mentioned, are the procedures that
must be completed by a manufacturer before the CE mark can be placed on a product and
a product placed on the market. It is not feasible to subject all medical devices to the most
rigorous conformity-assessment procedures available. A graduated system of control is
more appropriate, and a medical device classification system serves to channel medical
devices into the proper conformity-assessment route.
For class I devices (simple dressings, corrective glasses, operating tables, and wheelchairs),
the manufacturers are entirely responsible for conformity assessment. The manufacturers
must ensure that devices comply with ERs using risk analysis to establish
whether any risks present are acceptable. For class I products, the manufacturers must
maintain technical documentation and create a declaration of conformity—available to
CAs upon request—before placing the device on the market.
In the case of class IIa products (syringes, contact lenses, dental filling materials, and
hearing aids), the manufacturer is responsible for the conformity assessment during the
design of the devices, but an independent certification body must approve the products
during the manufacturing stage. Class IIb products (e.g., implants, intraocular lenses,
X-ray equipment, anesthesia machines, ventilators, and high-frequency surgical equipment)
and class III (heart valves, resorbable implants, and medicated devices) are subjected
to certification by an NB at the design and the manufacturing stages.
For class IIa, IIb and III devices when a third party intervention is required, the
manufacturer may choose between at least two applicable procedures: the certification
of products or the certification of the manufacturing system. In the latter case, the
continuous maintenance of the manufacturer’s quality system is subject to a thirdparty
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