Design Control Guidance - Food and Drug Administration

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SCOPE AND LEVEL OF DETAIL. Design input requirements must becomprehensive. This may be quite difficult for manufacturers who are implementing asystem of design controls for the first time. Fortunately, the process gets easier withpractice. It may be helpful to realize that design input requirements fall into threecategories. Virtually every product will have requirements of all three types.• Functional requirements specify what the device does, focusing on the operationalcapabilities of the device and processing of inputs and the resultant outputs.• Performance requirements specify how much or how well the device mustperform, addressing issues such as speed, strength, response times, accuracy, limitsof operation, etc. This includes a quantitative characterization of the useenvironment, including, for example, temperature, humidity, shock, vibration, andelectromagnetic compatibility. Requirements concerning device reliability andsafety also fit into this category.• Interface requirements specify characteristics of the device which are critical tocompatibility with external systems; specifically, those characteristics which aremandated by external systems and outside the control of the developers. Oneinterface which is important in every case is the user and/or patient interface.What is the scope of the design input requirements development process and how muchdetail must be provided? The scope is dependent upon the complexity of a device and therisk associated with its use. For most medical devices, numerous requirementsencompassing functions, performance, safety, and regulatory concerns are implied by theapplication. These implied requirements should be explicitly stated, in engineering terms,in the design input requirements.Determining the appropriate level of detail requires experience. However, some generalguidance is possible. The marketing literature contains product specifications, but theseare superficial. The operator and service manuals may contain more detailedspecifications and performance limits, but these also fall short of being comprehensive.Some insight as to what is necessary is provided by examining the requirements for a verycommon external interface. For the power requirements for AC-powered equipment, it isnot sufficient to simply say that a unit shall be AC-powered. It is better to say that theunit shall be operable from AC power in North America, Europe, and Japan, but that isstill insufficient detail to implement or validate the design. If one considers the situationjust in North America, where the line voltage is typically 120 volts, many systems arespecified to operate over the range of 108 to 132 volts. However, to account for thepossibility of brownout, critical devices may be specified to operate from 95 to 132 voltsor even wider ranges. Based on the intended use of the device, the manufacturer mustchoose appropriate performance limits.There are many cases when it is impractical to establish every functional and performancecharacteristic at the design input stage. But in most cases, the form of the requirement canbe determined, and the requirement can be stated with a to-be-determined (TBD)numerical value or a range of possible values. This makes it possible for reviewers toSection C. Design Input 3/11/97 Page 16
assess whether the requirements completely characterize the intended use of the device,judge the impact of omissions, and track incomplete requirements to ensure resolution.For complex designs, it is not uncommon for the design input stage to consume as muchas thirty percent of the total project time. Unfortunately, some managers and developershave been trained to measure design progress in terms of hardware built, or lines ofsoftware code written. They fail to realize that building a solid foundation saves timeduring the implementation. Part of the solution is to structure the requirementsdocuments and reviews such that tangible measures of progress are provided.At the other extreme, many medical devices have very simple requirements. For example,many new devices are simply replacement parts for a product, or are kits of commodityitems. Typically, only the packaging and labeling distinguishes these products fromexisting products. In such cases, there is no need to recreate the detailed design inputrequirements of the item. It is acceptable to simply cite the predecessor productdocumentation, add any new product information, and establish the unique packaging andlabeling requirements.ASSESSING DESIGN INPUT REQUIREMENTS FOR ADEQUACY. Eventually,the design input must be reviewed for adequacy. After review and approval, the designinput becomes a controlled document. All future changes will be subject to the changecontrol procedures, as discussed in Section I (Design Changes).Any assessment of design input requirements boils down to a matter of judgment. Asdiscussed in Section E (Design Review), it is important for the review team to bemultidisciplinary and to have the appropriate authority. A number of criteria may beemployed by the review team.• Design input requirements should be unambiguous. That is, each requirementshould be able to be verified by an objective method of analysis, inspection, ortesting. For example, it is insufficient to state that a catheter must be able towithstand repeated flexing. A better requirement would state that the cathetershould be formed into a 50 mm diameter coil and straightened out for a total offifty times with no evidence of cracking or deformity. A qualified reviewer couldthen make a judgment whether this specified test method is representative of theconditions of use.• Quantitative limits should be expressed with a measurement tolerance. Forexample, a diameter of 3.5 mm is an incomplete specification. If the diameter isspecified as 3.500±0.005 mm, designers have a basis for determining how accuratethe manufacturing processes have to be to produce compliant parts, and reviewershave a basis for determining whether the parts will be suitable for the intended use.• The set of design input requirements for a product should be self-consistent. It isnot unusual for requirements to conflict with one another or with a referencedindustry standard due to a simple oversight. Such conflicts should be resolvedearly in the development process.Section C. Design Input 3/11/97 Page 17
Page 1: Center for Devices and Radiological
Page 5 and 6: PREFACEEffective implementation of
Page 7: TABLE OF CONTENTSFOREWORD .........
Page 10 and 11: are described in comments received
Page 12 and 13: The importance of the design input
Page 14 and 15: patient. Because the problem was no
Page 16 and 17: III. DISCUSSION AND POINTS TO CONSI
Page 18 and 19: design and development team, and pr
Page 20 and 21: more likely to be made with appropr
Page 22 and 23: Unfortunately, there are a number o
Page 26 and 27: • The environment in which the pr
Page 28 and 29: the design and development plan, an
Page 30 and 31: Section D. Design Output 3/11/97 Pa
Page 32 and 33: capabilities. The external focus is
Page 34 and 35: Qualifications. Formal design revie
Page 36 and 37: action. In other cases, the reviewe
Page 38 and 39: manufacturers are encouraged to use
Page 40 and 41: Another self-documenting verificati
Page 42 and 43: III. DISCUSSION AND POINTS TO CONSI
Page 44 and 45: Section G. Design Validation 3/11/9
Page 46 and 47: Historically, shortcomings in the p
Page 48 and 49: DOCUMENT CONTROL. The features of a
Page 50 and 51: Section I. Design Changes 3/11/97 P
Page 52 and 53: software in each machine. The contr

Design Control Guidance - Food and Drug Administration

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