Medical device maintenance basics.

Not every device needs the same attention. A risk score ranks a device by its function, its physical risk and its maintenance needs, and decides whether and how often it is maintained. The Fennigkoh-Smith method (1989) adds points for these three to decide inclusion and the planned maintenance frequency.

The maker's interval is the starting point. A common example: every 6 months for life-critical equipment such as defibrillators, or the maker's interval. PM yield, the share of planned jobs that find a fault needing action, shows whether an interval is too short or too long.

Medical devices are tested to IEC 62353 rather than with general portable appliance testing, because IEC 62353 covers the applied parts that touch the patient. An electrical safety analyser runs the tests and records the results.

Leakage can be measured three ways. The direct method measures current in the earth path with the device running normally. The differential method measures the imbalance between live and neutral. The alternative method shorts the mains parts together and applies a test voltage, so the device is not powered normally.

Performance verification tests prove a device meets its specification, such as delivered flow, energy or pressure, using calibrated test equipment. For example, a defibrillator output test discharges at set energies into the analyser's 50 Ω load and reads the delivered energy, which must be within ±15% or ±3 J, whichever is greater (IEC 60601-2-4).

Calibration compares a device's readings against a traceable reference and, if needed, adjusts it. The result must state the measured error and uncertainty, with an unbroken chain of calibrations back to national or international standards.

• Asset register: every managed device with its ID, model, serial number, location, owner and status. The base for maintenance, recalls and capital planning.
• CMMS: the software that holds the asset register, schedules planned maintenance and records work orders.
• Work order: one piece of work on a device: what was done, the parts, the time and who did it.
• Equipment tag: the label with the asset number and often the date of the last test or the next service due.

A recall is the return, removal or correction of a device already supplied, because of a safety or performance problem. A field safety notice from the manufacturer tells users about the action, such as a fix, extra checks or a recall, and must be acted on and recorded. The asset register finds the affected units, and the UDI on the device identifies the model and the batch or serial number.

Two rules never change: follow the manufacturer's instructions for use and your institution's procedures, and never bypass an interlock or an alarm.