Medical Equipment and Systems
Core concepts
A clinical engineer must know the functional blocks common to most devices: power supply, sensor/transducer, signal conditioning, processor, actuator, and alarm/output stage. Understand the difference between diagnostic, therapeutic, monitoring, and life-support classifications, and how device class drives maintenance interval and redundancy expectations. Know the principles behind common modalities: ECG/SpO2/NIBP monitoring, infusion pumps (flow accuracy, occlusion alarms, free-flow protection), ventilators (tidal volume, PEEP, FiO2, alarm limits), electrosurgery (return electrode monitoring, dispersive pad placement), defibrillators (energy delivery, biphasic waveforms), and imaging physics at a conceptual level.
Traps
Questions often confuse preventive maintenance with performance verification or calibration. PM is scheduled inspection/cleaning/parts replacement; performance verification confirms the device meets spec against a reference; calibration adjusts output to a standard. Another trap: mixing accuracy (closeness to true value) with precision (repeatability). Watch for questions that assume a device is "safe because it passed PM" - PM reduces but does not eliminate risk.
Rule of thumb
For infusion devices, a common acceptance threshold is flow accuracy within ±5% of set rate; know that occlusion alarm time varies with rate and tubing compliance. When in doubt on a device question, ask: what is the failure mode, and what does the device do to protect the patient?
Worked example
A syringe pump set at 5 mL/h alarms late on occlusion. At low rates, pressure builds slowly because compliance in the line absorbs volume before the threshold is reached - so alarm latency is expected and is a design trade-off, not necessarily a fault.