CHBT Electrical Safety and Biomedical Engineering Principles 1 — Questions and Answers
Question 1: What is the maximum allowable leakage current for patient-connected medical equipment according to AAMI/IEC standards?
- 10 microamperes
- 50 microamperes
- 100 microamperes (Correct answer)
- 500 microamperes
Correct answer: 100 microamperes
AAMI/IEC 60601-1 sets 100 microamperes (0.1 mA) as the maximum allowable patient leakage current for Type B applied parts under normal conditions.
Question 2: Which type of grounding system is specifically required for patient care areas in dialysis units to minimize electrical hazards?
- Standard two-wire grounding
- Equipotential grounding system
- Double-insulated system
- Isolated power system (Correct answer)
Correct answer: Isolated power system
Isolated power systems (IPS) are required in critical care patient areas including dialysis to prevent ground fault currents from passing through the patient.
Question 3: In the context of hemodialysis equipment, what does 'macroshock' refer to?
- Current above 1 mA applied to the skin surface (Correct answer)
- Current applied directly to the heart via a catheter
- Electrical discharge from a capacitor
- Static electricity buildup on equipment
Correct answer: Current above 1 mA applied to the skin surface
Macroshock refers to currents above approximately 1 mA that are perceptible at the skin surface and can cause muscle contraction, respiratory arrest, or ventricular fibrillation at higher levels.
Question 4: What is the primary purpose of a line isolation monitor (LIM) in a dialysis unit?
- To measure voltage output of dialysis machines
- To detect loss of isolation in an isolated power system (Correct answer)
- To regulate current flow to the blood pump
- To monitor water quality in the dialysate circuit
Correct answer: To detect loss of isolation in an isolated power system
A line isolation monitor continuously measures the impedance between the isolated power lines and ground, alarming when the fault hazard current exceeds safe limits (typically 2 mA or 5 mA).
Question 5: Which class of medical electrical equipment relies solely on basic insulation for patient protection with NO protective earth connection?
- Class I
- Class II (Correct answer)
- Class III
- Type CF
Correct answer: Class II
Class II equipment (double-insulated) uses reinforced or double insulation rather than a protective earth connection to protect against electric shock.
Question 6: What is the recommended frequency for electrical safety testing of patient-connected hemodialysis equipment per AAMI standards?
- Monthly
- Every 6 months (Correct answer)
- Annually
- Every 2 years
Correct answer: Every 6 months
AAMI recommends electrical safety inspection and testing of patient-connected equipment at least every 6 months or per the manufacturer's recommendations.
Question 7: What is 'microshock' hazard in hemodialysis patients particularly relevant for those with central venous catheters?
- Currents of 1–100 mA applied externally to the body
- Currents as low as 10–20 microamperes applied directly to the heart (Correct answer)
- High-voltage discharges from capacitors
- Ground fault currents exceeding 5 mA
Correct answer: Currents as low as 10–20 microamperes applied directly to the heart
Microshock involves currents as low as 10–20 microamperes that bypass skin resistance via internal pathways (e.g., central catheters) and can induce ventricular fibrillation.
CHBT Electrical Safety and Biomedical Engineering Principles 1
What is the maximum allowable leakage current for patient-connected medical equipment according to AAMI/IEC standards?