Electrical Safety Knowledge of Active Medical Devices

Electrical Safety of Active Medical Devices

Numerous medical devices in modern hospitals play a vital role in diagnosis, treatment, and patient monitoring. The vast majority of these devices rely on electrical power as their energy source and are referred to as active medical devices. The precise definition of an active medical device encompasses any device that functions by utilizing electrical energy or other energy sources not directly derived from the human body or gravity.

01 Electrical Safety Must Not Be Overlooked

Compared to passive medical devices, active medical devices pose an undeniable risk of electrical injury to the human body. Neglected maintenance or frequent use may lead to malfunctions, which not only compromise treatment efficacy or cause misdiagnosis due to degraded performance metrics but can also, in severe cases, threaten patient lives.

For example, the defibrillator. It is hailed as a “life-saving device” for cardiac arrest patients. In cases of out-of-hospital cardiac arrest, survival rates can increase to 75% if an automated external defibrillator (AED) is used within five minutes of the incident. However, as a critical emergency device, defibrillators must maintain optimal performance and sufficient battery charge to deliver electrical shocks promptly during emergencies. If its functionality malfunctions, leading to reduced performance metrics or the delivery of inappropriate energy, it not only fails to successfully rescue the patient but may also cause death. This underscores why electrical safety for active medical devices is of paramount importance.

02 Three Key Electrical Safety Indicators

Numerous standards govern the electrical safety of medical devices, but the most fundamental is GB 9706.1 “Medical Electrical Equipment - Part 1: General Requirements for Safety.” This standard defines safety metrics for medical electrical equipment, with the three most critical indicators being leakage current, grounding resistance, and dielectric strength—withstand voltage.

Leakage Current

Leakage current is one of the most critical indicators reflecting the safety of medical equipment. All electronic devices exhibit a certain level of leakage current, categorized into ground leakage current, enclosure leakage current (e.g., leakage through a washing machine's outer casing), patient leakage current, and patient auxiliary current. This current escapes through the insulation materials of electrical equipment, posing potential hazards to users. If the current flowing through the insulation material of medical devices exceeds specified limits (typically ranging from 0.01 mA to 10 mA), it may pass through the human body, affecting the heart, nervous system, and bodily tissues. Mild effects include burns and muscle paralysis, while severe cases may result in death.

Protective Grounding Impedance

Protective grounding impedance quantifies the resistance of an electrical device's protective grounding circuit (commonly referred to as the “ground wire”) to current flow. Protective grounding provides a low-impedance path to prevent electric shock hazards during leakage, serving as a critical electrocution protection measure for medical electrical equipment. Generally, a lower measured value indicates lower impedance, meaning the protective grounding circuit conducts electricity more effectively, which is more beneficial for the safety of electrical equipment. Consider large household appliances like washing machines as an analogy. When a washing machine has poor insulation or operates in a humid environment, its outer casing may carry a slight leakage current. Touching it can cause a tingling sensation (resulting from the current flowing through the body after being diverted via the ground wire). However, most of this leakage current is safely discharged into the earth conductor through a wire connected to the appliance's metal casing. Only a minimal amount of current flows through the human body, thereby protecting personal safety.

Dielectric Strength

Dielectric strength is a crucial metric for evaluating electrical insulation, reflecting the maximum voltage an insulating material can withstand. It serves as a vital indicator for preventing electric shock injuries. In daily life, electrical wires are wrapped in thick insulation materials. If the insulation is poor or defective, applying voltage can cause breakdown, sparking, or damage. Breakdown manifests as leakage current. When a person contacts insulation that fails to meet safety standards, it may result in various physiological effects due to electric shock, causing injuries during medical procedures or even death—a highly serious consequence.

As electrical products, particularly medical devices, evolve from automation toward intelligence, the proportion of active medical devices will increase, and their applications will become increasingly widespread. Correspondingly, the testing and inspection technologies for these devices are also advancing at an accelerated pace. It is foreseeable that the standards system for active medical devices will become increasingly refined, manufacturers will place greater emphasis on product safety, and regulatory oversight will continue to strengthen. Consequently, active medical devices will grow progressively safer in the future.