Remember that the Line Isolation Monitor is Based on a Simple Principle of Electrical Safety: Make Sure the Patient Does Not Become Part of A Grounded Circuit



Remember that the Line Isolation Monitor is Based on a Simple Principle of Electrical Safety: Make Sure the Patient Does Not Become Part of A Grounded Circuit


Jeffrey D. Dillon MD

Richard Botney MD

Randal O. Dull MD, PhD



The issue of electrical safety in the operating room has several factors. Anesthesiologists must manage the risk for patient injury caused by electrical currents several orders of magnitude apart in amperage, and they must use complex equipment-laden electrical setups. In addition, the monitor primarily used by anesthesiologists to indicate electrical issues, the line isolation monitor, rarely sounds an alarm and, in reality, does not guarantee electrical safety. This subject can provoke anxiety in anesthesiologists and merits frequent review.

The presence of any electrical device in the operating room creates the possibility of an unintended completed current pathway or circuit. Basically, the goal is to prevent the patient (or staff member) from becoming part of that circuit. An analogy to household electrical circuits is helpful—the safety features used in operating rooms do not differ in purpose from those used in houses (ground fault circuit interrupters) and appliances (three-pronged cords).

Electrical current involves the flow of electrons down a potential (i.e., voltage) gradient, following the path of least resistance. Ohm’s Law defines the relationship between voltage (V), current (I), and resistance (R):

V = I R

For a shock to occur, the flow of electrons must complete a circuit. In most cases of shock, in both household and operating room situations, the circuit is completed by the flow of electrons from a source (usually an energized power line or faulty equipment), through the affected person, who is in contact with the ground, and then back to the original power source.

Electrical current harms a person at several current levels and in several ways. In general, electricity alters the electrochemical activity of the body and the organs and cells that it flows through. Exogenous electrical current causes nerve excitation and muscle contraction (exploited for clinical use with the nerve stimulator). Exogenous current also induces cardiac dysrhythmias
when it flows through the heart (exploited for clinical use with defibrillators). As electrical current encounters resistance as it flows through the tissues of the body, the electrical current loses energy in the form of heat, which can cause both external and internal burns. The amount of tissue damage relates to the amount of current, the duration of the exposure, the current’s frequency (i.e., frequencies that exceed roughly 10 kHz do not cause ventricular fibrillation), and the area over which the current is delivered (current density). Which specific injury occurs depends on the amount of current and the resistance in the electrical pathway. Microshock results when a current is applied internally in the body and bypasses the high resistance of the skin. Central venous catheters, pulmonary artery catheters, and pacemakers have all been known to conduct electricity internally and cause microshock. Currents as low as 100 µA have been reported to induce ventricular fibrillation. The second category of electrical injury is called macroshock, in which a large amount of current is applied externally to the skin; the patient usually perceives such shock. The amount of current, applied externally to dry skin, required to produce ventricular fibrillation is about 100 mA. Sensation of electrical current will occur around 1 mA and electrical burns occur at about 6 A.

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Jul 1, 2016 | Posted by in ANESTHESIA | Comments Off on Remember that the Line Isolation Monitor is Based on a Simple Principle of Electrical Safety: Make Sure the Patient Does Not Become Part of A Grounded Circuit
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