Microshock hazards

Published on 07/02/2015 by admin

Filed under Anesthesiology

Last modified 07/02/2015

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Microshock hazards

Brian A. Hall, MD

Electricity is ubiquitous in the operating room environment; its use poses inherent risks to health care workers and special risks to patients. Isolated power systems were developed several decades ago when ether was used in operating rooms. Line-isolation monitors (LIMs) were originally set to trigger at 2 mA, to decrease the chances of a spark occurring, which, in an ether-enriched environment, could create an explosion or fire. With the elimination of ether in operating rooms, in the late 1980s, the Occupational Health and Safety Administration increased the alarm threshold to 5 mA for LIMs used in operating rooms that had isolated power transformers to decrease the possibility of macroshocks occurring.

The 5-mA level was selected because (1) this level was thought to be potentially injurious to a grounded patient, depending on the site at which the current would contact the patient, thereby creating a path through which current might flow, and (2) the resistance (impedance) to current flow is estimated by convention to be 500 Ω.

A potential current leak to ground can occur and will go undetected by the LIM if the leak is well below the detection threshold. For this reason, the American National Standards Institute mandates that the maximum 60-Hz current leakage from an indwelling device not exceed 10 μA. This level is well below the ventricular fibrillation threshold (∼100 μA).

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