Published on 07/02/2015 by admin
Filed under Anesthesiology
Last modified 07/02/2015
This article have been viewed 957 times
Brian A. Hall, MD
Efforts to reduce the risk of explosions and to improve electrical safety in operating rooms (ORs) were first instituted when flammable inhalation agents were in use. These endeavors have continued because, even though explosions are unlikely to occur today, the amount of electrical equipment used throughout health care facilities and in the OR, in particular, has dramatically increased. Any electrical equipment has the potential to create macroshock, an electric shock on the order of 5 mA to 1000 mA or more that can burn a patient or fibrillate the patient’s heart. Patients in the OR are at particular risk for incurring a macroshock because the normal resistance of dry skin (∼ 100 kΩ) is reduced if the skin is wet or abraded (∼ 1 kΩ).
The two types of power systems used in health care facilities include a grounded power system (GPS) and an isolated power system (IPS). Which system is used in a specific area depends upon the patient care provided at that location as well as the characteristics of the electrical system that supplies the patient care area.
The main wiring in an OR is similar to that of a typical home in the United States—a GPS—comprised of a live (hot, positive) wire carrying alternating current at 120 V (120 VAC), a neutral (cold, negative) wire that completes the circuit by transmitting the current from the house back to the power-generating station, and an earth wire, or ground wire. If a person is grounded and comes in contact with the hot limb of a GPS, an electric shock will be delivered.
In a home, ground-fault circuit interrupters (GFCIs) are installed in a GPS that is used in wet locations (e.g., bathrooms and kitchens). Likewise, in the OR, GFCIs can be placed on each circuit of a GPS to minimize the likelihood of a macroshock occurring. The circuit will “trip” in milliseconds if a current greater than 4 to 6 mA begins to flow between the live wire and any other pathway other than the neutral wire. The concern with using GFCIs in an OR, however, is that, if the circuit trips, every electrical device plugged into that circuit will lose power.
In a “dry” OR with a GPS, the live (hot) wire is connected to the narrower of the two parallel prongs of an electrical plug and can be inserted only into the wider of the two parallel holes in the outlet. The neutral wire has the same potential difference from ground as the ground wire itself (i.e., 0 V). The single pole switches used in a GPS disconnect only the “hot” wire. If a person or a patient standing or lying in water comes in contact with the neutral or ground wire, no current flows. However, if the person contacts the hot wire, possible electrocution could occur unless protected by a GFCI.
Electricity in IPS is supplied by a transformer that is separate from the power-station electrical supply. The term isolated means precisely that—isolated from earth ground; the electrons in the circuit are not seeking the path of least resistance back to the power-generating station.
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