Chapter 37: Electrical Safety

INTRODUCTION

Since anesthesia machines and monitors are electrically powered, it is important to have a good understanding of electricity and electrical safety. Burns, electrocution, and fires are hazards of electricity in the operating room (OR). Morbidity and mortality from electrocution depends on type (direct vs. alternating), amount, pathway, density, and duration of the electrical current.

BASIC CONCEPTS

In electronics, solids are classified as conductors, insulators, and semiconductors.

Conductors have loosely bound electrons in their outer shell which can move freely under application of electrical potential. Conductors such as metals, saline, and carbon-containing matter are able to conduct electricity well. Conversely, insulators have tightly bound electrons in their outer shell which do not move freely. Insulators such as rubber, mica, and glass do not conduct electricity well. Semiconductors such as silicon, germanium, and lead behave like nonconductors unless subjected to high temperature.

The three basic quantities in electricity are:

1. Voltage (V)—Voltage is the electrical force that drives the current. One volt is the potential difference applied to a conducting wire in which 1 A of current flows.

2. Current (I)—Current is measured in amperes. One ampere, or amp (A), represents the flow of 1 coulomb or 6.24 × 10¹⁸ electrons past a given point in the conductor.

3. Resistance (R)—Resistance, measured in ohms, is the opposition to the flow of current when a voltage is applied. A good conductor will have low resistance, whereas a good insulator will have high resistance.

Ohm’s law relates these three quantities in the equation V = I∗R. Electrical current must flow in circuits. Electrical safety in the OR focuses on current as the most important variable, and so it is necessary to rearrange Ohm’s law into the relationship I = V/R. Because of the use of electronic devices in the OR, there is particular concern about current density flowing through an area such as skin.

In the United States, electricity is provided as alternating 60 Hz current based on 120 V with peak amplitude of 150 V. Alternating current is more dangerous than direct current. Lower frequencies cause more morbidity than higher frequency currents. This alternating current can flow across resistors and capacitors. The power company provides two lines—a “hot” lead and a neutral or “ground” lead. The neutral lead is connected to ground at the power company as well as at the point at which the electrical wiring enters the building. There is a third lead known as the “ground wire” that connects the device to return any current leaking from device (known as the “chassis current”) back to the ground.

ELECTROCUTION

Current flowing across the thorax can precipitate dysrhythmias such as ventricular fibrillation or asphyxia due to tetany of respiratory musculature. Current that passes ...