Chapter 21

### Introduction

Keywords

• alarms and safety features

• operating rooms

• electrical grounding

• isolation transformers

• basic electronics

• macro and micro current hazards

As we all know, electrical equipment is a big part of our lives. At home, out and about, in hospitals and the operating room (OR), electricity is flowing and powering our lives. The OR is a special area with special electrical requirements and unique dangers that we will explore. Naturally, part of that discussion involves some basic physics about electricity and discussion about circuitry. Even as we go through the definitions, keep in mind why the discussion about electricity is important. Besides the fact that electricity powers most of the equipment in an OR, electricity can be a major source of injury to patients, staff, and us by fire or by shock (Figure 21-1).

###### Figure 21-1

One-circuit configuration for operating room (OR) isolation.

### Basics

Let’s start off with a classic equation of electricity, Ohm’s law, which is V = I × R. V is the force or voltage difference in volts, I is the current in amperes, and R is the resistance in ohms. If we rearrange the symbols to I = E/R, the flow, or current in amperes, is equal to the voltage difference divided by the resistance. So, the higher the voltage difference for a given resistance, the higher the flow of current is and vice versa. Following along in the equation, the higher the resistance for a given voltage, the lower the flow will be, and again, the reverse is also true. Another way to think of is to compare this to water behind a dam. As long as the dam is intact, there is no flow across the dam, but the water pressure behind the dam is still there. And the more water the dam is holding back, the higher the water pressure is behind the dam, and the more potential flow there would be if the dam were to fail. That is like the voltage in an electrical circuit. If there is a hole in the dam, then there will be flow, and that is similar to the amperage in the circuit (electrical current is electrons in motion). If you make a hole in a dam that has very little water behind it, the flow through the hole in the dam won’t be as great compared with a dam that has a lot of water behind it. This is the same as in an electrical circuit, where the higher the voltage or potential difference is, the more current will flow for a given resistance. This example also holds up for resistance. If you make a huge hole in a dam, the resistance to water flow through the dam will be less than if the hole is really small so there would ...

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