Electricity is ever-present in the perioperative environment, powering tables, lamps, blood warmers, monitors and cautery devices. It's easily conducted by liquids such as IV and irrigation solutions and interstitial fluids, increasing the chances of electrical shock. Further, there are unique electrical risks to patients because of the electrical charges we apply to them - and anesthetized patients are unable to report or withdraw from a painful electrical current, which increases the risk of burns or cardiac arrest. We must take precautions to ensure safety in these circumstances.

Electricity and the human body
In the OR, the main materials that conduct electricity are metal, salt and water. The flow of electricity is measured in amperes (A). Flow - and the effect of electricity on the body - depends on the magnitude of the current as well as the composition of the tissues through which the current passes. The skin is the body's primary barrier to electrical current; ohms are the units of measure of resistance to electrical flow. Dry skin has a resistance of 1,000 to 10,000 ohms. Here's a sampling of how electricity affects the body.

• Currents of less than 1mA (milliampere - one-thousandth of an ampere) are below the threshold of human sensation, but that doesn't mean they don't have any effect. If you bring even low currents into proximity of the cardiac conducting system (by an intracardicac catheter or electrode) you can cause microshock, which will disrupt the cardiac rhythm.
• Currents between 1mA and 10mA cause tingling. Put the contact end of a 9-volt battery to your tongue: What you feel is low-current electricity.
• Currents in the 10mA to 100mA range cause muscular contractions. This can actually be quite useful; anesthesiologists use it daily with neuromuscular "twitch" monitors to monitor blocks.
• Currents between 100mA and 5A usually cause ventricular fibrillation if they pass through the chest.
• Currents in excess of 5A passing through the chest cause complete ventricular standstill, letting the heart resume a normal rhythm when the current is removed. This is also known as cardiac defibrillation which, as you know, is used to restart the heart. Electrical current at this flow can still cause damage without flowing through the chest.
• Currents of 100mA passing through the brain will cause seizures (electroconvulsive therapy).
• Currents in the 1A range passing through extremities can cause severe burns, not only to the skin but also to the underlying tissue.

The two main electrical risks patients face are microshock and electrosurgical burns. Because the currents that cause microshock are so small, you must take special precautions when, for example, a patient has a pacemaker. Laparoscopic electrosurgical burns damage underlying tissue, which is hard to visualize. This makes the burns hard to catch and treat, which can impede recovery.

Avoiding microshock
Relatively small voltages may cause microshock because intracardiac catheters or pacing wires bypass skin resistance. Built-in safety precautions, such as isolated power, ground fault interrupters and equipment safety grounding, can't prevent micro-shock. You must electrically isolate all monitoring equipment attached to intracardiac catheters or electrodes by preventing a connection between the wiring attached to the patient, such as ECG and pressure transducers, and the wiring of the monitoring equipment. In her presentation "The Case for Competencies" at AORN's 2005 annual meeting, Vangie Dennis, RN, CNOR, CMLSO, provided these tips for safety during electrosurgery on a patient with a pacemaker:

• Check the pacemaker manufacturer for instructions and have the resource number available.
• Have a defibrillator immediately available.
• Continuously monitor patient and pacemaker.
• Maintain the shortest distance possible between the active electrode and the grounding pad while ensuring the current path they create doesn't pass near the heart or implanted pacemaker.
• Place the pad and pencil as far as possible from the intracardiac electrode.
• Keep ESU cords and cables away from the pacemaker and leads.
• Use the lowest ESU setting and bipolar mode.
• Have a magnet or control unit available.

A note of caution: Grounding an intracardiac catheter or electrode increases microshock risk because other devices in contact with the patient may not be electrically grounded. If a patient's skin is in electrical contact with the operating table via moisture on the sheets, and the table isn't properly grounded becuase of a frayed or loose grounding conductor, current could pass to ground via the grounded intracardiac catheter, which would likely cause V-fib. The same scenario could occur if cardiac pacing wires were to touch the table, even though it's theoretically grounded.

Electrocautery essentials
The ESU cuts and coagulates tissue using a high-density electrical current concentrated on a small area. Remember, electricity always flows to ground and along the path of least resistance. This explains why the parts of the patient not directly under the cauterizing electrode are unaffected; immediately after entering the tissue, the current spreads out, looking for the path of least resistance, which minimizes heating and spares tissue.

The return electrode or grounding pad provides a destination for the current to complete the circuit. This pad dissipates the current over a wide enough area to prevent accidental heating or burning of the region under the pad. If the return pad isn't attached to the patient, current will seek an alternative route to the generator.

Because the electrocautery produces high-frequency alternating current, current can actually be conducted between two adjacent conductors, even if they're not in electrical contact. This is capacitive coupling, which will lead to electrosurgical burns. Electrical isolation of monitoring equipment and power systems is ineffective at these frequencies; if the return electrode isn't attached to the patient, the current may return to the generator through ECG electrodes or other metallic objects in contact with the patient, such as the OR table. These inadvertent return paths provide a smaller contact area, concentrating the current, which makes burns more likely.

Most ESUs won't function unless both halves of the pad contact the patient. Using active electrode monitoring will also shut down the current in such a situation. Incidentally, the pad isn't grounded; this prevents it from inadvertently conducting macro or microshock currents into the patient. Even though the ESU delivers currents exceeding those required to cause ventricular arrhythmias, it doesn't because of the skin effect. High frequency alternating current is carried by the skin and subcutaneous tissues rather than penetrating to the cardiac conduction systems. It's even possible to use the ESU on the epicardial surface of the heart without affecting the internal conducting system.