E=IR

Voltage= Amperage x Resistance 

Amperage x Resistance

E=IR 

Measured in watts

Voltage x Amperage

E x I 

Watts x seconds 

Measured in Joules

Direct Current

(DC)

Alternating Current 

(AC)

Impedance

(Z)

Frequency x inductance 

or 

1

frequency x capacitance 

15-20 A

Do no protect against lethal shock 

Disruption of normal cellular electrical activity

Thermal Injury 

Large amount of current flow

in excess of 5 mA

Ungrounded

Accomplished with isolation transformer

Equipment casings will be grounded and allow discharge of leakage current 

Monitor the integrity of power system

Measures circuit impedence to ground 

Indicated in mA total possible current flow to ground

2-5 mA

Alarms when faulty piece of equipment allows more than 5 mA

Alarms sum of many small leakages from various equipment reach 5 mA

Cannot detect a faulty gorund wire 

Ground Fault Circuit Interpreter

(GFCI)

Monitors the current in hot and neutral wires 

If reaches > 5mA then the circuit is interupted 

Catheter or wire in the heart can deliver very high current density 

100 microamps can induce V-Fib

Isolate power supply from patients

Use very high impedence (small wires) 

Deliver < 10 microamps

Ex. pacemakers 

High Frequencies: 500,000 - 1,000,000 Hz

Heat produced is inversley proportional to the area delivered 

High Frequency (0.2-2 MHz) do not induce V-Fib

Must use large return pad 

Preferable and cause less induction

(all can cause problems with pacemakers and AICDs)

Used with lowest possible settings

Used in brief periods as possible

DO NOT use within 15 cm of pacemaker or AICD