Electricity and OR Electrical safety Flashcards
What is current?
the flow of electrons
What is capacitance?
stored charge is discharged from defibrillator
What is Ohm’s Law?
I= V/R
where V= voltage= electromotive force= potential difference
I= current- quantity of electrons measured in Amperes
R= resistance-force in opposition to flow of electrons measured in Ohms
analogous to Q= P/R
What is electric current?
how much charge (how many electrons) pass a certain point in a circuit per unit time
What is a Coulomb?
a unit of measure of electric charge
just like “gram” is a unit of measure of mass
How many electrons are needed to generate 1 Coulomb?
6.24 x 10^18 electrons carry a charge of 1 Coulomb
Each electron has a charge of 1.60 x 10^-19
1 ampere is
the movement of charge carried by 6.24x10^18 electrons passing a certain point in 1 sec
or 1 Ampere of current the movement of 1 Coulomb of electric charge passing a certain point in 1 sec
In order to have flow, there must be
a complete circuit
Voltage is lost as
electrons move through area of resistance
What is impedence?
resistance to current flow that changes with frequency
consists of resistance plus other factors that effect electron flow
how resistance changes with changes in frequency
A watt is
the unit of power (work done/unit time)
the product of voltage and current
A watt-second is
work or energy
How is energy measured in a home versus in a defibrillator?
defibrillator- Watt-sec
home- Kilowatt-hours
Power is equal to
current x voltage
A closed loop must have:
driving pressure (voltage) to force a current (ampheres) to flow through a Resistance in accordance with Ohm’s Law
What is the current if the voltage is 120 and the resistance is 240 ohms?
current is 0.5 amps
A conductor is
any substance that permits a flow of electrons
I.e. metals & human tissue
substance has loosely attached and easily lost electrons which permits flow electrons
A nonconductor or insulator
have tightly bound electrons which do not permit electron flow
include: glass, rubber, plastic, dry wood, pure water
What is a direct current versus an alternating current?
a direct current (DC, batteries)- the electron flow is always in the same direction
an alternating current (AC, electric company)- the electron flow reverses direction (Oscillates) at regular intervals
the oscillating frequency is measured in cycles per second or Hertz
How many cycles of electrons (wavelength) can we get in 60 seconds?
60 Hertz (US)
What is capacitance and a capacitor?
a measure of a substance’s ability to store a charge
a capacitor is an electrical device used for storing electric charge
How does capacitance work?
it consists of 2 parallel conductors separated by an insulator (non-conductor)
can be AC or DC circuits
Insulated wires running next to each other will produce capacitance
simply by being plugged in even though the equipment is NOT turned on
The strength of the electric field is much greater when
there is more coiled wire which allows more atoms to be oriented–> stronger magnet
Having an iron core with coil wrapped around
produces a much stronger magnet than with the coil alone (has more atoms and thus generates more electric field)
Electrons flow from
negative to positive
The electromagnetic field can
do work; it can push and pull magnets and push and pull electrons
Electromagnetic fields can influence
other circuits in close proximity
a circuit where electrons are flowing generates a magnetic field that pulls or pushes electrons that are nearby (and can easily be pushed and pulled) and this generates a second current
If the wire is coiled repeatedly around an iron core
the magnetic field induced can be very powerful
In an AC circuit, inductance can electromagnetically
generate an opposing electromotive force (current in a nearby wire)
A motor is
when we have a fixed magnet and rotating metal bar
the electric fields from the magnet are repelling the electric field from the wire
allows us to use repulsion between two sources of electromagnetic fields that oppose one another to do work
A generator works by
have rotating magnets and a fixed bar; the electromagnetic fields are sufficient to move electrons through inductance which generates an electric current
High impedance results in
low current flow
Low impedance results in
high current flow
Utility companies supply electrical energy in the form of
AC current of 120 V and 60 Hz
To have a current flow, there must be a complete circuit with
a voltage source to drive the current through the resistance
A short circuit or fault is defined by
a condition in which there is ZERO impedance with a high current flow
A power cord consists of 2 conductors:
“Hot” conductor returns the current through the impedance
“Neutral” conductor returns the current to the source
the potential difference between the 2 conductors is 120 V
A person can be shocked by
touching a wire directly or touching a conductor that is touching a wire
Grounding equipment is
a way to prevent someone from being part of the circuit by attaching a metal wire from the device to the ground
Electric shock can occur by
contacting AC or DC current (takes about 3x DC as AC to cause vfib)
A person must contact the electric circuit at
2 points and there must be a voltage source causing current to flow in order to be shocked
What is a macroshock?
large amount of current flow through a person
What is a microshock?
very small amount of current flow through a person (Conditions: external conductor in direct contact with the heart such as a PA catheter) much smaller current would be needed to cause vfib in this situation because it has a direct line to the heart
The severity of the shock depends on:
the amount of current (Amperes) and the duration of contact
If an individual contacts an external source of electricity damage can be produced in 2 ways:
current can disrupt normal electrical function of cells
current passing through a resistance (the body) raises the temperature of the substance and can produce a burn
At 100-300 mA
ventricular fibrillation will start, but respiratory center remains intact
The recommended maximum allowable 60-Hz leakage current is
10 microamperes
100 microamperes can cause
ventricular fibrillation if in direct contact with the heart such as a PA catheter
If there is any buildup of charge on a device that is grounded
the grounding element allows the charge to go down to the ground and be discharged
In the OR, our source is
not grounded but our equipment is
Grounding can be used to describe several different principles:
the grounding of the primary electrical power supply
the grounding of electrical equipment itself
Faulty equipment in the OR does
not present a shock hazard when plugged into an isolated power system
In the OR, even though the power system is isolated from the ground,
the equipment case is still connected to an equipment ground
All AC power systems and electrical devices
manifest some degree of capacitance
There is a small amount of ________ ________ to the ground with our devices in the OR
“Leakage” current
The OR system is set to alarm for anything above 5 mA which may indicate a short circuit
The electrically susceptible patient is
a patient with a direct external connection to the heart such as a PA catheter
The electrically susceptible patient is protected against microshock
by an intact ground wire
-if the equipment ground wire is broken all 100 microamps of leakage current could flow through the catheter causing v-fib
The Bovie or electrosurgical unit operates by
generating very high-frequency AC currents of anywhere from 500,000 to 1 million Hz
produces voltage as high as 3000 V
Produces close to 400 watts of power
Heat is generated whenever a current passes through
resistance
The amount of heat produced is
directly proportional to the square of the current and inversely proportional to the area through which the current passes
The heat formula for ESU:
H= I^2 x A
High frequency currents have
low tissue penetration and do not excite contractile cells and therefore do not cause V-fib
The current for the Bovie must
enter the patient and be routed back to the ESU through using a return plate
Energy passes through the patient to the return plate with a large surface area that returns it safely to the ESU
A properly applied return plate
covers a large surface area. No harmful heat is generated and no tissue damage
The placement of the return plate needs to be
close to operative site
as far away as possible from EKG pads
ensure adequate gel and sufficient skin contact
not placed over scar tissue, hair, or implants
The dispersive plate must cover
a large area so that the current density is below a level that will cause burns
The current will seek to return to the ESU through alternate conductors if:
the dispersive plate is not properly applied to the patient
return plate is dislodged during the procedure
return plate cord is damaged or not properly connected
insufficient conductive gel
Alternate conductors of current include
anything attached to the patient such as ECG leads/temperature probe
What are the types of ESU units?
unipolar- current returns to unit via dispersive pad
bipolar: two electrodes that look like forceps-dispersive pad is not necessary and less energy than unipolar
Argon beam coagulator (unipolar)-uses a stream of argon gas to support the electric current
