Electrical Safety in the Operating Theatre Flashcards
(37 cards)
How does mains electricity travel from the substation?
In two conductors - live wire (potential of 240V) - neutral wire (connected to earth and thus at the same potential as earth) This is the same as the positive and negative wires used in DC
What happens if a connection is made between the live wire and earth?
The current will flow through that connection - including if this connection is a patient
How can electricity cause damage to the body?
Electrocution Burns Ignition of a flammable material
What are the factors affecting the damage caused by electrocution?
The amount of electricity that flows (current) Where the current flows (current pathway) Density of current The type of current (AC vs DC) Current duration
What is current?
A flow of electrons, measured in amps (SI unit)
What would a current passing through the chest cause?
VF or asphyxia due to tetany of the respiratory muscles
What would a current passing through the body vertically cause?
Loss of consciousness and spinal cord damage
What would a 1 mA of 50Hz current flowing between each hand cause?
Tingling
What would a 15 mA of 50Hz current flowing between each hand cause?
Muscle tetany, pain, asphyxia
What would a 75 mA of 50Hz current flowing between each hand cause?
VF
What current applied directly to the heart (or in close proximity) can cause VF?
50 milliamps at 50Hz (microshock)
What equipment might allow microshock?
CVCs Intracardiac pacemakers with external lead Temperature probe placed in the oesophagus immediately behind the left atrium
Why is alternating current at 50Hz the most dangerous current?
The myocardium is most susceptible to the arrythmogenic effects of electric currents at this frequency and the muscle spasm prevents the victim letting go of the source
How are sparks prevented in theatre?
Spark proof switches and electric socket outlets which prevent the plug being withdrawn whilst the switch is turned on.
What are the ways in which electricity can flow through the body?
Resistive or capacitive coupling
What is resistive coupling?
When the body provides a direct physical connection to let electricity flow through the body. This happens if the body comes into contact with electricity and the earth directly eg. faulty equipment
What is capacitive coupling?
When the body forms a connection between an electrical source and earth by acting as one plate of a capacitor.
What is the formula for impedance in a capacitor?
impedance = distance between plates / (current frequency x plate area)
What happens if direct current is applied to a capacitor?
Current flows only until the positive plate is charged to the same potential as the electrical source, then the current stops
Give an example of capacitive coupling in the clinical setting
MRI scanner - the scanner creates a changing electromagnetic field that can induce currents in conductors such as the wire or metal of a standard pulse oximeter probe - capacitive coupling allows the patient to become part of an electrical circuit which may cause a burn
What methods can we use to reduce the risk of electrocution?
General measures Equipment design Equipotentiality Isolated Circuits Circuit Breakers
What are the general measures to reduce risk of electrocution?
Adequate maintenance Regular testing of equipment Ensuring patient not touching earthed objects Wearing antistatic shoes
What are the equipotentiality to reduce risk of electrocution?
If different piece of equipment have different potentials relative to earth and are in close proximity - a connection may be made between them by the user. A current would then flow from higher to lower potential via the user. To avoid this - the terminals of each piece of equipment in a stack can be connected to each other bringing them all to the same potential.
What are the isolated circuits measures to reduce risk of electrocution?
This provides a circuit where the connection between the electrical source and earth does not allow current to flow. It consists of an isolating transformer which is 2 coils electrically insulated from each other. The mains circuit is earthed but the patient circuit is not (floating).
