Revised and reviewed 2 August 2015
OVERVIEW
- You may have noticed that much of the equipment used in critical care runs on something called electricity… Hence, it is useful to know the basics!
- Critical care practitioners may be exposed to, and need to mitigate, electrical hazards
- Basic electrical concepts are also relevant to the treatment of victims of electrical injuries
DEFINITIONS
Current (I)
- charge per unit time (unit is A – ampere)
-  described in terms of the direction of current flow – alternating (AC e.g. mains power) or direct (DC e.g. a battery)
- simplistically, the ability of a material to conduct current depends on “how tightly the electrons in the outer atoms are packaged, with less conduction occuring when they are very tightly bound”
Conductor
- material that allows current to flow (e.g. metals)
Insulator
- material that doesn’t allow current to flow (e.g. rubber)
Semiconductor
- material that permit current flow intermediate to that of a conductor and insulator (e.g. crystalline inorganic solids)
Resistance (R) and Impedance
- Resistance measure of how much a material resists the passage of current (unit is Ω – ohm)
- called Impedance if it is resistance to AC current as opposed to DC current
- the inverse of resistance is Conductance (unit is S – siemens)
Potential (aka electrical potential)
- energy per unit time
Potential difference (Voltage)
- the difference in electrical potential between two points in an electric circuit or field (unit is V – volt)
- current will only flow through a circuit when a potential difference exist, from negative to positive
- sources of potential difference include batteries, generators and being plugged into the ‘electrical grid’
Ohm’s law
- describes the relationship between potential difference, current and resistance
- V = I x R
ELECTRICAL STANDARDS
- different electrical standards for electrical safety in hospitals apply in different countries
- In Australasia the relevant electrical standard is AS/NZS3003: Electrical installations: patient treatment areas of hospitals and medical and dental practices
- In Australia, like the UK and New Zealand, mains electricity is supplied as 50 Hz AC at a potential of 230V.
AS/NZS3003 divides treatment areas into:
- Cardiac protected electrical area
- areas where patients may have electrical conductors near or inside their hearts with a risk of microshock
- these areas have equipotential earthing and Residual current devices (RCDs)/Line isolation monitors (LIMs)
- Body protected electrical area
- areas where patients are attached to equipment that lowers their natural resistance to current injury but are not at risk of microshock
- RCDs/LIMs are used
Equipment
- classified by the risk of current leak
— Type B have no restriction
— BF items may only leak a maximum of 5 mA
— CF items are allowed a maximum leak of 50 microA - ‘Defibrillator proof’ refers to items that can safely remain attached to the patient during discharge of a shock
See Electrical Safety Devices for an overview of electrical safety equipement
References and Links
LITFL
- CCC — Electrical injury
- CCC — Electrical Safety
- CCC — Hands On Defibrillation
Journal articles
- Singh. Basics of electricity for anaesthetists. Contin Educ Crit Care Pain 2011;11(6):224-228 [Free Full Text]
- Boumphrey, S et al. Electrical Safety in the Operating Theatre.Contin Educ Crit Care Pain 2011;3(1):10-14Â [Free Full Text]
FOAM and web resources
- HowEquipmentWorks.com — Electricity Basics
- HowEquipmentWorks.com — Electrical Safety
Leave a Reply