Electrical Concepts, Definitions and Standards

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 occurring 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 equipment


References and Links

LITFL

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):10-14 [Free Full Text]

FOAM and web resources


CCC 700 6

Critical Care

Compendium

Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also the Innovation Lead for the Australian Centre for Health Innovation at Alfred Health and Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of two amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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