BT_SQ 1.7 Describe microshock and macroshock and the mechanisms for preventing these, with particular reference to ensuring the compatibility of medical procedure, treatment area, and medical equipment used.


Earth Wire 3

Electrical safety is a subject which many candidates seem to have trouble with.

The examiners consider it an important topic and ask it regularly.

Because of the environment you are practising in, you may underestimate the importance of electrical safety. In a hospital I worked at some time ago, there were several staff members who received electrical shocks before RCDs were introduced.

I gave a talk on the topic when I was a registrar, and dug up all sorts of reports of electrocutions. Anesthesiology 1973 Feb. 38:181-3 has an example of this kind of incident.

Rather than give True/False statements in this post, I will give a series of questions, which cover the important areas in the topic.

  1. Why is the domestic power supply “earthed”?
  2. What risks occur because of the “earthing” of the power supply?
  3. What is the earth wire connected to?
  4. If you touch a live wire, how is a circuit formed?
  5. What is an RCD and how does it protect against shock?
  6. What is the difference between an RCD and a circuit breaker?
  7. Why does shock from domestic power induce VF, whilst shock from a defibrillator terminates it?

The answer to the first few questions can be found in Magee & Tooley.

RCDs are explained well in Russell if you can find a copy.

The 2015 Miller Cap. 109 covers electrical safety, but I find the explanations somewhat unclear. It has a lot on isolated power supplies, and does have a diagram which you can extrapolate to answer question 4. They call RCDs Ground Fault Current Interrupters.

The previous edition of Miller has electrical safety in chapter 100. Both editions have a couple of dubious statements on earthing. More on that in a later post…

BT_SQ 1.19 Describe the principles of surgical lasers, their safe use and the potential hazards

TRUE/FALSE  CO2 lasers may cause retinal damage if protective eyewear is not worn

TRUE/FALSE  Nd-YAG lasers cause injury confined to the cornea if eye protection is not worn

TRUE/FALSE  A laser may ignite material under a drape without igniting the drape

TRUE/FALSE  “Laser” stands for light amplification by stimulated electron radiation

TRUE/FALSE  Laser hazards include atmospheric contamination


BT_SQ 1.18 Discuss the principles of surgical diathermy, its safe use and the potential hazards

T/F Diathermy units operate at frequencies of approximately 100Hz to minimise the risk of VF

T/F Unipolar diathermy is contra-indicated in patients with implanted pacemakers

T/F Bipolar diathermy cannot be used for cutting tissue

T/F It is ok to leave metal jewellery on a patient as long as a capacitative coupling ground electrode is used

T/F The neutral wire of the diathermy is earthed to reduce the risk of electric shock


Bonus Question:What is this device, and how does it work?Megadyne