Macroshock

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_GS 1.53 Describe the synergism between anaesthetic agents, opioids and regional blockade and how this is used clinically

TRUE/FALSE  Moderate doses of opioids can reduce MAC of volatile agents by as much as 75%.

TRUE/FALSE  50% reduction in doses is expected when propofol and midazolam are used together for hypnosis.

TRUE/FALSE  The exact degree of drug synergism can be calculated from pharmacokinetic data of individual agents.

TRUE/FALSE  The bispectral index is additive when propofol and remifentanil are used in total intravenous anaesthesia.

TRUE/FALSE  Midazolam has no effect on the ketamine dose required to suppress movement to a noxious stimulus.

BT_GS 1.50 Describe the concept and clinical application of MAC in relation to inhaled anaesthetic agents

TRUE/FALSE  MAC-AWAKE for Nitrous Oxide is approximately 30% of its MAC-Value

TRUE/FALSE  Sevoflurane is metabolised by the cytochrome p450 enzyme 2E1

TRUE/FALSE  The MAC of sevoflurane in a 6 month child is approximately 2%

TRUE/FALSE  The higher the inspired anesthetic concentration, the less it then diminishes because of uptake

TRUE/FALSE  Administration of 50% Nitrous oxide will double the volume of air-filled spaces

Aviation 4 – Time of Useful Consciousness – Part 1

Flying Officer Reynolds was flying combat air patrol just north of Cairo.

He sighted a Ju86P with two pilots sitting securely in a pressure cabin.  He then pursued the Ju86 north towards Alexandria at ever increasing height.

At 37,000 ft he closed in and began to zigzag to prevent overshooting past the Ju86, the Ju86 zigzagged in the same way trying to stay above the Spitfire and force it to lose height.

The duel continued to 40,000 ft where Reynolds realised he could not climb any higher until the aircraft weight was lightened.

Calculating how much fuel he could use and still reach home safely,  he threw out his life jacket and dingy, keeping only the parachute.

In the middle of these calculations he temporarily blacked out having only sufficient time to turn his oxygen supply to full emergency to bring himself around.

BT_PO 1.36  Discuss the physiological effects of hypoxaemia

BT_RT 1.11 Describe the physiological consequences of hypoxaemia 

The time of useful consciousness is the “time interval after loss of pressurisation or mask function during which the crew member is able to recognise and take action to correct the situation”

<18,000 ft = hours/days

18,000 ft = 20 – 30 min

25,000 ft = 3 – 5 min

30,000 ft = 1 – 2 min

35,000 ft = 30 – 60 sec

>43,000 ft = 9 – 12 sec

Crusing Altitude

As you can see from this photo, taken recently at airliner cruising altitude, if there is a sudden depressurisation, you will have less than 30 seconds to get to your oxygen mask.

TRUE/FALSE Hypoxaemia caused by ascending to altitude results in a left shift of the oxygen haemoglobin dissociation curve

TRUE/FALSE In cerebral hypoxia, acidosis causes more damage than depletion of high energy compounds

In an airliner:

TRUE/FALSE when the oxygen masks drop down from the ceiling put you child’s mask on first

TRUE/FALSE oxygen is already running when you put on the mask

Aviation 3 – Pressure Breathing

Helmet Shot

Today we continue the aviation theme.  The last aviation post asked what could be done to improve oxygenation when 100% oxygen was not enough.

Pilots flying at high altitude have access to “pressure breathing” or in medical terms: continuous positive airway pressure (CPAP).  An example of such a mask is seen in the photo above.

BT_PO 1.35 Discuss the physiological consequences of intermittent positive pressure ventilation and positive end-expiratory pressure

As you know, CPAP is commonly used for treatment of sleep apnoea, patients with pulmonary oedema and other conditions.

While these conditions are not examinable in the Primary Exam, the physiological effects of CPAP are important to understand.

TRUE/FALSE CPAP increases respiratory compliance

TRUE/FALSE CPAP reduces venous return

TRUE/FALSE Gastric dilation is a common problem during CPAP

TRUE/FALSE CPAP has no effect on cardiac output

TRUE/FALSE The limit to the level of CPAP that can be tolerated by an awake patient is 15 mmHg

 

Study Tips: “I keep six honest serving men (they taught me all I knew); Their names are What and Why and When And How And Where and Who.” – Rudyard Kipling, The Elephant’s Child

The vivas are over for another year, which means that it is less than six months until the next written exam.

For those of you planning to sit the first exam in 2018 it is probably time to revisit your study plan to see how you are tracking.

For those aiming for the second sitting next year, it is time to put pen to paper and make a study plan and timetable.

Here is a list of  the types of resources you could include:

  • ANZCA Curriculum (Learning outcomes mapped to the primary examination) – here is great site
  • Online MCQ collections (a previous study tips post covered the Black Bank and also applies to newer collections)
  • Past SAQ papers (including examiner reports)
  • Operating theatre teaching – Rudyard Kipling can help with this one
  • Primary LO of the Day (a bit of recursive promotion)

  • Other internet resources (try googling ‘anaesthesia exam technique resources’)
  • Study notes from past trainees – bear in mind that the real benefit of study notes comes from creation not consumption
  • Exam technique resources
  • Psychology support – managing exam anxiety

If there are others you know about feel free to leave a comment below.

Aviation 2 – Duel in the Stratosphere

To add to the interest, we will be following the fortunes of two remarkable pilots from World War Two.

Flying Officer’s Emmanuel Galitzine and G.W.H. Reynolds were Spitfire pilots who, in 1942, came up against German Junkers 86 (Ju86) high altitude bombers in two different theatres of war: Galitzine over England and Reynolds over North Africa.

To understand the incredible feats of these pilots it is important to know that some high altitude duels happened at over 40,000 ft and that the Ju-86’s had pressurised cabins but the Spitfire’s cockpit did not.

BT_PO 1.22 Describe the composition of ideal alveolar and mixed expired gases

Using the alveolar gas equation, calculate the alveolar oxygen tension at each of the following altitudes.

Altitude      Atmospheric pressure

18,000 ft     380 mmHg (Mt Everest Base camp)

33,000 ft     190 mmHg

40,000 ft     142 mmHg

45,000 ft     111 mmHg

50,000 ft     87 mmHg

Did you allow for changes in carbon dioxide tension caused by the response to hypoxaemia?

Our Spitfire pilots had face masks and regulators that allowed delivery of up to 100% oxygen.

Re-calculate the alveolar oxygen tensions at the altitudes above assuming 100% oxygen was being administered.

Do you think 100% oxygen would have allowed our pilots to function at these altitudes?

What else could be done to improve oxygenation in this situation?

How might the effective atmospheric pressure be increased?

Aviation 1 – Introduction

Today we start a periodic series of posts with an aviation theme.

I am sure you have heard tropes comparing aviation and anaesthesia: human factors, crisis management, check lists, take off, cruise and landing to name a few.

You may not be aware that many physiological principles relevant to anaesthesia are also relevant in aviation and space travel.

The environmental stressors experienced by pilots and astronauts are similar to those experienced by patients, but magnitude of these stressors and the physiological effects can be more extreme.

Thinking about these effects can test and hopefully extend your understanding of the underlying principles.

There is only one primary exam learning outcome (BT_PO 1.37) that specifically mentions altitude and this has been the subject of previous posts.  There is also one in the final exam curriculum (SS_IC 1.102).

However there are many others that have relevance to aviation physiology.

BT_SQ 1.6 Describe the methods of measurement applicable to anaesthesia, including clinical utility, complications and sources of error in particular: 

  • SI units 
  • Measurement of volumes, flows, and pressures, including transducers

Pressure is measured in different ways throughout anaesthesia and a working knowledge of conversion factors between various units is important.

TRUE/FALSE  1 atmosphere (ATM) = 760 mmHg

TRUE/FALSE  29 psi = 200 kPa

TRUE/FALSE  30 cmH2O = 22 mmHg

TRUE/FALSE  5 kPa = 40 mmHg

Some harder ones:

TRUE/FALSE In aviation, altitude is measured in feet not metres

TRUE/FALSE There is an exponential decline in pressure with increasing altitude

TRUE/FALSE There is a linear decline in temperature with increasing altitude

BT_RT 1.39 Interpret blood gas analysis in respiratory failure

TRUE/FALSE  When breathing room air, an arterial PO2 of less than 20 mmHg is not compatible with life.

TRUE/FALSE  Respiratory failure is ruled out if blood gas analysis shows an arterial PCO2 of 27 mmHg.

TRUE/FALSE  Generally, arterial PO2 gives a better indication of respiratory failure in comparison to arterial PCO2.

TRUE/FALSE  Arterial PCO2 in excess of 85 mmHg is usually never due to iatrogenic causes.

TRUE/FALSE  It takes only 30 seconds to develop hypoxaemia with acute hypoventilation in room air.

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