SAQ 2017.2 Question 6

Describe the effects of morbid obesity on the respiratory system.

The material to answer this is scattered through the recommended texts and most of it can be deduced if you have a reasonable general understanding of respiratory physiology. It’s also nicely summarised in Foundations on Anesthesia : Basic Sciences for Clinical Practice by Hemmings and Hopkins Chapter 71 if you can find a copy.

It’s Friday so instead of making this a TRUE/FALSE post I’ll talk about answering an SAQ using this question as the base.

One of the examiners gives the advice :

1.  THINK OF A FACT
2.  ASSESS ITS RELEVANCE AND RETURN TO STEP 1 IF IRRELEVANT
3.  WRITE IT DOWN
4.  RETURN TO STEP 1

This is great advice. Unfortunately a lot of exam answers have step 2 omitted. Step 2 is very important, and in the heat of the exam it is easy to forget it. I have had a sneak preview of the exam report and for this question the marking examiner commented that ‘Notably there were no marks achieved for describing the metabolic, endocrine or cardiovascular effects of morbid obesity’.

I would build on his advice and say an even better answer would be created by :

1.  THINK OF A FACT
2.  ASSESS ITS RELEVANCE AND RETURN TO STEP 1 IF IRRELEVANT
3.  WRITE DOWN BOTH THE FACT AND WHY IT IS RELEVANT
4.  RETURN TO STEP 1

For example with this question you could write : (note use of point form, common abbreviations and clear arrows showing direction of change – all acceptable and even encouraged by examiners)

•  FRC ↓ or FRC ↓ so oxygen store ↓ esp with pre-oxygenation (does this decrease in FRC have other implications too?)
• ↑ pulmonary blood volume or  ↑ pulmonary blood volume → ↓ compliance → ↑WOB   (this change in blood volume is also relevant to gas exchange, why?)
• diaphragm displaced cephalad → why is this relevant to the preload of this muscle?

 

 

 

 

SAQ 2017.2 Question 5

Outline the factors which influence the time taken for loss of consciousness with an inhalational induction of anaesthesia.

Loss of consciousness will be faster with a smaller FRC     TRUE/FALSE

Loss of consciousness will be faster in a patient who is anxious and struggling    TRUE/FALSE

Loss of consciousness will be faster with a more soluble anaesthetic agent    TRUE/FALSE

Loss of consciousness will be faster with an increased cardiac output    TRUE/FALSE

Benzodiazepine premedication may speed the process in some patients, and slow it in others    TRUE/FALSE

 

 

SAQ 2017.2 Question 4

Describe the generation and features of a normal awake EEG (15)

Briefly discuss the processing performed by EEG monitors (BIS/Entropy) to produce a single dimensionless number from the EEG (10)

This material is adequately covered in a couple of the books on the recommended reading list – Magee & Tooley, and Davis & Kenny. There are some better review articles around, and a mob of FANZCAs in Cairns paralysed each other sans anaesthesia using BIS monitoring and published it (British Journal of Anaesthesia, Volume 115, Issue suppl_1, 1 July 2015, Pages i95–i103).

The EEG measures action potentials     TRUE/FALSE

As a patient becomes more deeply anaesthetised their EEG drops in amplitude and frequency    TRUE/FALSE

Burst suppression becomes more pronounced with deeper levels of anaesthesia    TRUE/FALSE

Phase coherence becomes more pronounced with deeper levels of anaesthesia    TRUE/FALSE

Frowning will increase RE (response entropy) more than SE (state entropy)    TRUE/FALSE

SAQ 2017.2 Question 3

a) Describe the immediate cardiovascular responses to the sudden loss of 30% of the blood volume in a healthy awake person
b) How are these responses different if the patient is undergoing anaesthesia with sevoflurane?

The decrease in blood volume will be detected by the high pressure baroreceptors in the atria    TRUE/FALSE

The response will be mediated by the cardiovascular centre in the medulla    TRUE/FALSE

There will be arterial but not venous constriction    TRUE/FALSE

Sevoflurane will impair contractility    TRUE/FALSE

Sevoflurane will depress baroreceptor signalling    TRUE/FALSE

 

National Anaesthesia Day: Part 1

Today is a very significant one particularly if you are an anaesthetist.  On this day, 171 years ago, William Thomas Green Morton (pictured above) administered the first successful anaesthetic publically at what is now termed the ‘Ether Dome’ in Massachusetts General Hospital, Boston. I am biased but think this is the most significant medical discovery ever. What is perhaps surprising is that the demonstration didn’t happen many years earlier- ether is not a novel chemical nor is it difficult to synthesize. The analgesic and sedative properties of nitrous oxide had been known about for almost half a century but no one had bothered to apply this knowledge to the more expedient need of surgical anaesthesia. To be fair, Morton’s contemporary, Horace Wells, used nitrous oxide successfully for dental extractions before unfortunately ‘failing’ when he demonstrated it publically on the same stage as Morton would subsequently have success.  I put the ‘failing’ in apostrophes because although Wells’ patient (he was a medical student with a toothache) groaned when under the influence- eliciting the derisory, “Bah humbug!” comment from the surgeon- the patient later stated that he did not recall the procedure and that it had caused him no pain. Surgeons have forever since equated movement or vocalisation from the patient as evidence of inadequate anaesthesia.

Although we commemorate this event with the respect that it deserves, the pioneering anaesthetists of the day were not the most respectable or reputable bunch. For the most part they were greedy, self-serving dentists out to make a quick buck. Nonetheless we are indebted to them.

The following statements relate to October 16, National Anaesthesia Day:

It has always been celebrated on this date in Australia  TRUE/FALSE

Morton tried to patent ether calling his mystery drug ‘Letheon’  TRUE/FALSE

Morton was running late on the momentous day setting an unfortunate precedent  TRUE/FALSE

Morton was the first person to administer ether successfully for a surgical procedure  TRUE/FALSE

Morton killed himself by cutting his femoral artery at the age of 48 while imprisoned. He was incarcerated for throwing acid in a prostitute’s face  TRUE/FALSE

Answers another time. Happy Anaesthesia Day!

 

 

 

 

Evolution of an SAQ

A colleague wrote some evolution of a viva posts so I thought I’d give some insight on the development of an SAQ.

An SAQ is initially written by an individual and placed into a bank of questions. Once we decide to include that question in a paper a group of us will look at it and try to remove any ambiguity. An answer grid is then written (often not by the original author). An answer grid comprises the points we think address the question, with weighting to more important points and often with weighting towards answers which demonstrate understanding. Marks are allocated such that an excellent candidate could achieve full marks well within 8 minutes. Other examiners will then inspect and edit the grid – we are not expecting you to guess the thought processes of one individual. The grid is not set in stone, if a candidate writes correct and relevant points in their answer they will be given marks even if they are not in the final grid. The question is often re-edited at this stage to take out any more ambiguity or to to narrow or widen its breadth.

 

 

SAQ 2.17 Question 2

Using a labelled diagram, describe how a mechanical (non-cassette) variable bypass vaporiser achieves the concentration set on the dial. Describe the mechanisms that compensate for temperature and downstream pressure changes.

The vaporiser is encased in insulating material    TRUE/FALSE

The vaporiser’s heat sink has low thermal capacity   TRUE/FALSE

The maximal output of the vaporiser is dependent upon the saturated vapour pressure of the anaesthetic agent   TRUE/FALSE

As a liquid vaporises its temperature drops   TRUE/FALSE

A large vaporising chamber will assist in compensating for pressure changes due to the pumping effect   TRUE/FALSE

SAQ 2.17 Question 1

Time to look at the last written paper…

Q1.  Describe the visceral and somatic pain of labour with particular reference to the anatomy and pain pathways. 

Visceral pain predominates in the first stage of labour      TRUE/FALSE

Chemoreceptors are involved in pain modulation     TRUE/FALSE

Nociceptors detecting stretch are involved in the pain of second stage     TRUE/FALSE

Head descent can stimulate the lumbosacral plexus    TRUE/FALSE

Pain can be referred to the thighs in first stage only    TRUE/FALSE

Aviation 6 – Decompression Illness

Today we return to North Africa.  Flying Officer Reynolds flew 25 missions above 40,000 feet over a single month.  The German Ju 86’s flew at ever increasing altitudes as three out of the four available aircraft had been shot down by British Spitfires.  The final Ju 86 flight was at nearly 50,000 ft and Reynolds was again in pursuit.

He had been at over 45,000 feet for over an hour and he was suffering from the effects of altitude:

“his whole cockpit, instrument panel, control column and perspex were thickly coated with ice; his body was racked with pain and his arms temporarily paralysed, and his eyesight also failing with weakness.”  — John Frayn Turner.   British Aircraft of the Second World War

Reynolds was probably suffering from “The Bends” or decompression illness.  You may have encountered this condition in the context of diving but it is also well recognised in high altitude aviation.

Occasionally and ironically, tourists are diagnosed with decompression illness in Alice Springs. How is this possible you ask?

Well, they go diving in North Queensland and then fly to the Red Centre, the exposure to altitude soon after diving is enough to “Bend” them.

The relevance of decompression illness to anaesthesia may seem a little obscure.  The body in decompression illness is simply behaving like a human vapouriser where nitrogen is the volatile agent.

BT_SQ 1.12 Describe the principles and safe operation of vaporisers

TRUE/FALSE Henry’s Law is relevant to vaporiser functioning 

TRUE/FALSE The Aladin cassette vaporiser is an example of an injection vaporiser system

TRUE/FALSE Modern vaporisers use an electrical heating coil to compensate for the cooling caused by latent heat of vaporisation

TRUE/FALSE A plenum vaporiser is designed so that the gas leaving the bypass is fully saturated under normal conditions

TRUE/FALSE The Tec Mark 5 vaporiser is designed to be ‘tip resistant’

As an extra exercise, see if you can find or work out the properties of nitrogen and the circumstances that relate to it “vapourising” in the body at altitude (in the same the way you would think about an inhalational agent).

Aviation 5 – Time of Useful Consciousness – Part 2

BT_PO 1.31 Discuss the carriage of oxygen in blood, the oxyhaemoglobin dissociation curve, oxygen stores in the blood and their clinical significance and implications

The previous aviation post looked at how altitude affects the time it takes to for a person to become ineffective.  Today’s post is a series of questions and problems to solve, relating to the physiology underlying the rapid development of hypoxaemia.

The times of useful consciousness quoted previously were determined empirically (probably “volunteers” in an altitude chamber). See if you can come up with similar values as a desktop exercise.

• Work out the total body stores of oxygen sitting in an airliner at a cabin altitude of 6000 feet.  (Remember to include FRC, arterial blood, venous blood, myoglobin and other tissues.)
• What is a normal minutely consumption of oxygen for someone sitting in an airliner?
• What happens to these stores if the cabin altitude suddenly changes to 35,000 feet (as might happen if a modern aircraft cabin is suddenly depressurised)?
• Would the oxygen consumption increase?
• Is it better to hold your breath or breath rapidly?
• Oxygen usually moves from alveolus to blood.  Can the reverse occur?  What would this do to arterial oxygen tension?
• How would you describe the shape of the graph of arterial oxygen tension versus time?
• You will also need to consider regional blood flow and oxygen consumption as well as the volume of blood and oxygen content in various anatomical locations
• Remember that this exercise involves dynamic not static situations

Feel free to post your calculations in the comments section