Corpus Curare Spiritumque

There have been some really good study / exam tips lately, so I thought I’d post something with a motivational flavour. (Also, I resisted doing a history post because it’s too close to the exam to risk taking you on a procrastination tangent).

 

ANZCA motto

 

“Corpus Curare Spiritumque” is the Latin motto which appears on the ANZCA coat of arms.

It translates as “To care for the body and its breath of life”. I think this encapsulates really well, so much of what anaesthetists do.

Whether we are in theatre, attending a trauma, in pre-admission clinic, or on a ward round, we are always focused on the whole patient. Especially in theatre, sometimes we are the only doctors who seem to have a handle on the big picture!

We are doctors who are good at keeping people alive. However, the full meaning of the “breath of life” can extend to include every aspect of homeostasis.

In order to live up to the lofty motto chosen by the Founding Fellows of the College, anaesthetists need a solid grounding in basic sciences.  That’s because we are surrounded every day by pharmacology, altered physiology, and technology.

At the end of the day, I hope that you can see the value and impact of all your study for the primary exam, in terms of your ability as an anaesthetist to “care for the body and its breath of life”.

 

 

Thiopentone

BT_GS 1.30 Describe and compare the pharmacokinetics of intravenous induction agents …

BT_GS 1.31 Describe and compare the pharmacodynamics of intravenous induction agents …

Thiopentone is a terrific drug. Unfortunately, the current generation of trainees lack familiarity and confidence with it. 

T / F  compared with propofol, a standard induction dose of thiopentone causes less vasodilation and less hypotension

T / F  when diluted with 20 mL water, 500 mg thiopentone makes a 2.5% solution, with a pH of 11  (regarding the pH, can you explain why you think this is true or false? Why is this pH necessary / not necessary?)

T / F  in plasma, thiopentone is 80% bound to albumin

T / F  thiopentone is a weak base with pKa 7.6 – therefore, 12% of an injected dose will be available to cross the blood brain barrier

T / F  the majority of thiopentone is metabolised to inactive metabolites

T / F  thiopentone effectively blunts the upper airway reflexes

♦♦♦♦♦

Now that you’ve become fascinated by thiopentone, it would be useful to use this knowledge to answer some SAQ’s.

  1. Write short notes on the pharmacology of thiopentone.
  2. Compare and contrast the pharmacology of propofol and thiopentone.
  3. Explain the advantages and disadvantages of propofol and thiopentone for induction of general anaesthesia.

These 3 SAQ’s are in ascending order of complexity, in terms of the level of understanding they are testing. Regurgitating your summary notes (Q1) is low level knowledge – a candidate may score highly without really understanding what they are writing. But Q3 requires not only the application of PK and PD data – this information must be further organised to address the advantages and disadvantages. Scoring well on this question would demonstrate a high level of understanding (appropriate given the “core” nature of the drugs in question).

Have a go at answering the 3 SAQ’s above. While the 3 answers will each contain some of the same information, the final answers will be quite different. Hopefully this will help you reflect on the importance of reading the question!!

 

 

Calcium

BT_PO 1.88 Outline the regulation of plasma calcium including the actions and control of vitamin D, parathyroid hormone and calcitonin

T / F  of the total calcium in plasma, 20% is present in the free ionised form

T / F  a decrease in plasma calcium causes the release of parathyroid hormone

T / F  PTH acts by directly (i) releasing calcium from bone, (ii) increasing calcium absorption from the GIT, and (iii) decreasing renal calcium excretion

T / F  vitamin D is converted to 1,25-dihydroxy cholecalciferol by UV light, which then acts to increase calcium absorption from the GIT

T / F  hypocalcaemia can prolong the QT interval

T / F  10 mL of 10% calcium chloride contains 6.8 mmol Ca++, and 10 mL of 10% calcium gluconate contains 2.2 mmol Ca++

Extra discussion questions:

  1. Following a total thyroidectomy, patients can develop hypocalcaemia. Can you explain why? What symptoms would develop, and what physiology explains these?
  2. Patients with bony metastases can develop hypercalcaemia. What is the mechanism of this? What symptoms would develop, and what physiology explains these?

Insulin

BT_PO 1.90 Describe the pharmacology of insulin preparations …
BT_PO 1.85 Describe the control of blood glucose

T / F  the beta cells of the islets of Langerhans secrete proinsulin, which is then cleaved in the plasma to insulin

T / F  soluble insulin (Actrapid) starts working 30 minutes after S/C injection

T / F  insulin aspart (Novorapid) is more rapidly absorbed than Actrapid because it consists of only the A chain of amino acids

T / F  insulin glargine (Lantus) is slowly absorbed because the insulin is complexed with zinc and protamine

T / F  biguanides act by increasing cellular sensitivity to insulin

T / F  insulin increases the uptake of glucose into the liver, by upregulating the number of GLUT-4 transporters

ETCO2

BT_SQ 1.6 Describe methods of measurement (including) … gas analysis, including capnography
BT_PO 1.29 Discuss regional ventilation-perfusion inequalities

Each of the following T/F statements applies to a cardiac arrest with CPR being performed

T / F  an ETCO2 of 15 mmHg would indicate good CPR

T / F  the PaCO2 will correlate with the ETCO2

T / F  the lower ETCO2 is due to a reduced venous CO2 content

T / F  the lower ETCO2 is due to absent aerobic cellular respiration

T / F  the lower ETCO2 is due to increased alveolar dead space

Can you provide a rationale for the correct statements above, from first principles? Hint… this blog relates to learning outcome BT_PO 1.29

 

ANZAC Day

ANZAC day is an opportunity for us to reflect on how fortunate we are to live in a peaceful, democratic country like Australia or New Zealand. It’s also the one day when most of us stop to think about and appreciate our armed forces.

Many of the advances in resuscitation, anaesthesia and surgery have developed through the tragedies of war.

Today I want to pay tribute to Dr Arthur Guedel (1883-1956), an American anesthesiologist who served with the US Army during World War I, in France.

guedel_1 Dr Arthur Guedel

Faced with thousands of wounded, he devised a method of training nurses and medics to give simple open ether anesthesia. Guedel’s four stages of anaesthesia, and the associated breathing patterns, eye signs etc. are still referred to today. A fascinating training film (made in 1945) on the stages of anaesthesia can be viewed here.

guedel_4Guedel’s Stages of Anaesthesia

Guedel is best remembered for his eponymous oropharyngeal airway. Originally made of black rubber, it improved upon earlier metal airways, and instantly became an essential tool for airway management.

guedel_3 Guedel airway

Guedel was also involved with the development of cuffed endotracheal tubes. To prove that the cuff would prevent aspiration, he anaesthetised his own dog, inserted a cuffed tube, and then submerged him under water in a fish tank. One hour later, the dog was woken up, with perfectly dry lungs. The trivia buffs out there would already know that Guedel’s dog was named “Airway”.

guedel_3“Airway”

Thanks to all the military anaesthetists, past and present, who have made so many advances to our specialty.

Tips for the Viva Exam

By now, your preparation for the upcoming vivas should be well under way. Here are some tips which you may find useful.

(1) Develop confidence with talking out loud.

Many trainees are surprised at how difficult it is to explain even simple concepts, when talking out loud. Drawing a graph while explaining it at same time can leave you tongue-tied!

Hopefully, you have engaged with a study group throughout the year, and pestered consultants with questions in theatre. If so, you are well on the way to performing well in vivas. Even so, much more focused preparation is now needed.

Try to have 2 vivas per day. This number enables you to remember and reflect on what was asked, and polish up areas of deficiency. A lot of the onus falls to you to ask for vivas – it is all too easy to withdraw to private study and avoid the uncomfortable experience of being grilled… but you avoid opportunities for practise at your peril.

As you develop more confidence, get someone to video some of your vivas. You can review these in private, and reflect on your answering style. Similarly, it is valuable to observe other registrars having vivas.

The self-confidence which develops during this process will pay rewards. One obvious example is managing an emergency situation, where you certainly need a calm, clear head, a confident voice, and the ability to solve a problem on the fly.

(2) “Go with the flow”

Each 20-minute viva will consist of 4 topic areas of 5 minutes each. The examiner wants you to score points, so they won’t let you go off on a tangent. This means the examiner might interrupt you, or redirect you, so that you keep answering the questions being asked. Similarly, when 5 minutes is up, the examiner will move to the next topic.

Please understand that these interruptions are in your favour. Hopefully you will get used to this during practise vivas.

(3) What if there’s a slightly “clinical” question?

Sometimes, a viva can include a question with a “clinical” flavour. For example “Your patient’s blood pressure is 70/30 post-induction. What drugs can you use to manage this?” This is not meant to be a segue into a scenario (like in the final exam). Do NOT embark on describing how you would treat this patient. We don’t want to hear “I would simultaneously diagnose and treat, firstly checking ABC…….”

To answer the above question, give a sensible list of drugs like metaraminol, ephedrine and phenylephrine. The viva will probably then proceed by focusing on the pharmacology of one or more of these drugs, and/or the physiology of hypotension.

(4) Graphs

Some candidates really seem to struggle with drawing graphs. This is almost always due to inadequate practise. However, here are some graph-related tips.

  • Don’t draw a tiny graph – use the majority of the page.
  • Label the axes, but don’t overdo it. You don’t need each axis numbered 0 – 100 and all drawn to scale…. this just wastes time. Consider the oxyhaemoglobin curve – you should be able to draw it accurately, with a few key points numbered, in about 15 seconds.
  • Consider whether the curve passes through the origin, or does it cross the x or y-axis at a different point?
  • Practise drawing and explaining at the same time. If you find this impossible, it is acceptable to draw it first and then explain.

(5) What if you slip up / say something silly?

Examiners realise how easy it is to say increase instead of decrease, etc. Commonly, we would allow you to re-state your answer if we think it is a small slip up. This can be done by asking the question again, but in a different way. Or, the examiner might just say “Are you sure?” The latter is never used to try to trick a candidate when they have said something correct. The examiner is giving you a chance to take a breath and re-think what you have just said so that you can correct your error.

(6) What if you don’t know?

Move on! Admit if you don’t know, and move on. There are marks to be scored with other questions. Don’t make something up.

(7) What if you never seem to be able to answer the last question?

Vivas tend to start with something easy / broad, and progressively drill down to test your level of understanding. Don’t panic if you never seem to be able to answer the last question! You may have well and truly passed the viva. The fact that you have progressed as far as a difficult question might actually be a good sign.

Additional viva tips can be sourced from a series of videos showing mock-vivas. This is available via Networks on the ANZCA website.

 

BT_PO 1.126 Explain how the body defends against infection

T / F  IgG antibodies are released from memory B cells (plasma cells) as part of a secondary (learned) immune response.

T / F  “Innate” immunity would include intact mucosa, stomach acid, and lysozyme, but not neutrophils.

T / F  Administering tetanus vaccine is an example of an “active” way of providing acquired immunity.

T / F  The passive immunity provided to a neonate by trans-placental antibodies only lasts for about 1 month after birth.

T / F  The complement cascade results in lysis of bacteria. This can only be activated when IgG or IgM antibodies are bound to the bacteria.

BT_GS 1.23 Describe the physical properties of inhalational agents, including the principles of vaporisation

ether

Fig 1. The above image shows an “open ether” anaesthetic (ether being dripped onto a wire mask covered with gauze).

T / F   It is possible to use ether as shown in Fig. 1 because it is very potent, with a low MAC.

T / F  The patient in Fig. 1 is breathing room air. Administering open ether could cause the inspired oxygen concentration to be significantly reduced. (Can you explain your answer?)

T / F (If you understand the answers to the first 2 questions, this one should be easy!) The boiling point of ether is lower than sevoflurane.

iso

Fig 2. Isoflurane vaporiser

T / F  This device might contain a bimetallic strip, to provide flow compensation.

T / F  If you (hypothetically!!) filled this vaporiser with sevoflurane, the % shown on the dial would be lower than the % delivered to the patient.

BT_GS 1.23 Describe the physical properties of inhalational agents, including the principles of vaporisation BT_GS 1.26 Describe the toxicity of inhalational agents

penthrox-inhaler

T / F  Using the device shown above, a high inspired concentration of methoxyflurane can be achieved because it has a high saturated vapour pressure.

T / F  Methoxyflurane is more potent than sevoflurane.

T / F  Methoxyflurane produces analgesia at sub-anaesthetic concentrations.

T / F  The oil:gas partition coefficient is 950. This means, at equilibrium, the partial pressure of methoxyflurane in fat would be 950 times higher than in alveoli.

T / F  Nephrotoxicity can occur with prolonged methoxyflurane use, due to intra-renal metabolism to inorganic fluoride (F¯).