2017.2 SAQ 12

Describe the clinical effects of non-steroidal anti-inflammatory drugs including the mechanisms through which they exert these effects.

 

Anaesthetists prescribe NSAIDS frequently. These drugs are very effective analgesics, but have significant potential adverse effects. Obviously, an in depth pharmacological knowledge is required.

T / F  NSAIDS produce analgesia by inhibiting the synthesis of prostaglandins in injured tissue. Prostaglandins act directly on free nerve endings to produce pain.

T / F  inhibiting prostaglandin synthesis decreases renal blood flow because PGE2 maintains efferent arteriolar dilation

T / F  an advantage of COX-2 selective agents is that there is less inhibition of PGE2 and therefore less reduction in renal blood flow

T / F  NSAIDS produce gastric mucosal ulceration via a direct irritant effect – therefore, they should not be taken on an empty stomach

T / F  NSAIDS provide an overall reduction in the risk of acute coronary events because they inhibit platelet thromboxane

T / F  inhibition of either COX-1 or COX-2 promotes the production of leukotrienes from arachidonic acid, which can precipitate asthma in some patients

 

 

2017.2 SAQ 11

Describe the immunology, mediators and pathophysiology of anaphylaxis. Do not discuss management.

Anaphylaxis continues to be a major cause of anaesthetic morbidity and mortality. Understanding the pathophysiology is essential in order to comprehend the management of this complex, challenging emergency.

T / F  histamine is released from MAST cells during anaphylaxis – it causes bronchospasm via H1 receptors

T / F  anaphylaxis to muscle relaxants can occur due to prior sensitisation from exposure to some cosmetics, or pholcodeine cough mixture

T / F  MAST cell degranulation occurs when an allergen binds to IgG on the MAST cell surface

T / F  histamine, leukotrienes and platelet activaing factor all increase vascular permeability during anaphylaxis – many litres of IV fluid can be needed during resuscitation

T / F  patients with anaphylaxis will reliably show a rash or urticaria

T / F  if you suspect a penicillin allergy, 100 mg of cephazolin can be given IV to determine if it is safe to give that drug

 

Simplicity beyond complexity

Last week I advised a rather algorithmic SAQ approach of thinking of and writing relevant facts. Excellent candidates however are already writing and succinctly explaining relevant facts because they understand the material well enough to distil out what is important. Oliver Wendell Holmes coined the term ‘simplicity beyond complexity’ which is where you want to aim for – to understand the material well enough to know what’s important, sum it up and explain it. If you’ve not heard of Oliver Wendell Holmes before then read Letter to Dr Morton.

2017.2 SAQ 9

Draw and explain the characteristics of a quantal dose-response curve that describes the major clinical effects of rocuronium. Outline medications and medical conditions that shift the curve to the left or the right.

Neuromuscular blockers and opioids can be used as clinical examples to test candidates’ understanding of the various types of dose response curves. Why do we recommend 2 to 3 times the “ED95” as the intubating dose for muscle relaxants?

T / F  a quantal dose-response curve is semi-logarithmic

T / F  the y-axis shows % twitch height reduction, from 0 to 100%

T / F  for the specific case of muscle relaxants, the ED50 refers to 50% of the population achieving a 95% reduction in twitch height, and is also referred to as the ED95, or ED50(95%)

T / F  a right shift in the curve reflects reduced potency, and could be caused by a recent dose of neostigmine, or one week of bed rest

T / F  hypothermia increases the potency of rocuronium

T / F  patients with myasthenia gravis would have a left shifted curve

2017.2 SAQ 8

Discuss the factors affecting duration of action of a local anaesthetic block to a major peripheral nerve.

Candidates have difficulty with the LA duration of action and speed of onset questions, often confusing the two. Many candidates try to force the answer into Fick’s law of diffusion, with disappointing results.

T / F  an increased local anaesthetic concentration, but not the total dose, will prolong duration of action

T / F  plasma cholinesterase deficiency will prolong the duration of cocaine

T / F  increased lipid solubility will prolong the duration of action, AND increase the speed of onset of a local anaesthetic

T / F  the presence of an active metabolite will contribute to LA duration of action

T / F  lignocaine is shorter acting than bupivacaine because its pKa is closer to physiological pH

T / F  with a brachial plexus block, analgesia of the hand will last longer than analgesia of the shoulder

SAQ 2017.2 Question 7

Simple and relevant material gains points.

Compare and contrast the pharmacology of ephedrine and norepinephrine (noradrenaline).

Noradrenaline is predominantly active at β2 adrenoreceptors    TRUE/FALSE

Noradrenaline is a mixed acting sympathomimetic   TRUE/FALSE

Ephedrine can be administered IM   TRUE/FALSE

Ephedrine has a half life of 2 minutes   TRUE/FALSE

Noradrenaline demonstrates tachyphylaxis   TRUE/FALSE

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