BT_PO 1.37 The effects of ageing on the respiratory system

I have previously posted on the cardiovascular changes that occur with ageing .

Today the effects on the respiratory system. You will find all of today’s answers in Nunn’s Respiratory physiology, which covers the effects of ageing quite well.

I was searching for a fitting photo for today’s post and, not being a fan of self portraits, decided on this one… IMG_2523.JPG

…although I suspect this person was actually quite young in 79AD (seen at Pompeii)

BT_PO 1.37 Describe the effects of ageing (and many other things) on ventilation

Advanced age causes a widening of the distribution of V/Q ratios    TRUE/FALSE

Normal ageing causes a decrease in lung compliance    TRUE/FALSE

DLCO decreases linearly with increasing age  TRUE/FALSE

FRC gradually declines with age during adult life     TRUE/FALSE

Closing capacity increases with age and equals FRC in the upright position at the age of about 75 yrs    TRUE/FALSE

BT_PO 1.108 Alteration in drug response due to hepatic disease

If I want to check a registrar’s understanding of a certain topic, I will often ask about the basic physiology or pharmacology and then add a complication. This might be a disease process, a drug or an altered state of physiology. Those who have memorised an answer soon come unstuck when they are asked to apply their knowledge.

When you look through the ANZCA Primary Syllabus, such that it is, you will find a number of LOs related to these “complications”, including this one…..

BT_PO 1.108 Describe alterations to drug response due to hepatic disease

This little guy was in the case with the bears from yesterday’s photo (oh, how times have changed….)

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The clearance of propofol is minimally affected by hepatic disease  TRUE/FALSE

Patients with hepatic failure have a hyper-dynamic circulation, which will protect them from the cardiac depression effects of an induction dose of propofol     TRUE/FALSE

Reduced plasma protein levels may result in a longer than expected duration of action for highly protein bound drugs     TRUE/FALSE

All volatile anaesthetic agents have been shown to decrease hepatic blood flow independent of a reduction in mean arterial pressure   TRUE/FALSE

Oral bioavailability of drug with a high extraction ratio, such as morphine, may be markedly reduced in patients with severe liver disease     TRUE/FALSE

 

 

BT_PM 1.16 Opioid dose conversion

Ok this is a bit of a weird one for the primary syllabus in my books. It could be asked in an MCQ but I don’t think it would be asked in a viva, because we all know it is virtually impossible to do mental arithmetic under pressure!

It is of practical consideration for us though and is something we do all the time, when managing patients in the post operative period.

There are various opioid conversion tables out there, including an app produced by the FPM. If you look the app, I would suggest that you look at the “practical considerations” in the information section (it is a bit hidden at the bottom of the Opioid Dose Equivalence  page)

I think this poor patient needs more of whichever opioid he has received…. Taken at the Legend of Hong Kong Toys exhibition. I hate to think what happens when you turn that toy on…..

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BT_PM 1.16 Outline the dose conversion between commonly used opioids

No change in tramadol dose is required when switching from oral to s/c dosing  TRUE/FALSE

Twice as much oral compared with intravenous morphine is required to produce the same analgesic effect   TRUE/FALSE

It is easy to calculate an equipotent dose of morphine for a patient taking methadone  TRUE/FALSE

When switching a patient between one opioid and another, equipotent doses of the two drugs tend to underestimate the amount of the new opioid that will be required  TRUE/FALSE

A buprenophine patch 20mcg/hr is equipotent to a 12.5mcg/hr fentanyl patch  TRUE/FALSE

Pin Index System

BT_SQ 1.10 Describe the supply of medical gases (bulk supply and cylinder) and features to ensure supply safety including pressure valves and regulators and connection systems

Pin Index.png

T/F The Bodok seal shown on the right contains latex

T/F The Pin Index System can be defeated by placing two Bodok seals over the nipple

T/F The seal must not be combustible because of the high temperatures achieved when the cylinder is turned on

T/F The Pin Index for Oxygen is a single pin at the 6 o’clock position

T/F The Pin Index system is not used in the main hospital manifold

Have you ever wondered why we only use the pin index system for cylinders and not for gas hoses? The answer was in the recent A&IC History Supplement. If the connection is inserted upside-down, it is possible to fit the wrong coupling into the yoke. This is less of a problem with cylinders for obvious reasons.

Evolution of a viva- Part 2

In Part 1 we formulated a viva and I ran through it with my shadow a few times. Now we need to properly ‘test run’ the viva. This entails doing it with trainees, candidates and other people preparing for the exam. I don’t test a viva that will be used in the next exam. But it is important to test a viva because you invariably learn things- eg. what you thought was a straight forward question may turn out to be ambiguous to candidates. You might find that your viva is too long (they are never too short) or too hard (God forbid). A really hard viva does no one any favours. I sometimes find that candidates consistently get a particular question wrong- I need to discern whether it is worth asking that point or not and often end up discarding that question. For example, I asked in a BIS viva what cells in the brain are responsible for producing the EEG waveforms. I wanted people to say ‘cortical pyramidal cells’ but no one did so I canned it. Getting bogged down half way through a viva because of one point is not a productive exercise.

There are other changes that result from testing. I often find I change the wording of my questions or prompts after test running a viva. The ultimate test is using it in the actual exam of course and a viva can even undergo changes during the course of an exam. Believe it or not we want to maximise the chances of the candidate demonstrating to us an understanding of a given viva topic. The challenge for the examiner is to find the best way to extract the desired information. Sometimes the exam experience is very different from that with my local candidates. I have certainly ‘decommissioned’ a viva after an unsatisfactory performance! It is always surprising and enlightening to see what aspects of a particular viva candidates find challenging. It is quite satisfying when candidates consistently do well with a particular viva. This doesn’t necessarily mean it is easy. Indeed the same viva may be done poorly in another sitting of the exam.

That is all I will say for now about writing vivas. But I will give you a little heads up. One of the disturbing  recent trends examiners have noted is that the vivas that were done poorly tended to be on core topics eg. core anaesthetic drugs, PK and PD, cardiac physiology, respiratory mechanics. This tends to reliably distress us examiners (“they should know that etc”) so there is a good chance these topics will be revisited in future exams.

Oops

SalineI drew up some saline from the drawer in the birth suite to flush the cannula before putting in an epidural.

When I checked again I found that the drawer was filled with a mixture of saline and lignocaine.

 

 

 

 

 

 

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BT_RA1.3  Discuss the pharmacology of local anaesthetic agents including:
· Mechanisms of action
· Comparative pharmacology of different agents
· Toxicity
· Use of adjuvant agents to enhance the quality or extend duration of block
· Pharmacokinetics of drugs administered in the epidural and subarachnoid space

 

 

 

 

 

If I had given the 20mls as an intravenous bolus:

T/F The best volume of distribution to estimate the peak plasma concentration would be V area.

T/F The most likely arrhythmia to occur would be Ventricular Fibrillation

T/F Seizures occur at a plasma concentration of 5µg/ml

T/F Cardiac arrhythmias occur at a plasma concentration of around 2 times that which cause seizures

T/F Lignocaine causes dose dependent negative inotropy

Bonus questions:

Why is bupivacaine more cardiotoxic than lignocaine?

Is ropivacaine less toxic than bupivacaine?

Why should you treat the seizures?

Pharmacoeconomics of volatile anaesthesia

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

Following on from yesterday’s post is another about volatile agents.

While pharmacoeconomics is not part of the primary exam it does have an LO in the curriculum (AR_MG 3.2) but the answers to most of the following questions require primary exam knowledge.

  1. Demonstrate that liquid volatile usage in ml per hr, for agents used in 2017, is approximately 3 x fresh gas flow (l/min) x inspired concentration (%)
  2. Estimate the amount of sevoflurane used the next time it is part of your anaesthetic.
  3. Some anaesthetic machines will provide you with an exact usage.  See how close you can get with your calculations.
  4. How much did the sevoflurane cost?

Schrödinger’s Registrar – Part 2

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

Yesterday the following was asserted:

“You will be anaesthetised if you smash a bottle of sevoflurane in an anaesthetic room (assume the air-conditioning is broken and the doors are sealed)”

If you had some trouble coming to a conclusion then here are a few hints:

Assume the sevoflurane completely vaporises.

Assume the room is a certain size – e.g. 5m x 4m x 3m

How much gaseous sevoflurane is produced from the liquid sevoflurane?

Avogadro is important here (PV = nRT)

What concentration of sevoflurane will cause anaesthesia?

Tomorrow, we will be looking at the reverse situation – i.e. how much liquid sevoflurane is consumed from a certain amount of gaseous sevoflurane.

 

 

 

 

Schrödinger’s Registrar – Part 1

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

This LO has been the subject of previous posts, but volatiles and vaporisation are core knowledge and a detailed understanding is important.

Today there is only one question.  You can treat it as a True/False statement or consider a longer answer by treating it as a discussion point.  You decide which will lead you to greater understanding.

This question will require you to make a few assumptions in addition to the two provided. See if you can varying those assumptions to change your conclusion.

“You will be anaesthetised if you smash a bottle of sevoflurane in an anaesthetic room (assume the air-conditioning is broken and the doors are sealed)”

If you are having trouble with this question, stay tuned for hints tomorrow.

 

Evolution of a viva- Part 1

Before you get your hopes up I will not be revealing the intimate details of a viva but I will attempt to convey some of the thought processes that are employed in the creation of a viva. I can only speak for myself here but I suspect my colleague examiners do similar things.

It begins with an idea (as do most things) which is often formed during the actual viva exams. I think to myself, “Gee the candidates don’t know much about basic propofol pharmacokinetics.” Often this thought is engendered as I watch a colleague examine on a particular topic. I like to examine on topics that satisfy a few criteria:

  • I think anaesthetists should know this stuff
  • The topic is clinically relevant (hopefully these two aren’t mutually exclusive)
  • I have seen a knowledge deficit about the topic in my trainees (if they already know it then someone else can ask them that!)
  • The ‘answers’ or responses I want need to be in the set texts (this can be quite difficult and has scuppered a few viva ideas along the way)
  • Another person with a FANZCA would at least understand most of what the viva was getting at
  • The nature of the topic lends itself to being asked in a viva format

Once I have the idea I write down what the main points I want candidates to demonstrate an understanding of are. (I also need to make sure there is a learning objective pertaining to the viva!!) Each viva topic is only five minutes long so the path to pass responses needs to be direct and hopefully short. Next I hit the books and confirm that the topic is adequately covered. Occasionally I discover that my understanding of the topic is at odds with what the books say! Not uncommonly I may have to look at six different books and it is frustrating for all of us if they say six slightly different things. Next I need to formulate the questions to get the information I want. Each viva should ideally start with a simple and brief question to allow the candidate to answer the opening question correctly and begin in a good frame of mind. So, for a propofol PK viva I might ask “What is the induction dose of propofol for a healthy unpremedicated 20 year old?” Subsequent questions need to flow on naturally from the opening question. I like a diagram or two in a viva but it needs to be simple and easily drawn. Sometimes it may be better to provide a diagram. It may be deliberately incomplete. Lastly I run through the viva myself a few times to check the timing and make sure the flow of the viva is alright. Then the real hard work starts. Part 2 will elaborate.