Anaphylaxis

I hadn’t noticed that the patient was sunburned until we started positioning. The oximeter had fallen off the finger and the assistant was leaning on the BP cuff whilst tucking in the warming blanket. All you would need is the nurse to ring from recovery to ask for a mod for the parturient with a BP of 100 and everything would be completely normal.

The title of the post rather gives it away, but at the start of a crisis it can often be difficult to realise that it is even happening. The thing that made me reach for the adrenaline was that I noticed that the ETCO2 was low.

Here is a portion of the anaesthetic record, reproduced with permission. The jagged parts are artefact.

The ETCO2 is the gray filled area at the bottom, with units in mmHg. Initially the patient was mask ventilated, which is why the trace has gaps in it. The green line is the plethysmograph amplitude. You can see that by 8 minutes after induction both the CO2 and the plethysmograph amplitude are dropping. The purple syringes are doses of adrenaline. The CO2 immediately rose with the first dose. Just as I was giving the adrenaline the trace was starting to show bronchospasm—which went away immediately.

The agent responsible was found to be rocuronium. Apparently the rate of rocuronium anaphylaxis has increased since COVID, which the allergy specialist thinks might be a result of greater use of cough suppressants.

The important take away messages are:

• Anaphylaxis rash may look like a sunburn
• If you see a low CO2, think low cardiac output

BT_PO 1.27 Discuss West’s zones of the lung

I am not brave enough to suggest that this is the only possible reason, but…

Low cardiac output states can cause hypocapnoea in a ventilated patient because:

1. Pulmonary hypotension increases anatomical shunt
2. Pulmonary hypotension increases West zone 1
3. Pulmonary hypotension increases West zone 3
4. Systemic hypotension increases the relative proportion of bronchial artery blood flow
5. Systemic hypotension decreases CO2 carriage in the blood

Answers can be found in Nunn 8th ed Cap 7.

Do you have the height, weight and ASA…

RAT Testing

BT_PO 1.2

Describe the features of a diagnostic test, including the concepts of sensitivity, specificity, positive and negative predictive value and how these are affected by the prevalence of the disease in question.

Don’t blame me for the LO. In general I think probability testing and correlation are much more important, although they do have one application which is currently topical.

A quote from today’s Sydney Morning Herald about RAT Testing:

Professor Skerritt said it would have been “outright dangerous” to have people testing themselves earlier in the year, when there were fewer cases and health authorities were still heavily relying on contact tracing to suppress the virus.

“You would have had people with false positives, and immediately you also would have missed a significant number of infections,” he told the hearing.

If we use values for the Panbio oropharyngeal RATs of 81% sensitivity and 99.1% specificity, and PCR of 61% and 99.5%:

T/F Sensitivity is the rate of true positives. True Positive/(True Positive + False Positives)

T/F Specificity is affected by the prevalence of disease

T/F The negative predictive value of this test is now much higher than it was when COVID was less prevalent

T/F The negative predictive value of a PCR was higher than a RAT test when disease was less prevalent

Just for fun:

T/F If the prevalence of COVID is now 1%, over half of positive tests will be wrong (Use an online calculator for this. You won’t be asked to do the maths in the exam 😱)

Any book on statistics will give you the answers, or even the page on Wikipedia.

A big thank you to Dom Perrottet for making this photo possible.

Medical Gas Supply

BT_SQ 1.10

Earlier this week I did the witnessing for commissioning of some new medical gas outlets. Whilst personally I don’t think commissioning per se is really a primary topic, I thought some photos might be interesting.

The Australian Standard for medical gas supply was updated in 2021, in part to address the issues seen in the Bankstown disaster. The College guidelines contains the new testing requirements under the 2021 standard.

There are a lot of tests involved in testing compliance. The anaesthetist is only responsible for verifying gas composition and the non interchangeable connectors. The hospital is supposed to provide someone with a good understanding of medical gas supply to verify the others. I wonder who that will be 🤣.

These are the devices used for static and dynamic pressure testing. The Sleeve Index System uses a the same sized thread for all connections. As these devices don’t have a sleeve, they can be connected to all of the outlets.

The brass hexagonal nut in the valve box, is there to allow connection to a cylinder, in the event of a hospital wide gas failure.

This is the tool used to test that the correct sleeve has been placed on the outlet. They are essentially the opposite of the testing devices above. They have the collar, but not the threaded connector.

One of the tests is to check that there are no particulates. They blow gas through these filters. One of the outlets hadn’t been purged properly, so you can see the discolouration in the filter on the right. When they are brazing the pipes, they are filled with CO2, so the gas composition on this outlet was also incorrect until after it was purged.

• T/F Piped CO2 supplies should contain between 18 and 23% Oxygen to prevent hypoxia
• T/F Piped Oxygen and Air should have a humidity of 45-55%
• T/F The high usage of oxygen from VIE tanks during the UK COVID wave triggered the gas pressure alarms because the VIE temperature fell
• T/F If the collar of a Sleeve Index System outlet is removed, it will connect to any gas fitting
• T/F Medical air can be supplied using a VIE or a manifold

Answers can be found in the relevant sections on gas supplies, and also in the College document on verification.

Fun Friday Quiz

SS_OB 1.10, BT_RA 1.2

I don’t have time to post regularly at the moment, but I couldn’t overlook such a beautiful illustration of physiology & pharmacology.

This is part of the anaesthetic chart from a patient having caesarian section under SA. The black line is heart rate, the red bars NIBP and the green line is plethysmograph amplitude.

Why is the pleth amp so low on the left side of the graph?

Delivery was the time marked by the orange arrow. Which of the following drugs could have caused the observed changes? Bonus marks if you can explain why.

Carbetocin

Dexamethasone

Paracetemol

Parecoxib

Acute Pain Scientific Evidence 5th ed is out

BT_PM 1.22

This is a weighty tome and no-one would expect you to read it cover to cover. It does, however, have really good sections describing the individual drugs, pharmacogenetics and drugs in pregnancy and lactation. The range of opiates described should also give you an idea of the spread of drugs used across different hospitals.

T/F tramadol is an effective against neuropathic pain

T/F thirty percent of the effect of tapentadol is from seretonin re-uptake inhibition

T/F buprenorphine has a ceiling effect for analgaesia, but not respiratory depression

T/F respiratory depression from buprenorphine cannot be completely reversed with naloxone

T/F sufentanil has an active metabolite, nor-sufentanil which causes antanalgaesia

Answers in APSE 5th ed section 4.3

Sending you best wishes

I recall that ladybirds are a symbol of good luck. I love them because they eat the aphids on my roses. May many ladybirds be shining on you during the vivas….

Sorry that this is a super last minute post, but I wanted to send a big dose of best wishes to the New Zealand and NSW candidates who will be sitting the vivas over the next few days.

For many of you it has been an unexpectedly long and drawn out process. You are almost at the end now. Time to wow the examiners and then you are done!

I will be thinking of you all and will raise a virtual toast to you for making it to this point in what has been an extraordinary year.

Very best wishes to you all!

Best wishes for the exam

Perhaps in the next couple of days you could take a walk on a quiet beach, like the kangaroo who left these prints on aptly named Kangaroo Island

For those of you who have chosen to sit the ANZCA primary exam this month, my very best wishes for you with the written component on Tuesday.

I hope those of you sitting have been able to maintain the focus on your studies amid the very unsettled world we find ourselves living in.

Perhaps today and tomorrow are a time to do something solely for you. What is possible will obviously differ depending on where in Australasia you live, but something enjoyable and relaxing doesn’t need to be done far from home.

I have previously written a post on the benefits of taking a short break before the exam It seems as though that post was written in a different world, but the message still holds true.

I will be thinking of you all on Tuesday – best wishes.

You are in my thoughts

KAWS exhibition at the NGV last year

We are living in a very topsy turvey world at the moment and I really feel for those of you preparing for the exam. We as human beings are poorly equipped to deal with uncertainty and yet that is what we a faced with constantly at the moment.

Today I thought I would give you links to some study tips I have posted in the past. Many of them relate to our own behaviours and habits, which are things which we still have control over.

Please remember that if you need extra help at this time, ANZCA provides access to free psychological support. Do not hesitate to access this service if you think it will benefit you in the run up to the exam.

Aim to pass the exam rather than avoid failing it – in this post I discuss the influence of a positive emotion on success and there are some tips on how to cultivate these emotions..

Study tip – avoid getting too much of a good thing… – this post talks about the double edged sword of stress. In the current climate, I think that we all need to be consciously addressing our stress levels in order to maintain ourselves in a constructive zone.

Study Tip: Gain knowledge and understanding, not familiarity  – in addition to those who are sitting the exam for a second or subsequent time, this post may be worthwhile for those of you coming back to your studies, by preparing for the vivas, having sat the written in exam in March.

The Primary Exam in just one step on a lifelong path  The words of this post, although initially intended for those who had been unsuccessful in the exam, may provide solace for those of you who feel stuck in limbo this year and had your exams and/or training plans disrupted.

I hope that all of you are able to find some moments of joy in your lives this weekend. Please know that you are all in my thoughts…

2020.1 SAQ 15 Ageing and the respiratory system

I recently visited Kangaroo Island which was ravaged by bushfires earlier this year. One thing that has flourished amidst the devastation is the grass tree. They are very slow growing, so these beautiful specimens are old but doing all they can to ensure the species survives.

Discuss the effects of ageing on the respiratory system.

Increasingly, we are having to anaesthetise older and extremely old patients. It is important to know how their physiology differs from younger patients in order to deliver the best possible care.

BT_PO 1.37 Discuss the effect of ageing on ventilation

There is another post on this topic here and as I mentioned in that post, I think that Nunn’s Applied Respiratory Physiology is the best for this subject (unfortunately the references are dotted throughout the book)

PaCO2 levels rise as a part of normal ageing due to a reduced capacity for diffusion T/F

PaO2 levels fall gradually as part of the normal ageing process T/F

The ventilatory response to hyercapnoea is blunted with ageing T/F

Compliance of the chest wall decreases with ageing due to decreased mobility of the costochondral joints T/F

FRC decreases as part of the normal process of ageing T/F

Static compliance of the lungs falls with advancing age T/F

2020.1 SAQ 14 Adverse effects of neostigmine

This photo was not taken by me. I found it at The Toxicologist Today. It is a photo of the beautiful Amanita muscaria which will produce many, but not all, of the same side effects as neostigmine.

Describe the adverse effects of neostigmine.

Another drug we use on a daily basis (at least where I work as sugammadex is deemed too expensive for routine reversal).

Over 15 yrs ago, (but still seared on my brain) I made one of the 3 drug errors I know of. I gave a baby a 5x excess dose of neostigmine having mistakenly drawn up my calculated volume from the adult rather than baby sized ampoule. One side effect was prominent. What do you think it would have been? It responded very quickly to atropine, which I assumed I had forgotten to give. It was only on inspection of my ampoules once the situation had resolved that I discovered my mistake…

You will find decent information on this topic in any pharmacology text.

BT_GS 1.40 Describe the adverse effects of anticholinesterase agents 

Neostigmine will slow the breakdown of ACh throughout the body T/F

Neostigmine will produce weakness via actions at the NMJ regardless of the dose used T/F

Bradycardia is main effect of neostigmine on the cardiovascular system T/F

Neostigmine is highly lipid soluble, so seizures are likely to occur when large doses are given T/F

Neostigmine may cause diarrhoea T/F

Patents taking neostigmine have an increased risk of acute angle glaucoma T/F

There is another post on this material here if you want some more practice.