2018.1 SAQ 15 Platelet Physiology

Describe platelets and their role in haemostasis.

Surgery causes bleeding and platelets help to stop it. Our patients often take drugs, or have diseases, that interfere with these little fragments and it is important to have an understanding of their normal function (which is really quite cool…)

Platelets will be covered in all physiology books, but for an article with an anaesthetic flavour, look here. If you would like to give yourself some more practice, I have previously posted on this topic here (where co-incidentally I recommend the same BJA Education article)

I decided not to put this as a T/F statement, but did you know that approximately a billion platelets are produced each day!!! (per person, not in the entire world 😉)

BT_PO 1.112 Describe the physiology of haemostasis, including the role of platelets

Platelets have a role in both primary and secondary haemostasis T /F

Thrombopoeitin, which is produced at a constant rate, is removed from the plasma by circulating platelets, helping to regulate platelet levels T/F

Platelets adhere to intact endothelium T/F

Platelet activation and aggregation is an example of a postive feedback loop T/F

Platelets release factors that promote wound healing T/F

2018.1 SAQ 12 Neostigmine and sugammadex

Compare and contrast the pharmacology of neostigmine and sugammadex

“Anaesthesia reversal”, as these drugs are referred to on an automated theatre record we used to use, has always stuck me as a funny term – I hope I never have an anaesthetic where either of these two drugs is sufficient to reverse it! These are drugs we give on a daily basis, although sugammadex is used rarely in the institution I work in because of the cost. Is that its only limitation?

You should find these drugs covered adequately in the  pharmacology books on the reading list

BT_GS 1.39 Describe the reversal of neuromuscular blockade using anti- cholinesterase agents, anticholinergics and sugammadex and the physiological effects of reversal

Both neostigmine and sugammadex will reverse all aminosteriod non depolarising muscle relaxants T/F

Sugammadex can be used safely in patients with severe renal impairment (eGFR < 30ml/min) T/F

Unlike neostigmine, sugammadex has no effect on acetylcholine T/F

In a patient with a TOF ratio ≥ 2, equipotent doses of sugammadex and neostigmine with have a similar time to onset of effect T/F

There is a significant risk of oral contraceptive pill failure in patients who have received sugammadex T/F

2018.1 SAQ 9 Renal blood flow

Discuss the determinants of renal blood flow.

Kidneys often receive a multitude of insults in the peri-operative period, both physiological and pharmacological. If you know how normal renal blood flow is controlled, you will be best positioned to preserve it under anaesthesia.

Principles of physiology for the anaesthetist 3e by Power and Kam Ch 7, handles this topic better than many of the other recommended texts. Although this is an important topic, its coverage can be quite confusing.

BT_PO 1.62 Explain the physiology of renal blood flow

Blood flow to the kidneys is regulated to maintain glomerular filtration rather than oxygen supply to the kidney T/F

Renal blood is auto-regulated between a systolic blood pressure of about 80mmHg and 180mmHg T/F

In response to reduced presentation of sodium to the juxtaglomerular apparatus, afferent arterioles will dilate to increase glomerular filtration T/F

Renal blood flow is auto-regulated at the level of the glomerular capillaries T/F

Myogenic regulation of renal vascular resistance is rapid T/F

2018.1 SAQ 4 Hazards of CO2 absorbents

Outline the hazards associated with the use of CO2 absorbents within a circle breathing system and how the risks can be minimised.

We use a CO2 absorber as part of a circle circuit on a daily basis. It is important to be cognisant of potential hazards associated with its use. The CO2 absorbents are continually evolving to help eliminate some of the absorbent specific risks, but the are a number of general risks that exist regardless of the absorbent used.

Miller’s Anaesthesia Ch 29 covers this topic well, including a discussion of the newer Ca(OH)2 and LiOH based absorbents.

Please note however that there is an error in Miller with regard to soda lime and Compound A production. Compound A production and buildup is favoured by dry soda lime, contrary to what Miller says. I have been in contact with the editor regarding the mistake.

The risks of using desiccated absorbent, especially those containing strong alkalis, are significant and it is important to be mindful of this.

BT_SQ 1.15 Outline how CO2 is absorbed in a circle system and the hazards associated with the use of CO2 absorption

4-8 mesh granules provide the optimal balance between surface area of CO2 absorption and resistance in the circuit  T/F

Ultra low flow anaesthesia (<0.5L/min FGF) increases the risk of carbon monoxide (CO) buildup in the circuit  T/F

Higher fresh gas flows, may increase the rate of CO production by drying the absorbent T/F

The CO2 canister is a common site for a circuit leak T/F

Inspiratory CO2 monitoring is a less reliable measure of detecting expired CO2 absorbent than a pH sensitive dye T/F

The use of sevoflurane or a Ca(OH)2 based absorbent will prevent potential CO poisoning T/F

2018.1 SAQ 2 CVS changes with morbid obesity

Describe the cardiovascular changes that occur with morbid obesity.

In the 20 yrs since I started anaesthesia, an increasing number of our patients are now morbidly obese. Obesity has implications for most body systems, but the interaction of the drugs we use with the cardiovascular system, makes this of particular relevance to us.

I have previously written a post on this topic where I have suggested some good resources. I would suggest you look at that post if you would like some further reading material (and also some more T/F statements to check your knowledge)

BT_PO 1.50 Describe the cardiovascular changes that occur with morbid obesity

Stroke volume increases linearly with BMI in part due to an increased preload  T/F

In the absence of another pathology, systemic vascular resistance is reduced in the morbidly obese T/F

All of the hormones secreted by visceral adipocytes are detrimental to the CVS  T/F

Both concentric and eccentric hypertrophy of the left ventricle occur in morbid obesity T/F

Morbid obesity is a hypercoaguable state T/F

 

 

A little time to pause and reflect

I saw that there was no post scheduled for this morning – I suspect everyone is a bit exhausted after this week’s vivas!

I thought I would take this opportunity to encourage you to take a moment to pause and reflect….

Sometimes in our busy lives it can be easy to lose sight of what is truly important to us. We get carried along by the tide of work, study and other commitments as life rushes by.

Some people will be elated this week having just passed the exam, whilst for others the feeling may be at the other end of the emotional spectrum – angry, frustrated, despondent.

Wherever you are placed, take some time to stop and think about who and what really matters to you. It may take some careful consideration to still your mind enough to locate the answer, but when you do, celebrate it.

I hope that everyone has a relaxing and peaceful weekend – you all deserve it. I am on holidays now, looking at the view above, and am looking forward to some time to pause and reflect myself.

BT_RA 1.14 Describe factors influencing dose and choice of anaesthetic agents for spinal anaesthesia

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Something with many spines…. (Ecuador)

This is a very clinical LO, and something that you have probably thought about when performing spinals yourselves. The LO also talks about epidurals, but I think we can tackle that in a separate post.

Why is it that we use bupivacaine almost exclusively as our local anaesthetic in the subarachnoid space?

Miller’s Anesthesia 8e Ch 56 gives a detailed description of this topic.

BT_RA 1.14 Describe factors influencing dose and choice of anaesthetic agents for spinal anaesthesia and epidural anaesthesia/analgesia

If other factors are kept constant, an increased dose of local anaesthetic (LA) will usually result in a higher block T/F

Use of a hyperbaric LA solution increases the ease of obtaining a saddle block T/F

Transient neurological symptoms have been associated with the use of lignocaine with 5% dextrose T/F

The addition of adrenaline to LA in a spinal anaesthetic may improve analgesia by direct α2 agonism  T/F

The addition of clonidine to a spinal improves analgesia without prolonging motor block T/F

 

BT_RT 1.7 Describe blood groups and the physiological basis of transfusion reactions

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As a person with an O negative blood group who has had children, I find the physiology of blood groups quite interesting. I feel very thankful for the free availability of Anti-D [Rh(D) immunoglobulin], in Australia, as I suspect my second Rh positive child would, if she knew the potential implications for her.

In Australia, the source of Anti-D is still kind volunteers who have be sensitised to the Rhesus antigen. Here is a newspaper article celebrating 50 yrs of use of Anti-D ( a warning that the start of the story mentions an intrauterine foetal death. However, the the story as a whole is quite uplifting)

BT_RT 1.7 Describe blood groups and the physiological basis of transfusion reactions

ABO blood groups are named according to the presence of A or B antigen on the red blood cells T/F

Antibodies form in plasma against non self antigens  T/F

A person with O blood has no antibodies to ABO blood groups in their plasma  T/F

ABO incompatibility occurs when the recipient’s antibodies react with the donor antigen T/F

Only people who are Rhesus negative can develop Anti-D antibodies T/F

Best wishes for the vivas next week

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With the ANZCA Primary vivas being held in Melbourne next week, I would like to take the opportunity to extend my very best wishes to all of you!!

All of the examiners whom you will be meeting, have been through the primary examination process too (for a couple it was the FRCA primary, but the vast majority sat the ANZCA exam). Although the format of the exam has changed a bit over the past 20 yrs, the essence has remained the same. We all are aware of how stressful the experience is, and it is our genuine desire to see you perform to the best of your capabilities.

I would like to remind you that regardless of the outcome next week, the primary exam does not define you.

I hope that you are able to find some peace in the next few days, feel confident in the study that you have undertaken, and prepare yourself to shine in the vivas – the day is all about you!

See you at the new venue. Best wishes!!!!

SS_PA 1.23 Temperature regulation in the newborn

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Photo via National Geographic

Any of you who have been at the birth of a child or involved with anaesthesia of a neonate, will probably have guessed that little humans are not fantastic at keeping themselves warm, especially when wet. Everything is done to naked babies under a warming lamp and they are wrapped up at the earliest opportunity – no that is not just to make them look even cuter! They are also not great at cooling down when in a hot environment, although this tends to a bit less of an issue as they have a high thermoneutral zone.

It seems that even baby animals, like the cubs above, adapted to living in a cold environment, are similarly vulnerable to heat loss as newborns (according to these fun facts)

As with the last two posts, my go to book for this topic would be Power and Kam.

SS_PA 1.23 Define the thermoneutral zone, describe temperature regulation in the neonate and the physiological responses to lowered and raised environmental temperature, the effects of anaesthesia on these responses and how this changes with growth and development

The body surface area/weight ratio of an newborn is a third that of an adult T/F

The main source of heat production in a neonate is non shivering thermogenesis, which can increase the basal metabolic rate of the neonate by 3x T/F

The thermoneutral zone for a term newborn is around 32-34° C T/F

Preterm newborns have a lower thermoneutral zone compared with term babies T/F

Neonatal hypothermia increases the risk of hypoxaemia  T/F

Newborns have a decreased ability to sweat compared with adults T/F