BT_PO 1.71 Explain the effects on anaesthesia on renal function

I didn’t realise that this LO existed – found it when I was looking for a renal topic to post on, as there seem to be a dearth of renal posts on this site.

This is actually an important topic as relatively minor reductions in renal function are associated with worse peri-operative outcome.

I don’t have any kidney photos. Below is the best I could do for the genitourinary system. There are a whole series of these (some much more X rated) on view at MONA


BT_PO 1.71  Explain the effects on anaesthesia on renal function

Any anaesthetic agent which results in a reduction of blood pressure is likely to reduce GFR   TRUE/FALSE

Attenuation of the stress response to surgery is renal protective   TRUE/FALSE

Volatile anaesthetic agents may provide protection against ischaemia- reperfusion injury of the kidney TRUE/FALSE

IPPV improves renal blood flow TRUE/FALSE

Metabolic acidosis increases the kidneys’ vulnerability to nephrotoxins TRUE/FALSE

BT_PO 1.37 Describe the effect of morbid obesity on ventilation

Sticking with the topic of obesity.. The reference sources from  yesterday  will be valuable…

Look at that dessert (and the look of glee on my daughter’s face!). I can’t remember what it was called – obscene? -but just looking at it makes me put on weight 😊



BT_PO 1.37 Discuss the effect of the following on ventilation:

  • Changes in posture
  • Exercise
  • Altitude
  • Anaesthesia
  • Ageing
  • Morbid obesity

Morbid obesity is associated with decreased compliance of the respiratory system    TRUE/FALSE

FRC is 25% lower in a person with a BMI of 30kg/m2 compared with a person with a BMI of 20kg/m2    TRUE/FALSE

Resting  respiratory rate is increased by morbid obesity      TRUE/FALSE

The alveolar to arterial gradient (A-a gradient) of oxygen is increased with morbid obesity      TRUE/FASLE

The effects of obesity on the respiratory system are improved by lying down TRUE/FALSE

Are your patients talking about this…..

Two posts in one day!! Thought I might as well post about this whilst it was back in my brain.

On June 7 Richard Fidler conducted an interview on ABC local radio, on the topic of consciousness and anaesthesia.

Two patients asked me about it within 24 hrs of it airing……

One, who had listened to it on the day of his procedure, was mildly terrified by the interview ( I hadn’t heard it at that stage, but did my best to reassure him).

I listened to the interview on my walk in to work the following morning.

The first patient of the day mentioned the interview to me. She was fascinated! She had me repeat a random word to her throughout the case to see if she could recall it after the event – she couldn’t! [although I didn’t hypnotise her]

It came to mind today as I was listening to one of my favourite podcasts, Chat10Looks3 , where the interview is discussed again.

It is worth listening to. Make up your own minds about it. It is always good to be cognisant of the information out patients are receiving about our specialty – the information doesn’t always come from us…..

BT_PO 1.50 Describe the cardiovascular changes that occur with morbid obesity


I know those guys guys above are highly trained athletes, but…..

BT_PO 1.50  Describe the cardiovascular changes that occur with morbid obesity

This topic is not well covered in the standard primary exam texts. A textbook previously on the primary examination reading list, Foundations of Anaesthesia , had a whole chapter (Ch 71) devoted to the topic. Unfortunately, the new iteration of the book, Pharmacology and Physiology for Anaesthesia by Hemmings and Egan (a great book to look at), has dispensed with the subject – drats!!

The ANZCA library has three ebooks devoted to the peri-operative management of the morbidly obese. Each of these books has sections detailing the basic alterations of physiology associated with obesity. The most comprehensive of these is Morbid obesity: perioperative management 2e edited by Alvarez et al.

For those of you without access to the ANZCA library, here is a overview of some of the issues, from the little CME journal produced by the same group as the BJA.

Cardiac output increases linearly in proportion to free fat mass          TRUE/FALSE

Blood volume on a mL/kg bases is increased in the morbidly obese    TRUE/FASLE

Left ventricular hypertrophy (LVH) is common in morbid obesity, even in the absence of hypertension      TRUE/FALSE

Standard ECG criteria for diagnosing LVH are valid in morbid obesity   TRUE/FALSE

Angiotensinogen is produced by visceral adipocytes resulting in excessive angiotensin II TRUE/FALSE

Obstetrics and the primary exam

SS_OB 1.1

Describe the physiological changes and their implications for anaesthesia that occur during pregnancy, labour and delivery, in particular the respiratory, cardiovascular, haematological and gastrointestinal changes.


Normal physiological changes begin in the first trimester of pregnancy. TRUE/FALSE

The largest increase in cardiac output in a pregnant woman occurs immediately after delivery. TRUE/FALSE

The closing capacity in normal pregnancy does not change. TRUE/FALSE

Gastrin is secreted by the placenta TRUE/FALSE

Progesterone from the gestational sac may cause changes in the renin-angiotensin-aldosterone system in the first trimester, promoting sodium absorption and water retention. TRUE/FALSE

Hats off to those of you who sit this exam pregnant!




Patient of the week

Recently I was anaesthetising an adult with a congenital syndrome. I was quite worried about the airway—but in the end it wasn’t that which caught me out. She had no congenital heart disease, but had a pericardial effusion drained a few years previously. I was quite sparing with the induction agents as I wanted to maintain spontaneous respiration, but nonetheless…

About 5 minutes after induction, I noticed the blood pressure was 54/28.

BT_SQ 1.6

T/F At low levels of blood pressure, the NIBP tends to give spuriously low values.

T/F The most accurate component of the NIBP is the mean.

At the same time, her saturation dropped to 88, even though she was breathing 100% oxygen. The pleth had a good volume and looked normal.

BT_SQ 1.6BT_PO 1.29

T/F The fall in SpO2 was most likely to be artifactual.

I gave three doses of 1mg metaraminol, but, although the saturation improved, the blood pressure remained in the low 70s. Heart rate was in the 40s. Worried that I might see another fall in saturation I decided to run a noradrenaline infusion.

BT_PO 1.52

In such a situation, the most appropriate vasoactive agent would be:

a) Ephedrine

b) Metaraminol

c) Adrenaline

d) Noradrenaline

e) Isoprenaline

After a 20µg bolus dose of noradrenaline, the heart rate dropped to 28.

T/F The most likely cause of the fall in heart rate is alpha 1 receptor agonism in the SA node.

I found out, after the (otherwise uneventful) operation, that she normally has quite a low blood pressure. A good reminder that, when having trouble with anaesthesia, one should first look to the proximal end of the needle.

BT_PO 1.93 Describe the physiology of sleep

I think this glass spinning wheel looks like something straight out of Sleeping Beauty. I haven’t really captured it’s brilliance, the gallery was shutting its doors as I happened upon it! It is worth taking a look the the artist Andy Paiko ‘s, website to view some more of his amazing creations. 

Clearly normal sleep and anaesthesia are not the same, but most of our patients, hopefully, sleep within 24 hrs of anaesthetic. Recent GA can have an impact on sleep and may exaggerate some of the normal physiological effects.  

BT_PO 1.93 Describe the physiology of sleep 

Arterial CO2 and O2 levels are unaffected by sleep TRUE/FALSE

Tidal volume reduces during sleep TRUE/FALSE

General anaesthesia often disrupts sleep architecture on the first post-operative night TRUE/FALSE

Responsiveness to increased arterial CO2 is reduced by sleep TRUE/FALSE

Loss of REM sleep on one night is often associated with increased REM sleep on subsequent nights TRUE/FALSE

BT_RA 1.12 Determinants of ICP and their regulation Pt 2

This sculpture by Barry Flanagan will hopefully put you in a thinking mood…..

Today a little exercise to work through.

It will enable you to answer the question, “How can you manipulate blood pressure to minimise cerebral blood volume ( within the limits of cerebral autoregulation)?”

Before we start, what is you first thought?

Over 90% of registrars, to whom I have posed this question, come up with the incorrect answer.

When I start to probe their reasoning, most draw a graph which relates cerebral blood flow to MAP. It is a reasonable place to start.  Have a go at drawing that graph.

Now write an equation that shows the relationship between flow and pressure.

What is the third variable?

If flow remains constant in the face of changing pressure, what else is changing? Which direction does this change occur in order to maintain constant flow at both a high and low MAP?

Returning to your original graph, what is the relative calibre of the blood vessels at each end of the flat portion of the curve?

Have you changed your answer to the original question?

I’ll be back on the weekend with some more on this ….

UPDATE 20/5: you can find some more on this topic here

BT_RA 1.12 Determinants of ICP and their regulation 

I am going to spend two days in this topic. 

Today to get you thinking about the topic and tomorrow, an exercise for you to help you clarify an issue that has tripped up many a registrar in vivas.

I have recently had a much more pleasant kind of trip, to Washington DC for the IARS meeting. For those of you who have been following this blog for a while, you may remember my post mentioning the work of Yayoi Kusama. Well, she currently has an exhibition in DC and I spotted one of her pumpkins!

BT_RA1.12  Outline the factors determining intracranial pressure and discuss its regulation
The Monroe- Kellie doctrine can be represented graphically as an elastance curve TRUE/FALSE

Reduction CSF production as ICP rises helps maintain a normal ICP TRUE/FALSE

An intact blood brain barrier is necessary for intravenous mannitol to decrease brain water TRUE/FALSE

Factors the reduce CMRO2 generally reduce cerebral blood volume TRUE/FALSE

Doses of volatile anaesthetic agents less than 1MAC cause an uncoupling of the relationship between CMRO2 and cerebral blood flow TRUE/FALSE