BT_SQ 1.6 Describe methods of measurement (including) … gas analysis, including capnography
BT_PO 1.29 Discuss regional ventilation-perfusion inequalities

Each of the following T/F statements applies to a cardiac arrest with CPR being performed

T / F  an ETCO2 of 15 mmHg would indicate good CPR

T / F  the PaCO2 will correlate with the ETCO2

T / F  the lower ETCO2 is due to a reduced venous CO2 content

T / F  the lower ETCO2 is due to absent aerobic cellular respiration

T / F  the lower ETCO2 is due to increased alveolar dead space

Can you provide a rationale for the correct statements above, from first principles? Hint… this blog relates to learning outcome BT_PO 1.29


Study tip: Answering SAQs – make the most of your unconscious brain, but don’t let it fool you….

Ok, that title is a little cryptic, but bear with me….

We have probably all had experiences when we are asked to recall something which we are sure that we know (for me this is often a person’s name), but seems impossible to drag up from the depths of our brain. We give up and then the answer just pops into our consciousness. Perhaps this is your unconscious brain at work.

How can you use unconscious brain to your advantage during the SAQs? As soon as you read the questions your brain will start working on them. Make sure that you read all of the questions carefully in the first 10 minutes. Spend a bit of time carefully checking to see exactly what the question is asking, as you want to set your brain off on the right track. I will assume that you have studied well and have a good knowledge base. In spite of this, some questions may initially seem tricky: perhaps the information doesn’t spring to mind; you may not be sure how to structure the answer. That’s ok – don’t panic! Panic is shocking for your memory. Send these questions to the unconscious mind and get on with answering the questions you feel more confident with. When the time comes to answer the questions that you have set aside, hopefully your mind will have worked on them in the background and that knowledge will be easier to access.

Now for your second part – don’t let the unconscious brain fool you. This part applies to your SAQ practice. I suspect, and hope, that all of you are practising past SAQs. How do you do this? Here are some options:

  1. Do you select 6 questions at the start of your study session to write at the end?
  2. Do you choose some questions the day before to attack the following day?
  3. Have you put a whole lot of individual past SAQs in a box, from which you randomly pick a selection to look at and answer straight away?
  4. Do you have a friend/colleague put a set of questions in a sealed envelope to open and answer under exam conditions?

If you picked 3 or 4 – perfect! You are receiving a true reflection of how you could answer that question in the exam. The results may be confronting, but it will show your where a brush up is needed.

If you picked 1 or 2, I would contend that you are giving yourself an advantage that you will not have in the exam. You are giving your brain extra time to work on these questions even if you consciously try not to think about them.

There are still a couple of weeks until the next written exam. It’s not too late to give yourself some good quality SAQ practise. Any holes that you find in your knowledge should be easier to learn as this information is likely to have meaning for you.

Good luck everyone!! I am not sure that I will be back on the blog until after the written, but I wish you all of the best…..

….and just to finish, I couldn’t leave you photo free.


“Brain” jellyfish, Mljet, Croatia

BT_PO 1.36 Discuss the physiological effects of hypoxaemia

Keeping with a similar theme….

I have to admit I was feeling a bit low on inspiration as I was writing this post and was wondering which LOs would be of specific interest to you, the reader.

If you have any LOs which you would  like to see a post on, please leave a comment and I will write on them at a future date. A full list of the more than 300 options can be found here

I have updated the Oxygen Cascade post to include quite a nice little article from BJA education…

…and here is another photo from the Plitvice Lakes….


BT_PO 1.36 Discuss the physiological effects of hypoxaemia, hyper and hypocapnia, and carbon monoxide poisoning

Hypoxaemia causes activation of the sympathetic nervous system  TRUE/FALSE

Hypoxaemia causes vasodilation in all tissue beds    TRUE/FALSE

Hb concentration rises acutely with hypoxia due to auto transfusion from the spleen TRUE/FALSE

Alveolar ventilation increases linearly as PaO2 falls below normal levels    TRUE/FALSE

In response to significant hypoxia, neuronal tissue initially becomes hyperpolarised TRUE/FALSE

BT_PO 1.41 Nitric Oxide

Staying on a vaguely respiratory topic….

This little molecule is actually mentioned in two LOs, so double bang for your buck today.


But perhaps Nitric Oxide itself will give you the most bang!!

BT_PO 1.41 Outline the pharmacology of drugs used to treat pulmonary hypertension including nitric oxide

BT_PO 1.58 Describe the pharmacology of anti-hypertensive agents and their clinical application, including the following agents:

  • nitric oxide
  • plus lots of others….


Nitric oxide is synthesised from l -arginine                                   TRUE/FALSE

Nitric oxide for inhalation is stored in cylinders diluted with nitrogen   TRUE/FALSE

Nitric oxide inhibits platelet activation                                           TRUE/FALSE

Inhaled nitric oxide improves oxygenation by reducing V/Q mismatch   TRUE/FALSE

Effects of NO on the immune system are beneficial                     TRUE/FALSE


BT_SQ 1.6 Oximetry

There have been a couple of posts on this topic before, but as we were talking about oxygen, I thought it might be worth revisiting.

Here is a comprehensive review of the sources of error with pulse oximetry, following a discussion of the principles. See the link to the CinderHK page below for more information on good references.


Slightly off topic,  though I think fascinating, here is a picture of the absorption spectrum of different contaminants of glass. The glass used in long distance telecommunication fibre optic cables is ultra pure. The signal is transmitted in the IR spectrum, at about 1.5μm, such that the attenuation of the signal is only 0.2dB per km! I took this photo at the Hong Kong Science Museum.

BT_SQ 1.6 Describe the methods of measurement applicable to anaesthesia, including clinical utility, complications and sources of error in particular:

  • Oximetry
  • Plus heaps of others 😉


Pulsatile venous flow may cause an over estimation of SpO2                              TRUE/FALSE

The red:IR absorption modulation ratio (R) equals 1 at SpO2 85%                      TRUE/FALSE

Intravenous injection of indocyanine green causes a transient reduction in SpO2   TRUE/FALSE

The accuracy of SpO2 in humans has not been calibrated below 70%               TRUE/FALSE

Red nail polish is likely to cause inaccurate SpO2 readings                                  TRUE/FALSE

BT_PO 1.23 Oxygen Cascade


This may seem like a pretty easy topic and, I agree, it is easy to memorise the step wise decreases in oxygen tension as you move from the atmosphere to the the tissue.

Why to these changes occur? Have you thought about the implications, on the oxygen cascade, of environmental and patient factors and how they may exacerbate the natural fall in oxygen partial pressure? Ask yourself these questions and, if you have a patient who is hypoxaemic, look to the oxygen cascade to give you an answer…

There is an great diagram, and accompanying text, in Ch 10 Nunn’s Applied Respiratory Physiology which will help you with your exploration of this topic. This article from BJA Education also contains some good information.


The most amazing cascades I have seen, even in the pouring rain,  – Plitvice Lakes National Park, Croatia….

BT_PO 1.23  Describe the oxygen cascade

Increasing alveolar ventilation will generally increase PAO2     TRUE/FALSE

The effect of a low inspired oxygen concentration can be offset by increased alveolar ventilation TRUE/FALSE

Hypoxaemia caused by increased shunt can be overcome by increasing FiO2  TRUE/FALSE

A sudden reduction in cardiac output will cause an immediate decrease in PAO2 TRUE/FALSE

Diffusion capacity limits oxygen uptake at the the pulmonary capillary in the healthy subject at rest   TRUE/FALSE

Study Tip: Describe, Explain, Compare, Discuss, Outline

I am sure you have seen these words at the start of short answer questions. Have you taken much notice of them? Do these words actually mean anything to you?

They are called action or reporting verbs and it is worth having a working knowledge of them.

Good answers to short answer questions usually have a structure. For example, an answer to a question about a drug might use headings like pharmaceutics, pharmacokinetic and pharmacodynamics. The detail under each of these headings will depend on the action verb.

The Anaesthesia Training Program Curriculum (v1.6) provides some definitions (p16) but there are other sources for example here and here that are more informative.

Having your own easy to remember definitions will help you in the exam. Here are a few to get you started:

Describe – What

Explain – How and Why

Discuss – Multiple Whats and Whys

Outline – An organised description, usually with big picture points

Taking more notice of the action verbs in questions can help improve the structure of you answers and earn you more marks.

Temperature Measurement

BT_GS 1.69a Describe how a patient’s temperature is monitored and discuss the indications for temperature monitoring with the advantages and disadvantages of particular sites and methods (also refer to monitors and monitoring standards, which is covered in the Safety and quality in anaesthetic practice clinical fundamental)

This is also covered by BT_SQ 1.6, but I didn’t want BT_GA 1.69a to feel left out.

There are plenty of posts so far on the effects of temperature, but how do you measure it?

T/F Nasopharyngeal temperature probes use thermocouples

T/F Thermistors demonstrate hysteresis

T/F A smaller thermistor will have a faster response time

T/F An infrared thermometer works by emitting IR radiation and measuring the amount reflected by the tympanic membrane

T/F A Swan Ganz catheter incorporates a thermistor


Supplementary Questions:

Temp Probe.jpgWhat kind of device is this?

How does its output vary with temperature?

What temperature ranges is it accurate over?


BT_SQ 1.5BT_SQ 1.5 “Describe basic physics applicable to anaesthesia in particular:

· Principles of humidification and use of humidifiers


T/F A Heat and Moisture Exchanger (HME) primarily reduces heat loss by warming the inspired gas.

T/F A Heat and Moisture Exchanger (HME) warms inspired gases to a temperature of 35-37°C

T/F At this temperature a Heat and Moisture Exchanger (HME) achieves a humidity of 85-93%

T/F A Heat and Moisture Exchanger (HME) reduces the risk of bacterial and viral cross-infection between patients.

T/F A Heat and Moisture Exchanger (HME) is less effective when using high gas flows in a circle system.



BT_PO 1.38 Define humidity and outline the importance of humidification


Not a riveting topic, but giving dry gas to a patient can cause problems, so you need to know something about it.

T/F at a relative humidity of 100%, a litre of gas at 21 degrees Celcius will contain the same amount of water as a litre of gas at 37 degrees Celcius

T/F In an awake person, during quiet nasal breathing, humidification of inhaled air occurs in the upper airway

T/F Airway lining fluid acts as heat and moisture exchanger during respiration

T/F Relative humidity levels need to be monitored and controlled in the operating theatre

T/F Administration of dry gases may impair surfactant activity