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


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 1.23 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

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

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.

2017.1 : SAQ 11

Draw an expiratory flow volume curve obtained from a maximal expiratory effort after a vital capacity breath, for a person with:

A.  normal lungs

B.  restrictive lung disease

C.  obstructive lung disease

(10 marks)

Explain how and why these curves (and the derived parameters) are different in each disease state (15 marks)

We see a lot of patients with pulmonary function tests, their associated curves and parameters. Understanding the physiology, aids interpretation of the results.

BT_PO 1.20

A vital capacity breath is from expiratory reserve volume (ERV) to total lung capacity (TLC)  TRUE/FALSE

The effort independent component is due to dynamic airways closure TRUE/FALSE

The TLC is increased in obstructive lung disease TRUE/FALSE

The effort independent component is steeper in restrictive lung disease TRUE/FALSE

A normal peak expiratory flow rate would be 10 L/min TRUE/FALSE



BT_PO 1.12 Discuss ‘fast’ and ‘slow’ alveoli, including the concept of ‘time constants’

Theme for the day: mindfulness.

Q. Deflation and Inflation of alveoli can be considered an exponential process. TRUE/FALSE

Q. “Fast” and “Slow” alveoli refers to the compliance/resistance relationship between the alveoli and its supplying bronchiole. TRUE/FALSE

Q. A relatively non compliant alveolus paired with a patent wide bronchiole will comprise a slow lung unit TRUE/FALSE

Q. In the normal lung, alveoli in the apex are “slower” because compliance is less in the apex. TRUE/FALSE

Q. At fast respiratory rates, “slow” lung units may not have completed filling before the onset of expiration. TRUE/FALSE

BT_PO 1.11 Define compliance (static, dynamic and specific) and relate this to the elastic properties of the lung

Twice. So good, they named it twice.

Q. Most studies of lung compliance under anaesthesia indicate a decrease compared to the awake state T/F

Q. Age increases lung compliance T/F

Q. Dynamic compliance may be greater than static compliance T/F

Q. An elephant has greater compliance than a mouse T/F

Q. Stress relaxation is a component of dynamic compliance T/F


SS_PA 1.24 : paediatric physiology

Not a bad textbook, Evers & Maze… But rubbish for paediatric pharmacodynamics… So I’ve swapped over to some paediatric physiology instead. I used Miller as it was handy.

SS_PA 1.24 Describe the physiology of the cardiovascular, respiratory, renal and neurological systems in the neonate and the changes that occur with growth and development and the implications of this for anaesthetic care

During the first 2 weeks of age a neonate can flip back into a foetal circulation   TRUE/FALSE

The neonate has more compliant ventricles than an adult   TRUE/FALSE

Infants have more type I muscle fibres in their diaphragm   TRUE/FALSE

Neonates have decreased intracardiac calcium stores   TRUE/FALSE

Oxygen consumption in infants is higher than in adults   TRUE/FALSE

BT_PO 1.37 The stressed respiratory system

BT_PO 1.37 Discuss the effect of the following on ventilation:

· Changes in posture

· Exercise

· Altitude

· Anaesthesia

· Ageing

· Morbid obesity


Peru. 4200m. #lifeafterexam


TRUE/FALSE Periodic breathing while asleep leading to oxygen saturations of 50% is common when first ascending over 4000 m

TRUE/FALSE  Minute ventilation is proportional to oxygen consumption at all levels of exercise

TRUE/FALSE  Response to hypoxaemia and hypercapnia are usually unaffected by obesity

TRUE/FALSE  FRC is reduced to a greater extent during anaesthesia, when a muscle relaxant is used than when one is not used

TRUE/FALSE  1 MAC of anaesthesia preserves diaphragmatic function but can abolish EMG activity of other inspiratory muscles (If this is true how would this affect your anaesthesia plan for renal and ureteral lithotripsy?)