BT_GS 1.23 Describe the physical properties of inhalational agents, including the principles of vaporisation BT_GS 1.26 Describe the toxicity of inhalational agents


T / F  Using the device shown above, a high inspired concentration of methoxyflurane can be achieved because it has a high saturated vapour pressure.

T / F  Methoxyflurane is more potent than sevoflurane.

T / F  Methoxyflurane produces analgesia at sub-anaesthetic concentrations.

T / F  The oil:gas partition coefficient is 950. This means, at equilibrium, the partial pressure of methoxyflurane in fat would be 950 times higher than in alveoli.

T / F  Nephrotoxicity can occur with prolonged methoxyflurane use, due to intra-renal metabolism to inorganic fluoride (F¯).

BT_GS 1.23 Describe the physical properties of inhalational agents, including the principles of vaporisation

T / F  At sea level the carrier gas leaving a sevoflurane vaporising chamber always contains approx. 21% sevoflurane.

T / F  With increasing altitude, a vaporiser progressively delivers a lower partial pressure of anaesthetic than what is intended..

T / F  At their boiling point, all substances have a saturated vapour pressure equal to the atmospheric pressure.

T / F  A liquid becomes cold as it is vaporised, because heat energy contained in the liquid is converted to kinetic energy in the molecules which are escaping as a vapour.

T / F  To maintain a constant temperature of the liquid anaesthetic, vaporisers are constructed of a good insulator such as copper.

Two bonus questions 🙂

  1. Our vaporisers are often referred to as “plenum” vaporisers. What does plenum mean in this context?
  2. The anaesthetic apparatus shown above includes a vaporiser. How does it work in conjunction with the breathing system shown?

This too shall pass

This saying came into the English language in the 1850s in Edward Fitzgerald’s retelling of a Persian folktale, “Solomons’s Seal”, in which King Solomon is asked for a phrase which would suit all occasions.

There will be those of you who thought that the exam on Monday could have gone better and perhaps are feeling a bit down in the dumps. Even those of you who initially felt fine, may over the course of the week, have thought of numerous things you failed to include in your answers. That’s normal.

It’s OK. Feel secure in the knowledge that you studied hard and gave it your best effort. No-one will ever answer every question perfectly – such is the nature of the exam.

There is nothing more to be done for the written exam – it has passed. Hopefully you have had a relaxing week and have something lovely planned for the weekend.

Next week it is time to refocus your energy on being as well prepared as possible for the vivas. Speak about the primary material at every possible opportunity: in your study group; in theatre and; at every viva practice session that is offered in your region. Think about the concepts which are difficult to explain and get them straight, first in your head and then coming out of your mouth.

We will be posting a few viva tips on the blog in the coming weeks, so stay tuned and remember this too shall pass….

BT_RA 1.16 Neuraxial Opiates

Candidates are often a bit vague on neuraxial opiates in the vivas. These are used very commonly in clinical practice, so it is unwise to overlook this topic.

BT_PM 1.18 Describe the pharmacology of opioids deposited in the epidural space or cerebrospinal fluid

BT_RA 1.16 Describe the drugs which may be injected into the intrathecal or epidural space as adjuvant agents to a central neuraxial block and discuss their risks and benefits

TRUE/FALSE The analgaesic effect from continuous epidural infusion of hydroPHILIC opioids is primarily from systemic absorption

TRUE/FALSE Intrathecal morphine provides analgaesia to more spinal levels than intrathecal fentanyl

TRUE/FALSE Significant amounts of epidural morphine are sequestered in epidural fat

TRUE/FALSE Epidural infusion of fentanyl may lead to systemic concentrations high enough to produce pharmacological effects

TRUE/FALSE The peak period for respiratory depression with intrathecal morphine is from 18-24 hours after injection

BT_GS 1.59 TCI

BT_GS 1.59 Describe the pharmacological principles of and sources of error with target controlled infusion

I am sure you have all looked at this screen. Here are some questions to test your knowledge of these models.

TCI Interface.png

TRUE/FALSE Inaccurate drug delivery from the infusion pump contributes to 55% of the overall inaccuracy of a TCI infusion

TRUE/FALSE With most modern TCI algorithms actual plasma concentrations are within 20-30% of predicted concentrations 95% of the time

TRUE/FALSE The Marsh model uses age and weight to calculate the compartment size

TRUE/FALSE The Schnider model may calculate a negative lean body mass in very obese patients

TRUE/FALSE The most clinically reliable method is to target the effect site concentration observed at loss of consciousness.

BT_SQ 1.6 Flow Measurement

Having observed a day’s silence in memory of those suffering yesterday, we return to our regular programming with some questions on an old favourite LO 😉

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

· SI units

· Measurement of volumes, flows, and pressures, including transducers. 

· Measurement of blood pressure

· Measurement of cardiac output

· Measurement of temperature

· Oximetry

· Gas analysis, including capnography

· Methods used to measure respiratory function, including:

– Forced expiratory volume

–  Peak expiratory flow rate

–  Vital capacity

–  Flow-volume loops

–  Functional residual capacity and residual volume

TRUE/FALSE If exhaled gas is not warmed to patient temperature in a pneumotachograph, volume will be underestimated
TRUE/FALSE Volume is the area under a flow/time curve

TRUE/FALSE A pneumotachograph calculates flow from a known resistance and a measured pressure difference
TRUE/FALSE A pneumotachograph uses the hydraulic version of Ohms Law

TRUE/FALSE A pneumotachograph measures flow accurately only when it is turbulent

This is a Dräger flow sensor from one of the limbs of a circle circuit. If you look closely you can see a fine wire between the top two prongs. The wire between the lower two prongs isn’t shown so clearly. What principle is this flow sensor using?


Here are two different views of the sensor that modern GE machines use for measuring flow in a circle. The two tubes are hollow, and you can see on the photo on the left that they are open to the circuit. What principle is this flow sensor using? How do you think that it works?

There’s an exam on Monday

We wish everyone sitting on Monday well. You’ve been working hard now for months and now is the time you get to show off all your knowledge and understanding!

Remember to read every SAQ carefully so that everything you write is answering the question. Write in point form and leave lots of empty lines on the page between points. Stick to 10 minutes per question. The college know there is a lot of anxiety out there about time keeping  and they are ensuring there are easy to read clocks available. Answer every MCQ – there is no negative marking.

Go out and enjoy yourself afterwards! I recommend taking a week off from study so you can come back to it fresh and enthused. Spoil yourself next week.


Study tip – interpreting examiner reports

The examiner report for an exam is an aid to study. Today I’ll try to give you some insight into what the examiner is thinking when they write them so you can put your own use into context.

The report for each question is written by the examiner who marked that question, so there will be variability between question reports in any paper. The exam report is usually written just after marking the papers, and while examiners mark they’ll usually keep notes of what people are struggling with. Many reports become an example of reporting by exception – the key points that everyone has gotten right aren’t mentioned, just the ones that everyone hasn’t. The examiner may also feel that it is not worth adding factual material which is well covered in the books – as it is well covered in the books.

Over the years there has been a spectrum of interference by the exam chair regards editing of the reports. So sometimes the examiner’s disappointment has shone through, particularly in the clinically relevant questions where it seems many candidates have not been able to apply science to everyday practice. Remember, the examiners are clinicians who consciously apply the primary material to their work every day which is a major reason why they find the material so interesting and memorable.

I would recommend you therefore read the examiner reports in the context of what you have learnt from other sources on the topic. They are not model answers.


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?)




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

TRUE/FALSE  FRC in healthy adult males, is reduced by approximately 500ml when supine

TRUE/FALSE  Ventilatory adaptation to high altitude takes approximately one week

TRUE/FALSE  During bag/mask ventilation, total dead space (apparatus and physiological) comprises approximately half the tidal volume

TRUE/FALSE  FRC reduces with age

TRUE/FALSE  Increased respiratory resistance in obesity is mostly due to increased airways resistance