SS_PA 1.53 Describe the changes in the pharmacodynamics of volatile agents, analgesics, opioids and neuromuscular blocking agents in the neonate and the changes that occur with growth and development and the implications for anaesthesia

This is the last paediatric one for a while. However, it’s probably the most relevant one so plenty of questions. Miller has a nice chapter on this (8e Ch93). Given that yesterday’s post was so short, you get some bonus statements today!

When sevoflurane first came out it was heinously expensive compared to halothane and so we weren’t allowed to use it very often at the parsimonious unnamed children’s hospital in Victoria. Halothane inductions took a while (why? and why particularly with spontaneous ventilation?) and the advice was “when you think they are anaesthetised, wait another couple of minutes” before instrumenting the airway. We could use sevoflurane for quick inductions (to save money) but not for the case. Halothane also took a lot longer to wear off than sevoflurane (why?), so the Recovery Room was a quiet, full place. When sevoflurane came into routine use it was often called “screamothane” by the Recovery staff. Why was that?

T/F  MAC of sevoflurane for neonates is about 3.3%

T/F  the incidence of emergence excitement and agitation is higher with sevoflurance than halothane

T/F  the induction dose of propofol should be reduced in infants compared to older children

T/F  TCI propofol should not be used in children because of the risk of propofol infusion syndrome

T/F the required dose of suxamethonium in infants is twice that of older children

Enough of the easy ones, how about these:

T/F  ketamine as a sole anaesthetic agent preserves the gag reflex

T/F  rocuronium can be administered intramuscularly in children

T/F  sugammadex may not be administered to children under 12

And finally, for the real experts:

T/F  clearance of alfentanil is reduced in children compared to adults

T/F  newborns have a slower clearance of morphine than older neonates

2018.1 SAQ 6

BT_GS 1.24 (Inhalational agents – pharmacokinetics)

Describe the washout of sevoflurane from a patient following two hours of general anaesthesia. You may wish to use a graph to illustrate the description.

Anaesthesia is unique in medicine for many reasons, one is our need to control offset of action of drugs as closely as onset. Desired effects become adverse effects once the patient is wheeled out of the operating theatre.

The scale on the abscissa (y axis) of this graph is logarithmic  T/F

This graph is modeled with a single exponential function T/F

High solubility drugs will wash out more quickly than relatively insoluble ones T/F

This graph takes into consideration metabolism of drugs in the liver  T/F

The initial rapid decline is due to washout from well perfused organs such as the heart  T/F

 

2018.1 SAQ 3 Mechanisms of anaesthesia

BT_GS 1.49

Outline the theories, both current and discredited, as to how volatile anaesthetic agents cause loss of consciousness.

This is an issue which is currently in the media. It also serves as a cautionary tale about how mathematics can be misused to prove what you wish to see. A log-log plot will often make variables appear to be linearly related, particularly if points which are not on the line are discarded.

Some questions inspired by common misconceptions in the SAQ:

T/F Mammals have cell walls, in which volatile anaesthetic agents dissolve

T/F The mechanism of anaesthesia is a combination of cerebral oedema, hypoxia and hypercarbia

And some more serious ones:

T/F volatile agents cause immobility by acting on the GABA receptor

T/F volatile agents cause effects at the 5HT3 receptor

T/F the effect of volatile agents on lipid bilayers can be mimicked by a change in temperature of 1°C

T/F volatile agents do not exhibit isomerism

T/F xenon and nitrous oxide induce unconsciousness by actions on the GABA receptor

Nitrous Oxide

BT_GS 1.27 Describe the pharmacology of nitrous oxide

 

T / F   nitrous oxide does not support combustion

T / F   nitrous oxide acts synergistically with volatile agents to produce anaesthesia

T / F   nitrous oxide does not cause any peripheral vasodilation

T / F   nitrous oxide acts on GABA receptors in the brain

T / F   nitrous oxide use is associated with post-operative MI

BT_AM 1.3 Describe the effect of anaesthetic agents and other drugs on airway reflexes

Hello again my friends! It feels like ages since I have posted on the blog, but I am happy to be back…

Today, a fairly core bit of business for us.

Part of my absence involved a holiday. We visited the Science Museum in London (not my favourite to be honest) where I came across this delightful contraption.

img_2001-2.jpg

We all know what nicotine does to the airways when inhaled, but how about when given rectally as this device was designed for ?!? It was used in patients who had drowned in the hopes of reviving them….

BT_AM 1.3 Describe the effect of anaesthetic agents and other drugs on airway reflexes

This article looks at the problem of laryngospasm, but does discuss the impact of anaesthetic agent on airway reflexes.

All iv induction agents EXCEPT ketamine depress laryngeal reflexes equally  TRUE/FALSE

Hypercapnoea protects against laryngospasm   TRUE/FALSE

Of the modern volatiles, sevoflurane causes the greatest depression of airway reflexes  TRUE/FALSE

A surgical depth of anaesthesia is in itself a protection against laryngospasm TRUE/FALSE

In addition to its irritant effect on the airways, nicotine stimulates the respiratory centre   TRUE/FALSE

 

SAQ 2017.2 Question 5

Outline the factors which influence the time taken for loss of consciousness with an inhalational induction of anaesthesia.

Loss of consciousness will be faster with a smaller FRC     TRUE/FALSE

Loss of consciousness will be faster in a patient who is anxious and struggling    TRUE/FALSE

Loss of consciousness will be faster with a more soluble anaesthetic agent    TRUE/FALSE

Loss of consciousness will be faster with an increased cardiac output    TRUE/FALSE

Benzodiazepine premedication may speed the process in some patients, and slow it in others    TRUE/FALSE

 

 

SAQ 2017.2 Question 3

a) Describe the immediate cardiovascular responses to the sudden loss of 30% of the blood volume in a healthy awake person
b) How are these responses different if the patient is undergoing anaesthesia with sevoflurane?

The decrease in blood volume will be detected by the high pressure baroreceptors in the atria    TRUE/FALSE

The response will be mediated by the cardiovascular centre in the medulla    TRUE/FALSE

There will be arterial but not venous constriction    TRUE/FALSE

Sevoflurane will impair contractility    TRUE/FALSE

Sevoflurane will depress baroreceptor signalling    TRUE/FALSE

 

Aviation 6 – Decompression Illness

Today we return to North Africa.  Flying Officer Reynolds flew 25 missions above 40,000 feet over a single month.  The German Ju 86’s flew at ever increasing altitudes as three out of the four available aircraft had been shot down by British Spitfires.  The final Ju 86 flight was at nearly 50,000 ft and Reynolds was again in pursuit.

He had been at over 45,000 feet for over an hour and he was suffering from the effects of altitude:

“his whole cockpit, instrument panel, control column and perspex were thickly coated with ice; his body was racked with pain and his arms temporarily paralysed, and his eyesight also failing with weakness.”  — John Frayn Turner.   British Aircraft of the Second World War

Reynolds was probably suffering from “The Bends” or decompression illness.  You may have encountered this condition in the context of diving but it is also well recognised in high altitude aviation.

Occasionally and ironically, tourists are diagnosed with decompression illness in Alice Springs. How is this possible you ask?

Well, they go diving in North Queensland and then fly to the Red Centre, the exposure to altitude soon after diving is enough to “Bend” them.

The relevance of decompression illness to anaesthesia may seem a little obscure.  The body in decompression illness is simply behaving like a human vapouriser where nitrogen is the volatile agent.

BT_SQ 1.12 Describe the principles and safe operation of vaporisers

TRUE/FALSE Henry’s Law is relevant to vaporiser functioning 

TRUE/FALSE The Aladin cassette vaporiser is an example of an injection vaporiser system

TRUE/FALSE Modern vaporisers use an electrical heating coil to compensate for the cooling caused by latent heat of vaporisation

TRUE/FALSE A plenum vaporiser is designed so that the gas leaving the bypass is fully saturated under normal conditions

TRUE/FALSE The Tec Mark 5 vaporiser is designed to be ‘tip resistant’

As an extra exercise, see if you can find or work out the properties of nitrogen and the circumstances that relate to it “vapourising” in the body at altitude (in the same the way you would think about an inhalational agent).

BT_GS 1.53 Describe the synergism between anaesthetic agents, opioids and regional blockade and how this is used clinically

TRUE/FALSE  Moderate doses of opioids can reduce MAC of volatile agents by as much as 75%.

TRUE/FALSE  50% reduction in doses is expected when propofol and midazolam are used together for hypnosis.

TRUE/FALSE  The exact degree of drug synergism can be calculated from pharmacokinetic data of individual agents.

TRUE/FALSE  The bispectral index is additive when propofol and remifentanil are used in total intravenous anaesthesia.

TRUE/FALSE  Midazolam has no effect on the ketamine dose required to suppress movement to a noxious stimulus.

BT_GS 1.50 Describe the concept and clinical application of MAC in relation to inhaled anaesthetic agents

TRUE/FALSE  MAC-AWAKE for Nitrous Oxide is approximately 30% of its MAC-Value

TRUE/FALSE  Sevoflurane is metabolised by the cytochrome p450 enzyme 2E1

TRUE/FALSE  The MAC of sevoflurane in a 6 month child is approximately 2%

TRUE/FALSE  The higher the inspired anesthetic concentration, the less it then diminishes because of uptake

TRUE/FALSE  Administration of 50% Nitrous oxide will double the volume of air-filled spaces