Chris Hellyar Profile picture
Sep 27, 2021 16 tweets 9 min read Read on X
This #novice anaesthesia thread is about spinal anaesthesia.

Thanks to @anaecritmed for the suggested topic.

Once again I’ve made a summary infographic. I’ll break it down as we go and direct you to some useful resources and websites for further reading

Comments welcome
1/n Image
first off -a Comprehensive summary from THE online resource for regional anaesthesia (@NYSORA)
nysora.com/techniques/neu…

I also strongly encourage you to look at this 3-d model to visualise the spine. It helps troubleshoot failed spinal
sketchfab.com/3d-models/lumb…
2/n
Spinals are a form of neuraxial block.
Specifically a block in the subarachnoid space.

The first reported case was by August Bier in 1898 using cocaine (Ester) who gave himself and assitant post-dural picture headache. Opiates were first added in 1901 by Racoviceanu-Pitesti
3/n Image
The spinal cord extends down to the conus medullaris at L1 in adults (L3 in infants)

CSF resides between the pia and arachnoid mater (subarachnoid space)

Although the arachnoid is delicate it presents a formidable barrier to drug translocation
4/n
In accessing the subarachnoid space using a midline approach we have to traverse
Skin and subcutaneous tissue
Supraspinous ligament
Interspinous ligament
Ligamentum flavum
Dura mater
Arachnoid mater
ykhoa.org/d/image.htm?im…

5/n Image
Sites of action of the injected drugs are:
1 - Spinal cord
2 - Spinal nerve roots
3 - Dorsal root ganglia

(c-spine for illustrative purposes)
By user:debivort - Own work, CC BY-SA 3.0, commons.wikimedia.org/w/index.php?cu…

6/n Image
Size, surface area and degree of myelination of nerves affect the speed and penetrance of anaesthesia
So not all nerves are blocked at identical concentrations
So not all sensory modalities are blocked at the same level
This is the premise of a differential sensory block
7/n Image
This means checking cold modality only with your ethyl chloride spray will not tell you the height at which pain is blocked. So if you use this, make sure you have gone 2 dermatomes above the level required!
8/n
How to get the right level?
The main factors determining the block height are:
Dose (volume x concentration) = MLAC
Baricity
CSF volume
Advanced Age
Extremes of Height+weight
Pregnancy
Positioning of patient

doi.org/10.1093/bjacea…
MLAC discussed here
doi.org/10.1093/bja/ae…
9/n Image
We can tilt the patient to affect the spread under gravity of hyperbaric solutions. However after 25mins the level is fixed
10/n
The duration of the block is clearly important and affected mostly by the dose (vol x conc), the local anaesthetic, additives used.

But also by the height of block needed

Charts that compare local anaesthetic duration often include time to T10 and T4 (from NYSORA)
11/n Image
In assessing the spinal block, test three modalities:
Sensation - ethyl chloride (cold 2 levels above pain level required)
Motor - SLR (reflects lumbosacral fibres)
Sympathetic - warm touch/BP or HR changes (T1-L2 for peripheral vasodilatation, T1-T4 for cardiac fibres)

12/n Image
Not everyone can/should have a spinal

Absolute contraindications - refusal, cardiovascular instability, active skin infection at injection site, raised ICP

Everything else is "relative"

@AAGBI has a resource for anti coagulated patients:
onlinelibrary.wiley.com/doi/full/10.11…

13/n ImageImageImage
Part of informed consent is explaining the risks

Quotable risks to patients come from NAP3
doi.org/10.1093/bja/ae…
nationalauditprojects.org.uk/NAP3_home

14/n Image
High spinal is a particular complication to be aware of.
It occurs as the level of the block rises and follows predictable symptoms as it affects different levels

The @AAGBI has an excellent QRH resource for managing complications. excerpt here
anaesthetists.org/Portals/0/PDFs…

15/n Image
Lastly a point on performing the procedure - positioning is key!
Failing to prepare = preparing to fail
Take your time in getting this right and in identifying the midline

The needle used can either be cutting or pencilpoint. Types explained here: dx.doi.org/10.1586/174344…

16/n Image

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More from @GasNovice

Sep 21, 2021
This #novice thread is all about inhaled anaesthetic agents (Volatiles)

It starts with a detailed infographic, which we will break down as we go along.

I’ve linked some resources that are worth exploring (for other content as well beyond this thread)

Comments welcome!
1/n
I want to recommend this YouTube channel from @UKAnesth Randall Schell has made lots of videos and they are very exam focused and comprehensive. So have a watch while exercising or commuting...

2/n
Read 19 tweets
Sep 12, 2021
This thread is all about Monitoring Neuromuscular Blockers (NMBs) for anaesthetic novices

I think this is often underplayed in clinical practice and we can be lazy

I’ll start with this summary infographic and elaborate as we go along.

#anaesthesia #novice
1/n
NMBs are not benign drugs. Their use (or lingering effect) is associated with:
- Risk of awareness (NAP5)
- Laryngeal weakness
- Aspiration
- Patient distress
- Adverse airway events
- Reduced hypoxic drive

…all of which we want to avoid and shouldn't leave for the PACU

2/n
The duration of action quoted for NMBs is the duration until recovery to 25% of original twitch height (roughly just after the 4th twitch is visible as far as I can tell)

Not time to full function
Not time to elimination
Not time to extubation
doi.org/10.1213/000005…

3/n
Read 11 tweets

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