Asthma

Take home messages

• The triad of asthma is bronchoconstriction, airway inflammation, and mucus hypersecretion
• The key killers of intubated asthmatics are tension pneumothorax and dynamic hyperinflation
• Aim for a low respiratory rate, low PEEP and prolonged expiratory time

A case

The decision that scared me most (aside from Rule 10) while working as a core trainee anaesthetist was the 'when do I intubate asthma' conundrum.

• I'd seen some consultants and registrars intubate asthma
• I'd seen other consultants and registrars do everything in their power to avoid it
• I did not have a robust 'definitely intubate at this point' heuristic to comfort me on my lonely ITU night shifts

So when I was called by ED at one in the morning on a Sunday and asked to come and assess whether their tripodding asthma patient needed intubating, I rather bricked it a little.

Reluctantly, I let the ITU nurse in charge know that I was reviewing a possible admission, and dutifully wandered on down to resus.

"Hey thanks for coming, it's the guy in bed three..." the ED registrar at the nurses' station pointed vaguely towards resus while handing an ECG back to the nurse on his left, and picking up the ringing red phone on his left.

Hello bed 3

I took what in retrospect was an insensitively deep breath, and pulled back the curtain to bed 3, wondering whether I was going to have the knowledge and courage to make the correct decision myself, or whether my boss was to receive an unwelcome wake up call.

In front of me lay a slim, pale man in his thirties.

• He was lying flat on his back
• His eyes were closed
• His heart rate was 30
• His respiratory rate was 0
• His chest was silent
• The PaCO2 on the arterial blood gas the nurse handed to me was 20 kPa
• The look on the nurse's face suggested this was all rather recent

Decision made.

What is it?

Asthma is a chronic, reversible, obstructive airways disease, characterised by chronic inflammation and hyper-responsiveness of the bronchial muscles and mucus hypersecretion.

The inflammation

The less-than-helpful T helper 2 cells, along with mast cells and B cells all work together to trigger a cascade resulting in release of histamine, leukotrienes and prostaglandins.

Who gets it?

Some history

Asthma comes from the Greek ἆσθμα (ásthma), meaning "panting" or "breathlessness."

Hippocrates is thought to have described asthma in around 400 BC as a condition caused by the environment, linking it to dust and city living.

Oh and we also used to think 'asthma cigarettes' where a good idea.

Some actual treatments

Isoprenaline - the first β agonist - was introduced in the 1940s and formulated into an inhaler.

These were revolutionary, to the point where they were overused so much that they started increase mortality again (via their cardiovascular effects) until the slightly more selective salbutamol came along in 1966.

How bad is it?

When do I get involved?

The anaesthetist isn't called when the patient starts wheezing, they're called when the patient stops wheezing.

This is when you're headed into 'life-threatening' territory, and the patient is exhausted.

You can find the full BTS guidance on how to categorise the severity of an asthma attack here, but for now we'll focus on what's most relevant to us.

To tube or not?

This is the tricky bit - making the decision to intubate - because you know that once that tube is in, the real challenge is going to be trying to ventilate.

Imagine ventilating a brick. One that doesn't want to be ventilated. That's what ventilating a good going asthmatic lung feels like.

There are essentially two schools of thought:

• An exhausted asthmatic needs a rest, so intubate them before they get too tired
• Intubation and ventilation is horrific and should be avoided until all other options have been exhausted

The true correct answer is probably somewhere in between. Either way, when you do get your scope and tube out, you need to have a plan.

RSI vs DSI

Nobody is going to criticise you for executing a smooth standard or modified RSI for a life-threatening asthma attack.

They might say something like 'sux releases histamine' but in reality you've done a good job.

But you might want to pause and consider the benefits of a delayed sequence induction with ketamine in asthma.

Don't blow it

Ventilating asthma is hard.

The reduced airway calibre massively increases resistance and contributes to gas trapping, while mucus hypersecretion causes plugging and desaturation.

The biggest killer in ventilated asthma patients is dynamic hyperinflation, which is discussed beautifully in the video at the bottom of this post.

Can I use BiPAP?

Non-invasive ventilation is weirdly controversial in asthma, given how useful it can be.

This is largely because there isn't much evidence floating around to back up its use, rather than it being actively harmful.

The Verdict

Consider BiPAP to buy time and preoxygenate while you get ready to intubate, but don't rely on it as a definitive strategy by itself, and don't let it delay intubation.

Here's an awesome LITFL video

Video link if the embed doesn't work.

Useful Tweets

References and Further Reading

Management of life-threatening asthma in adults

Asthma is a disease of predominantly reversible airway obstruction characterized by a triad of bronchial smooth muscle contraction, airway inflammation, and inc

OUP AcademicDavid Stanley, MRCP FRCA

Non-invasive ventilation (NIV) and asthma

Non-invasive ventilation (NIV) is widely used for severe asthma in Australasia yet remains a controversial topic

Life in the Fast Lane • LITFLChris Nickson

Asthma | British Thoracic Society | Better lung health for all

The British Thoracic Society exists to improve standards of care for people who have respiratory diseases and to support and develop those who provide that care.

British Thoracic Society

Primary FRCA Toolkit

While this subject is largely the remit of the Final FRCA examination, up to 20% of the exam can cover Primary material, so don't get caught out!

Members receive 60% discount off the FRCA Primary Toolkit. If you have previously purchased a toolkit at full price, please email anaestheasier@gmail.com for a retrospective discount.

Discount is applied as 6 months free membership - please don't hesitate to email Anaestheasier@gmail.com if you have any questions!