Acute severe asthma: the evidence 2011

All of these recent posts and commentary on severe COPD has lead to a few discussions about the management of the Acute Severe Asthmatic around my workplace.  It is fair to say that this is an area where tradition and long-held beliefs have a grip, but there is a bit of recent evidence to suggest we have some options with good efficacy which we should use in this nasty disease of largely young people.  So I have had a look at the evidence and reviews and come up with my usual super-summarised version for the simple folk like me to read…

Oxygen is good. Give it. No evidence, just do it.

In Australia this is salbutamol [albuterol in the US]. This is proven to be effective and reduces hospital admission / physiological parameters etc. There is a Cochrane review looking at continuous vs. intermittent nebs which showed a modest benefit to continuous vs intermittent nebs.  So how does this change my practice?  In reality we give nebs, and give a lot, so just give as many as you can probably no downside to continuous and in practice you will have gaps, ce la vie.  I think you need to be aware of the side effects – watch the K+ and heart rate, try and keep it as normal as you can.

In Oz this is ipratropium.  The evidence here is less convincing.  The summary from the Cochrane review – adding anticholinergics to B2-A in severe asthma is as follows:  A single dose of an anticholinergic agent is not effective for the treatment of mild and moderate exacerbations and is insufficient for the treatment of severe exacerbations. Adding multiple doses of anticholinergics to beta2 agonists appears safe, improves lung function and would avoid hospital admission in 1 of 12 such treated patients.   

So I say – go for it, give multiple doses of ipratropium to the severe asthmatics. Anecdotally it causes less tachcardia, and appears to have little downside.  But don’t settle for just one neb – I have been guilty of this I fear.

Steroids are well proven and part of the woodwork when it comes to asthma of all severity it seems.  In severe asthma they are given IV usually – hydrocortisone or methylpred.  The NNT is about 8, so well worthwhile I reckon.  Most of these patients get a guernsey on the ward – so how much steroids becomes a question for the ward team to ponder.  Turns out some is as good as a lot according to the Cochrane folks:  equivalent of 400 mg hydrocortisone per day was adequate with no benefit to higher doses.

Also some evidence to say early steroids might reduce admission – so give them early (first hour) and you might save a bed’s occupancy (not my favourite end-point)

There are 2 Cochrane reviews on this – one for kids and one for adults and the data turns out to be about the same. In practical terms aminophylline seems to have some effect on bronchodilation but no difference in the patient-oriented outcomes of – intubation, mortality or symptom reduction. Aminophylline has a narrow therapeutic index and high rate of side effects- eg, vomiting [which is even less fun when you are in respiratory failure and you might inhale a carrot] So the jury is tied but not moving anywhere – I think I will give it a miss unless everything else has failed, even then, not a good drug to give to an already super-sick patient.

Magnesim keeps popping up everywhere it seems. So in severe asthma – what is the deal? Well magnesium looks very good for severe asthma – the NNT is 2 – 3 for “admission”! Nothing is that good in our day-day work.  Once again – this end-point is a bit shaky – I am going to admit them anyway if they are severe enough to need Mg, however there was no documented harm – so I think I will keep doing it. How much do you need?  I used the same dose we do for eclampsia – are there any guidelines out there?  This recent Brit study also showed Mg (thanks was good at limiting tachycardia in these patient – which is a bonus given how much B2-agonist we are using – has to help the CO a bit to keep the HR down?

However beware – no benefit found for less severe asthma – so this is easy – if they are not sick enough to get a drip, don’t give IV mag.

There is some evidence for nebulised MgSO4 – in this review it improved pulmonary function but not clinically important outcomes – admission, symptoms etc

Giving iV salbutamol is one of hose things we do in bad asthma, but is it a good idea?  Well, maybe not.  The best review I could find was 10 years old and showed no benefit, some worse physiology and lets face it – it makes you feel pretty crappy.  Positive chronotropy plus increased O2 demand seem like bad things in asthma.  So I think I will leave this out until further review.  Kane from LITFL has reminded me that an adrenaline infusion is worth a try in the severe asthmatic not getting better on all the rest – probably OK in place of salbutamol – works on the same receptors – any evidence – not sure….

Now we get to the meat of the matter. This seems to divide ED folk.  The teaching has for a while been – NIV for COPD but not for asthma.   So lets look at the evidence…  well not so easy, as there is not a lot of good quality data out there – no RCTs, only some case series and observational studies.  It seems very tricky to make a clear choice based on the available evidence as it is almost certainly biased by the fact that given the current culture only the sickest status asthmaticus patients would be getting a trial of NIV.  The Cochrane group looked into NIV and found it was proven to help with some endpoints, no different for others and negative effect – it depends which outcome you look at.  We need a good RCT on this.

In my opinion it would make sense to put a severe asthma with respiratory failure on NIV if you are planning to intubate otherwise – Scott Weingart @ Emcrit has posted on this a few times.  However, my understanding is that NIV works by assisting ventilation in the patient with respiratory muscle fatigue, and rising CO2.  So why not use it early in the severe asthmatic and prevent this from occurring as much as possible?  Is there a downside?  Sure you need to watch the preload and BP, but they are usually fitter from a cardiac POV than the average COPD patient with chronic lungs / pulm. hypertension and a bit of IHD from all the cigarettes.  So should we use it earlier – not wait until they are on the brink of intubation?

DrGDH has a new blog – he appears to be slightly obsessed with all things NIV – check out his posts on the topic – NIV in Asthma? no point right?.  Covers all the current available evidence in a page of internet – check it out.  The theme seems to be – lots of small, non-randomised trials that show a decrease in the need for intubation / IPPV in the severe asthmatics, but not enough good data to say for sure it works.  So – what to do?

I think it is worth a try, still need to do all the medical management, and I would definitely prefer a course of NIV if it were me!  In our little hospital I think this is a smart move – intubation mandates a long air transfer with significant risk.  After all – we can still tube them if the NIV fails – but once you have intubated – you have committed to a long, expensive and potentially hazardous transfer.

So once all else has failed – you have an otherwise healthy patient with respiratory failure and the end of the road if intubate and ventilate. Sounds good – but be warned – this is a tough road, ventilating a patient with this degree of obstruction is tricky. And you had better have a good plan for induction and getting the vent running – because a minute of fiddling might be the difference between a bad situation and a disaster. I am not the expert – Dr Scott Weingart at EmCrit has a great podcast on this scenario – so I direct you there for some gold! In summary:

  • Prepare, plan and plan B, C ready.
  • Have the patient on NIV for the induction – and have the vent set to go once you are in.
  • Use ketamine for your induction – it is a bronchodilator and keeps the CO up.  You might want to ensure adequate preload before switching to IPPV.

USe the “obstructive lung vent strategy” as per Dr Weingart

There are only 4 things you need to remember for an obstructive patient

  1. Vt (Tidal Volume) = 8 ml/kg, don’t mess with it
  2. Flow Rate = shorter insp times, 80-100 lpm
  3. Resp Rate = Lung protection, start at 10 work your way down if necessary
  4. FiO2/PEEP = Oxygenation, should need much O2 (40%)m I recommend PEEP of 0, but certainly keep it less than 5


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