Andrew Tagg. Asthma for Ambos, Don't Forget the Bubbles, 2016. Available at:
Tonight I had the privilege to talk to the team at the Werribee branch of Ambulance Victoria. I was given the brief to talk on something to do with paediatric respiratory problems so I thought I would focus on one of their most common presentations – asthma.
Asthma is a common condition and affects one in ten Australians. Approximately 17.2% of all kids in Victoria have been diagnosed with it. The incidence in Aboriginal or Torres Strait Islanders is higher at around 20%. Whilst a large number of these will never need to go to hospital, of those that do go, 43% per cent need admission. This is much higher than their adult counterparts. A large number can be safely managed at home with their pre-written asthma action plan (though only 41% of kids under 15 years of age have one) but some children are more at risk of critical or life-threatening asthma than others. Fortunately, the death rate in the under 15-year-old sub-population is around 0.2 per 100,00 people.
Risk factors for a more severe attack include:-
- A previous severe asthma attack requiring an ICU admission
- Two or more hospital stays because of asthma in the last year
- Use of more than two reliever inhalers in the last month
- Exposure to tobacco smoke
- Previous allergic rhinitis, food allergies or hay-fever
There is a seasonal peak in ED visits in late summer and autumn for children, whereas more adults present in the winter. This may possibly be due to the increased incidence of viral upper respiratory tract infections among grown-ups at this time of year.
Some people are more likely to call an ambulance than others. They include those with :-
- Poor knowledge about asthma
- No asthma action plan
- Poor self-management skills
- Limited access to primary care
Paramedics are very experienced in managing it because asthma is such a common condition. I want to focus on some areas where what should happen and what does happen might diverge.
Myth – Oxygen saturations are useful in the management of asthma
An acute attack is characterised by bronchospasm, coupled with mucosal oedema and hypersecretion of mucus. This leads to aV/Q mismatch as there is hypoxic vasoconstriction and decreased blood flow to the under-ventilated lung in order to match pulmonary perfusion with alveolar ventilation.
In the hospital setting, oxygen saturations of less than 91% may predict the need for prolonged bronchodilator therapy.
Hypoxaemia and hypocarbia only occur in the presence of life-threatening asthma. If you take into account the haemoglobin-oxygen dissociation roller-coaster it is easy to see how many children may teeter on the precipice of collapse before critical desaturation occurs. Whilst low oxygen saturations mean that a patient is unwell it should be clinically obvious at this point. On the flip side, normal oxygen sats do not mean the patient is fine. There is a concern that oxygen administration may lead to a delay in recognising clinical deterioration. Low oxygen saturations may also represent a degree of mucus plugging that may be helped with repositioning.
Hyperoxia can lead to absorption atelectasis as well as intra-pulmonary shunting with a subsequent reduction in cardiac output. As the 78% nitrogen in the alveoli gets washed out with increasing amounts of supplemental oxygen, tt is resorbed. This leads to a reduction in alveolar volume and collapse.
Myth – Nebulizers are better than spacers
A recent Cochrane review comparing nebulizers with spacers found that there was no real difference in hospital admission rate with either mode of delivery. Lung function tests and oxygen saturations were also unaffected by the mode of medication delivery. What was different, however, was the adverse effect profile. If you used a nebulizer you were much more likely to see tremor and tachycardia.
Old British Thoracic Society guidelines suggested using up to 50 puffs of salbutamol via spacer but this is probably a bit excessive. The current recommendation is that 400mcg of salbutamol via spacer is probably equivalent to 2.5mg via nebulizer.
So do you know how to use a spacer? I took the Werribee team through the procedure. If you are not sure then take a look at this great instructional video from Asthma Australia:-
Whilst spacers are cheap, those of you with the MacGyver instinct may want to make your own.
These jerry rigged spacers have certainly been shown to be as effective as conventional devices in resource poor settings.
Myth – You can never give enough salbutamol
Inhaled B2 agonists relieve bronchospasm and improve oxygenation. The minor side effects that we have all seen include tremor, anxiety, headache, dry mouth and palpitations. If given, without oxygen, they have also been shown to cause or worsen hypoxaemia. Pulmonary vasodilation leads to a worsening ventilation-perfusion mismatch.
Inhaled salbutamol may also cause metabolic acidosis even when the mechanical work of breathing has been improved with paralysis and ventilation this still occurs. In the non-paralysed patient, the body compensates for this acidosis by increasing the respiratory rate to blow off the CO2. Be mindful that the tachypnoea in your asthmatic patient may be due to excess beta-agonist and not their asthma.
So how does one recognise potential salbutamol toxicity in the pre-hospital setting? Consider it in all children who are wheezy, restless, tachycardic and have had large doses of beta-agonist.
Normal doses of inhaled salbutamol have been shown to cause hypokalaemia but the clinical significance of this is unknown. Hypokalemia, coupled with worsening respiratory and metabolic acidosis can have catastrophic cardiac effects.
Myth – Adrenaline is dangerous in asthma
One of the most most obvious reasons for using adrenaline in the setting of apparent severe or life threatening asthma is that the diagnosis may be in doubt. Asthma and atopy often co-exist. Patients with known food allergies and asthma are much more likely to die due to anaphylaxis than those without asthma. A child with severe anaphylaxis may initially have no more signs than a wheeze and worsening air hunger that is mistakenly treated as asthma. The diagnosis of anaphylaxis should be considered in all who fail to respond to initial therapy.
Nebulized adrenaline may be helpful in acute asthma via direct beta adrenoceptor mediated bronchodilatation. It is possible that there are also some alpha effects via reduction in localized oedema and reduction in microvascular leakage. Small studies have shown no difference between nebulized adrenaline and nebulized salbutamol in terms of increased peak expiratory flow. The may also be less of a drop off in PaO2 due to the V/Q mismatch seen with salbutamol use due to alpha action. In younger children, bronchospasm may be less of an issue than mucosal oedema.
Remember all inhaled therapies are ineffective if they don’t go anywhere. If the child is so tight that they can barely inhale then salbutamol or nebulized adrenaline are likely to be of benefit and so alternative route should be sought. IM adrenaline can be given quickly to the critically ill asthmatic whilst IV access is obtained. At the time of writing a clinical trial into the potential benefit of IM adrenaline as an adjunct to inhaled B2 agonists is recruiting in the US
Myth – If the child is wheezing, they have asthma
Around 17% of infants experience wheeze with the first three years of life. Not all of these end up with a diagnosis of asthma. By the age of 4-5 the incidence of wheeze is around 21.7% which is almost double the incidence of asthma (11.5%) in this population. By the school years, the incidence of wheeze and asthma are near identical.
Wheeze is characterized by “a continuous whistling sound during breathing that suggests narrowing or obstruction in some part of the respiratory airways.” With that definition in mind, there are a number of clinical entities that may cause a wheeze. There is a grey area between those children with obvious asthma and obvious bronchiolitis. Whilst bronchodilators would be appropriate in asthma a large Cochrane review found them to be ineffective in bronchiolitis. Most clinicians would give a one-off trial of salbutamol as long as it did not interfere with other management. There is also no evidence of benefit for the use of systemic corticosteroids in pre-school wheeze. Other potential diagnoses to consider include inhaled foreign bodies, pneumonia or pneumonitis, tracheomalacia or complications of congenital conditions.
So the presence of wheeze does not guarantee that the child has asthma. It is also worthwhile mentioning that the absence of a wheeze does not rule it out either. If there is severe bronchospasm and mucosal oedema not enough air entry will occur to cause a wheeze
Asthma in Australia: with a focus chapter on chronic obstructive pulmonary disease. 2011 Full text
Oxygen saturations are useful in the management of asthma
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Helmerhorst HJ, Schultz MJ, van der Voort PH, de Jonge E, van Westerloo DJ. Bench-to-bedside review: the effects of hyperoxia during critical illness. Critical Care. 2015 Aug 17;19(1):1.
Nebulizers are better than spacers
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Castro-Rodriguez JA, Rodrigo GJ. β-Agonists through metered-dose inhaler with valved holding chamber versus nebulizer for acute exacerbation of wheezing or asthma in children under 5 years of age: a systematic review with meta-analysis. The Journal of pediatrics. 2004 Aug 31;145(2):172-7.
You can never give enough salbutamol
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Adrenaline is dangerous in asthma
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If the child is wheezing they have asthma
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