Asthma – ED Treatments & The Evidence

The commonly used treatments for acute asthma in the Emergency Department as well as the available evidence, are described here:

– inhaled Salbutamol and Ipratropium

Inhaled salbutamol is the the mainstay of management, this is usually delivered using a metered dose inhaler (MDI) and a spacer. If hypoxic, oxygen can be delivered via nasal prongs. If more oxygen is required, nebulisers can be used. In very severe patients dosing can be escalated to continuous.

Inhaled ipratropium when used in addition to inhaled salbutamol, has been found in a recent Cochrane review, to reduce hospital admission and improve lung function in paeds and a previous meta-analysis confirmed benefit in adults as well. This is typically administered as 3 doses.

– Corticosteroids

Systemic steroids provide significant benefit (NNT=8) and should be used early.

Generally prednisolone 1mg/kg (up to 50mg) is given. Where oral can’t be tolerated or if very severe consider IV hydrocortisone or methylprednisolone, though IV dosing has not been shown to be superior to my knowledge.

– add IV Magnesium Sulphate 

The evidence for magnesium sulfate is mixed. A Cochrane review in 2000 found it beneficial in severe asthmatics only. A more recent systematic review and meta-analysis in 2007 confirmed benefit of IV magnesium at least in paeds and possibly adults and this was supported in a later published review article in 2008. While traditionally magnesium was used in the more severe asthmatic that had failed to respond to repeated bronchodilators, the data suggested it probably has a place earlier in management given several studies found a significant benefit in reducing hospital admission.

However the recently published largest RCT to date in adultsthe 3Mg trial, found no benefit of IV or nebulised magnesium over placebo but there was a trend towards benefit of IV magnesium for reducing hospital admission (OR= 0.73, p=0.08). Of note a low dose of Mg was used (8mmol instead of the frequently used 20 mmol) and the trial was stopped about 100 patients early due to funding so a significant benefit might have been found otherwise. In addition life threatening asthma was excluded and the study was not powered to detect differences in severe outcomes such as intubation, mortality etc.

On the upside, magnesium is a very cheap and safe treatment so it is still probably worth using relatively early in the moderate-severe asthmatic. It is typically administered as a single one-off dose.

– IV Aminophylline: in paeds some evidence of benefit in improving lung function but did not decrease symptoms, number of nebulisers or length of hospital stay while increasing vomiting. However special note should be made of Yung 1998, which contributes almost half (163) of the patients in the Cochrane review. In this study of only severe paeds asthmatics, of the 5 intubations that occurred post study enrolment, they all occurred in the placebo group with none occurring in the aminophylline group. For all intubated patients there was a non-signficant reduction in time intubated (8 v 34hrs, p =0.09). Clearly larger trials are required to address these more severe outcomes in the severe asthmatic sub group.

In adults, aminophylline has no place in management as the recent update to the Cochrane review found no evidence of benefit and substantial harms (arrhythmias and vomiting).

– IV Salbutamol: frequently used but the very limited evidence available suggests that in adults it does not provide benefit when added to maximal inhaled bronchodilator therapy.  By contrast only a single tiny 29 patient study showed such a benefit in Paeds.

– IV Adrenaline: almost complete absence of literature to guide practice here but is used in many ED’s in adults.

Heliox: theoretically the lower density than air should reduce turbulent flow and create a relative easing of airway obstruction. The evidence of benefit is not clear with a suggestion of possible benefit only in the most severe asthmatics that requires further study.

Non Invasive Ventilation (NIV): minimal literature but theoretically of benefit with widespread anecdotal reports of benefit. May avoid/delay intubation. Used in asthmatic who is failing to ventilate due to respiratory fatigue and as such bi-level ventilation with IPAP is administered with low EPAP (eg 0-2cm H20). Risk of barotrauma exists but this is likely significantly less than with intubation/ventilation which NIV is being used it to avoid so logic suggests it is worth a try, but still remains controversial.

– Intubation & mechanical ventilation: ventilation of the asthmatic mechanically is technically difficult and highly risky (breath stacking and barotrauma). Truly a last resort in the asthmatic who has fatigued and failed other therapies. A prolonged expiratory time with a low respiratory rate is the key to the ventilator settings.

Sadly a lack of definitive evidence to support or refute several of the frequently used treatments in severe asthmatics. Inhaled bronchodilators and corticosteroids remain the evidence based bedrock of the management of most acute asthmatic patients in ED but given the risks involved with intubation and ventilation of the asthmatic patient, it not surprising that in the truly severe asthmatic, doctors tend to take a “kitchen sink” approach, throwing in whatever they can.

Check out these great emcrit podcasts on:

the severe asthmatic

ventilator settings for patients with obstructive airway disease

the coding asthmatic on the ventilator

 

 

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