Acute Asthma

An acute exacerbation of asthma is characterised by a rapid deterioration in symptoms. This could be triggered by any of the typical asthma triggers such as infection, exercise or cold weather.



  • Progressively worsening shortness of breath
  • Use of accessory muscles
  • Fast respiratory rate (tachypnoea)
  • Symmetrical expiratory wheeze on auscultation
  • The chest can sound “tight” on auscultation with reduced air entry


Grading Acute Asthma


  • PEFR 50 – 75% predicted


  • PEFR 33-50% predicted
  • Resp rate >25
  • Heart rate >110
  • Unable to complete sentences


  • PEFR <33%
  • Sats <92%
  • Becoming tired
  • No wheeze. This occurs when the airways are so tight that there is no air entry at all. This is ominously described as a “silent chest”.
  • Haemodynamic instability (i.e. shock)



As a junior doctor you should not underestimate the danger of acute asthma. Patients can deteriorate quickly and it can be life threatening. Generally don’t hesitate to keep adding treatment and escalate early to seniors and HDU / ICU if not improving or there are signs of severe asthma.

If asthma is severe treatment decisions such as aminophylline, IV salbutamol and IV magnesium are normally under senior guidance.


  • Nebulised beta-2 agonists (i.e. salbutamol 5mg repeated as often as required)
  • Nebulised ipratropium bromide
  • Steroids. Oral prednisolone or IV hydrocortisone. These are continued for 5 days
  • Antibiotics if there is convincing evidence of bacterial infection


  • Oxygen if required to maintain sats 94-98%
  • Aminophylline infusion
  • Consider IV salbutamol

Life threatening:

  • IV magnesium sulphate infusion
  • Admission to HDU / ICU
  • Intubation in worst cases – however this decision should be made early because it is very difficult to intubate with severe bronchoconstriction

ABGs in asthma:

Initially patients will have a respiratory alkalosis as tachypnoea causes a drop in CO2. A normal pCO2 or hypoxia is a concerning sign as it means they are tiring and indicates life threatening asthma. A respiratory acidosis due to high CO2 is a very bad sign in asthma.


To monitor the response to treatment you can use:

  • Respiratory rate
  • Respiratory effort
  • Peak flow
  • Oxygen saturations
  • Chest auscultation


Additional Notes on Treatment

Monitor serum potassium when on salbutamol as it causes potassium to be absorbed from the blood into the cells. Salbutamol also causes tachycardia (fast heart rate).

Optimise asthma control after an acute attack. Discharge patients with an “asthma action plan” that provides them with a clear plan for everything they need to know about their asthma in one place. Consider prescribing a “rescue pack” or steroids for the person to initiate in the future if they have another exacerbation of asthma. NICE suggest referral to a respiratory specialist after 2 attacks in 12 months.


Last updated February 2019
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