Pedagogical disambiguation: Emergency Medicine Lecture Notes and Evidence Based emergency medicine principles with regular review and updates.
Evidence based review of acute severe asthma including clinical recognition and management
Clinical recognition of severe or critical asthma
- Severe asthma indicated by any one of (admit every patient with severe):
- PEFR (or FEVI) >33 50% predicted or best, or < 100 L/min (or I L for FEVI).
- Unable to complete sentences in one breath.
- Resps 25 / min.
- Pulse 120 / min (110 / min British Guideline).
British Thoracic Society. Scottish Intercollegiate Guidelines Network. British guideline on the management of asthma. A national clinical guideline. Published May 2008, revised June 2009. (PDF full guideline) or (PDF quick reference guide).
National Heart Lung and Blood Institute. Expert Panel Report 3 (EPR 3). Guideline for the diagnosis and management of asthma. Section 5. Managing exacerbations of asthma. (PDF published Aug 2007).
National Asthma Council Australia. Asthma Management Handbook 2006. (6th edition of handbook 2006).
- Life-threatening or critical asthma has any one of (admit to ICU):
- PEF 33% predicted or best
- Silent chest, feeble breaths, cyanosis.
- Bradycardia, hypotension.
- Exhaustion, confusion, coma.
- Measure ABG if SaO2 92% on oxygen or any of the features above present, and look for PaO2 8 kPa (60 mmHg), low pH, raised PaCO2 6.0 kPa (45 mmHg), and low K+.
- Note concern that long-acting beta-agonists salmeterol and formoterol with or without inhaled corticosteroids have increased risk intubation / death (OR 2.1)
Holley A, Boots R. Review article: Management of acute severe and near-fatal asthma. Emerg Med Australas 2009;21:259-68. [Reference]
Management of Acute Asthma
[Note the American, Canadian, British, Australian and GINA guidelines all subtly differ in drug and dose recommendations].
- Beta agonists
- Continuous oxygen-driven salbutamol nebulisers with 5-10 mg (1-2 ml) in 2 ml saline are appropriate in unresponsive severe, or critical asthma.
- Reduce to 5 mg 1-, 2-, or 3-times hourly nebs if improve. Note that there is a huge variation in respirable dose delivered by the different types of nebuliser.
- Intravenous salbutamol 3-10 mcg/kg then 5-20 mcg/min (dose unknown!) reserved for non-response to above, as side effects including hypokalaemia, arrhythmias and lactic acidosis are greater IV.
- IM or IV adrenaline reserved for precipitate anaphylactic asthma, or moribund asthmatic / respiratory arrest (see later).
- Anticholinergic therapy
- Ipratropium 500 g added to first beta agonist nebuliser and repeated once after first hour, then 4 – 6-hourly. Has additive effects with salbutamol.
- Improves severe asthmatics, those not responding to salbutamol alone, and PEFR / FEV1 in all, though not necessary in mild asthma.
- Wide range of doses used, but little to support “more is better.”
- Give oral prednisone 0.5 – 1.0 mg/kg; or IV hydrocortisone 250 mg 6-hourly (British guideline considers hydrocortisone 100 mg 6-hourly as efficacious) only if vomiting / obtunded, as all IV steroid preparations can cause severe anaphylaxis.
- Parenteral methyl prednisolone shown to improve PEFR within 1-2 hours (likely class effect).
- Magnesium 2g IV infusion over 20 mins once, if fail to improve after 1 hour of therapy. Improves PEFR and reduces admissions in severe cases in children. Adult data more limited. Note potential for NMJ blockade, hypotension and sedation in the non-ventilated patient.
- Nebulised isotonic solution of magnesium sulphate in addition to beta-2 agonist improves pulmonary function in severe asthma in adults. Paeds data limited effect.
Blitz M et al. Inhaled magnesium sulphate in the treatment of acute asthma. Cochrane Database Systemic Review 2005 Oct 19. [Reference]
- Reduces need for intubation in severe asthma (children), but side effects of palpitations, nausea + vomiting and tremor common. Rare use in near fatal asthma in adults. Not recommended.
- CXR only for suspected consolidation, pneumothorax / pneumomediastinum, failure to respond to treatment. Not ‘routine’.
- Antibiotics – only indicated if definite bacterial illness.
- Fluid load – no published ‘evidence’, but necessary particularly prior to intubation when acute drop in preload is likely, or for K+ replacement in hypokalaemia from β2 agonists / steroids / (aminoph).
- Adrenaline – if in extremis, give up to 5 µg/kg slowly IV as 1:10 000 or 1:100 000 dilution. Or give 0.3 – 0.5 mg IM for asthma in anaphylaxis.
- Heliox – (helium/oxygen 80:20 or 70:30). High flow rate to increase respirable gas mass. Data mixed / not compelling + poor availability!
- Must achieve 75% of predicted or best known PEFR for at least 1-2 hours off treatment AND not have any features of a severe attack to be allowed home.
- Oral prednisone for 5-7 days, stopped abruptly.
- Oral prednisone for 10-14 days tapered off, if patient has a background of unstable or undertreated asthma; or has relapsed.
- ‘Asthma Action Plan’
- Action Plan for present attack, and future episodes should be drawn up, ideally in conjunction with LMO + see NAC Australia’s website.
British Thoracic Society. Scottish Intercollegiate Guidelines Network. 6 Management of acute asthma. Thorax 2008;63(Supp IV):iv51-iv60. [PDF Reference]
Aldington S, Beasley R. Asthma exacerbations. 5: Assessment and management of severe asthma in adults in hospital. Thorax 2007;62:447-58. [Reference]
Currie G et al. Recent developments in asthma management. BMJ 2005;330:585-9. [Reference]