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).
- 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.
Stoodley RG, Aaron SD, Dales RE. The role of ipratropium bromide in the emergency management of acute asthma exacerbation: a meta-analysis of randomised clinical trials. Ann Emerg Med 1999; 34:8-18. [Reference]
- 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).
Krishnan J, Davis S, Naureckas E et al. An umbrella review. Corticosteroid therapy for adults with acute asthma. Am J Med 2009;122:977-91. [Reference]
- 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.
Mohammed S, Goodacre S. Intravenous and nebulised magnesium sulphate for acute asthma: systematic review and meta-analysis. Emerg Med J 2007;24:823-30. [Reference]
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.
Parameswaran K, Belda J et al. Addition of intravenous aminophylline to beta-2 agonists in adults with acute asthma (Cochrane Review). The Cochrane Library 2001; Issue 3, Oxford. [Reference]
- 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.
Vanden Hoek T, Morrison L, Shuster M et al. Part 12: Cardiac arrest in special situations: 2010 AHA Guidelines for CPR and ECC. Circulation 2010;120(suppl 3):S829-S861. [Reference]
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]