Life in the Fast Lane

AFTB lecture notes - Acute asthma

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.
• Respiratory Rate ≥ 25 / min.
• Pulse > 120 / min (≥110 / min British Guideline).

British Thoracic Society. Scottish Intercollegiate Guidelines Network. British guideline on the management of asthma. Thorax 2008;63(Supp IV):iv1-iv121. Published in May 2008. [Reference]

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. (published Aug 2007). [Reference PDF] 

National Asthma Council Australia. Asthma Management Handbook 2006. [Reference]

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)
• Low K+.

Rowe B, Camargo C. Emergency department treatment of severe acute asthma. Ann Emerg Med 2006;47:564-6. [Reference]

MANAGEMENT ACUTE ASTHMA

Beta agonists

• Continuous oxygen-driven salbutamol nebulisers 10 mg (2 ml) in 2ml saline are appropriate in unresponsive severe, or critical asthma.
• Reduce to 5 mg 1-, 2-, or 3-hourly nebs if improve. Note that there is a huge variation in respirable dose delivered by different nebulisers.
• Intravenous salbutamol 250 mg then 5-20 mg/min should be reserved for non-response to above, as side effects including hypokalaemia and lactic acidosis are greater.
• IM or IV adrenaline reserved for precipitate anaphylactic asthma, or moribund asthmatic / respiratory arrest (see later).

Anticholinergic therapy

• Ipratropium 500 mg added to first beta agonist nebuliser and repeated 2 - 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]

Corticosteroids

• Wide range of doses used but little to support “more is better.”
• Give oral prednisolone 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 IV can cause severe anaphylaxis.
• Parenteral methyl prednisolone shown to improve PEFR within 1-2 hours (likely class effect).

Lin RY, Pesola GR, Bakalchuk L et al.  Rapid improvement of peak flow in asthmatic patients treated with parenteral methyl prednisolone in the ED: a randomised controlled study.  Ann Emerg Med 1999; 33:487-94. [Reference] (Editorial Gallagher EJ: 561-4). [Reference]

Aminophylline

• 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.

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]

Miscellaneous

• Magnesium 1.2 - 2g IV infusion over 20 mins once. Improves PEFR and reduces admissions in severe cases. Potential danger of neuromuscular 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.

Silverman RA et al. IV magnesium sulfate in the treatment of acute severe asthma: a multicenter randomized controlled trial. Chest 2002;122;489-97. [Reference]

Blitz M et al. Inhaled magnesium sulfate in the treatment of acute asthma. Cochrane Database Systemic Review 2005 Oct 19. [Reference]

• Fluid load - no published ‘evidence’ at all, but necessary particularly prior to intubation when acute drop in preload is likely, or for K+ replacement in hypokalaemia from β2 agonists / steroids / (aminoph).
• CXR only for suspected consolidation, pneumothorax / pneumomediastinum, failure to respond to treatment.
• Antibiotics - only indicated if definite bacterial illness.
• Adrenaline - for asthma in anaphylaxis,  give 0.3 - 0.5 mg IM, or if in extremis up to 5 µg/kg slowly IV as 1:100 000 or 1:10 000 dilution.
• Heliox - (helium/oxygen 80:20 or 70:30) is not currently recommended in British guideline. Data mixed and not compelling + availability!

DISCHARGE

• Must achieve 75% of predicted or best known PEFR for at least 4-6 hours off treatment AND have never had any features of a severe attack to go home.
• Steroids:
  • 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.
• 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. [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]

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