Treatment of acute asthma in adults

Many patients with acute severe asthma are hypoxaemic.^581-584 Supplementary oxygen should be given urgently to hypoxaemic patients, using a face mask, Venturi mask or nasal cannulae with flow rates adjusted as necessary to maintain SpO2 of 94–98%,⁵⁷⁸ taking care to avoid overoxygenation which may be detrimental.⁵⁸⁵

Emergency oxygen should be available in hospitals, ambulances and primary care.

Hypercapnia indicates the development of near-fatal asthma and the need for emergency specialist/anaesthetic intervention. In this situation care should be taken to avoid hypoxia as well as overoxygenation.

If intravenous β₂ agonists are used, consider monitoring serum lactate to monitor for toxicity.

In patients with acute asthma with acute-severe or life-threatening features the nebulised route (oxygen-driven) is recommended.

In patients with acute asthma with acute-severe or life-threatening features the nebulised route (oxygen-driven) is recommended.

In most cases inhaled β₂ agonists given in high doses act quickly to relieve bronchospasm with few side effects.^586-588

Oxygen-driven nebulisers are preferred for nebulising β₂ agonist bronchodilators because of the risk of oxygen desaturation while using air-driven compressors.⁵³¹, ⁵⁶⁶, ⁵⁹²

A flow rate of 6 L/min is required to drive most nebulisers. Where oxygen cylinders are used, a high-flow regulator must be fitted.⁵⁷⁸

The absence of supplemental oxygen should not prevent nebulised therapy from being administered when appropriate.⁵⁹³

Repeat doses of β₂ agonists at 15–30 minute intervals or give continuous nebulisation of salbutamol at 5–10 mg/hour (requires the appropriate nebuliser) if there is an inadequate response to initial treatment. Higher bolus doses, for example 10 mg of salbutamol, are unlikely to be more effective.

Continue prednisolone (40–50 mg daily) until recovery (minimum 5 days).

[BTS/SIGN 2019]

Do not stop inhaled corticosteroids during prescription of oral corticosteroids.

[BTS/SIGN 2019]

Steroids reduce mortality, relapses, subsequent hospital admission and requirement for β₂ agonist therapy. The earlier they are given in the acute attack the better the outcome.⁵⁹⁸, ⁵⁹⁹

Steroid tablets are as effective as injected steroids, provided they can be swallowed and retained.⁵⁹⁸ Prednisolone 40–50 mg daily or parenteral hydrocortisone 400 mg daily (100 mg six hourly) are as effective as higher doses.⁶⁰⁰ Where necessary soluble prednisolone (sodium phosphate) 5 mg tablets are available. In cases where oral treatment may be a problem consider intramuscular methylprednisolone (160 mg) as an alternative to a course of oral prednisolone.⁶⁰¹

Following recovery from the acute asthma attack steroids can be stopped abruptly. Doses do not need tapering provided the patient receives ICS (apart from patients on maintenance steroid treatment or rare instances where steroids are required for three or more weeks).⁶⁰², ⁶⁰³

Combining nebulised ipratropium bromide with a nebulised β₂ agonist produces significantly greater bronchodilation than β₂ agonist alone, leading to faster recovery and shorter duration of admission. Anticholinergic treatment is not necessary and may not be beneficial in milder asthma attacks or after stabilisation.^606-608

Magnesium sulphate (1.2–2 g IV infusion over 20 minutes) should only be used following consultation with senior medical staff.

[BTS/SIGN 2019]

The safety and efficacy of repeated intravenous (IV) doses of magnesium sulphate have not been assessed. Repeated doses could cause hypermagnesaemia with muscle weakness and respiratory fatigue.

Use IV aminophylline only after consultation with senior medical staff.

[BTS/SIGN 2019]

In an acute asthma attack, IV aminophylline is not likely to result in any additional bronchodilation compared with standard care with inhaled bronchodilators and steroids. Side effects such as arrhythmias and vomiting are increased if IV aminophylline is used. ⁶¹⁴

Some patients with near-fatal asthma or life-threatening asthma with a poor response to initial therapy may gain additional benefit from IV aminophylline (5 mg/kg loading dose over 20 minutes unless on maintenance oral therapy, then infusion of 0.5–0.7 mg/kg/hr). Such patients are probably rare and were not identified in a meta-analysis of trials.⁶¹⁴ If IV aminophylline is given to patients already taking oral aminophylline or theophylline, blood levels should be checked on admission. Levels should be checked daily for all patients on aminophylline infusions.

Current evidence on oral leukotriene receptor antagonists does not support their use in patients with acute asthma.⁶¹⁵ Further studies are required to assess whether IV treatment is effective and safe.

When an infection precipitates an asthma attack it is likely to be viral. The role of bacterial infection has been overestimated.⁶¹⁶ Decision making regarding the use of antibiotics in patients with acute asthma should be guided by objective measures including procalcitonin where available.⁶¹⁷, ⁶¹⁸

The use of heliox, (helium/oxygen mixture in a ratio of 80:20 or 70:30), either as a driving gas for nebulisers, as a breathing gas, or for artificial ventilation in adults with acute asthma is not supported.⁶¹⁹, ⁶²⁰

There are no controlled trials, observational or cohort studies of differing fluid regimes in patients with acute asthma. Some patients require rehydration and correction of electrolyte imbalance. Hypokalaemia can be caused or exacerbated by β₂ agonist and/or steroid treatment and must be corrected.

Although theoretically furosemide may produce bronchodilation, a review of three small trials failed to show any significant benefit of treatment with nebulised furosemide compared to β₂ agonists.⁶²³

In adults with acute asthma and a poor response to standard therapy (inhaled bronchodilators, steroids, oxygen and intravenous bronchodilators) other therapies may be considered in the appropriate critical care setting with the appropriate available expertise. There is little high-quality evidence to guide treatment at this stage of an acute asthma attack and it is important to involve a clinician with the appropriate skills in airway management and critical care support as early as possible.

Indications for admission to intensive care or high-dependency units include
patients requiring ventilatory support and those with acute severe or lifethreatening asthma who are failing to respond to therapy, as evidenced by:

• deteriorating PEF
• persisting or worsening hypoxia
• hypercapnia
• arterial blood gas analysis showing fall in pH or rising hydrogen concentration
• exhaustion, feeble respiration
• drowsiness, confusion, altered conscious state
• respiratory arrest.

Extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is thought to help to provide adequate gas exchange whilst helping to prevent the barotraumas caused by aggressive mechanical ventilation. Currently, there are five centres in the UK with ECMO facilities for adults (Glenfield Hospital, Leicester; Papworth Hospital, Cambridge; Wythenshawe Hospital, Manchester; Guy’s & St Thomas’ Hospital, London; Royal Brompton & Harefield Hospital, London).

Recombinant human deoxyribonuclease

Adults with asthma not responding to standard treatment should be evaluated by a specialist with the appropriate experience and skills to use and assess medication encountered in critical care settings.

[BTS/SIGN 2019]

In patients with acute severe or life-threatening asthma, anaesthetists and intensivists should be notified as soon as possible if there is no improvement in or deterioration of asthma.

[BTS/SIGN 2019]

Not all patients admitted to the intensive care unit (ICU) need ventilation, but those with worsening hypoxia or hypercapnia, drowsiness or unconsciousness and those who have had a respiratory arrest require intermittent positive pressure ventilation. Intubation in such patients is very difficult and should be performed by an anaesthetist or ICU consultant.⁵⁶⁶, ⁵⁶⁷

NIV should only be considered in an ICU or equivalent clinical setting.

[BTS/SIGN 2019]

Non-invasive ventilation (NIV) is well established in the management of ventilatory failure caused by extrapulmonary restrictive conditions and exacerbations of COPD. Hypercapnic respiratory failure developing during an acute asthmatic attack is an indication for urgent ICU admission. It is unlikely that NIV would replace intubation in these very unstable patients but it has been suggested that this treatment can be used safely and effectively.⁶²⁷

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