Asthma in Adults BTS SIGN Exam Breakdown

Algorithm at a glance

Adult asthma is a core Emergency Department presentation and a high-yield UK exam topic. It tests rapid assessment, severity recognition, safe escalation, and guideline-based treatment under pressure. In MRCEM and FRCEM, the key principle is simple: classify severity first, then treat according to the worst feature present. One life-threatening feature is enough to change both urgency and management.

Why the Asthma BTS SIGN Guideline Matters for FRCEM and MRCEM

Acute asthma is common, dynamic, and potentially fatal. Most candidates know the drug list. Marks are usually lost because they fail to:

• recognise life-threatening features early
• state the oxygen target clearly
• choose the correct bronchodilator delivery method
• give steroids promptly
• escalate appropriately when first-line treatment fails
• make a safe admission or discharge decision

Examiners repeatedly test the distinction between acute severe and life-threatening asthma. This is not semantics. It reflects whether the patient is still compensating or is starting to fail.

For UK exams and practice, anchor answers to BTS/SIGN acute asthma guidance, standard RCEM Emergency Department practice, and Resuscitation Council UK principles where overlap exists, especially if anaphylaxis is a possible alternative diagnosis.

Key Definitions

Classify the attack according to the most dangerous single feature. Do not average the observations.

Exam rule: one life-threatening feature makes the attack life-threatening, even if other observations look less dramatic.

Essential Pathophysiology

Acute asthma causes lower airway narrowing due to bronchospasm, mucosal oedema, and mucus plugging. This increases airway resistance, especially during expiration, leading to:

• air trapping and hyperinflation
• increased work of breathing
• ventilation-perfusion mismatch
• hypoxaemia
• eventual respiratory muscle fatigue

Early in an attack, patients usually hyperventilate and have a low PaCO₂. A normal PaCO₂ in a breathless asthmatic is therefore abnormal and concerning. A raised PaCO₂ suggests failing ventilation and severe decompensation.

A loud wheeze means air is still moving. A silent chest is worse, because airflow has become critically reduced.

Clinical Presentation

Typical features include:

• shortness of breath
• wheeze
• cough
• chest tightness
• reduced exercise tolerance
• nocturnal or early morning worsening

Features suggesting a more severe attack include:

• inability to speak normally
• marked tachypnoea
• tachycardia
• accessory muscle use
• agitation or distress
• reduced peak flow
• hypoxia

Features suggesting decompensation include:

• exhaustion
• poor respiratory effort
• silent chest
• confusion
• drowsiness
• cyanosis
• hypotension
• bradycardia

Red Flags and High-Risk Features

These matter both in the current attack and when deciding disposition.

Red flags in the current presentation

• SpO₂ less than 92%
• silent chest
• normal or raised PaCO₂
• exhaustion or poor respiratory effort
• confusion or reduced conscious level
• hypotension, bradycardia, or arrhythmia
• PEF less than 33% predicted or best

Risk factors for fatal or near-fatal asthma

• previous ICU admission or previous ventilation for asthma
• hospital admission for asthma in the last year
• recent Emergency Department attendance
• excess short-acting beta agonist use
• poor inhaled corticosteroid adherence or no preventer therapy
• recent or repeated oral steroid courses
• psychosocial problems, including poor engagement
• food allergy or anaphylaxis history

Previous ICU admission or ventilation is especially high yield in exams and should always influence your risk assessment.

Differential Diagnosis

Not all wheeze is asthma. Consider alternatives, especially if the presentation is atypical, there is focal chest pathology, or the patient is not responding as expected.

Initial ED Assessment

Use an ABCDE approach. In severe asthma, treatment starts during assessment, not after it.

Immediate priorities

• sit the patient upright
• call for senior help early if severe or life-threatening features are present
• apply continuous monitoring: SpO₂, HR, RR, BP, mental state
• give oxygen as needed to maintain saturations 94 to 98%
• assess speech, work of breathing, air entry, wheeze, and fatigue
• measure PEF if safe and feasible, but do not delay treatment

Focused history once treatment has started

• onset and trigger
• previous ICU admission or ventilation
• recent admission or ED attendance
• current inhalers and adherence
• recent oral steroid use
• excess reliever use
• possible trigger: viral illness, allergen, smoke, occupational exposure, NSAID, beta-blocker
• features suggesting anaphylaxis
• pregnancy if relevant to imaging or prescribing

Examination pearls

• reduced wheeze is not always improvement
• accessory muscle use suggests significant work of breathing
• agitation may reflect hypoxia
• confusion or drowsiness suggests impending respiratory failure
• pulsus paradoxus is not a useful frontline exam discriminator in the ED

Investigations

Investigations should answer two questions:

• how severe is the attack?
• is there a complication or alternative diagnosis?

They must not delay treatment.

Peak expiratory flow

• use the best of three attempts if the patient can do it safely
• compare with predicted or personal best
• repeat after treatment to assess response
• do not force repeated attempts in an exhausted or life-threatening patient

PEF is useful, but in a crashing patient treatment comes first.

Arterial blood gas

ABG is indicated in:

• SpO₂ less than 92%
• life-threatening features
• deterioration or poor response to treatment
• suspected ventilatory failure
• possible ICU escalation

Interpretation points:

• low PaCO₂ is common early
• normal PaCO₂ in a breathless asthmatic is ominous
• raised PaCO₂ indicates life-threatening asthma
• PaO₂ less than 8 kPa is a life-threatening feature

Use ABG when oxygenation or true CO₂ assessment matters. VBG does not replace ABG for this purpose.

Chest x-ray

Chest x-ray is not routine in uncomplicated asthma.

Consider it if there is:

• suspected pneumothorax or pneumomediastinum
• suspected pneumonia
• focal chest signs
• poor response to treatment
• atypical presentation
• need for ventilation
• concern about an alternative diagnosis

ECG

Consider ECG in severe asthma, marked tachycardia, chest pain, suspected arrhythmia, or concern about hypokalaemia.

Blood tests

Blood tests are not routinely diagnostic for asthma itself. They may help with complications, differential diagnosis, or admission workup.

• U&E, especially potassium after repeated beta agonists
• FBC and CRP if infection is suspected
• blood gas as above
• lactate if clinically relevant

Repeated beta agonists can cause hyperlactataemia. This may contribute to tachypnoea and can be mistaken for worsening bronchospasm. Interpret lactate alongside air entry, wheeze, work of breathing, and gas results.

Management in the Emergency Department

Management is driven by severity and response to treatment.

Immediate treatment priorities

1. ABCDE assessment and senior help if severe or life-threatening
2. Oxygen to maintain saturations 94 to 98%
3. Inhaled bronchodilator therapy promptly
4. Steroids early
5. Reassess repeatedly
6. Escalate early if poor response or life-threatening features

Oxygen

Give oxygen as needed to maintain SpO₂ 94 to 98% in most adults with acute asthma.

In severe or life-threatening asthma, nebulisers should usually be oxygen-driven if oxygen is required. Do not leave a hypoxic patient on air-driven nebulisers.

Bronchodilators

Salbutamol

First-line bronchodilator treatment is inhaled salbutamol.

• Moderate asthma: pressurised metered-dose inhaler with spacer is often appropriate
• Acute severe or life-threatening asthma: nebulised salbutamol is usually required

Typical adult nebulised dose: 5 mg, repeated according to response and severity.

In moderate attacks, repeated salbutamol via spacer can be effective and avoids unnecessary nebulisation.

Ipratropium bromide

Add nebulised ipratropium bromide in acute severe or life-threatening asthma, particularly if the response to initial beta agonist therapy is incomplete.

Typical adult nebulised dose: 500 micrograms.

Steroids

Give steroids early. Do not wait to see whether bronchodilators alone work.

• Prednisolone by mouth is preferred if the patient can swallow safely
• IV hydrocortisone is appropriate if oral treatment is not possible

Typical adult doses used in UK practice:

• Prednisolone 40 to 50 mg orally
• Hydrocortisone 100 mg IV

Oral steroids are not inferior simply because the attack is severe. The route depends on whether the patient can take tablets safely and reliably.

Magnesium sulfate

Consider IV magnesium sulfate early in acute severe or life-threatening asthma, especially if there is poor response to initial inhaled bronchodilators and steroids.

Typical adult dose: 1.2 to 2 g IV over around 20 minutes.

This is a common exam escalation step.

Reassessment after initial treatment

Reassess after each treatment cycle. Document:

• respiratory rate
• heart rate
• oxygen saturation
• speech
• work of breathing
• air entry and wheeze
• mental state
• PEF if feasible

Improvement in wheeze alone is not enough. The whole clinical picture must improve.

When the patient is not improving

Poor response should trigger senior review and escalation. Think about:

• wrong diagnosis or complication
• poor drug delivery
• fatigue and impending ventilatory failure
• need for repeat ABG
• critical care involvement

IV bronchodilators and specialist therapies

IV bronchodilators such as IV salbutamol or aminophylline are not routine first-line treatment in the ED. They are specialist decisions, usually after senior or critical care discussion, in refractory cases.

For exams, the safe answer is:

• optimise inhaled therapy, oxygen, steroids, and magnesium first
• seek senior and ICU input early if the patient is failing
• do not casually escalate to IV bronchodilators without acknowledging specialist involvement

Antibiotics

Do not give antibiotics routinely in acute asthma. Use them only if there is evidence of bacterial infection.

Fluids and supportive care

• maintain hydration if needed
• avoid unnecessary sedation
• treat fever or pain if relevant
• consider thromboprophylaxis if admitted and appropriate

Critical care escalation

Discuss early with ICU or anaesthetics if there is:

• life-threatening or near-fatal asthma
• rising or normalising PaCO₂ in a distressed patient
• exhaustion or poor respiratory effort
• confusion, drowsiness, or reduced conscious level
• persistent hypoxia despite treatment
• silent chest
• haemodynamic instability
• deterioration despite maximal initial therapy

Ventilation and intubation

Intubation in severe asthma is high risk and should be performed by experienced clinicians with critical care support. It is not a routine next step and should not be undertaken lightly.

Exam-safe principles:

• call ICU or anaesthetics early
• recognise that intubation may precipitate deterioration
• avoid delaying escalation in a failing patient
• non-invasive ventilation is not routine in acute asthma and should not delay definitive care

Disposition, Referral and Follow-Up

Disposition depends on severity, response to treatment, and future risk.

Who should be admitted

• all patients with life-threatening or near-fatal asthma
• patients with persistent acute severe features after initial treatment
• patients with poor or unsustained response
• patients with significant risk factors for fatal asthma
• patients with social or practical barriers to safe discharge

Who needs HDU or ICU level discussion

• near-fatal asthma
• hypercapnia
• exhaustion
• altered mental state
• persistent hypoxia
• haemodynamic instability
• need for ventilatory support

When discharge may be appropriate

Discharge is only appropriate if improvement is clear and sustained, the patient is clinically stable, and there are no major safety concerns.

Typical features supporting discharge include:

• symptoms improved significantly
• no features of acute severe or life-threatening asthma
• PEF improved satisfactorily, often towards more than 75% of best or predicted
• oxygen saturation stable in the normal target range on air
• response sustained after treatment and observation
• patient can use inhalers correctly
• follow-up and safety-netting arranged

No single number determines discharge. The decision is clinical.

Discharge bundle

• complete a course of oral steroids if indicated
• review and optimise inhaled corticosteroid therapy
• check inhaler technique
• provide clear written and verbal safety-net advice
• arrange follow-up, usually within 48 hours in primary care or asthma services depending on local pathway
• advise urgent return if symptoms worsen, reliever need increases, or peak flow falls

Excess reliever use and poor preventer adherence are major relapse risks and should be addressed before discharge.

Special Groups

Paediatrics

This article is focused on adults. Do not import adult severity thresholds or drug pathways into paediatric answers. Children use different severity markers, dosing, and escalation pathways.

Pregnancy

Treat acute asthma in pregnancy promptly and effectively. Maternal hypoxia is dangerous for both mother and fetus. Standard acute asthma treatment is generally used, including oxygen, inhaled bronchodilators, and steroids when indicated. Do not undertreat because of pregnancy.

Older adults

Consider alternative or additional diagnoses such as COPD, heart failure, pneumonia, or pulmonary embolism. Polypharmacy, beta-blocker use, and arrhythmia risk may complicate management.

Immunosuppressed patients

Be more alert to infection, atypical presentations, and complications. A wheezy immunosuppressed patient may not simply have asthma.

Common Pitfalls

• failing to classify severity before treatment decisions
• missing that SpO₂ less than 92% is a life-threatening feature
• being reassured by a quiet chest
• thinking a normal PaCO₂ is normal in a distressed asthmatic
• delaying treatment while waiting for peak flow, ABG, or chest x-ray
• forgetting early steroids
• forgetting ipratropium in severe or life-threatening asthma
• forgetting magnesium when the response is poor
• giving antibiotics routinely without evidence of bacterial infection
• missing anaphylaxis in a wheezy hypotensive patient
• discharging a patient based on one improved peak flow without considering the whole picture

FRCEM and MRCEM Exam Tips

• Open with ABCDE, oxygen target 94 to 98%, and severity classification.
• Say explicitly that one life-threatening feature is enough.
• State that treatment should not wait for investigations.
• In severe or life-threatening asthma, mention senior review and early ICU awareness.
• If asked about blood gases, say that a normal PaCO₂ is concerning and a raised PaCO₂ is life-threatening.
• If asked about wheeze, say that a silent chest is worse than a loud wheeze.
• If the stem suggests allergen exposure, urticaria, airway swelling, or hypotension, think anaphylaxis rather than isolated asthma.
• For discharge questions, mention inhaler technique, preventer therapy, steroid course, follow-up, and safety-netting.

OSCE or viva opening structure

A safe opening answer is:

I would assess and treat simultaneously using ABCDE, sit the patient upright, apply monitoring, give oxygen to maintain saturations 94 to 98%, assess severity using BTS/SIGN criteria, start inhaled salbutamol promptly, add ipratropium if severe, give steroids early, check peak flow if safe, perform ABG if there are life-threatening features or saturations below 92%, and escalate early to senior and critical care support if there is poor response, exhaustion, silent chest, or hypercapnia.

How This Appears in SBA Questions

Typical question stems

• breathless adult with wheeze, RR 30, HR 120, unable to complete sentences
• asthmatic with SpO₂ 90% and a normal PaCO₂
• patient whose wheeze has become quieter and who now looks tired
• poor response after repeated nebulisers
• discharge planning after apparent improvement
• wheeze after nut exposure with hypotension and rash

Key discriminator clues

• SpO₂ less than 92% means life-threatening
• normal PaCO₂ in a breathless asthmatic is bad
• silent chest means critically reduced airflow
• previous ICU admission increases risk
• poor response after initial therapy should prompt magnesium and escalation
• anaphylaxis features change the treatment pathway

Common wrong answer traps

• routine antibiotics
• routine chest x-ray in uncomplicated asthma
• waiting for ABG before giving bronchodilators or steroids
• reassurance because wheeze is less obvious
• using only salbutamol without ipratropium in severe attacks
• discharging without addressing inhaled corticosteroid therapy or follow-up

Key Takeaways

• Classify severity first using the worst single feature present.
• Acute severe asthma is defined by any one of: PEF 33 to 50%, RR 25 or more, HR 110 or more, inability to complete sentences in one breath.
• Life-threatening asthma is defined by any one of: PEF less than 33%, SpO₂ less than 92%, PaO₂ less than 8 kPa, normal or raised PaCO₂, silent chest, cyanosis, exhaustion, poor respiratory effort, hypotension, bradycardia, arrhythmia, confusion, reduced conscious level.
• Give oxygen to maintain saturations 94 to 98%.
• Start inhaled salbutamol promptly; add ipratropium in acute severe or life-threatening asthma.
• Give steroids early: oral prednisolone if possible, IV hydrocortisone if not.
• Consider IV magnesium sulfate early if severe or poorly responsive.
• ABG is required in life-threatening asthma, SpO₂ less than 92%, deterioration, or suspected ventilatory failure.
• A normal PaCO₂ in a breathless asthmatic is concerning; a raised PaCO₂ is life-threatening.
• Do not give antibiotics routinely.
• Do not delay treatment for peak flow, ABG, or chest x-ray.
• Discharge requires sustained improvement, safe inhaler use, appropriate medication, follow-up, and safety-netting.

Further Reading

• BTS/SIGN British guideline on the management of asthma
• NICE asthma guidance for diagnosis, monitoring and chronic management
• RCEM learning resources on acute asthma and acute respiratory presentations
• Resuscitation Council UK guidance on anaphylaxis
• British Thoracic Society guidance on oxygen use in adults in healthcare and emergency settings

Related on EM Final Exams

• Top 10 RCEM Guidelines You Must Know for FRCEM
• Top 15 Paediatric Emergencies for MRCEM
• Most Examined NICE Guidelines for Emergency Medicine
• Diabetic Ketoacidosis Guidelines Explained

Authoritative Sources

• British Thoracic Society (BTS)
• SIGN (Scottish Intercollegiate Guidelines Network)

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