In an acute asthma exacerbation, which red‑flag signs (e.g., inability to speak full sentences, severe tachypnea, hypoxemia, peak expiratory flow ≤50% predicted, hypercapnia, prior intubation or ICU admission) require immediate emergency department referral, and what outpatient management and specialist referral criteria should be applied otherwise?

Acute Asthma Exacerbation: Emergency Referral Criteria and Management

Immediate Emergency Department Referral – Red Flags

Any patient presenting with life-threatening features requires immediate emergency department transfer without delay. 1

Life-Threatening Features Requiring Immediate ED Referral:

• Peak expiratory flow (PEF) <33% of predicted or personal best 1, 2
• Silent chest, cyanosis, or feeble respiratory effort 1, 3
• Altered mental status (confusion, drowsiness, exhaustion, or coma) 1, 3
• Bradycardia or hypotension 1, 3
• Normal or elevated PaCO₂ ≥42 mmHg in a breathless patient (indicates impending respiratory failure) 1, 2, 3
• Severe hypoxia: PaO₂ <8 kPa (60 mmHg) despite oxygen therapy 1, 2
• Prior intubation or ICU admission for asthma (high-risk patient requiring lower threshold for admission) 3

Severe Exacerbation Features Requiring ED Referral:

Immediate hospital referral is required when any of the following persist after initial outpatient treatment: 1

• Inability to speak full sentences in one breath 1, 2
• Respiratory rate >25 breaths/min 1, 2
• Heart rate >110 beats/min 1, 2
• PEF <50% of predicted or personal best 1, 2
• PEF 15-30 minutes after initial nebulization remains <33% of predicted 1

Lower Threshold for Admission Applies When:

• Presentation in afternoon or evening (rather than morning) 1, 3
• Recent nocturnal symptoms or worsening symptoms 1
• Previous severe attacks, especially with rapid onset 1
• ≥2 hospitalizations or ≥3 ED visits in past year 3
• Recent hospitalization or ED visit within past month 3
• Concern over patient's ability to assess severity 1
• Poor social circumstances or inadequate support 1, 3

---

Outpatient Management (When Safe to Treat at Home)

Patients may be managed at home only if they can complete sentences, have respiratory rate <25/min, heart rate <110/min, and PEF >50% predicted after initial treatment. 1

Immediate Outpatient Treatment Protocol:

1. High-dose inhaled β₂-agonist: Salbutamol 5 mg or terbutaline 10 mg via oxygen-driven nebulizer, OR 4-8 puffs via MDI with spacer every 20 minutes for 3 doses 1, 3

2. Systemic corticosteroids immediately: Prednisolone 30-60 mg orally (do NOT delay while "trying bronchodilators first") 1, 3

3. Reassess PEF 15-30 minutes after first bronchodilator dose 1, 2

Response-Based Management:

Good Response (PEF >75% predicted):

• Continue usual maintenance therapy 1, 3
• Monitor symptoms and PEF on chart 1
• Follow-up within 48 hours 1, 3

Incomplete Response (PEF 50-75% predicted):

• Give prednisolone 30-60 mg 1
• Step up usual treatment 1
• Surgery review <48 hours 1

Poor Response (PEF <50% predicted or persistent severe features):

• Arrange immediate hospital admission 1, 3
• Repeat nebulized β-agonist 1
• Add ipratropium 0.5 mg to nebulizer 1

Critical Pitfall to Avoid:

Never underestimate severity based on subjective assessment alone—objective PEF measurement is mandatory, as failure to measure objectively is the most common preventable cause of asthma deaths. 1, 3

---

Specialist Referral Criteria (After Stabilization)

Mandatory Follow-Up Schedule:

• Primary care follow-up within 1 week of any acute exacerbation 1, 3
• Respiratory specialist clinic within 4 weeks 1, 3

Indications for Respiratory Specialist Referral:

• Any patient requiring hospital admission 1
• Moderate exacerbations requiring systemic corticosteroids (consider referral) 1
• Recurrent exacerbations (≥2 hospitalizations or ≥3 ED visits in past year) 3
• Previous life-threatening attack or ICU admission 1, 3
• Poor symptom control despite treatment escalation 3

Discharge Requirements Before Leaving ED/Clinic:

• PEF ≥70% of predicted or personal best 3
• Stable for 30-60 minutes after last bronchodilator dose 3
• Verify correct inhaler technique 1, 3
• Provide written self-management plan with PEF zones 1, 3
• Supply peak flow meter if patient doesn't have one 3
• Prescribe oral prednisolone 40-60 mg daily for 5-10 days (no taper needed) 3
• Initiate or continue inhaled corticosteroids 3

---

Absolute Contraindications in Acute Asthma

Never administer sedatives of any kind—this is absolutely contraindicated and potentially fatal. 1, 3