In a patient with asthma (child or adult), how should peak‑flow readings be interpreted and what actions correspond to the green (≥80% of personal best), yellow (50‑79%), and red (<50%) zones?

Peak Flow Zone Interpretation and Action Plan for Asthma Management

Understanding the Zone System

Peak flow zones should be based on personal best values (not predicted values), with the green zone representing ≥80% of personal best, yellow zone 50-79%, and red zone <50%, and each zone requires specific escalation of treatment to prevent severe exacerbations. 1

Personal best peak flow is determined as the highest reading achieved over a 2-week period during good asthma control, and reaches plateau levels after only 3 weeks of inhaled corticosteroid treatment with twice-daily monitoring. 2 However, be aware that 45% of inner-city patients report inaccurate personal best values, so verification through actual measurement is essential. 3

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Green Zone (≥80% of Personal Best): Safe Zone

Patients in the green zone should continue their regular maintenance medications without changes and require no additional intervention. 1

Actions for Green Zone:

• Continue current controller medications (typically inhaled corticosteroids) at prescribed doses 1
• Use short-acting beta-agonists (SABA) only as needed for symptom relief 1
• Maintain regular monitoring with twice-daily peak flow measurements 2
• No medication adjustments are necessary 1

Key Point:

The green zone indicates good asthma control with minimal symptoms and normal activity levels. 1

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Yellow Zone (50-79% of Personal Best): Caution Zone

Patients entering the yellow zone require immediate escalation of treatment with systemic corticosteroids and increased bronchodilator use to prevent progression to severe exacerbation. 4, 1

Immediate Actions for Yellow Zone:

• Increase SABA use: Administer albuterol 2-4 puffs via MDI with spacer every 4 hours as needed, or 2.5-5 mg via nebulizer 5
• Start oral corticosteroids: Adults should take prednisolone 30-60 mg daily; children should receive 1-2 mg/kg/day (maximum 40-60 mg) 5, 6
• Continue for 5-10 days without tapering if the course is less than 10 days 5
• Contact healthcare provider within 24-48 hours for reassessment 1

Monitoring in Yellow Zone:

• Measure peak flow before and after each bronchodilator treatment 4
• If readings improve to green zone and symptoms resolve, continue oral steroids for full course 5
• If readings decline toward red zone or symptoms worsen despite treatment, proceed to red zone actions immediately 1

Common Pitfall:

Do not delay starting oral corticosteroids while "trying bronchodilators first"—steroids must be given immediately as clinical benefits require 6-12 hours minimum to manifest. 5

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Red Zone (<50% of Personal Best): Medical Alert

Patients in the red zone require immediate emergency treatment and should proceed directly to the emergency department or call emergency services, as this represents severe or life-threatening asthma. 4, 1

Immediate Emergency Actions:

• Administer high-dose bronchodilators immediately:

  • Albuterol 5 mg via oxygen-driven nebulizer OR 4-8 puffs via MDI with spacer every 20 minutes for 3 doses 5, 6
  • For children <15 kg: use half doses (2.5 mg) 5

• Give systemic corticosteroids without delay:

  • Adults: Prednisolone 40-60 mg orally OR IV hydrocortisone 200 mg 5, 6
  • Children: Prednisolone 1-2 mg/kg (maximum 40-60 mg) 5, 6

• Add ipratropium bromide for severe cases:

  • 0.5 mg via nebulizer every 20 minutes for 3 doses, then every 4-6 hours 5, 6

• Administer oxygen to maintain SaO₂ >90% (>95% in pregnant patients or those with heart disease) 5, 6

• Proceed immediately to emergency department 4, 1

Life-Threatening Features Requiring ICU Consideration:

• Peak flow <33% of predicted or personal best 1, 5
• Silent chest, cyanosis, or feeble respiratory effort 1, 5
• Altered mental status, confusion, or exhaustion 1, 5
• Bradycardia or hypotension 1, 5
• Normal or elevated PaCO₂ (≥42 mmHg) in a breathless patient 5, 6

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Critical Pitfalls to Avoid

• Never administer sedatives of any kind to patients with acute asthma—this is absolutely contraindicated 5, 6
• Do not underestimate severity based on subjective assessment alone; always use objective peak flow measurements 1, 5
• Avoid delaying corticosteroids while attempting bronchodilator therapy first 5
• Do not rely solely on patient-reported personal best values without verification, as 45% may be inaccurate, particularly in inner-city populations 3
• School staff may respond more to subjective symptoms than objective peak flow readings, so written action plans must emphasize the importance of zone-based actions 7

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Special Considerations for Children

• Children over 5 years can typically use peak flow meters reliably 4
• Use half doses of bronchodilators for children weighing <15 kg 5, 6
• Prednisolone dosing: 1-2 mg/kg/day (maximum 40-60 mg) for exacerbations 5, 6
• Peak flow variability >13% in children is suggestive of asthma (compared to >10% in adults) 4
• Blood gas measurements are rarely helpful in deciding initial management for children 4

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Discharge and Follow-Up Criteria

Patients should not be discharged until peak flow reaches ≥75% of predicted or personal best, with diurnal variability <25%, and they remain stable for 30-60 minutes after the last bronchodilator dose. 4, 1

At Discharge:

• Ensure patient has been on discharge medications for 24 hours 4
• Verify inhaler technique and document it 4
• Provide written self-management plan with clear zone-based instructions 4, 1
• Prescribe peak flow meter if not already available 4
• Arrange GP follow-up within 1 week 4
• Schedule respiratory clinic appointment within 4 weeks 4