What is the recommended dosage for continuous intravenous salbutamol infusion in an adult with severe acute asthma and in children weighing at least 12 kg?

Continuous Intravenous Salbutamol Infusion Dosage

For adults with severe acute asthma not responding to initial treatment, use a continuous IV salbutamol infusion starting at 3-20 mcg/min (small patient 750 mg/24 hours, large patient 1500 mg/24 hours for aminophylline as alternative), though the British Thoracic Society guidelines recommend salbutamol or terbutaline infusion as an alternative to aminophylline when patients are still not improving after intensive conventional therapy. 1, 2

Adults

Initial bolus and maintenance dosing:

• Bolus dose: 250 mcg IV over 10 minutes (only if life-threatening features present and patient not already on oral theophyllines) 1, 2
• Continuous infusion: The guidelines reference salbutamol or terbutaline infusion as an alternative to aminophylline but do not specify exact mcg/min rates 2
• This is reserved for patients who are still not improving after:
  • High-dose nebulized β-agonists (up to every 15-30 minutes)
  • Systemic corticosteroids
  • Addition of ipratropium

Clinical context for use:

• Only initiate when patient shows no improvement after 15-30 minutes of intensive nebulized therapy 1
• Life-threatening features must be present: PEF <33% predicted, silent chest, cyanosis, bradycardia, hypotension, exhaustion, confusion, or coma 1, 2
• Consider as a bridge therapy before intubation in impending respiratory failure

Children (≥12 kg)

The guidelines do not provide specific continuous IV infusion dosing for children. However, research evidence provides guidance:

From pediatric research 3:

• Loading dose: 1 mcg/kg/min over 10 minutes
• Initial maintenance: 0.2 mcg/kg/min
• Titration: Increase by 0.1 mcg/kg/min increments according to response
• Maximum dose: 4 mcg/kg/min
• This regimen achieved sustained PaCO2 reduction in 69% of children with respiratory failure unresponsive to conventional therapy

Important caveat: The British Thoracic Society guidelines for children with life-threatening asthma recommend IV aminophylline (5 mg/kg over 20 minutes followed by 1 mg/kg/h maintenance) rather than salbutamol 2, 1

Critical Implementation Points

Monitoring requirements:

• Continuous cardiac monitoring (expect heart rate increase from baseline ~161 to ~183 bpm in children) 3
• Serial PEF or FEV1 measurements every 15-30 minutes initially 1
• Pulse oximetry maintaining SaO2 >92% 1
• Electrolytes (risk of hypokalemia with high-dose β-agonists) 1
• Blood gas measurements within 2 hours if initial PaO2 <8 kPa or PaCO2 normal/raised 1

When to escalate to ICU:

• Deteriorating PEF despite infusion
• Worsening or persistent hypoxia/hypercapnia
• Exhaustion, feeble respirations, confusion, or drowsiness
• Prepare for intubation 1

Common Pitfalls

1. Starting IV salbutamol too early: The guidelines are clear this is only for patients failing intensive nebulized therapy, not first-line treatment 2

2. Inadequate concurrent therapy: IV salbutamol must be given alongside:

   • High-flow oxygen (40-60%)
   • Systemic corticosteroids (prednisolone 30-60 mg daily or IV hydrocortisone 200 mg every 6 hours)
   • Continued nebulized bronchodilators 1, 2

3. Ignoring alternative diagnoses: If bronchospasm doesn't resolve with high-dose therapy, consider paradoxical bronchospasm from preservatives (benzalkonium chloride) and trial a different bronchodilator 4

4. Delaying intubation: Do not delay intubation once deemed necessary; IV salbutamol is a temporizing measure, not a substitute for mechanical ventilation in true respiratory failure 5

Note on nebulized vs. IV route: The FDA labeling and recent guidelines emphasize that nebulized salbutamol remains the primary delivery method, with continuous nebulization (10-15 mg/hour) preferred over IV infusion for most severe cases 5, 4. IV infusion is specifically for those who cannot tolerate or respond to nebulized therapy.