What is the effect of salbutamol (albuterol) in relieving bronchospasm?

Effect of Nebulized Salbutamol (Asthalin)

Nebulized salbutamol is highly effective for rapid relief of bronchospasm in asthma and COPD by relaxing airway smooth muscle through beta-2 adrenergic receptor activation, with onset of action within 6 minutes and peak effect at 50-55 minutes. 1

Mechanism of Action and Clinical Effects

Salbutamol preferentially activates beta-2 adrenergic receptors on bronchial smooth muscle, leading to increased cyclic AMP, which inhibits myosin phosphorylation and lowers intracellular calcium, resulting in smooth muscle relaxation from the trachea to terminal bronchioles 1. This produces:

• Bronchodilation: Mean duration of 15% FEV1 increase lasts 3 hours, with some patients experiencing effects up to 6 hours 1
• Volume improvements: Reduces end-expiratory lung volumes and improves inspiratory capacity, even when flow responses (FEV1) are minimal 2
• Symptom relief: Decreases work of breathing and improves exercise tolerance by reducing gas trapping 2

Dosing Guidelines by Age and Indication

Asthma Exacerbations

• Children <5 years: 0.63 mg/3 mL nebulized 2
• Children 5-11 years: 1.25-5 mg in 3 cc saline 2; alternatively 0.15 mg/kg (minimum 2.5 mg) every 20 minutes for 3 doses 3
• Adults: 2.5 mg in 3 cc saline 2
• Severe exacerbations: May double the dose 2

COPD Exacerbations

• Standard dose: 2.5 mg nebulized 2
• Higher doses (up to 400 mcg cumulative via MDI, equivalent to ~10 mg nebulized) produce significant dose-dependent FEV1 improvements (mean 0.165L increase) without significant adverse effects 4

Response Patterns and Clinical Considerations

Flow vs. Volume Responses: Not all patients show FEV1 improvement, but this does not mean treatment failure 2:

• In COPD, 41% show neither flow nor volume response, 23% show volume response only, 12% show flow response only, and 24% show both 2
• Volume responders (characterized by lower baseline FEV1/FVC and higher residual volume) benefit from reduced gas trapping even without FEV1 improvement 2
• More severe COPD patients (GOLD grade 4) show smaller flow responses (mean 50 mL) but may have greater volume responses 2

Special Populations:

• Infants with bronchospasm: 200 mcg via MDI with spacer improves compliance and resistance 5
• Bronchopulmonary dysplasia: 55% of children with recurrent wheezing respond positively, compared to 12.5% without wheezing 6
• Preoperative use: 2.5 mg (<20 kg) or 5 mg (>20 kg) given 30 minutes before anesthesia reduces perioperative respiratory complications by 50% 5, 3

Safety Profile and Monitoring

Cardiovascular Effects:

• Standard doses (2.5 mg) do not significantly affect heart rate in most populations 7
• Only doses 5-10× standard (12.5-25 mg) cause 20-30 beat/min heart rate increases 7
• High doses cause mild QTc prolongation (360→390 ms) but no clinically significant arrhythmias 7
• Arrhythmia incidence is similar to placebo, even in ICU populations and patients with cardiac comorbidity 7

Common Adverse Effects 2:

• Tachycardia (dose-dependent)
• Tremor
• Transient oxygen desaturation
• Nervousness

Critical Caveat: Paradoxical bronchospasm is rare but life-threatening 8. If wheezing worsens after salbutamol administration, immediately discontinue and consider alternative bronchodilators (ipratropium) 2.

Combination Therapy

With Ipratropium: Adding ipratropium 250-500 mcg to salbutamol provides additive benefit in moderate-to-severe exacerbations, particularly in the emergency department setting 2, 3. The combination is safe and does not induce bronchospasm despite containing EDTA 2.

With Corticosteroids: For acute exacerbations requiring salbutamol >2-3 times daily, add inhaled corticosteroids 2. In severe exacerbations, give oral prednisolone 1-2 mg/kg (max 60 mg) immediately 3.

Contraindications to Routine Use

Do not use salbutamol routinely in:

• Sepsis-induced ARDS without bronchospasm (increases 28-day mortality: 34% vs 23%, RR 1.4) 2
• Asymptomatic infants without obvious bronchospasm (variable response, potential side effects) 5

Tachycardia or underlying heart disease are NOT contraindications to salbutamol use in acute bronchospasm 7.