What are the next steps in managing an inpatient with acute asthma exacerbation who has been given magnesium sulfate (MgSO4)?

Management of Acute Severe Asthma After Magnesium Sulfate Administration

Continue aggressive bronchodilator therapy with continuous nebulized salbutamol (10-15 mg/hour), maintain high-dose systemic corticosteroids (prednisolone 30-60 mg daily or hydrocortisone 200 mg IV every 6 hours), ensure oxygen therapy targeting 92-95% saturation, and add ipratropium bromide 0.5 mg nebulized every 6 hours if not already maximized. 1, 2

Immediate Reassessment (15-30 Minutes Post-MgSO4)

• Measure peak expiratory flow (PEF) or FEV1 to determine response to magnesium sulfate—if PEF remains <40% predicted or <339% of best value after initial treatment, the patient requires escalation of therapy 3, 1
• Monitor oxygen saturation continuously and maintain SpO2 92-95% with supplemental oxygen at 40-60% 1
• Assess clinical markers of severity: respiratory rate ≥25/min, heart rate ≥110/min, inability to complete sentences, use of accessory muscles, or silent chest indicate life-threatening features requiring intensive care consideration 1, 2

Intensify Bronchodilator Therapy

• Switch to continuous nebulized salbutamol at 10-15 mg/hour if the patient shows inadequate response to intermittent dosing, as continuous nebulization is more effective than intermittent in severe exacerbations 1, 2
• Alternatively, increase frequency of nebulized β-agonists to every 15 minutes if continuous nebulization is unavailable 3
• Add or continue ipratropium bromide 0.5 mg nebulized every 6 hours until improvement is seen, as anticholinergics provide clinically meaningful improvement in lung function when combined with β-agonists 3, 1

Maintain Corticosteroid Therapy

• Continue high-dose systemic corticosteroids with prednisolone 30-60 mg orally daily or hydrocortisone 200 mg IV every 6 hours, recognizing that anti-inflammatory effects take 6-12 hours to manifest 3, 1, 2
• Do not reduce corticosteroid dose prematurely—patients should remain on prednisolone 30 mg daily or more for 1-3 weeks after discharge 3

Consider IV Aminophylline for Refractory Cases

• Administer IV aminophylline if the patient remains severely obstructed after 1 hour of intensive treatment: loading dose of 5 mg/kg (approximately 250 mg) over 20 minutes, followed by maintenance infusion of 1 mg/kg/hour 3, 2
• Do not give bolus aminophylline to patients already taking oral theophyllines to avoid toxicity 3
• Alternative parenteral β-agonist: IV salbutamol or terbutaline 250 µg over 10 minutes can be considered instead of aminophylline 3

Monitoring and Supportive Care

• Measure PEF every 15-30 minutes initially, then every 4 hours as the patient improves 3
• Obtain chest radiography to exclude pneumothorax, consolidation, or pulmonary edema 3
• Check plasma electrolytes, urea, and blood count; obtain ECG in older patients 3
• Continue oxygen therapy throughout treatment to maintain adequate oxygenation 3, 1

Criteria for Intensive Care Unit Transfer

• Transfer to ICU if any of the following develop: deteriorating PEF, worsening or persisting hypoxia (PaO2 <8 kPa) despite 60% inspired oxygen, hypercapnia (PaCO2 >6 kPa), exhaustion, feeble respiration, confusion, drowsiness, coma, or respiratory arrest 3
• Patients with life-threatening features (FEV1 <20% predicted, silent chest, altered mental status) require intensive monitoring by experienced staff even if not requiring mechanical ventilation 3, 1

Repeat Magnesium Sulfate Dosing

• Consider repeat dose of 2 g IV magnesium sulfate over 20 minutes if the patient has severe exacerbation (FEV1 or PEF <40% predicted) that remains severe after 1 hour of intensive conventional treatment 1, 4
• The standard adult dose is 2 g over 20 minutes, which reduces hospital admissions by approximately 7 per 100 patients treated 1, 4
• Do not use magnesium sulfate for mild or moderate exacerbations, as it shows no benefit in these populations 4

Exclude Alternative Diagnoses

• Consider pneumothorax, pneumonia, pulmonary embolism, or vocal cord dysfunction in cases of true refractory asthma that fails to respond to escalating therapy 2
• Verify adequate delivery of initial therapy including oxygen-driven nebulizers and appropriate magnesium sulfate dosing before escalating treatment 2

Common Pitfalls to Avoid

• Do not give antibiotics unless bacterial infection is confirmed—they are not helpful in uncomplicated asthma exacerbations 3
• Avoid sedation entirely, as any sedation is contraindicated in acute asthma 3
• Do not perform percussive physiotherapy—it is unnecessary and potentially harmful 3
• Do not discharge the patient prematurely—PEF should be above 75% of predicted or best level, with diurnal variability below 25% and no nocturnal symptoms before discharge 3