What is the recommended dose of ketamine (anesthesia medication) for asthma exacerbation?

Ketamine Dosing for Asthma Exacerbation

Ketamine is not recommended as a first-line treatment for asthma exacerbations, but may be considered as an adjunct therapy in severe refractory cases, particularly when intubation is planned, at a loading dose of 0.2 mg/kg IV followed by a continuous infusion of 0.5 mg/kg per hour. 1

Role of Ketamine in Asthma Management

Ketamine is a parenteral, dissociative anesthetic with bronchodilatory properties. It also stimulates copious bronchial secretions and has sedative and analgesic properties that may be useful when intubation is being considered for severe asthma exacerbations unresponsive to standard therapy.

Evidence on Efficacy:

• The American Heart Association guidelines mention that one case series suggested substantial efficacy, but two randomized trials in children found no benefit of ketamine compared with standard care 1
• A Cochrane review of ketamine for acute asthma in children did not show significant benefit over placebo in non-intubated children 2

Standard Treatment Algorithm for Asthma Exacerbations

Before considering ketamine, ensure standard therapies have been maximized:

1. First-line treatments:

   • Inhaled short-acting beta-agonists (SABA) like albuterol: 2.5-5 mg every 20 minutes for 3 doses, then 2.5-10 mg every 1-4 hours as needed, or 10-15 mg/hour continuously via nebulizer 1
   • Systemic corticosteroids
   • Ipratropium bromide: 0.5 mg every 20 minutes for 3 doses then as needed 1

2. Second-line treatments for severe refractory asthma:

   • IV magnesium sulfate: 2 g administered over 20 minutes in adults 1
   • Epinephrine (for severe cases): 0.3-0.5 mg subcutaneously every 20 minutes for 3 doses 1

3. Consider ketamine when:

   • Patient has severe refractory asthma not responding to above measures
   • Intubation is being considered or planned
   • Other standard therapies have been exhausted

Ketamine Dosing Recommendations

When standard therapies fail and ketamine is considered appropriate:

Adult Dosing:

• Loading dose: 0.2 mg/kg IV 3
• Maintenance infusion: 0.5 mg/kg per hour for 1-2 hours 1, 3

Alternative Dosing Regimens from Research:

• Some studies have used higher doses:
  • Loading dose of 1 mg/kg IV followed by continuous infusion of 0.75 mg/kg/hour 4
  • Doses of 0.4-0.5 mg/kg IV followed by infusion of the same dose over 30 minutes have shown better improvement in peak expiratory flow rate compared to 0.3 mg/kg 5

Important Considerations and Precautions

1. Monitoring requirements:

   • Continuous cardiac monitoring
   • Frequent vital sign assessment
   • Oxygen saturation monitoring
   • Mental status evaluation

2. Potential side effects:

   • Emergence reactions/hallucinations (may require benzodiazepines)
   • Increased secretions
   • Tachycardia
   • Hypertension
   • Increased intracranial pressure

3. Contraindications:

   • Severe hypertension
   • Severe coronary artery disease
   • Increased intracranial pressure
   • History of psychosis

Clinical Pearls

• Ketamine should only be used by clinicians experienced in airway management
• Have benzodiazepines available to treat emergence reactions
• Consider anticholinergic premedication to reduce secretions
• Ketamine may be particularly useful when intubation is anticipated, as it provides both bronchodilation and sedation
• For patients requiring mechanical ventilation, higher doses may be needed, but pharmacokinetics can be altered in critically ill patients 6

Remember that the evidence supporting ketamine use in asthma is limited, and it should be reserved for cases where standard therapies have failed and respiratory failure is imminent.