Intravenous Ketamine in a Dissociating Dose as a Temporizing Measure to Avoid Mechanical Ventilation in Adult Patient With Severe Asthma Exacerbation

Gil Z. Shlamovitz, MD; Tracy Hawthorne, MHS, PA-C


J Emerg Med. 2011;41(5):492-494. 

In This Article


Studies have shown an increase in prevalence and severity of asthma during the last 20 years despite publication and dissemination of evidence-based guidelines for the management of acute and chronic asthma.[1–5] Patients experiencing severe asthma exacerbation occasionally deteriorate to respiratory failure and require mechanical ventilation. Mechanical ventilation in the setting of severe asthma exposes the patient to substantial iatrogenic risks, including pneumothorax, pneumomediastinum, nosocomial pneumonia, worsening bronchospasm, and circulatory depression, and therefore should be utilized only after other measures have failed.[6–9]

Ketamine is a dissociative sedative frequently used by Emergency Physicians for procedural sedation and analgesia as well as an induction agent in status asthmaticus patients.[10–14] Ketamine has demonstrated bronchodilatatory properties in both in vitro studies (relaxing bronchial smooth muscles) and mechanically ventilated status asthmaticus patients (decreasing mean airway pressure and PaCO2 and increasing PaO2).[14–19] Suggested mechanisms of bronchodilatation include: sympathomimetic effect, direct relaxant effect, antagonism to histamine and acetylcholine, calcium influx blockage, and a membrane-stabilizing effect, as with local analgesics.[17,18,20,21] It is also possible that the dissociating effect of ketamine may result in anxiolysis and a decrease in the work of breathing without depressing the respiratory drive.

Our review of the literature (PubMed, accessed November 20, 2007) identified 14 case reports in which pediatric patients treated with ketamine successfully avoided mechanical ventilation.[22–25] The administered dosages of ketamine in these case reports varied significantly and ranged from an intravenous bolus of 0.6 mg/kg to an intramuscular bolus of 4.8 mg/kg. The continuous intravenous ketamine infusions varied between 0 and 2.4 mg/kg/h. All children entered a dissociative state followed by marked clinical improvement, and none of them required mechanical ventilation.

We identified two randomized, double-blind placebo-controlled trials evaluating the effectiveness of intravenous ketamine in asthma. Howton et al. studied 44 adults with severe asthma exacerbation and found no significant difference in outcome between the ketamine and placebo groups.[26] Allen and Macias studied 68 children with moderate-to-severe asthma exacerbation and found no incremental benefit to standard therapy in the cohort group given ketamine.[27] However, both studies used very low doses of ketamine (0.2 mg/kg bolus) and none of the patients entered a dissociative state. We believe that this low dosing is likely to explain the authors' findings.


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