A patient in stable narrow-complex tachycardia with a peripheral IV in place is refractory to the first dose of adenosine. Which dose would you administer next?
The Correct Answer and Explanation is :
The correct next dose of adenosine in a patient who is refractory to the first dose of adenosine in stable narrow-complex tachycardia is 12 mg.
Explanation:
Adenosine is a medication used to treat certain types of supraventricular tachycardias (SVT), particularly those caused by reentrant pathways such as in atrioventricular nodal reentry tachycardia (AVNRT). Adenosine works by briefly blocking conduction through the atrioventricular (AV) node, interrupting the reentrant circuit and restoring normal sinus rhythm.
Dosing Protocol:
- First dose: The typical starting dose of adenosine is 6 mg administered rapidly via a peripheral IV, followed by a flush with saline. This dose is effective in about 60-90% of cases.
- Second dose: If the first dose of 6 mg is ineffective, the dose is increased to 12 mg and administered in the same manner. The higher dose is more likely to be effective, particularly in cases where the arrhythmia persists or is caused by a more resistant reentrant circuit.
Why the second dose is 12 mg:
Adenosine has a very short half-life, typically around 10 seconds, which is why it is given as a rapid IV bolus. If the initial dose of 6 mg does not terminate the tachycardia, a second dose of 12 mg is recommended, as this will increase the likelihood of successful conversion to normal sinus rhythm. The increased dose is necessary because the tachycardia may be more resistant to the lower dose, and the 12 mg dose ensures enough of the drug reaches the AV node to interrupt the reentrant circuit.
Additional Considerations:
- Administration: Adenosine should be given as a rapid IV push followed by a saline flush.
- Refractory Cases: If the patient remains in tachycardia despite the second dose, further management may involve other antiarrhythmic drugs (e.g., calcium channel blockers, beta-blockers) or synchronized cardioversion, depending on the clinical status of the patient.
It is important to monitor the patient closely for any adverse effects of adenosine, such as transient bradycardia, chest discomfort, or flushing, all of which are typically short-lived.