Adenosine is a rapid-acting medication used to manage certain heart rhythm disturbances. Its quick action makes precise administration technique important, especially in emergency settings. It is typically given intravenously.
Purpose of Adenosine
Adenosine is a primary treatment for supraventricular tachycardia (SVT), a condition with an abnormally fast heart rate originating above the heart’s lower chambers. During SVT, the heart can beat between 150 to 220 times per minute, compared to the typical 60 to 100 beats per minute. This rapid rhythm results from faulty electrical signals or a re-entry circuit within the heart’s upper chambers or the atrioventricular (AV) node. Adenosine works by temporarily slowing or blocking electrical conduction through the AV node, interrupting the abnormal circuit and restoring a normal heart rhythm. This effect is transient, lasting only a few seconds due to its short half-life.
Prior to Administration
Before administering adenosine, healthcare professionals must ensure proper patient monitoring and prepare equipment. Continuous electrocardiogram (ECG) monitoring is essential to observe the heart’s rhythm. Vital signs, including blood pressure and oxygen saturation, should also be continuously assessed. Establishing secure intravenous (IV) access, preferably in a large vein close to the heart like the antecubital vein, is crucial for rapid drug delivery.
Preparing the medication involves drawing up the prescribed dose of adenosine and a saline flush in separate syringes. For adults, the initial dose is 6 mg, followed by a 20 mL normal saline flush. A second dose of 12 mg may be administered if the first dose is ineffective. Verifying the correct dosage and ensuring syringes are ready for immediate use are important steps.
Administering Adenosine
Administering adenosine requires a rapid technique due to its short half-life of less than 10 seconds. The medication must reach the heart quickly before metabolism. The standard method involves a rapid intravenous bolus, injecting the medication swiftly into a vein.
Connect the adenosine syringe to an IV injection port closest to the patient. Immediately following the adenosine, rapidly administer a 20 mL normal saline flush through the same port. Some techniques involve attaching both syringes to the same IV line, with the saline flush pushed immediately after the adenosine to ensure the drug clears the tubing and reaches central circulation. Elevating the patient’s arm after injection for 10 to 20 seconds can further aid circulation to the heart. The entire process, from adenosine injection to saline flush, should ideally take 1 to 3 seconds.
Post-Administration Monitoring
Following adenosine administration, patients often experience transient physiological effects. A brief period of asystole, where the heart temporarily stops beating, or significant bradycardia (slow heart rate) is common and typically lasts only a few seconds. Patients may also report flushing, chest discomfort or tightness, and shortness of breath. These effects are short-lived and resolve quickly as the medication is metabolized.
Continuous ECG monitoring is essential to observe the heart’s response and determine if a normal rhythm is restored. Healthcare providers watch for successful conversion to sinus rhythm or for arrhythmia recurrence, which may necessitate further intervention or a second dose. The patient’s vital signs are closely monitored to assess their stability and response to treatment.
Key Safety Considerations
Adenosine administration requires careful consideration of precautions and contraindications. It should not be used in patients with certain pre-existing heart conditions, such as second- or third-degree heart block, unless a functioning artificial pacemaker is present. Patients with sinus node disease or symptomatic bradycardia also should not receive adenosine, unless they have a pacemaker. Adenosine is contraindicated in individuals with known bronchoconstrictive or bronchospastic lung diseases, such as asthma, due to the risk of severe respiratory difficulties.
Certain medications can interact with adenosine, potentially altering its effects or increasing adverse reactions. Drugs like dipyridamole and carbamazepine can enhance adenosine’s effects, requiring a reduced initial dose. Conversely, methylxanthines, found in caffeine and theophylline, can reduce adenosine’s effectiveness. Adenosine should only be administered by trained healthcare professionals in a clinical setting where resuscitative equipment is immediately available.