Adenosine is a pharmacological agent used to treat Supraventricular Tachycardia (SVT), an abnormally fast heart rhythm originating above the ventricles. The drug acts by stimulating receptors on the Atrioventricular (AV) node, temporarily blocking electrical conduction. This action interrupts the re-entry circuit responsible for the rapid heart rate. Adenosine is metabolized rapidly, having an extremely short half-life of less than ten seconds, necessitating a highly precise and rapid intravenous push technique.
Essential Pre-Administration Setup
Successful administration of adenosine begins with preparation. The first step involves securing appropriate intravenous access, ideally using a large-bore catheter, such as an 18-gauge, placed in a proximal vein. The antecubital fossa (bend of the elbow) is the preferred site due to its proximity to the central circulation, minimizing the distance the medication must travel. If a central venous access line is used, the initial dose must be significantly reduced due to the direct route to the heart.
The patient must be positioned supine, and the procedure should be explained beforehand to manage anxiety. Full cardiac monitoring is required, involving continuous Electrocardiogram (ECG) monitoring, blood pressure measurement, and pulse oximetry. The ECG monitor must be set to record the rhythm strip continuously before, during, and immediately after administration to capture the moment of conversion or diagnostic pause. All necessary resuscitation equipment, including a defibrillator and airway devices, must be immediately available at the bedside prior to initiating the procedure.
Determining Dosage and Preparing the Syringes
Preparation involves drawing up adenosine and the saline flush into separate, clearly labeled syringes. The standard adult dosing sequence begins with an initial rapid intravenous bolus of 6 milligrams (mg). If the first dose is unsuccessful in converting the rhythm, a subsequent dose of 12 mg may be administered after one to two minutes. A third 12 mg dose is sometimes considered if the second attempt fails, based on the patient’s clinical status and guidelines.
Special considerations apply to patients on certain medications or with specific medical histories, as they may be hypersensitive to adenosine. For instance, in individuals with a transplanted heart, those on dipyridamole, or if the drug is administered via a central line, the initial dose is often reduced to 3 mg. Preparing the saline flush is important, as a large volume is required to rapidly propel the drug toward the heart. A 10 to 20 milliliter (mL) syringe of normal saline is typically prepared for the flush to clear the drug from the peripheral IV line and tubing.
Executing the High-Speed IV Push Technique
The technique for administering adenosine is the most critical factor influencing its effectiveness due to the drug’s short half-life. The goal is to deliver the drug to the central circulation as an undiluted, concentrated bolus, requiring a coordinated, two-person approach. The preferred method involves connecting the adenosine syringe and the 20 mL saline flush syringe to the IV port closest to the patient’s body, often utilizing a three-way stopcock. This setup minimizes the travel distance and allows for a rapid transition between the drug and the flush.
One clinician rapidly and forcefully injects the adenosine over a period of just one to two seconds. Immediately following the drug, the other clinician delivers the 20 mL saline flush with equal force and speed. The flush is the mechanism that drives the adenosine out of the IV tubing and into the bloodstream, where it then travels to the heart. Elevating the patient’s extremity where the IV is inserted immediately after the push can also assist gravity in accelerating the drug’s journey. This entire process must be executed seamlessly and without hesitation.
Immediate Patient Response and Required Monitoring
The rapid and direct action of adenosine on the AV node elicits a transient physiological response that requires continuous observation. The most immediate effect is a brief, temporary pause in electrical activity, which may appear as a short period of asystole or a high-grade heart block on the ECG monitor. This is an expected manifestation of the drug’s effect as it interrupts the re-entry circuit. Since this pause lasts only a few seconds, it resolves quickly as the drug is metabolized.
Patients often experience pronounced, though short-lived, subjective side effects due to the drug’s vasodilatory properties. Common complaints include facial flushing, a feeling of chest discomfort or pressure, and breathlessness. These symptoms typically resolve within seconds, mirroring the drug’s short half-life. Continuous ECG monitoring is mandatory to confirm if the SVT has converted to a normal sinus rhythm. If the initial 6 mg dose is unsuccessful, the team should observe the patient for one to two minutes before administering the second, larger 12 mg dose, following the same rapid administration technique.