Rx Update: March 2001

ACLS Guidelines Update

Mary Ross, R.Ph., M.B.A.
Peer Review Status: Internally Reviewed

Vasopressin
Vasopressin is a naturally occurring antidiuretic hormone. In high doses, vasopressin acts as a non-adrenergic peripheral vasoconstrictor. When given during CPR, vasopressin increases coronary perfusion pressure, vital organ blood flow, ventricular fibrillation (VF) median frequency, and cerebral oxygen delivery. It may be more effective than epinephrine as a pressor agent for promoting the return of spontaneous circulation in cardiac arrest. Vasopressin may be used as an alternative pressor to epinephrine in the treatment of adult shock-refractory VF and it may be useful for hemodynamic support in vasodilatory shock (e.g., septic shock). Evidence in human clinical trials is limited, but has been consistently positive. The lower adverse effects profile of vasopressin may be the major reason for use. Vasopressin is not recommended for responsive patients with coronary artery disease because the increased peripheral resistance may provoke angina pectoris. Vasopressin is administered as a single bolus dose of 40 units intravenously. After 10 to 20 minutes, if there is no clinical response to vasopressin, epinephrine 1 mg every 3 to 5 minutes can be given. Currently, vasopressin is only recommended to be given once.

Esmolol
Esmolol is a short-acting b1-selective b-adrenergic blocker that has been added to UIHC Emergency Drug Trays. Esmolol is recommended for the acute treatment of supraventricular tachyarrhythmia (SVT), including paroxysmal supraventricular tachycardia (PSVT), rate control in nonpreexcited AF or atrial flutter, ectopic atrial tachycardia, inappropriate sinus tachycardia, and polymorphic VT due to torsades de pointes or myocardial ischemia.

Esmolol is administered as an IV loading dose of 0.5 mg/kg over one minute, followed by a maintenance infusion of 50 mcg/kg per minute for 4 minutes. If the response is inadequate, a second bolus of 0.5 mg/kg is infused over one minute, with an increase of the maintenance infusion to 100 mcg/kg/minute. The bolus dose and the titration of the infusion dose (addition of 50 mcg/kg/minute) can be repeated every 4 minutes to a maximum infusion rate of 300 mcg/kg/minute. Infusions can be maintained up to 48 hours if needed. Esmolol requires no dosage adjustments with renal or hepatic impairment. Esmolol is a very short acting agent with an average half-life of 9 minutes in adults.

Adenosine
Adenosine injection has also been added to UIHC Emergency Drug Trays. Adenosine is an endogenous nucleoside with potent antiarrhythmic activities. Most forms of PSVT involve a reentry pathway including the AV node. Adenosine is effective in terminating these arrhythmias. Although it is not effective in the treatment of arrhythmias that do not involve the AV or sinus node, its use may produce transient AV or retrograde (ventriculoatrial) block that may clarify the diagnosis. Adenosine should only be used to treat arrhythmias when a supraventricular source is strongly suspected.

The initial dose of adenosine is 6 mg IV bolus over 1 to 3 seconds, followed by a 20 ml 0.9% NaCl flush. If no response is observed after 1 to 2 minutes, a second dose of 12 mg is given in the same manner. Because adenosine has a half-life of less than 5 seconds, PSVT may recur. Repeat episodes may be treated with additional doses of adenosine or a calcium channel blocker. Hypotension is more likely to occur with the use of adenosine in a patient whose arrhythmia does not terminate. Adverse effects of adenosine are common, but transient, and include flushing, dyspnea, and chest pain. Theophylline and related methylxanthines block the electrophysiologic and hemodynamic effects of adenosine. The effects of adenosine are prolonged in patients who also have received dipyridamole and carbamazepine, as well as patients with denervated transplanted hearts. Dose adjustments or alternate therapy should be considered in these patients.

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