Epinephrine, also known as adrenaline, is a naturally occurring hormone and a medication used in emergency situations. It plays a significant role in the body’s stress response and is a key intervention in life-threatening medical emergencies, particularly those involving the heart.
Epinephrine: The Emergency Hormone
Epinephrine is a hormone and neurotransmitter produced naturally in the adrenal glands, located on top of the kidneys, and by certain nerve cells. It is central to the body’s “fight or flight” response, which prepares an individual for sudden, vigorous action in times of stress. When released, epinephrine causes widespread effects by binding to specific receptors on various cells throughout the body.
Its physiological effects include an increased heart rate and force of contraction, which helps pump more blood. It also dilates the airways in the lungs, allowing for deeper and faster breathing. Additionally, epinephrine causes blood vessels to constrict, redirecting blood flow to muscles and vital organs, and stimulates the liver to release glucose for quick energy. The synthetic form of epinephrine is used as a medication to mimic these natural responses in a controlled manner.
Why Epinephrine Is Used in Cardiac Arrest
Epinephrine is a first-line medication for cardiac arrest due to its effects on the cardiovascular system. During cardiac arrest, the heart stops beating effectively, leading to inadequate blood circulation to the brain and other organs. Epinephrine helps address this by stimulating various adrenergic receptors.
Its primary benefit comes from its alpha-adrenergic effects, which cause peripheral vasoconstriction, meaning it narrows blood vessels outside the heart and brain. This vasoconstriction increases aortic diastolic pressure and improves coronary and cerebral perfusion pressure, which is the blood flow to the heart muscle and brain during cardiopulmonary resuscitation (CPR). Increasing this pressure is important for achieving a return of spontaneous circulation (ROSC), where the heart starts beating on its own again. Epinephrine also has beta-adrenergic effects that can increase heart rate and contractility, though these effects are sometimes debated for their overall benefit in cardiac arrest.
The Standard Cardiac Dose and Administration
For adults in cardiac arrest, the standard dose of epinephrine is 1 milligram (mg). This dose is administered intravenously (IV) or intraosseously (IO), meaning directly into a vein or bone marrow, every 3 to 5 minutes during resuscitation efforts.
Epinephrine for cardiac arrest is usually supplied as a 1:10,000 concentration, where 1 mg is equivalent to 10 mL of this solution. If intravenous or intraosseous access is not available, a higher dose of 2 to 2.5 mg can be administered via an endotracheal tube, diluted in 10 mL of normal saline. This administration is performed by trained healthcare professionals following standardized medical protocols.
Immediate Effects and Continued Care
Following epinephrine administration, medical professionals observe for the primary goal of restoring spontaneous circulation (ROSC). While the medication can cause a transient increase in heart rate or blood pressure, its main purpose is to improve the chances of the heart restarting by enhancing blood flow to the heart and brain during chest compressions. Studies show that epinephrine increases the likelihood of achieving ROSC and short-term survival.
Epinephrine is one component of a comprehensive resuscitation effort. It is administered alongside ongoing high-quality chest compressions and, when appropriate, defibrillation. After successful resuscitation and if ROSC is achieved, the patient requires immediate and ongoing advanced medical care and monitoring to manage potential post-resuscitation complications and support overall recovery.