What causes the depressor notch on the blood pressure curve?

The brief drop in pressure during the second phase is due to reflex vagal stimulation in response to the sharp spike in blood pressure.

What are the main side effects and risks associated with its use?

Potential risks include cardiac arrhythmias, sharp increases in blood pressure, tachycardia, and headaches. The drug is incompatible with inhalational anesthetics due to the risk of severe arrhythmias.

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Epinephrine

*Epinephrinum*

For medical students2 min readUpdated 2026-10-10

Epinephrine (adrenaline) is a biogenic catecholamine and an adrenal medulla hormone that stimulates all types of adrenergic receptors. The drug has a powerful effect on the cardiovascular system, metabolism, and smooth muscle.

Spectrum of actionActs on a1, a2, b1, and b2 receptors

Duration (IV)Short duration, approximately 5 minutes

Routes of administrationParenteral (SC, IM, IV) or topical

Drug of choiceFirst-line emergency treatment for anaphylactic shock

Dose-Dependent Effects and Receptors

The sensitivity of beta-adrenergic receptors to epinephrine is higher than that of alpha-receptors. This determines hemodynamic changes depending on the dose administered:

Low doses: Stimulation of sensitive beta2-receptors predominates. Skeletal muscle blood vessels dilate, total peripheral resistance (TPR) and diastolic pressure decrease, while systolic pressure increases due to cardiac beta1-receptor stimulation.
High doses: Alpha-receptors are activated. Vasoconstriction occurs in the skin, mucous membranes, and abdominal organs; heart rate and contractility increase; total peripheral resistance and systemic blood pressure rise.

Blood Pressure Dynamics and Metabolism

Rapid intravenous administration causes a four-phase blood pressure response:

Sharp rise due to increased cardiac output.
Brief stabilization or drop (reflex bradycardia).
Secondary pressor rise due to vasoconstriction and renin secretion.
Residual hypotension due to sustained beta2-vessel stimulation.

Myocardial oxygen demand increases sharply. Epinephrine stimulates lipolysis and glycogenolysis, leading to hyperglycemia, and causes hypokalemia due to active potassium uptake by skeletal muscle.

Clinical Application

The drug's properties determine its key medical indications:

Anaphylactic shock: First-line treatment to reverse critical hypotension and bronchospasm.
Bronchial asthma: Relief of acute bronchospasm via subcutaneous administration.
Local anesthesia: Addition to anesthetic solutions to cause vasoconstriction, reduce systemic absorption, and prolong the anesthetic effect.
Ophthalmology: Open-angle glaucoma to reduce intraocular pressure.

Mnemonic

Low dose hits beta (dilates muscle vessels), high dose turns on alpha (constricts all vessels and raises blood pressure).

Frequently asked questions

What causes the depressor notch on the blood pressure curve?: The brief drop in pressure during the second phase is due to reflex vagal stimulation in response to the sharp spike in blood pressure.
What are the main side effects and risks associated with its use?: Potential risks include cardiac arrhythmias, sharp increases in blood pressure, tachycardia, and headaches. The drug is incompatible with inhalational anesthetics due to the risk of severe arrhythmias.

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