Causes and types of arterial hypotension
Arterial hypotension is a pathological condition whose main diagnostic criterion is a drop in systolic blood pressure below 105 mm Hg. From a hemodynamic perspective, such a drop in pressure is caused by three main factors. First, it can be a decrease in cardiac output. Second, a drop in total peripheral vascular resistance (TPVR). Third, a combined effect of both factors is frequently observed.
Based on the clinical course, hypotension is classified into two major groups:
- Acute form. Develops rapidly and is life-threatening. It includes severe conditions such as various types of shock, vascular collapse, and acute massive blood loss.
- Chronic form. Subdivided into primary (also referred to as idiopathic) and secondary. Secondary chronic hypotension is a consequence of other pathologies and strictly requires appropriate pharmacotherapy.
Classification of vasopressor agents
Vasopressor agents are used for the pharmacological correction of low blood pressure. Depending on the predominant mechanism of their hemodynamic effect, all drugs in this category are divided into two main groups.
- Agents that increase cardiac output and peripheral vascular tone.
These drugs have a complex effect on the cardiovascular system. The main pharmacological group here is $\alpha, \beta$-adrenomimetics. A classic and most well-known representative of this group is epinephrine, also known in medical practice as adrenaline.
- Agents that primarily increase peripheral vascular tone.
The action of these drugs is primarily aimed at vasoconstriction. This group is further subdivided into two subgroups depending on chemical structure and sites of action:
- $\alpha$-adrenomimetics. Key representatives are norepinephrine (norepinephrine hydrogen tartrate) and phenylephrine (mesaton).
- Polypeptide drugs. The main representative is angiotensinamide, which is also known by the name hypertensin.
Features of the clinical use of adrenomimetics
Adrenomimetics are powerful tools in a physician's arsenal. The main indication for their prescription is acute arterial hypotension, when immediate intervention is required to restore adequate circulation.
There are strict rules regarding the routes of administration for these drugs. The primary and safest route is intravenous administration, performed as a controlled infusion. However, there is an exception to this rule: phenylephrine has specific properties that allow it to be administered not only intravenously, but also subcutaneously and intramuscularly.
Special attention should be given to the specific use of epinephrine. Due to its ability to rapidly restore hemodynamics, it is recognized as the drug of choice in the development of anaphylactic shock, demonstrating exceptionally high clinical efficacy in this situation.
Pharmacological profile of angiotensinamide
Angiotensinamide is a unique polypeptide drug. Chemically, it is an angiotensin II amide.
Its mechanism of action is radically different from adrenomimetics: the drug directly stimulates specific angiotensin receptors located in the walls of arterioles. The result of such stimulation is the development of a rapid and extremely potent vasoconstrictive effect. It is important to note that in terms of its pressor potency, angiotensinamide significantly surpasses epinephrine.
The drug's action has a clear localization. The most pronounced blood vessel spasm is observed in the visceral vascular bed, as well as in the skin and renal vessels.
In addition to its direct effect on vascular tone, angiotensinamide has a major impact on water-electrolyte balance via hormonal mechanisms. It actively stimulates the production of the hormone aldosterone. The consequence of this hormonal effect is a marked retention of sodium ions and water in the patient's body, which naturally leads to an increase in total extracellular fluid volume and further contributes to maintaining blood pressure.
To memorize the routes of administration for phenylephrine, use the mnemonic: "Phenylephrine — Universal format." Unlike other adrenomimetics that require infusion, it can be administered not only intravenously, but also subcutaneously and intramuscularly.
Class and exam questions
At what blood pressure is arterial hypotension diagnosed?
The criterion is a drop in systolic blood pressure below 105 mm Hg. This condition can be either acute or chronic.
What is the difference between the actions of epinephrine and norepinephrine?
Epinephrine increases both cardiac output and peripheral vascular tone. Norepinephrine acts more selectively, increasing primarily vascular tone.
How does angiotensinamide affect hormonal status and water-electrolyte balance?
The drug stimulates aldosterone production. This leads to sodium and water retention in the body, which contributes to an increase in extracellular fluid volume.
Can adrenomimetics be administered intramuscularly?
The main route of administration for this group is intravenous infusion. An exception is phenylephrine, which is permitted to be administered intramuscularly and subcutaneously.
What else to study on this topic
- Hemodynamic mechanisms of acute and chronic hypotension.
- Pharmacodynamics of $\alpha$- and $\beta$-adrenergic receptors.
- The role of aldosterone in the regulation of water-electrolyte balance.
- Comparative characteristics of the pressor effects of epinephrine and angiotensinamide.
- Principles of pharmacotherapy for anaphylactic shock.
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