Effect of basic anesthetics on the vascular bed
The overwhelming majority of basic local anesthetic drugs possess a pronounced vasodilatory effect. These drugs include classical molecules such as procaine, bupivacaine, as well as the widely used lidocaine and articaine. This pharmacological feature plays a key role in the development of potential complications and affects the quality of the anesthesia itself.
Clinical consequences of vasodilation in the injection zone:
- Accelerated resorption: the drug is absorbed into the systemic circulation too rapidly, causing its working concentration directly in the gum or periodontal tissues to drop sharply.
- Increased systemic toxicity: due to the active entry of anesthetic molecules into the bloodstream, the likelihood of undesirable side effects affecting various body systems increases sharply.
- Decreased efficacy: the duration of effective anesthesia is critically shortened as the active substance is quickly washed out from the target zone.
- Hemostasis problems: capillary dilation inevitably leads to increased bleeding at the injection site, complicating surgical manipulations.
The degree of vasodilation always varies. It depends on the specific chemical compound and the anatomical features of the blood supply in the area where the injection is performed.
Exception drugs: focus on mepivacaine
The only local anesthetic available in the Russian Federation that lacks a pronounced vasodilating effect is mepivacaine. Due to its lack of effect on vascular smooth muscle tone, this drug does not require the obligatory addition of vasoconstricting components to retain the molecule in the tissues. In dental practice, it is traditionally used as a 3% solution without the addition of a vasoconstrictor, making it the drug of choice for patients with a strict contraindication to adrenaline administration.
Adrenaline: concentrations and systemic risks
To neutralize the undesirable vasodilatory effect of most anesthetics, vasoconstrictors are integrated into their composition. The modern standard is the use of adrenaline (epinephrine). Its dosage is strictly regulated and usually amounts to 1:100,000 or 1:200,000 proportions.
- Optimal dosage (1:200,000): a concentration of 5 mcg/ml is considered the gold standard for routine outpatient appointments. It provides sufficient duration of anesthesia with minimal systemic risk.
- Increased concentration (1:100,000): is used exclusively in clinical situations where the surgeon needs to achieve pronounced local hemostasis (cessation of bleeding).
However, adrenaline resorption poses a direct threat to at-risk patients. Upon entering the systemic circulation, epinephrine provokes classic sympathomimetic effects, the most frequent of which is pronounced tachycardia. Paradoxically, these complications can occur even if the dentist flawlessly follows the safety protocol.
Auxiliary components and safety rules
In addition to the active substance and vasoconstrictor, the anesthetic solution is a complex chemical system. To maintain stability, the following are added:
- Stabilizers: sodium bisulfite is necessary to prevent chemical oxidation of adrenaline molecules, preserving its vasoconstrictive properties.
- Preservatives: parabens are used to prolong shelf life and maintain absolute sterility of the liquid in the carpule.
- Additional agents: sodium chloride for isotonicity and EDTA.
To minimize the risk of cardiovascular complications from epinephrine entering the bloodstream, the clinical protocol requires the physician to follow two essential rules. First, it is necessary to perform slow administration of the drug to avoid a sharp spike in tissue pressure. Second, it is critically important to perform repeated aspiration tests to reliably rule out accidental needle entry into the lumen of a blood vessel.
Briefly: answers to topical questions
What are the absolute and relative contraindications to the administration of vasoconstrictors in cardiac patients?
The administration of vasoconstrictors is not recommended for patients with severe forms of cardiovascular pathology; the materials do not divide these into absolute and relative contraindications. Cardiac contraindications include:
- Severe sinus bradycardia — a history of pathology in which vasoconstrictors are not recommended.
- Paroxysmal tachycardia — a condition limiting the use of vasoconstrictive drugs.
- Severe forms of cardiovascular pathology — a general group of diseases serving as a contraindication.
The use of vasoconstrictors in such patients can cause severe palpitations, a reactive state, and increased sweating.
To prevent tachycardia, remember the "ASV" rule: Aspiration and Slow Injection are the main steps for a safe adrenaline injection.
Class and exam questions
Why does an articaine or lidocaine solution rapidly cease to work if it lacks adrenaline?
These drugs possess their own potent vasodilatory effect. Without adrenaline, they are rapidly absorbed into the systemic circulation, leaving the injection site, which drastically reduces their local concentration and the duration of effective anesthesia.
Why is sodium bisulfite introduced into the carpule composition?
Sodium bisulfite acts as a stabilizer. Its main task is to protect the added vasoconstrictor (adrenaline) from premature oxidation and loss of vasoconstrictive properties.
In what cases is the use of an adrenaline concentration of 1:100,000 justified?
Such a high concentration of epinephrine is recommended only when there is an urgent need during surgery to improve hemostasis (stop bleeding).
Can the absence of tachycardia be guaranteed in an at-risk patient with proper anesthesia technique?
No, there is no absolute guarantee. Even with proper aspiration testing and very slow drug administration, the inevitable absorption of some adrenaline from the tissues can provoke systemic sympathomimetic effects.
What else to study on this topic
- Mechanism of development of sympathomimetic effects during systemic adrenaline resorption
- Comparative analysis of the vasodilatory properties of procaine, lidocaine, and articaine
- Technique and physical justification of the aspiration test in dentistry
- The role of preservatives (parabens) and EDTA in local anesthetic solutions
- Indications and limitations for the use of 3% mepivacaine solution in outpatient practice
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Other topics in "Chapter 4. Anesthesia in Oral Surgery (S.A. Rabinovich, S.T. Sokhov)"
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