Mechanisms of toxicity development in topical anesthesia
Although emergency conditions are often associated with systemic pathologies, a critical risk factor in dental practice is the pronounced toxic effect of local anesthetics. The primary drawback of surface (topical) anesthesia lies in the drug distribution mechanism.
Anesthetics applied to the mucous membrane are actively absorbed into the systemic circulation. This process occurs so intensively that extremely high, toxic concentrations of the active substance are generated in the blood. The rate of this process is absolutely comparable to the blood saturation rate upon direct intravenous administration of the medication, which poses a threat of both systemic and pronounced local toxic reactions.
Factors promoting rapid absorption
The process of rapid absorption and subsequent intoxication is driven by a number of specific characteristics of the solutions and gels used. The main factors that significantly accelerate the absorption of the drug into the blood include:
- High concentration of the active anesthetic in the applied product.
- Intrinsic vasodilating effect — the ability of the drugs themselves to cause blood vessel dilation, which increases the area and intensity of blood flow in the application zone.
- Absence of a vasoconstrictor (vasoconstricting component) in the topical formulations.
In addition, the level of toxicity directly depends on the physicochemical properties of the specific agent.
- Water-soluble agents (e.g., tetracaine and pyromecaine) carry the highest risk of rapid absorption and, consequently, maximum toxicity.
- Poorly water-soluble agents (lidocaine- and benzocaine-based drugs) demonstrate a significantly lower risk of rapid absorption.
Hazards of aerosol forms
The use of anesthetics in aerosol form is considered the least preferable approach in modern topical anesthesia. The main problem lies in the absolute difficulty of precisely controlling and adequately assessing the total dose of the drug sprayed onto the mucosa.
Treatment of the distal (posterior) parts of the oral cavity poses a particular hazard. Spraying in this area leads to dangerous complications:
- Deep suppression of critical patient protective reflexes (primarily the gag and laryngopharyngeal reflexes).
- Emergence of a high risk of accidental entry (swallowing or aspiration) of foreign bodies directly into the respiratory tract or gastrointestinal tract.
Methods for reducing pain during injections
To prevent stress reactions and minimize pain at the moment of soft tissue puncture (needle insertion) during injection anesthesia, the practitioner must apply a combination of special techniques.
The table below presents the main tactics for overcoming pain during injection:
| Method of action | Description of physician and patient actions |
|---|---|
| Psychological | Active distraction of the patient's attention from the moment of injection. |
| Mechanical | Compression (pronounced compression) of soft tissues held by the physician's fingers, immediately at the moment of injection. |
| Respiratory | Asking the patient to take a deep, measured breath right before needle insertion. |
| Pharmacological | Immediate administration of a small, starting volume of local anesthetic solution immediately after gentle, careful advancement of the needle bevel into the tissues. |
Briefly: answers to topical questions
What is the algorithm for basic life support during cardiac arrest in a dental setting?
The basic life support algorithm includes a sequence of actions: ensure personal safety, call for help, and initiate CPR. In modern resuscitation for adult patients, the CAB algorithm is used, where priority is given to early initiation of chest compressions. The steps of cardiopulmonary resuscitation include airway management, artificial ventilation, and artificial circulatory support; these first three steps must be mastered by all physicians, including dentists, and nursing staff.
What is the correct ratio of chest compressions to rescue breaths during CPR in an adult patient?
During basic life support for an adult patient, the ratio of chest compressions to rescue breaths is thirty to two. The compression rate should be at least one hundred per minute with a depth of at least five centimeters.
What drugs are used for topical anesthesia in dentistry?
For surface or topical anesthesia in dentistry, the following drugs are used: 3% pyromecaine ointment with methyluracil on collagen, Emla cream, as well as the combined Diplen-L.H. film. Additionally, 1–2% pyromecaine solution, 1–2% or 5% lidocaine solution, and 10% lidocaine aerosol are used.
To remember the factors of rapid absorption, use the "Three V's" rule: High concentration, Vasodilation (intrinsic), absence of Vasoconstrictor.
Class and exam questions
What is the main disadvantage of topical anesthesia?
Its main drawback is the pronounced toxic effect of local anesthetics. They are absorbed into the blood and create toxic concentrations at the same rate as with intravenous administration.
Why are aerosol forms of anesthetics considered less acceptable?
When using aerosols, it is extremely difficult to control and assess the total dose of the administered drug. Furthermore, when applied in the distal regions, they suppress the laryngopharyngeal reflex, creating a high risk of aspiration.
Which drugs carry the highest risk of toxicity?
Water-soluble agents such as pyromecaine and tetracaine carry the highest risk of rapid absorption and subsequent toxicity.
How can pain be reduced directly during needle insertion?
It is recommended to distract the patient's attention, perform soft tissue compression with fingers, ask the patient to take a deep breath before insertion, and immediately administer a small volume of solution after inserting the needle bevel.
What else to study on this topic
- Mechanisms of suppression of laryngopharyngeal and gag reflexes by local anesthetics.
- Comparative analysis of water-soluble and poorly water-soluble anesthetics.
- Intrinsic vasodilating effect of local anesthetics.
- Physicochemical properties of pyromecaine and tetracaine in the context of toxicity.
Master the entire topic in the course "Surgical Dentistry"
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Cardiopulmonary resuscitation in dentistry" and 866 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 28 video lessons on the subject
Other topics in "Chapter 4. Anesthesia in Oral Surgery (S.A. Rabinovich, S.T. Sokhov)"
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.