Advantages and Indications
The choice in favor of local anesthesia is often due to its clear advantages over general anesthesia (narcosis). The method does not require lengthy and complex preoperative preparation, and in the postoperative period, the patient does not need the same constant and meticulous monitoring as after emerging from general anesthesia. This makes local pain control an ideal choice for outpatient practice.
Furthermore, local anesthesia is indispensable when general anesthesia is contraindicated for a patient. The high-risk group for whom endotracheal anesthesia poses a threat to life (where the risk of anesthesia exceeds the risk of the surgery itself) includes:
- Elderly and senile individuals.
- Emaciated patients.
- Patients with severe respiratory or cardiovascular insufficiency.
Contraindications to the method
Despite its safety, the method has strict limitations. Contraindications include:
- Hypersensitivity and individual intolerance to anesthetics.
- Young age (under 10 years).
- Psychoneurological status: increased nervous excitability and psychiatric disorders.
- Local tissue changes: scars or inflammatory processes in the surgical area that hinder the adequate performance of infiltration anesthesia.
- Ongoing internal hemorrhage requiring emergency surgical intervention to stop it.
Comparative characteristics of local anesthetics
Drugs differ in potency and toxicity level. Traditionally, the efficacy and toxicity of procaine (novocaine) are taken as a conventional unit (1 conventional unit).
| Drug | Efficacy | Toxicity | Infiltration (%) | Epidural (%) |
|---|---|---|---|---|
| Procaine | 1 | 1 | 0,25–0,5 | 1,5–3 |
| Lidocaine | 3 | 1,5 | 0,25–0,5 | 1–2 |
| Mepivacaine | 3 | 2 | 0,25–0,5 | 1–2 |
| Bupivacaine | 15 | 10 | 0,125–0,25 | 0,25–0,75 |
| Tetracaine | 15 | 12 | 0,1–0,15 | 0,2–0,5 |
| Ropivacaine | 15 | 10 | 0,2–0,75 | 0,2–0,75 |
As seen from the table, modern drugs (bupivacaine, ropivacaine) outperform procaine in efficacy by 15 times, but their toxicity also increases proportionally (by 10–12 times).
Patient preparation and premedication
The success of local anesthesia largely depends on preparation.
Psychological preparation includes a conversation during which the essence of the method is explained to the patient: consciousness will be preserved, the patient will feel touches (tactile and deep sensitivity remain), but pain sensations are completely eliminated.
Pharmacological preparation (premedication) is performed before surgery. Standard practice involves injections of trimeperidine (promedol), atropine, and droperidol solutions. Patients with a labile nervous system are additionally prescribed tranquilizers a few days before the intervention.
Potentiation of effect and prevention of complications
The efficacy of anesthesia can be significantly enhanced using neuroleptanalgesia (NLA)—a combination of neuroleptics (droperidol) and narcotic analgesics (fentanyl). NLA not only enhances analgesia but also has a favorable effect on the patient's psycho-emotional status. This is combined with all types of local anesthesia (infiltration, conduction, epidural) and makes it possible to reduce the doses of local anesthetics, thereby decreasing their toxicity.
Complications are most commonly associated with allergic reactions, overdose of the anesthetic itself, or the epinephrine added to it. Particular attention requires the prevention of the toxic effect of procaine during limb surgeries. If the tourniquet is removed too quickly, the drug rapidly enters the systemic circulation. To avoid this, 2 ml of caffeine solution is administered subcutaneously before removing the tourniquet, after which the tourniquet is released very slowly.
Briefly: answers to topical questions
What is the mechanism of action of local anesthetics at the cellular level?
Local anesthetics block sodium channels of the axon, which disrupts the generation and conduction of the nerve impulse. This mechanism is uniform for all drugs in this group.
What are the clinical symptoms of local anesthetic overdose?
In case of procaine overdose, the following intoxication symptoms develop, escalating as the drug concentration increases:
- Dizziness
- Paresthesias
- Motor excitation
- Convulsions (including epileptiform ones)
- Dyspnea
- Collapse
During intraosseous anesthesia, weakness, dizziness, arterial hypotension, nausea, and vomiting are also possible after removing the tourniquet. Skin pallor, sweating, agitation, tachycardia, blood pressure decrease, respiratory disturbances up to apnea, and possible pulmonary edema have also been described.
For what purpose is epinephrine added to the local anesthetic solution?
Epinephrine is added to the local anesthetic solution to constrict blood vessels at the injection site, which reduces the absorption of the anesthetic into the blood and prolongs the local anesthetic effect.
- Reduction of resorptive toxicity — by slowing down absorption
- Prolongation of anesthesia — prolonging the drug's action
- Reduction of bleeding — decreasing capillary bleeding during surgery
Also, gauze pledgets soaked in adrenaline are used for hemostasis.
What is the maximum allowable dose of lidocaine for infiltration anesthesia?
The maximum total dose of lidocaine for injection is 4.4 mg/kg, but not exceeding 300 mg.
For surface anesthesia of mucous membranes, no more than 2 ml of a 10% lidocaine solution (200 mg) is used.
Class and exam questions
Will I feel anything during surgery under local anesthesia?
Yes, you will be conscious and retain tactile and deep sensitivity (sensation of touch and pressure), but the feeling of pain will be completely absent.
Why is neuroleptanalgesia used in combination with local anesthesia?
The combination of neuroleptics and strong analgesics improves the patient's psycho-emotional background, enhances pain relief, and allows the use of lower doses of the local anesthetic, reducing the risk of toxicity.
How to prevent procaine toxic shock after limb surgery?
Before removing the tourniquet, it is necessary to subcutaneously administer 2 ml of caffeine solution, after which the tourniquet should be removed slowly so that the drug does not enter the general circulation too quickly.
What else to study on this topic
- Infiltration anesthesia technique
- Nerve trunk and plexus block anesthesia
- Features of epidural and spinal anesthesia
- Allergic reactions to local anesthetics and emergency response algorithm
- Use of epinephrine in local anesthesia: benefits and overdose risks
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