Drugs included in Local Anaesthetics

Cocaine

The first local anesthetic was introduced by Karl Koller from the leaves of Erythroxylum coca. 1st used for eye surgery and as spinal anesthesia. It is a potent vasoconstrictor and should never be administered intravenously.

Chloroprocaine or Procaine

These are short-acting local anesthetics. Chloroprocaine is the shortest-acting local anesthetic. Procaine: the safest local anesthetic in malignant hyperthermia. Used in high dose + High concentration

Lignocaine

Other names: Lidocaine, xylocaine

Category: Belongs to the aminoamide group

Facts: The most commonly used local anesthetic worldwide. The most commonly used local anesthetic in intravenous regional anesthesia. The most common local anesthetic to cause malignant hyperthermia

Dose and Duration

Plain Lignocaine: 4.5 mg/kg acting for 45 minutes to 1 hour

Lignocaine + Adrenaline: 7 mg/kg acting for 2 hours

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Toxicity

1st sign of lignocaine toxicity: CNS manifestations

• Lignocaine toxicity 
• Perioral numbness
• Tremors
• Seizures
• Decreased SpO2
• Respiratory arrest
• Cardiac arrest

Treatment of lignocaine toxicity

• Antiepileptic medication: Midazolam, diazepam
• Intubate and ventilate the patient
• Intralipid 20% solution

Addition of lignocaine + Adrenaline

Concentration: 1:2,00,000

Concentration of lignocaine in various anesthesia techniques

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Bupivacaine

Category

Belongs to aminoamides group

Most commonly used local anesthetic in spinal anesthesia

Duration

Longer (2-3 hrs)

Dose

Plain Bupivacaine: 2-2.5 mg/kg

Bupivacaine + Adrenaline: 3 mg/kg

Longest to shortest acting local anesthetics

Dibucaine (Longest) > Tetracaine > Bupivacaine > Lignocaine > Procaine > Chloroprocaine

(Shortest). Dibucaine, Tetracaine: Most toxic local anesthetics

Route of administration

Not given in IV route

Also read: Local Anesthesia: Types, Administration Methods

Bupivacaine toxicity

Since bupivacaine is the most cardiotoxic drug, it should never be administered intravenously.

but the drug is safe in CSF. Administration of bupivacaine should be stopped if blood in the CSF is noticed; this can lead to increased BP, sudden fluctuations in heart rate, and arrhythmia on the ECG, leading to sudden cardiac arrest.

Treatment of Bupivacaine toxicity

CPR is started in cardiac arrest. If no cardiac arrest but arrhythmia is present. Antiarrhythmic drugs (bretylium, amiodarone, procainamide): 20% intralipid solution: 1.5 ml/kg bolus followed by 0.5 ml/kg infusion

Ropivacaine

Belongs to the aminoamide group. It is the antiomer of bupropion. Structurally similar to bupivacaine. Has less potency and cardiotoxicity. The potency of local anesthetics is determined by lipid solubility. More the lipid solubility, higher the potency

Dibucaine

Belongs to the aminoamide group. The most potent and most toxic local anesthetic. Has the longest duration of action. Only used for dibucaine number test

Also read: Inhalational Anesthetic Agents: Types use and Complications- Anesthesia

Clinical Scenario

A 30-year-old male posted for tonsillectomy under general anesthesia was given scoline and after surgery, in the reversal phase of anesthesia, the patient did not recover on time.

Explanation

• Case of delayed recovery
• Scoline: Muscle relaxant
• Action: 3-8 mins during metabolism by plasma pseudocholinesterase
• Patient with pseudocholinesterase deficiency: Prolong action of scoline
• Duration: 4 hrs. Dibucaine number test: Detects atypical pseudocholinesterase or pseudocholinesterase deficiency

Drugs metabolized by pseudocholinesterase

• Scoline
• Aminoesters
• Mivacurium

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Important MCQS 

Q. An 88-year-old male patient was admitted with a Colles fracture underlined comorbidities including HTN, CAD, COPD, and EF 25%. Which anesthesia is recommended?

1. Local anesthesia
2. Spinal anesthesia
3. Epidural
4. Nerve block
5. General anesthesia

Ans. Nerve block

Explanation :

Nerve block: Brachial plexus block

Complication: Pneumothorax: As we cannot afford to have this complication of pneumothorax, hence we proceed towards IVRA.

Q. Which drug can be administered to a 45-year-old male with alcoholic liver disease, undergoing open reduction and internal fixation, under a brachial plexus block using local anesthetics, without requiring dose adjustment?

Ans. Amino esters are recommended. Amino acids are not recommended as they are metabolized in the liver

Q. A 24-year-old boy presents to the surgical outdoor patient department with a complaint of swelling on his forehead, which is about 2 x 5 cm in size. On examination, it was a sebaceous cyst. The patient wants to remove that for which he was admitted, and the patient is told that it will be removed under local anesthesia. Alkalization of local anesthetic solutions by the addition of sodium bicarbonate has what benefit?

Ans. Sodium bicarbonate is added as an additive as it increases the speed of onset

Q. A 45-year-old patient is scheduled for hand surgery, and the anesthesia team is considering the use of intravenous regional anesthesia. In this case, which specific local anesthetic is deemed suitable for administration through the intravenous route to achieve regional anesthesia for the surgical procedure?

1. Bupivacaine
2. Lidocaine
3. Ropivacaine
4. Tetracaine

Ans. Lidocaine

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