Local Anesthetics Practice Questions

Q: Which drug is used to prolong the action of local anesthetics in hypertensive patients?

Felypressin. **Explanation:** Local anesthetics (LAs) are often combined with vasoconstrictors to decrease systemic absorption, reduce toxicity, and prolong the duration of action. **Why Felypressin is the correct answer:** Felypressin is a synthetic analogue of **Vasopressin (ADH)** that acts primarily on **V1 receptors** in the vascular smooth muscle. Unlike Adrenaline or Noradrenaline, it has minimal effects on the heart rate and blood pressure, making it the **vasoconstrictor of choice for hypertensive patients** and those with ischemic heart disease. It is commonly used in dental anesthesia (e.g., with Prilocaine). **Analysis of Incorrect Options:** * **Clonidine & Dexmedetomidine:** These are $\alpha_2$-agonists used as adjuvants to prolong the duration of spinal and peripheral nerve blocks. However, they are not primarily classified as "vasoconstrictors" used to prevent systemic absorption in the same context as Felypressin. Furthermore, they can cause hypotension and bradycardia, which are different hemodynamic considerations. * **Noradrenaline:** This is a potent $\alpha$ and $\beta_1$ agonist. It causes significant peripheral vasoconstriction and can lead to a dangerous rise in blood pressure, making it **contraindicated** in hypertensive patients. **High-Yield Clinical Pearls for NEET-PG:** * **Adrenaline (1:200,000)** is the most common vasoconstrictor used with LAs but should be avoided in patients with uncontrolled hypertension, hyperthyroidism, or in "end-artery" areas (fingers, toes, penis, nose) to prevent gangrene. * **Felypressin** is contraindicated in **pregnancy** as it has oxytocic properties and may cause uterine contractions. * **Maximum Dose of Lignocaine:** 3 mg/kg (plain) and 7 mg/kg (with Adrenaline).

Q: Which of the following statements about Bupivacaine is false?

It produces methaemoglobinemia.. ### Explanation **Correct Answer: D. It produces methaemoglobinemia.** **Why Option D is False:** Methemoglobinemia is a classic side effect associated with **Prilocaine** and **Benzocaine**, not Bupivacaine. Prilocaine is metabolized into *o-toluidine*, which oxidizes hemoglobin to methemoglobin, reducing the oxygen-carrying capacity of the blood. Bupivacaine does not have this metabolic pathway. **Analysis of Other Options:** * **Option A (True):** Bupivacaine must never be injected intravenously. Accidental IV injection can lead to severe **Local Anesthetic Systemic Toxicity (LAST)**, characterized by refractory arrhythmias and seizures. It is specifically contraindicated for Intravenous Regional Anesthesia (Bier’s Block). * **Option B (True):** Bupivacaine is significantly more cardiotoxic than Lignocaine. It has a high affinity for voltage-gated sodium channels in the myocardium and dissociates slowly during diastole ("fast-in, slow-out" kinetics), making resuscitation extremely difficult. * **Option C (True):** Bupivacaine exhibits **sensory-motor dissociation**. At a concentration of 0.5%, it provides an excellent sensory block, while lower concentrations (e.g., 0.125%) are often used for "walking epidurals" in labor analgesia to spare motor function. **High-Yield Clinical Pearls for NEET-PG:** * **Antidote for Toxicity:** Intravenous **Lipid Emulsion (20% Intralipid)** is the specific treatment for Bupivacaine-induced cardiotoxicity (the "Lipid Sink" theory). * **Levobupivacaine & Ropivacaine:** These are S-enantiomers developed to provide similar potency to Bupivacaine but with a **reduced risk of cardiotoxicity**. * **Maximum Dose:** The maximum dose of Bupivacaine is **2 mg/kg**. * **Potency:** Bupivacaine is roughly 4 times more potent than Lignocaine but has a slower onset and longer duration of action.

Q: Local anesthesia with adrenaline is absolutely contraindicated in which of the following conditions?

Hyperthyroidism. **Explanation:** The correct answer is **Hyperthyroidism**. **1. Why Hyperthyroidism?** Adrenaline (Epinephrine) is a potent sympathomimetic amine. In patients with hyperthyroidism, there is an increased expression of beta-adrenergic receptors and heightened sensitivity to catecholamines. Administering exogenous adrenaline can trigger a **Thyroid Storm** or severe cardiovascular complications, including malignant arrhythmias, extreme tachycardia, and acute heart failure. Therefore, it is considered an absolute contraindication. **2. Analysis of Incorrect Options:** * **First trimester of pregnancy:** While caution is advised due to potential uterine artery vasoconstriction (reducing placental blood flow), it is a **relative contraindication**, not absolute. Lignocaine is generally considered safe (FDA Category B). * **Hemophilia:** Adrenaline is actually beneficial here as its vasoconstrictive property helps in local hemostasis. The contraindication in hemophilia usually applies to the *route* of administration (avoiding deep nerve blocks/IM injections to prevent hematomas), not the adrenaline itself. * **Hypertension:** This is a **relative contraindication**. In controlled hypertension, low doses of adrenaline (1:200,000) are used cautiously. It is only avoided in severe, uncontrolled hypertension. **3. High-Yield Clinical Pearls for NEET-PG:** * **Absolute Contraindications for Adrenaline in LA:** Hyperthyroidism, Pheochromocytoma, Severe Hypertension, and use in "end-artery" areas (fingers, toes, tip of nose, ear lobules, and penis) due to the risk of gangrene. * **Max Dose of Lignocaine:** 4 mg/kg (plain) and 7 mg/kg (with adrenaline). * **Standard Concentration:** Adrenaline is typically added to local anesthetics in a concentration of **1:200,000**. * **Benefits of Adrenaline:** Increases duration of action, decreases systemic toxicity (by slowing absorption), and provides a bloodless surgical field.

Q: Which of the following is an ester-linked local anesthetic?

Cocaine. **Explanation:** Local anesthetics (LAs) are chemically classified into two categories based on the linkage between their aromatic and amine groups: **Esters** and **Amides**. **1. Why Cocaine is Correct:** Cocaine is a naturally occurring **ester-linked** local anesthetic. Esters are metabolized by plasma pseudocholinesterase and generally have a shorter duration of action (except for tetracaine). Cocaine is unique among LAs because it is the only one that possesses intrinsic vasoconstrictive properties by inhibiting the reuptake of norepinephrine. **2. Why the Other Options are Incorrect:** * **Lidocaine, Bupivacaine, and Dibucaine** are all **amide-linked** local anesthetics. Amides are metabolized primarily in the liver by cytochrome P450 enzymes and are generally more stable with a longer half-life than esters. **3. High-Yield NEET-PG Clinical Pearls:** * **The "i" Rule:** A simple mnemonic to differentiate the two is that all **Amides** have two "i"s in their name (L**i**doca**i**ne, Bup**i**vaca**i**ne, D**i**buca**i**ne, Pr**i**loca**i**ne, Rop**i**vaca**i**ne), whereas **Esters** have only one "i" (Cocaine, Procaine, Benzocaine, Tetracaine). * **Allergy:** Hypersensitivity reactions are more common with esters due to the production of **Para-aminobenzoic acid (PABA)** during metabolism. True allergy to amides is extremely rare. * **Dibucaine:** It is the most potent and toxic long-acting amide. The "Dibucaine number" is clinically used to detect atypical pseudocholinesterase deficiency. * **Bupivacaine:** Notable for its significant cardiotoxicity (S-enantiomer, Levobupivacaine, is less toxic).

Q: A solution contains 2% lignocaine with 1:100,000 epinephrine. If the total volume of the solution is 3 ml, how many milligrams of lignocaine and epinephrine are present?

60 mg lidocaine, 0.03 mg epinephrine. ### Explanation To solve this calculation, you must understand how drug concentrations are expressed in percentages and ratios. **1. Calculating Lignocaine (Percentage):** A percentage concentration represents grams per 100 ml. * **2% Lignocaine** = 2 g in 100 ml. * To convert to mg/ml: (2 × 1000 mg) / 100 ml = **20 mg/ml**. * For a **3 ml** volume: 20 mg/ml × 3 ml = **60 mg**. **2. Calculating Epinephrine (Ratio):** A ratio represents grams per milliliters. * **1:100,000** = 1 g in 100,000 ml. * To convert to mg/ml: (1 × 1000 mg) / 100,000 ml = 0.01 mg/ml (or 10 mcg/ml). * For a **3 ml** volume: 0.01 mg/ml × 3 ml = **0.03 mg** (or 30 mcg). Therefore, the solution contains **60 mg of Lignocaine and 0.03 mg of Epinephrine.** --- ### Analysis of Incorrect Options * **Option A:** Incorrectly calculates Lignocaine as 2 mg/ml and overestimates Epinephrine by a factor of 10. * **Option C:** Correctly calculates Epinephrine but underestimates Lignocaine (likely by confusing 2% with 2 mg total). * **Option D:** Overestimates Lignocaine by a factor of 10 and Epinephrine by a factor of 10. --- ### High-Yield Clinical Pearls for NEET-PG * **Shortcut Rule:** To find mg/ml from a percentage, simply multiply the percentage by 10 (e.g., 0.5% Bupivacaine = 5 mg/ml). * **Max Doses of Lignocaine:** * Plain Lignocaine: **3–4 mg/kg** * Lignocaine with Epinephrine: **7 mg/kg** * **Role of Epinephrine:** It acts as a vasoconstrictor, which decreases systemic absorption (reducing toxicity), prolongs the duration of action, and provides a relatively bloodless field. * **Contraindication:** Avoid epinephrine-containing LAs in "end-artery" areas (fingers, toes, penis, nose, ear lobes) to prevent ischemic necrosis.

Q: The addition of hyaluronidase to a local anesthetic solution might what?

Enhance diffusion of local anesthetic. **Explanation:** Hyaluronidase is an enzyme that hydrolyzes **hyaluronic acid**, a major constituent of the interstitial barrier in the connective tissue matrix. By breaking down this "intercellular cement," hyaluronidase significantly decreases the viscosity of the extracellular matrix. **Why Option D is Correct:** The primary purpose of adding hyaluronidase (typically 15 units/mL) to local anesthetics is to **enhance the diffusion** and spread of the drug through tissue planes. This leads to a faster onset of action and a more extensive block. It is most commonly used in ophthalmic blocks (e.g., peribulbar or retrobulbar blocks) to ensure the anesthetic reaches the nerves behind the globe effectively. **Why Other Options are Incorrect:** * **A & B:** Because hyaluronidase increases the spread and absorption of the drug into the systemic circulation, it actually **decreases the duration** of anesthesia and **increases the area** of the block (rather than limiting it). * **C:** Hyaluronidase does not have vasoconstrictive properties; therefore, it does not reduce bleeding. In fact, by increasing drug absorption, it may slightly increase local blood flow. Vasoconstrictors like **epinephrine** are used to reduce bleeding and prolong duration. **High-Yield NEET-PG Pearls:** * **Ophthalmic Anesthesia:** Hyaluronidase is the "spreading factor" of choice in peribulbar blocks to improve the quality of akinesia. * **Systemic Toxicity:** A major disadvantage is that increased diffusion leads to faster systemic absorption, potentially increasing the risk of **Local Anesthetic Systemic Toxicity (LAST)**. * **Allergy:** It is a protein enzyme; hence, it can occasionally cause hypersensitivity reactions.

Question 1

Which drug is used to prolong the action of local anesthetics in hypertensive patients?

Accepted Answer

Felypressin

Answer

Clonidine

Answer

Dexmedetomidine

Answer

Noradrenaline

Question 2

Local anesthetic is not effective in inflamed tissue because:

Accepted Answer

The pH is more acidic, rendering the local anesthetic ineffective

Answer

All impulses generated cannot be blocked

Answer

The myelin sheath is inflamed and does not absorb the solution

Answer

All of the above

Question 3

Which of the following statements about Bupivacaine is false?

Accepted Answer

It produces methaemoglobinemia.

Answer

It must never be injected into a vein.

Answer

It is more cardiotoxic than lignocaine.

Answer

0.5 percent is effective for sensory block.

Question 4

Alpha adrenergic agonists are used in combination with local anesthetics to:

Accepted Answer

Increase the concentration of local anesthetic at the receptor site.

Answer

Increase the rate of liver metabolism of local anesthetic.

Answer

Stimulate myocardial contraction.

Answer

Increase vascular absorption of local anesthetic.

Question 5

Local anesthesia with adrenaline is absolutely contraindicated in which of the following conditions?

Accepted Answer

Hyperthyroidism

Answer

First trimester of pregnancy

Answer

Hemophilia

Answer

Hypertension

Question 6

Which of the following is an ester-linked local anesthetic?

Accepted Answer

Cocaine

Answer

Lidocaine

Answer

Bupivacaine

Answer

Dubicaine

Question 7

Why is the dose of local anesthetics for peripheral nerve block decreased in patients with hypovolemic shock?

Accepted Answer

Preferential perfusion of vital organs in shock increases susceptibility to local anesthetic toxicity.

Answer

The drugs cannot be metabolized.

Answer

The sensitivity of voltage-gated channels increases in shock.

Answer

The drug is not systemically absorbed, thus requiring less.

Question 8

A solution contains 2% lignocaine with 1:100,000 epinephrine. If the total volume of the solution is 3 ml, how many milligrams of lignocaine and epinephrine are present?

Accepted Answer

60 mg lidocaine, 0.03 mg epinephrine

Answer

6 mg lidocaine, 0.3 mg epinephrine

Answer

6 mg lidocaine, 0.03 mg epinephrine

Answer

600 mg lidocaine, 0.3 mg epinephrine

Question 9

If a patient starts getting convulsions following the use of Lignocaine as a local anesthetic, what is the drug of choice for the control of these convulsions?

Accepted Answer

Diazepam

Answer

Chlorpromazine

Answer

Scoline

Answer

Any

Question 10

The addition of hyaluronidase to a local anesthetic solution might what?

Accepted Answer

Enhance diffusion of local anesthetic

Answer

Increase the duration of anesthesia

Answer

Limit the area of anesthesia

Answer

Reduce bleeding

Local Anesthetics — MCQs

Local Anesthetics — MCQs

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