Local Anesthetics Practice Questions

Q: What is the maximum safe dose of bupivacaine?

2 mg/kg. **Explanation:** The maximum safe dose of **Bupivacaine** is **2 mg/kg** (without epinephrine). Bupivacaine is an amino-amide local anesthetic known for its high potency and long duration of action. However, it is significantly more **cardiotoxic** than lidocaine because it dissociates slowly from cardiac sodium channels during diastole (the "fast-in, slow-out" kinetics) [1]. Exceeding the 2 mg/kg threshold increases the risk of Local Anesthetic Systemic Toxicity (LAST), which can lead to refractory ventricular arrhythmias and cardiac arrest [1]. **Analysis of Options:** * **A (1 mg/kg):** This is an underestimation. While conservative, it is not the standard maximum dose defined in clinical guidelines. * **B (2 mg/kg):** **Correct.** This is the standard maximum recommended dose for plain bupivacaine. When combined with epinephrine, some texts suggest a slight increase (up to 2.5 mg/kg), but 2 mg/kg remains the high-yield "safe" limit for exams. * **C (3 mg/kg):** This is the maximum dose for **Ropivacaine**, which is a S-enantiomer of bupivacaine designed to be less cardiotoxic. * **D (5 mg/kg):** This is the maximum dose for **Lidocaine** (plain). If lidocaine is used with adrenaline, the limit increases to 7 mg/kg. **High-Yield Clinical Pearls for NEET-PG:** * **Cardiotoxicity:** Bupivacaine has a low **CC/CNS ratio** (3.0), meaning the dose required to cause cardiovascular collapse is very close to the dose that causes seizures [1]. * **Antidote:** In case of bupivacaine-induced cardiac arrest, **20% Intravenous Lipid Emulsion (ILE)** is the specific treatment of choice (the "Lipid Sink" theory). * **Levobupivacaine:** The S-isomer of bupivacaine is preferred in modern practice as it is less cardiotoxic and neurotoxic.

Q: What is the concentration of epinephrine typically added to local anesthetic solutions?

1:200,000. **Explanation:** The addition of epinephrine (adrenaline) to local anesthetics (LA) serves as a **chemical tourniquet**. By inducing localized vasoconstriction, it decreases the rate of systemic absorption, which achieves three primary goals: prolonging the duration of action, decreasing systemic toxicity, and providing a bloodless surgical field. **Why 1:200,000 is Correct:** The standard clinical concentration for infiltration and regional blocks is **1:200,000** (equivalent to **5 mcg/mL**). This concentration provides an optimal balance between effective local vasoconstriction and minimal systemic side effects (such as tachycardia or hypertension). **Analysis of Incorrect Options:** * **1:10,000:** This is a highly concentrated solution used primarily in **cardiac arrest** (ACLS protocols). Using this with LA would cause severe tissue ischemia, necrosis, and significant systemic sympathomimetic toxicity. * **Options A & D:** These numerical values (0.736 and 1.430) are clinically irrelevant and do not represent standard pharmacological ratios or concentrations used in anesthesiology. **High-Yield NEET-PG Pearls:** * **Maximum Doses:** The addition of epinephrine increases the safe maximum dose of Lidocaine from **5 mg/kg to 7 mg/kg** and Bupivacaine from **2 mg/kg to 2.5–3 mg/kg**. * **Contraindications:** Avoid epinephrine-containing solutions in areas supplied by **end-arteries** (e.g., fingers, toes, nose, ears, and penis) due to the risk of gangrene. * **Calculation Tip:** To convert a ratio to mcg/mL, divide 1,000,000 by the ratio (e.g., 1,000,000 / 200,000 = 5 mcg/mL).

Q: Which of the following local anesthetics is the shortest acting, aiding in obstetric anesthesia?

Chloroprocaine. **Explanation:** **Chloroprocaine** is an amino-ester local anesthetic known for having the **shortest duration of action** (approximately 30–60 minutes) and the fastest onset among the options provided. **Why it is the correct answer:** The rapid metabolism of Chloroprocaine is due to its hydrolysis by **plasma cholinesterase**. In obstetric anesthesia, it is highly favored for emergency Cesarean sections or when a rapid block is required because: 1. **Low Systemic Toxicity:** Its rapid breakdown results in an extremely short plasma half-life (approx. 20–25 seconds). 2. **Minimal Fetal Transfer:** Because it is metabolized so quickly in the maternal circulation, very little drug reaches the fetus, minimizing the risk of neonatal depression. **Analysis of Incorrect Options:** * **A. Tetracaine:** An ester anesthetic, but it is **long-acting** with a slow onset. It is primarily used for spinal anesthesia, not for rapid-onset obstetric blocks. * **B. Bupivacaine:** An amide anesthetic that is **long-acting**. While it is the "gold standard" for labor analgesia due to its sensory-motor dissociation, it has a slow onset and carries a higher risk of cardiotoxicity. * **C. Prilocaine:** An intermediate-acting amide. It is rarely used in obstetrics due to the risk of causing **methemoglobinemia**, which can compromise fetal oxygenation. **High-Yield Clinical Pearls for NEET-PG:** * **Metabolism:** Esters (like Chloroprocaine) are metabolized by plasma pseudocholinesterase; Amides (like Bupivacaine) are metabolized by liver microsomal enzymes. * **Epidural Top-up:** Chloroprocaine is the drug of choice for converting a labor epidural to surgical anesthesia for an **Emergency C-section** due to its rapid onset. * **Toxicity:** It has the highest safety margin regarding Systemic Local Anesthetic Toxicity (LAST).

Q: What is the safety profile of EMLA cream in newborns?

Safe. **Explanation:** **EMLA (Eutectic Mixture of Local Anesthetics)** is a 1:1 oil-in-water emulsion of **2.5% Lidocaine and 2.5% Prilocaine**. 1. **Why it is Safe (Correct Answer):** Extensive clinical studies have established that EMLA is **safe** for use in full-term newborns (gestational age >37 weeks) for minor procedures like venipuncture, lumbar puncture, or circumcision. While there is a theoretical risk of methemoglobinemia due to the prilocaine component, when used at recommended doses and application times, it does not cause clinically significant elevation of methemoglobin levels. 2. **Analysis of Incorrect Options:** * **Contraindicated:** It is not contraindicated in newborns; it is widely used in neonatal intensive care units (NICUs). * **Does not cause methemoglobinemia:** This is technically incorrect. Prilocaine is metabolized into **o-toluidine**, which can oxidize hemoglobin to methemoglobin. While safe at low doses, the *potential* to cause methemoglobinemia exists, especially if used with other oxidizing agents. * **Should be given in reduced doses:** While dosage must be strictly monitored (max 1g over 10cm² for 1 hour), "Safe" is the more definitive clinical profile recognized in standard textbooks like Miller’s Anesthesia. **High-Yield Clinical Pearls for NEET-PG:** * **Composition:** 2.5% Lidocaine + 2.5% Prilocaine. The melting point of the mixture is lower than the individual components (Eutectic property), allowing it to exist as an oil at room temperature, enhancing skin penetration. * **Application Time:** Requires **45–60 minutes** under an occlusive dressing to achieve effective analgesia (depth of 3–5 mm). * **Caution:** Use with caution in infants <3 months or those taking methemoglobin-inducing drugs (e.g., sulfonamides, phenytoin, phenobarbital). * **Contraindication:** Do not apply to broken skin, mucous membranes, or near the eyes/ears (ototoxicity risk).

Q: What is the amount of vasoconstrictor in 1 ml of 2% Lignocaine solution with 1:200,000 adrenaline?

0.005 mg. ### Explanation **1. Understanding the Calculation (Why C is correct):** The concentration of a drug expressed as a ratio (e.g., 1:200,000) represents the weight of the drug in grams per volume in milliliters. * **1:200,000** means **1 gram** of Adrenaline is present in **200,000 ml** of solution. * To find the amount in 1 ml, we convert grams to milligrams: 1 gram = 1,000 mg. * Calculation: $1,000 \text{ mg} / 200,000 \text{ ml} = 1 / 200 \text{ mg/ml}$. * $1 \div 200 = \mathbf{0.005 \text{ mg/ml}}$ (or 5 micrograms/ml). **2. Analysis of Incorrect Options:** * **Option A (0.5 mg):** This would correspond to a 1:2,000 concentration, which is highly toxic and never used clinically for infiltration. * **Option B (0.05 mg):** This corresponds to a 1:20,000 concentration. While used in dental cartridges or for topical application, it is 10 times stronger than the standard 1:200,000 used in regional anesthesia. * **Option D (0.0005 mg):** This corresponds to a 1:2,000,000 concentration, which is too dilute to provide effective clinical vasoconstriction. **3. Clinical Pearls & High-Yield Facts:** * **Purpose of Adrenaline:** It causes vasoconstriction, which decreases systemic absorption (reducing toxicity), increases the duration of action, and provides a bloodless surgical field. * **Lignocaine Concentration:** A 2% solution means 2g/100ml, which equals **20 mg/ml**. * **Maximum Doses:** * Lignocaine (Plain): **3 mg/kg** * Lignocaine (with Adrenaline): **7 mg/kg** * **Contraindications:** Avoid adrenaline-containing local anesthetics in "end-artery" areas (fingers, toes, nose, penis, and ear lobes) to prevent ischemic necrosis. * **Standard Ratio:** 1:200,000 is the most common commercial preparation for major nerve blocks and infiltration.

Q: All of the following procedures can be performed using EMLA cream except?

Intubation. **Explanation:** **EMLA (Eutectic Mixture of Local Anesthetics)** is a 1:1 oil-in-water emulsion of **2.5% Lidocaine and 2.5% Prilocaine**. Its primary purpose is to provide topical anesthesia to **intact skin** by penetrating the keratinized layer, which standard local anesthetics cannot do. **Why Intubation is the Correct Answer:** Intubation requires anesthesia of the **mucous membranes** of the airway (oropharynx, larynx, and trachea). EMLA is specifically designed for **intact skin** and requires a significant application time (60 minutes) under an occlusive dressing to be effective. For intubation, rapid-acting topical sprays (like 10% Lidocaine spray) or nerve blocks are used. Furthermore, EMLA is not recommended for use on mucous membranes due to faster systemic absorption and potential toxicity. **Analysis of Other Options:** * **Split thickness skin graft (STSG) harvesting:** EMLA applied under occlusion for 2–5 hours provides sufficient depth of anesthesia for harvesting thin skin grafts. * **Laser removal of port-wine stain:** This is a common pediatric and cosmetic indication where EMLA prevents the pain of laser pulses on the skin. * **Lithotripsy:** EMLA is frequently used to provide cutaneous anesthesia at the site where Extracorporeal Shock Wave Lithotripsy (ESWL) probes contact the skin, reducing the need for systemic analgesics. **High-Yield Clinical Pearls for NEET-PG:** * **Composition:** 2.5% Lidocaine + 2.5% Prilocaine. The melting point of the mixture is lower than either drug alone (18°C), allowing it to exist as an oil at room temperature. * **Application Time:** Minimum 60 minutes for superficial procedures; 2 hours for deeper procedures (e.g., STSG). * **Contraindication:** Should not be used in infants <1 month or those with **Methemoglobinemia**, as the Prilocaine metabolite (o-toluidine) can worsen the condition. * **Depth:** Penetrates approximately 3–5 mm into the dermis.

Question 1

Following a nerve block, what is the typical sequence of recovery of sensation?

Accepted Answer

Skeletal Muscle Tone (SMT) > Proprioception > Touch > Temperature > Pain

Answer

Pain > Temperature > Touch > Proprioception > Skeletal Muscle Tone (SMT)

Answer

Skeletal Muscle Tone (SMT) > Proprioception > Temperature > Touch > Pain

Answer

Recovery sequence is random.

Question 2

What is the maximum safe dose of bupivacaine?

Accepted Answer

2 mg/kg

Answer

1 mg/kg

Answer

3 mg/kg

Answer

5 mg/kg

Question 3

Which of the following topical anesthetics is primarily used to anesthetize mucosa?

Accepted Answer

Bupivacaine

Answer

Benzocaine

Answer

Lidocaine

Answer

Tetracaine

Question 4

What is the earliest sign of systemic absorption of local anesthetic?

Accepted Answer

Circumoral numbness

Answer

Convulsions

Answer

Circulatory collapse

Answer

Respiratory arrest

Question 5

Cartridges should not be permitted to soak in alcohol because it:

Accepted Answer

Diffuses through rubber cap causing contamination

Answer

Destroys vasoconstrictor

Answer

Is less effective

Answer

Is warm in sensation

Question 6

What is the concentration of epinephrine typically added to local anesthetic solutions?

Accepted Answer

1:200,000

Answer

0.736111111

Answer

1:10,000

Answer

1.430555556

Question 7

Which of the following local anesthetics is the shortest acting, aiding in obstetric anesthesia?

Accepted Answer

Chloroprocaine

Answer

Tetracaine

Answer

Bupivacaine

Answer

Prilocaine

Question 8

What is the safety profile of EMLA cream in newborns?

Accepted Answer

Safe

Answer

Contraindicated

Answer

Does not cause methemoglobinemia

Answer

Should be given in reduced doses

Question 9

What is the amount of vasoconstrictor in 1 ml of 2% Lignocaine solution with 1:200,000 adrenaline?

Accepted Answer

0.005 mg

Answer

0.5 mg

Answer

0.05 mg

Answer

0.0005 mg

Question 10

All of the following procedures can be performed using EMLA cream except?

Accepted Answer

Intubation

Answer

Split thickness skin graft harvesting

Answer

Laser removal of port-wine stain

Answer

Lithotripsy

Local Anesthetics — MCQs

Local Anesthetics — MCQs

On this page

Practice by Chapter

Want unlimited practice?