LOCAL ANESTHETICS AND BLOCKS (MCQS)

By-Jini Abraham

Q1. Local anesthesia acts byA. Sodium channel inhibitionB. Calcium channel inhibitionC. Magnesium channel inhibitionD. Potassium channel inhibition

Answer – A. Sodium channel inhibition

Local anesthesia blocks the sodium channel from inside the cell membrane and raises the threshold of the channel opening

LA decreases the rate of depolarization in response to excitation, preventing the achievement of the threshold potential.

Q2. Afferent nerve fibre affected by local anesthesia firstA. Type AB. Type II – BC. Type CD. Type II

Answer – C. Type C

Smaller diameter fibres and non myelinated fibres are blocked more easily and at low concentration, than thicker myelinated fibres.

Larger diameter correlates with more rapid nerve conduction.

Sequence of block – Autonomic preganglionic sympathetic (1st) sensory (in order of pain, temperature, touch and pressure) motor

Q3. Shortest acting local anesthetic agent isA. ProcaineB. LidocaineC. TetracaineD. Bupivacaine

Answer – A. Procaine

Procaine and chloroprocaine are the shortest acting agents (15 – 30 minutes)

Lidocaine, mepivacaine and prilocaine have slightly longer duration of action (30 – 75 minutes)

Longer acting agents are tetracaine ( 2 – 3 hours), bupivacaine ( 2 – 4 hours) and etidocaine ( 2 – 3 hours).

Q4. Maximum dose of lignocaine with adrenaline isA. 3mg/kgB. 4mg/kgC. 5mg/kgD. 7mg/kg

Answer – D. 7mg/kg

Maximum dose of lignocaine without epinephrine is 4.5mg/kg (upto 300mg), effective for about 30 – 60min.

Maximum dose of lignocaine with epinephrine is 7mg/kg (upto 500mg), effective for about 90min.

Used for infiltration, peripheral block, epidural and spinal anesthesia

Produces local vasoconstriction, which limits systemic absorption of local anesthetic and prolongs the duration of action while having little effect on the onset of anesthesia.

Q5. Lignocaine in high dose produces all exceptA. ConvulsionB. Respiratory depressionC. HypotensionD. Cardiac arrestE. Hypothermia

Answer – E. Hypothermia

CVS – Bradycardia, arrythmia, hypotension and cardiac failure

CNS – Depression, restlessness, vertigo, tremor, convulsion

RS – Depress hypoxic drive, apnoea Allergic reaction – Bronchospasm, urticaria and

angioedema

Q6. Local anesthesia causing meth haemoglobinemiaA. ProcaineB. PrilocaineC. BupivacaineD. Cocaine

Answer – B. Prilocaine

Prilocaine undergoes rapid metabolism and low acute toxicity.

Administration of high doses (>600mg) may result in clinically significant accumulation of metabolite, ortho-toludine, an oxidizing compound capable of converting hemoglobin to methemoglobin.

This effect can be reversed by administration of methylene blue ( 1 to 2 mg/kg IV over 5 minutes)

Q7. Cardiac or central nervous system toxicity may result when standard lidocaine doses are administered to patients with circulatory failure. This may be due to the following reason:

A. Lidocaine concentration are initially higher in relatively well perfused tissues such as brain and heart

B. Histamine receptors in brain and heart gets suddenly activated in circulatory failure

C. There is a sudden out-burst of release of adrenaline, noradrenaline and dopamine in brain and heart

D. Lidocaine is converted into a toxic metabolite due to its longer stay in liver

Answer – A. Lidocaine concentration are initially higher in relatively well perfused tissues such as brain and heart

The highly perfused organs (such as brain, lung, liver, kidney) are reponsible for initial rapid uptake which is followed by slower redistribution to moderately perfused tissues (muscle and gut)

Decreased hepatic function or blood flow Reduce metabolic rate Systemic toxicity

Q8. Anesthetic agent with vasoconstrictor is contraindicated in?A. Finger blockB. Spinal blockC. Epidural blockD. Regional anesthesia

Answer – A. Finger block

Epinephrine should be avoided when performing peripheral nerve blocks in areas that may lack collateral flow (e.g., digital blocks).

Absolutely contraindicated for injection close to end arteries (ring blocks of fingers and toe digits, pinna and penis).

Q9. Bier’s block isA. Subarachnoid blockB. Infiltration and surface blockC. Intravenous blockD. Peripheral nerve and nerve root block

Answer – C. Intravenous block

Intravenous regional neural anesthesia (Bier block) is a method of producing anesthesia of the arm or leg.

It involves intravenous injection of large volumes of dilute local anesthetic solutions into an extremity after occlusion of the circulation by a tourniquet.

Q10. Which anesthetic modality is to be avoided in sickle cell disease?A. General anesthesiaB. Brachial plexus blockC. IV regional anesthesiaD. Spinal anesthesia

Answer – C. IV regional anesthesia

IVRA is contraindicated in situations in which tourniquets are contraindicated e.g., sickle cell disease, Raynaud’s disease and scleroderma.

During tourniquet application in IVRA, blood flow slows down and can precipitate acute hemolytic crisis in patients with sickle cell disease.

Q11. Pneumothorax is a complication of A. Axillary blockB. Brachial plexus blockC. Epidural blockD. High spinal block

Answer – B. Brachial plexus block

Brachial plexus block can be anesthetized along 4 anatomic locations – interscalene, supraclavicular, infraclavicular and axillary.

Common complication of supraclavicular block is pneumothorax, because of the close proximity of the lung to the brachial plexus at the level of the clavicle. Other complications are subclavian artery puncture, spread of local anesthetic to cause paresis of stellate ganglion, phrenic nerve and recurrent laryngeal nerve.

Q12. Pudendal nerve block involveA. L1L2L3B. L2L3L4C. S1S2S3D. S2S3S4

Answer – D. S2S3S4

Pudendal nerve block commonly used in the practice of obstetrics to relieve pain during the delivery of baby by forceps.

Anesthesia is produced by blocking the pudendal nerves near the ischial spine of the pelvis.

Q13. Most common complication of coeliac plexus block: A. PneumothoraxB. Postural hypotensionC. Retroperitoneal haemorrhageD. Intra-arterial injection

Answer – B. Postural hypotension

Most common complication of coeliac plexus block is postural hypotension due to lumbar sympathetic chain blockade leading to upper abdominal vessel dilation and venous pooling.

Intravenous fluids are required preblock to reduce the risk.

Q14. From which of the following routes absorption of local anesthetic is maximum?A. IntercoastalB. EpiduralC. BranchialD. Caudal

Answer – A. Intercoastal

Systemic absorption is directly proportional to blood supply. Local anesthetic is absorbed very rapidly in intercoastal blocks due to close location of blood vessels around the nerve.

Q15. Which one of the following local anesthetic is highly cardiotoxic?A. LignocaineB. ProcaineC. MepivacaineD. Bupivacaine

Answer – D. Bupivacaine

Bupivacaine, like lidocaine, blocks the sodium channels, this block being more slowly reversible.

Disturbance of sodium channels throughout heart decreased conduction speed throughout the conduction system

Bupivacaine, at toxic levels, has direct effect on contractility.

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