Regional Anesthesia
Brachial plexus blocks, neuraxial anesthesia, peripheral nerve blocks, complications. ← All topics
Q1. PDPH treatment
A 31-year-old develops a positional frontal-occipital headache 36 hours after an attempted epidural with multiple dural punctures. Conservative measures have failed. The most definitive treatment is:
A. Oral caffeine 300 mg every 6 hours for symptom relief
B. IV cosyntropin 1 mg bolus for ACTH-mediated effect
C. Sumatriptan 6 mg subcutaneously for serotonergic vasoconstriction
D. Epidural blood patch with approximately 20 mL autologous blood
E. Sphenopalatine ganglion block with local anesthetic injection
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Answer: D. Epidural blood patch is the gold standard treatment for post-dural puncture headache with 60–90% efficacy on first attempt, making it the most definitive option when conservative measures fail. The procedure involves injecting approximately 20 mL of autologous blood into the epidural space to seal the dural defect. Risk factors for PDPH include age less than 40, female sex, prior history, use of large-bore cutting needles (Quincke) rather than pencil-point needles (Sprotte, Whitacre), and loss-of-air technique versus saline. While caffeine and cosyntropin may provide temporary symptomatic relief, and sphenopalatine ganglion block is an emerging alternative, epidural blood patch remains the most definitive treatment with the highest success rate for resolving the underlying pathology.
Q2. Interscalene block nerve sparing
After an interscalene brachial plexus block, the patient can still feel his ulnar fingers. The most likely reason is:
A. Failed block due to inadequate volume or incorrect needle placement at the interscalene groove
B. The interscalene approach commonly spares the inferior trunk carrying C8–T1 fibers to ulnar distribution
C. Local anesthetic concentration too dilute to achieve adequate blockade of all brachial plexus trunks
D. Anatomic variant with aberrant ulnar nerve course outside the typical interscalene brachial plexus anatomy
E. Patient hyperalgesia causing perception of sensation despite technically adequate blockade of all nerve roots
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Answer: B. The interscalene approach reliably blocks the upper trunk and middle trunk of the brachial plexus (C5–C7) but commonly spares the inferior trunk (C8–T1), which provides ulnar distribution to the fourth and fifth fingers. This is an expected anatomic limitation, not a technical failure. The interscalene block is best suited for shoulder surgery and should not be chosen for hand surgery. Expected side effects include ipsilateral phrenic nerve blockade in approximately 100% of cases (avoid in severe pulmonary disease), recurrent laryngeal nerve block causing hoarseness, and Horner syndrome. For procedures requiring ulnar nerve coverage, a supraclavicular or infraclavicular approach is more appropriate.
Q3. Supraclavicular block complication
The most concerning complication of a supraclavicular brachial plexus block is:
A. Phrenic nerve palsy occurring in approximately 50% of cases
B. Horner syndrome from sympathetic chain involvement near the block site
C. Pneumothorax occurring in 1–6% of cases despite ultrasound guidance
D. Recurrent laryngeal nerve block from cephalad spread of local anesthetic
E. Hoarseness from vagus nerve involvement in the supraclavicular region
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Answer: C. Pneumothorax is the most serious complication of supraclavicular brachial plexus block, with an incidence of 1–6%. While ultrasound guidance has significantly reduced the risk of pneumothorax, it has not been eliminated entirely due to the proximity of the pleura to the injection site. Phrenic nerve blockade is actually the most common complication, occurring in approximately 50% of cases, but is generally well-tolerated and self-limited. The supraclavicular block is performed at the level of the trunks and divisions of the brachial plexus and is best suited for surgery distal to the mid-humerus. Other complications include Horner syndrome from sympathetic chain involvement, recurrent laryngeal nerve block, and hoarseness, but these are less concerning than pneumothorax.
Q4. Axillary block sparing
An axillary brachial plexus block frequently misses which nerve?
A. Median nerve, because it branches proximally before entering the axillary sheath
B. Ulnar nerve, because it travels posterior to the medial intermuscular septum
C. Radial nerve, because it exits through the triangular interval above injection level
D. Musculocutaneous nerve, because it exits the sheath early within the coracobrachialis muscle
E. Median antebrachial cutaneous nerve, because it lies superficial to the investing fascia
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Answer: D. The musculocutaneous nerve frequently is missed by axillary brachial plexus block because it exits the axillary sheath above the level of typical injection, penetrating into the coracobrachialis muscle early in its course. The axillary approach reliably targets the median, ulnar, and radial nerves, which travel together around the axillary artery within the sheath. To ensure complete anesthesia, the musculocutaneous nerve should be supplemented with a separate injection into the coracobrachialis muscle, located between the biceps and triceps. The median antebrachial cutaneous nerve, while sometimes missed, is less clinically significant than the musculocutaneous nerve for surgical anesthesia.
Q5. Brachial plexus anatomy by block
The infraclavicular block targets the brachial plexus at the level of:
A. Roots
B. Trunks
C. Divisions
D. Cords
E. Branches
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Answer: D. The infraclavicular block targets the brachial plexus at the level of the cords. Understanding the anatomic level targeted by each brachial plexus block approach is essential: the interscalene block targets roots and trunks (primarily C5–C7), the supraclavicular block targets trunks and divisions, the infraclavicular block targets cords, and the axillary block targets branches (the terminal nerves). This anatomic progression from proximal to distal corresponds to the clinical distribution of anesthesia achieved with each approach.
Q6. Femoral nerve block target muscle response
During a femoral nerve block with peripheral nerve stimulation, you observe twitch of the sartorius muscle (medial knee). To capture the main femoral nerve, redirect the needle:
A. Anteromedially to capture the posterior division of the femoral nerve
B. Posterolaterally to capture the posterior division of the femoral nerve
C. Caudally to capture the posterior division of the femoral nerve
D. Cephalad to capture the posterior division of the femoral nerve
E. Medially after withdrawal to capture the posterior division
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Answer: B. Sartorius muscle twitch indicates stimulation of the anterior branch of the femoral nerve, which is more superficial and medial. The desired response is quadriceps muscle twitch (patellar snap), which indicates stimulation of the posterior branch of the femoral nerve. The posterior branch provides motor innervation to the quadriceps and is the main target for femoral nerve blockade as it provides the bulk of analgesia for anterior thigh and knee surgery. To redirect from the anterior branch to the posterior branch, the needle should be advanced posterolaterally, moving deeper and slightly lateral to reach the main trunk and posterior division of the femoral nerve.
Q7. Adductor canal block
The adductor canal block primarily targets the:
A. Femoral nerve, providing motor blockade to the quadriceps muscle group
B. Saphenous nerve, the terminal sensory branch of the femoral nerve
C. Obturator nerve, providing motor blockade to the adductor muscle group
D. Sciatic nerve, providing sensory and motor blockade to lower leg
E. Lateral femoral cutaneous nerve, providing sensory blockade to lateral thigh
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Answer: B. The adductor canal block primarily targets the saphenous nerve, which is the terminal sensory branch of the femoral nerve. This block provides effective analgesia for the medial knee while preserving quadriceps motor strength, which is critical for early ambulation. For this reason, the adductor canal block is preferred over the femoral nerve block for knee arthroplasty procedures, as it allows patients to mobilize safely in the early postoperative period without the risk of quadriceps weakness and falls that can occur with more proximal femoral nerve blockade.
Q8. TAP block coverage
The transversus abdominis plane (TAP) block provides analgesia for dermatomes:
A. T6–T9, covering the upper abdominal wall dermatomes
B. T9–L1, covering the anterior abdominal wall dermatomes
C. L1–L3, covering the lower abdominal wall dermatomes
D. T10–S1, covering the abdominal and pelvic wall dermatomes
E. C8–T2, covering the upper thoracic wall dermatomes
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Answer: B. TAP block covers T9–L1 dermatomes, providing analgesia to the anterior abdominal wall by blocking the intercostal, subcostal, ilioinguinal, and iliohypogastric nerves. The block is adequate for somatic pain of the skin and muscle of the anterior abdominal wall but does NOT provide visceral pain relief. It is commonly used as an adjunct to general anesthesia. The landmark technique uses the triangle of Petit, while ultrasound guidance identifies the plane between the internal oblique and transversus abdominis muscles for local anesthetic deposition.
Q9. Sciatic nerve block components
Both common peroneal and tibial nerves must be blocked for foot anesthesia. They share an origin from:
A. Lumbar plexus
B. Sciatic nerve
C. Femoral nerve
D. Obturator nerve
E. Pudendal nerve
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Answer: B. The sciatic nerve (L4–S3) divides into the tibial nerve and the common peroneal nerve. The common peroneal nerve further divides into superficial and deep peroneal branches. For sciatic nerve blocks, the popliteal approach is convenient because it blocks the nerve above the point where it divides into its two major branches. Complete foot anesthesia also requires blocking the saphenous nerve, which originates from the femoral nerve (part of the lumbar plexus) and provides medial foot coverage. The lumbar plexus, femoral nerve, obturator nerve, and pudendal nerve do not give rise to both the tibial and common peroneal nerves.
Q10. Lumbar plexus block coverage
The lumbar plexus block (Winnie/3-in-1) covers:
A. Femoral, obturator, and lateral femoral cutaneous nerves
B. Sciatic, femoral, and posterior femoral cutaneous nerves
C. Pudendal, ilioinguinal, and genitofemoral nerves
D. Genitofemoral, iliohypogastric, and ilioinguinal nerves
E. Superior hypogastric plexus and inferior hypogastric plexus
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Answer: A. The lumbar plexus is formed by the ventral rami of L1–L4 with a contribution from T12. Its branches include the iliohypogastric (T12–L1), ilioinguinal (L1), genitofemoral (L1–L2), lateral femoral cutaneous (L2–L3), obturator (L2–L4), and femoral (L2–L4) nerves. The lumbar plexus block (also called the Winnie or 3-in-1 block) primarily covers the three major nerves of the lower lumbar plexus: femoral, obturator, and lateral femoral cutaneous. The sciatic nerve is not part of the lumbar plexus; it arises from the sacral plexus (L4–S3). The iliohypogastric, ilioinguinal, and genitofemoral nerves arise from the upper lumbar plexus and are not reliably blocked by this technique. The hypogastric plexus is an autonomic structure, not a somatic nerve plexus.
Q11. Stellate ganglion block clinical sign
The most reliable indicator of a successful stellate ganglion block is:
A. Horner syndrome (ptosis, miosis, anhidrosis)
B. Hoarseness from recurrent laryngeal nerve block
C. Ipsilateral skin temperature increase greater than 1°C
D. Patient report of complete pain relief
E. Loss of biceps reflex on ipsilateral side
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Answer: C. Ipsilateral skin temperature increase (greater than 1°C) is the most reliable sign of complete sympathetic block to the upper extremity. Horner syndrome (ptosis, miosis, anhidrosis) develops early but may reflect cephalad spread without complete sympathectomy of the upper extremity. Hoarseness indicates recurrent laryngeal nerve involvement but does not confirm sympathetic blockade. Pain relief is subjective and variable. Biceps reflex loss suggests brachial plexus involvement rather than isolated sympathetic block. Stellate ganglion block is used for complex regional pain syndrome, refractory angina, and vascular insufficiency.
Q12. Celiac plexus block
Celiac plexus block is used for analgesia of:
A. Pelvic visceral pain from malignancy or endometriosis
B. Upper abdominal visceral pain from pancreatic cancer or chronic pancreatitis
C. Lower extremity ischemic pain from peripheral vascular disease
D. Thoracic radicular pain from vertebral compression or metastases
E. Hepatic capsular pain only from liver distension or inflammation
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Answer: B. Celiac plexus block covers upper abdominal viscera through blockade of T5–T12 sympathetic innervation. It is most commonly used for pancreatic cancer pain and chronic pancreatitis. The celiac plexus does innervate multiple upper abdominal organs including the pancreas, stomach, liver, gallbladder, spleen, kidneys, and intestines to the splenic flexure, so it is not limited to hepatic capsular pain alone. Side effects include hypotension from sympathectomy, diarrhea from unopposed parasympathetic dominance, retroperitoneal bleeding, and rarely paraplegia from spinal artery spasm. Pelvic pain requires different blocks such as superior hypogastric or ganglion impar blocks.
Q13. Spinal anesthesia in infants
Compared to adults, spinal anesthesia in infants is characterized by:
A. Longer duration of action due to decreased cardiac output and slower drug clearance
B. Higher incidence of hypotension due to increased sympathetic nervous system activity
C. Faster onset and shorter duration of action due to immature sympathetic system
D. Lower volume requirement due to smaller subarachnoid space and reduced CSF volume
E. Requirement of general anesthesia for placement due to inability to cooperate
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Answer: C. Spinal anesthesia in infants has faster onset and shorter duration compared to adults. Duration is typically 75–90 minutes with bupivacaine versus several hours in adults. This is due to higher cardiac output, highly vascular pia mater, and immature sympathetic nervous system. Hypotension is rare in infants because of their immature sympathetic tone. Spinal anesthesia is particularly useful for preterm infants less than 60 weeks postconceptual age to reduce postoperative apnea risk. Typical dosing is approximately 0.8 mg/kg of 0.5% bupivacaine. Important anatomic consideration: the spinal cord ends at L3 in infants until approximately age 2 years, compared to L1 in adults.
Q14. Spinal cord termination peds
In a neonate, the spinal cord ends at approximately:
A. L1
B. L3
C. L5
D. S1
E. T12
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Answer: B. In neonates, the spinal cord terminates at approximately L3, which is more caudal than in adults where it ends at L1–L2. The cord reaches the adult level by approximately 2 years of age. The dural sac in neonates ends at S3, compared to S2 in adults. Because of the more caudal termination of the cord in neonates, a lower interspace should be used when performing lumbar puncture to minimize the risk of direct spinal cord trauma.
Q15. Caudal block dosing
For a caudal epidural in a 12 kg toddler, what volume of 0.25% bupivacaine provides analgesia up to mid-thoracic dermatomes?
A. 0.5 mL/kg (provides sacral-level analgesia)
B. 1.0 mL/kg (provides low thoracic-level analgesia)
C. 1.25 mL/kg (provides mid-thoracic-level analgesia)
D. 2.0 mL/kg (exceeds safe maximum dosing)
E. 0.25 mL/kg (provides inadequate sacral coverage)
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Answer: C. For caudal epidural blocks in pediatric patients, the volume of local anesthetic determines the height of the block, while the concentration determines the density or quality of the block. The standard dosing regimen is: 0.5 mL/kg provides sacral-level analgesia, 1.0 mL/kg provides low thoracic-level analgesia, and 1.25 mL/kg provides mid-thoracic-level analgesia. Common concentrations used include 0.125–0.25% bupivacaine or 0.2–0.3% ropivacaine. In this 12 kg toddler requiring mid-thoracic coverage, 1.25 mL/kg (15 mL total) of 0.25% bupivacaine is the appropriate volume. Volumes exceeding 1.25 mL/kg may approach or exceed maximum safe dosing limits for local anesthetics in small children.
Q16. Transient neurologic symptoms
Transient neurologic symptoms after spinal anesthesia are most associated with:
A. Bupivacaine spinal in obstetric patients undergoing cesarean delivery
B. Lidocaine spinal in outpatients undergoing knee arthroscopy in lithotomy
C. Ropivacaine spinal in elderly patients undergoing hip fracture repair
D. Procaine spinal in any patient undergoing lower extremity surgery
E. Mepivacaine epidural in laboring patients undergoing vaginal delivery
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Answer: B. Transient neurologic symptoms (TNS) present as buttock and thigh pain after uncomplicated spinal anesthesia without objective neurologic deficit. The highest risk occurs with hyperbaric 5% lidocaine spinal, particularly in patients positioned in lithotomy, undergoing knee arthroscopy, and having outpatient surgery. TNS is self-limited and typically resolves within 72 hours. It is not associated with bupivacaine or ropivacaine spinals. The syndrome occurs despite technically successful spinal anesthesia with no complications during needle placement or injection.
Q17. ASRA — clopidogrel hold
Per ASRA guidelines, clopidogrel must be held how long before neuraxial procedure?
A. 1–2 days before the neuraxial procedure
B. 5–7 days before the neuraxial procedure
C. 10 days before the neuraxial procedure
D. 14 days before the neuraxial procedure
E. 30 days before the neuraxial procedure
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Answer: B. Per ASRA guidelines, clopidogrel must be held 5–7 days before neuraxial procedures to allow adequate platelet recovery and minimize bleeding risk. This duration reflects the irreversible inhibition of the P2Y12 receptor and the time needed for new platelet generation. For comparison, other antiplatelet agents have different hold times: ticlopidine requires 10 days, prasugrel requires 7–10 days, and ticagrelor requires 5–7 days. Newer direct oral anticoagulants (DOACs) such as apixaban and rivaroxaban should be held 3 days, while dabigatran requires 5 days or longer if creatinine clearance is reduced.
Q18. ASRA — heparin neuraxial
For a patient on prophylactic subcutaneous unfractionated heparin (5,000 U TID), the minimum interval from last dose to neuraxial needle placement is:
A. 1 hour after the last subcutaneous dose
B. 4–6 hours after the last subcutaneous dose
C. 12 hours after the last subcutaneous dose
D. 24 hours after the last subcutaneous dose
E. No interval required; proceed immediately
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Answer: B. For prophylactic subcutaneous unfractionated heparin (such as 5,000 U TID), the recommended minimum interval before neuraxial needle placement is 4–6 hours after the last dose. This timing accounts for UFH's pharmacokinetics: peak effect occurs at 1–2 hours and duration of action is 4–6 hours. For therapeutic intravenous UFH, the same 4–6 hour interval applies, but normal coagulation studies must also be verified before proceeding. After neuraxial needle placement or catheter removal, heparin should not be restarted for at least 1 hour. If the patient has been receiving heparin for more than 4 days, platelet count should be checked before performing the block due to the risk of heparin-induced thrombocytopenia (HIT).
Q19. Awake fiberoptic airway block — superior laryngeal
The internal branch of the superior laryngeal nerve provides sensory innervation to:
A. Tongue base, epiglottis, aryepiglottic folds, and supraglottis down to the vocal cords
B. Trachea and subglottic region below the vocal cords and down to the carina
C. Posterior third of the tongue, vallecula, and lingual surface of the epiglottis
D. Anterior two-thirds of the tongue, floor of mouth, and sublingual mucosa bilaterally
E. Infraglottic larynx, including false vocal cords, ventricles, and upper tracheal rings
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Answer: A. The internal branch of the superior laryngeal nerve is a vagal afferent that provides sensory innervation to the supraglottis down to the level of the vocal cords, including the tongue base, epiglottis, and aryepiglottic folds. The recurrent laryngeal nerve provides sensory innervation below the vocal cords and motor innervation to all intrinsic laryngeal muscles except the cricothyroid (which receives motor from the external branch of the superior laryngeal nerve). For awake fiberoptic intubation, the internal branch of the superior laryngeal nerve can be blocked at the level of the hyoid by injecting 2 mL of 2% lidocaine through the thyrohyoid membrane on each side.
Q20. Subdural block
Compared to a spinal, the signs of an unintended subdural injection include:
A. Block height and density identical to intended spinal anesthesia with expected sympathetic involvement
B. Patchy, dense sensory block out of proportion to motor block with greater sympathetic involvement than expected
C. Rapid onset dense motor and sensory block lasting only fifteen minutes with minimal sympathetic involvement
D. Strictly unilateral sensory and motor block confined to one side with asymmetric sympathetic involvement
E. Block confined exclusively to sacral dermatomes with sparing of lumbar and thoracic sympathetic levels
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Answer: B. Subdural injection produces a characteristic pattern of dense sensory blockade (affecting posterior fibers) that is out of proportion to the variable motor blockade (which involves more anterior fibers), along with an unexpectedly high level of sympathetic block. The block typically has a patchy distribution. Onset is slower than spinal anesthesia but faster than epidural anesthesia. Management focuses on airway support and hemodynamic stabilization with vasopressors and fluids as needed. The block typically dissipates over several hours. This presentation differs from spinal anesthesia, which produces predictable sensory, motor, and sympathetic block heights, and from epidural injection, which has much slower onset and more predictable dermatomal spread.
Q21. Spinal vs epidural for TURP
For transurethral resection of the prostate, spinal anesthesia is generally preferred over GA because:
A. Faster onset allows earlier surgical start and shorter overall OR time
B. Awake patient allows real-time monitoring for mental status changes from TURP syndrome
C. Reduced fluid overload from decreased third-spacing and lower IV fluid requirements
D. Eliminates need for cell salvage equipment by reducing intraoperative blood loss
E. Prevents Compound A toxicity by avoiding sevoflurane exposure in low-flow circuits
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Answer: B. Spinal anesthesia is preferred for TURP primarily because the awake patient allows early detection of TURP syndrome, which results from hyponatremia and glycine toxicity manifesting as altered mental status, nausea, and visual changes. An awake patient can also report symptoms of bladder or prostatic capsule perforation, including shoulder pain, abdominal pain, and dyspnea. A T10 sensory level provides adequate analgesia and pelvic floor relaxation while preserving patient awareness. Hypothermia from irrigant absorption is also more readily detectable in the awake patient. While spinal anesthesia does have faster onset than general anesthesia, this is not the primary reason for its preference in TURP. Spinal anesthesia does not prevent fluid overload (irrigation fluid absorption still occurs), does not eliminate the need for cell salvage, and Compound A toxicity is not a relevant concern for TURP procedures.
Q22. Retrobulbar vs peribulbar block
Compared to retrobulbar block, peribulbar block has:
A. Faster onset of anesthesia and more rapid achievement of surgical conditions
B. Higher rate of central spread leading to brainstem anesthesia and complications
C. Lower risk of optic nerve injury, retrobulbar hemorrhage, and globe perforation
D. More dense akinesia of extraocular muscles and more complete motor blockade
E. Lower volume requirement of local anesthetic to achieve adequate surgical block
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Answer: C. Peribulbar block keeps the needle outside the muscle cone, resulting in a safer profile compared to retrobulbar block. The extraconal needle placement reduces risk of optic nerve injury, retrobulbar hemorrhage, globe perforation, and central spread to the brainstem. However, peribulbar block has slower onset (9–12 minutes versus 3–5 minutes for retrobulbar), less complete akinesia of the extraocular muscles, and requires higher volumes of local anesthetic (8–10 mL versus 3–4 mL for retrobulbar). Both techniques effectively attenuate the oculocardiac reflex by blocking the V1 trigeminal afferent pathway.
Q23. Bier block (IV regional)
Maximum safe time for tourniquet inflation during a Bier block is:
A. 10 minutes before ischemic pain becomes intolerable
B. 20 minutes before ischemic pain becomes intolerable
C. 90 minutes before ischemic pain becomes intolerable
D. 2 hours before ischemic pain becomes intolerable
E. 3 hours before ischemic pain becomes intolerable
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Answer: C. For a Bier block (intravenous regional anesthesia), the tourniquet is inflated and 0.5% lidocaine without epinephrine is injected distal to the tourniquet. The minimum tourniquet inflation time is 20 to 25 minutes to allow adequate tissue uptake of local anesthetic and avoid sudden systemic release of a toxic bolus. The maximum safe tourniquet time is approximately 60 to 90 minutes, after which ischemic pain from the tourniquet itself becomes intolerable and limits the utility of the technique. Beyond 90 minutes, the risk of tourniquet-related complications increases significantly.
Q24. Local anesthetic absorption rank order
From greatest to least systemic absorption after injection:
A. Intercostal > caudal > epidural > brachial plexus > subcutaneous
B. Subcutaneous > brachial plexus > epidural > caudal > intercostal
C. Brachial plexus > intercostal > caudal > epidural > subcutaneous
D. Caudal > brachial plexus > subcutaneous > intercostal > epidural
E. Epidural > sciatic > brachial plexus > intercostal > subcutaneous
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Answer: A. The rank order of systemic absorption of local anesthetics from greatest to least is remembered by the mnemonics "ICEBaLLs" or "BICEPS": IV > Intratracheal > Intercostal > Caudal/paracervical > Epidural > Brachial plexus > sciatic/femoral > Subcutaneous. Intercostal blocks have the highest systemic absorption of the routine regional anesthesia techniques due to the highly vascular intercostal space. This is clinically important because patients receiving intercostal blocks are at greater risk for local anesthetic systemic toxicity, especially when doses approach the maximum recommended. The correct sequence among common regional techniques is intercostal > caudal > epidural > brachial plexus > subcutaneous.
Q25. Continuous peripheral nerve catheter contraindications
Relative contraindications to an outpatient continuous peripheral nerve catheter include:
A. Severe hepatic or renal insufficiency, infection at the catheter site, anticoagulation therapy, and infusions affecting the phrenic nerve in patients with poor pulmonary reserve
B. Well-controlled type 2 diabetes mellitus without neuropathy, normal renal function, and adequate social support at home for catheter management
C. Age over 65 years with normal cognitive function, stable cardiovascular status, and ability to manage pump settings independently at home
D. Previous single-injection peripheral nerve block performed earlier the same day with complete resolution of motor blockade before catheter placement
E. Mild chronic obstructive pulmonary disease with FEV1 greater than 70 percent predicted and no baseline hypoxemia or hypercarbia
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Answer: A. Severe hepatic or renal disease increases the risk of systemic local anesthetic toxicity during prolonged infusion because of impaired drug metabolism and clearance. Infection at the catheter site is an absolute contraindication to placement. Anticoagulation and coagulopathy represent absolute contraindications for deep blocks due to bleeding risk. Infusions that affect the phrenic nerve, such as interscalene catheters, should be avoided in patients with poor pulmonary reserve because hemidiaphragmatic paresis can compromise respiratory function. Diabetes, advanced age alone, prior single-shot blocks, and mild COPD are not contraindications to outpatient continuous peripheral nerve catheters.
Q26. Local anesthetic mechanism
Local anesthetics produce nerve blockade by:
A. Reversibly blocking voltage-gated sodium channels from the intracellular side in their open or inactivated state
B. Reversibly blocking voltage-gated potassium channels from the extracellular side in their open or inactivated state
C. Irreversibly antagonizing GABAₐ receptors at the chloride channel pore from the intracellular binding site
D. Reversibly blocking nicotinic acetylcholine receptors at the neuromuscular junction from the extracellular side
E. Irreversibly inhibiting the Na/K-ATPase pump by binding to the phosphorylation site on the cytoplasmic domain
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Answer: A. Local anesthetics produce nerve blockade by reversibly binding to voltage-gated sodium channels from the intracellular side, preferentially in the open or inactivated state, thereby preventing depolarization. The unionized (lipophilic) form of the local anesthetic crosses the cell membrane, then the ionized (hydrophilic) form binds to the receptor site inside the channel. This mechanism exhibits use-dependent block, meaning nerves with higher firing rates are blocked first. Clinically, the order of blockade is typically sympathetic function, then temperature sensation, followed by pain, touch, and finally motor function. Small unmyelinated fibers (C) and small myelinated fibers (B and A-delta) are blocked before large myelinated fibers (A-beta and A-alpha).