A 4-year-old boy is brought to the emergency department by his mother after cutting his buttock on a piece of broken glass. There is a 5-cm curvilinear laceration over the patient's right buttock. His vital signs are unremarkable. The decision to repair the laceration is made. Which of the following will offer the longest anesthesia for the laceration repair?

Lidocaine mixed with bupivacaine

A 34-year-old man presents to the outpatient clinic with a complaint of right-sided jaw pain. The onset of pain was approx. 1 month ago and he is experiencing symptoms 2–3 times a day. Each episode of pain lasts for about 30 seconds. He describes the pain as severe (9 out of 10) with an electric and sharp quality. He denies having tear production or conjunctival injection on the affected side during attacks. What is the mechanism of action for the drug that will best treat this patient’s condition?

Increase the time of Cl- channel opening

Decrease the excitatory effects of glutamic acid

Increase the frequency of Cl- channel opening

An investigator is studying a local anesthetic that causes increased sympathetic activity. When given intravenously, it causes euphoria and pupillary dilation. Which of the following is the most likely effect of this drug at the synaptic cleft?

Decreased reuptake of norepinephrine

Increased release of norepinephrine

Decreased release of acetylcholine

Decreased breakdown of norepinephrine

A 25-year-old man presents to the emergency department with a severe pulsatile headache for an hour. He says that he is having palpitations as well. He adds that he has had several episodes of headache in the past which resolved without seeking medical attention. He is a non-smoker and does not drink alcohol. He denies use of any illicit drugs. He looks scared and anxious. His temperature is 37°C (98.6°F), respirations are 25/min, pulse is 107/min, and blood pressure is 221/161 mm Hg. An urgent urinalysis reveals elevated plasma metanephrines. What is the next best step in the management of this patient?

Phenoxybenzamine followed by propranolol

Propranolol followed by phenoxybenzamine

A 26-year-old G1P0 woman at 40 weeks estimated gestational age presents after experiencing labor pains. Pregnancy has been uncomplicated so far. Rupture of membranes occurs, and a transvaginal delivery is performed under epidural anesthesia, and the baby is delivered alive and healthy. The patient voids a few hours after the delivery and complains of mild irritation at the injection site on her back. On the second day, she complains of a severe headache over the back of her head. The headache is associated with pain and stiffness in the neck. Her headache is aggravated by sitting up or standing and relieved by lying down. The pain is relieved slightly by acetaminophen and ibuprofen. The patient is afebrile. Her vital signs include: pulse 100/min, respiratory rate 18/min, and blood pressure 128/84 mm Hg. Which of the following statements is the most accurate regarding this patient’s condition?

This patient’s condition can resolve on its own

A blockage of CSF is the cause of this patient’s headache

An infection is present at the epidural injection site

Excessive bed rest will worsen this patient’s condition

Immediate intervention is required

A 21-year-old G1P0 woman presents to the labor and delivery ward at 39 weeks gestation for elective induction of labor. She requests a labor epidural. An epidural catheter is secured at the L4-L5 space. She exhibits no hemodynamic reaction to lidocaine 1.5% with epinephrine 1:200,000. A continuous infusion of bupivacaine 0.0625% is started. After 5 minutes, the nurse informs the anesthesiologist that the patient is hypotensive to 80/50 mmHg with a heart rate increase from 90 bpm to 120 bpm. The patient is asymptomatic and fetal heart rate has not changed significantly from baseline. She says that her legs feel heavy but is still able to move them. What is the most likely cause of the hemodynamic change?

Intrathecal infiltration of local anesthetic

A 28-year-old man comes to the emergency department for an injury sustained while doing construction. Physical examination shows a long, deep, irregular laceration on the lateral aspect of the left forearm with exposed fascia. Prior to surgical repair of the injury, a brachial plexus block is performed using a local anesthetic. Shortly after the nerve block is performed, he complains of dizziness and then loses consciousness. His radial pulse is faint and a continuous cardiac monitor shows a heart rate of 24/min. Which of the following is the most likely mechanism of action of the anesthetic that was administered?

Inactivation of sodium channels

Activation of acetylcholine receptors

Inactivation of ryanodine receptors

Inactivation of potassium channels

Regional anesthesia techniques for USMLE Step 2 CK: High-Yield Surgery Lessons

💉 Core concept - The Big Numb Theory

Principle: Targeted delivery of local anesthetic to reversibly block nerve conduction for surgery or analgesia, sparing consciousness.
Mechanism: Blocks voltage-gated Na+ channels in nerve axons, preventing action potential propagation and signal transmission.
Types: Categorized by target site: neuraxial (spinal, epidural) and peripheral nerve blocks (PNB).

⭐ Differential Blockade: Sympathetic fibers (B-fibers) and pain/temp fibers (A-delta, C-fibers) are blocked first, followed by motor fibers (A-alpha). This explains early hypotension in spinal anesthesia.

🗺️ Anatomy - Nerve Maps & Targets

Brachial Plexus Anatomy for Regional Anesthesia

📌 Brachial Plexus: Really Tired Drink Coffee Black (Roots, Trunks, Divisions, Cords, Branches).

Block	Target Level / Nerve(s)	Key Landmark(s)
Interscalene	Roots/Trunks (C5-C7)	Between anterior & middle scalene muscles
Supraclavicular	Trunks/Divisions	"Corner pocket" lateral to subclavian artery
Femoral	Femoral N. (L2-L4)	Lateral to femoral artery, below inguinal lig.
Popliteal Sciatic	Tibial & Common Peroneal N.	Between biceps femoris & semitendinosus

🧪 Pharmacology - Local Anesthetic Potions

Mechanism: Reversible block of voltage-gated Na⁺ channels from the intracellular side. The non-ionized form crosses the membrane; the ionized form is active.
Pharmacokinetics:
- Onset: Faster with ↓ pKa. Infected (acidic) tissue ↓ efficacy.
- Potency: ↑ with ↑ lipid solubility.
- Duration: ↑ with ↑ protein binding.
Classification: 📌 Amides have 2 'i's (Lidocaine); Esters have 1 (Procaine).
- Amides: Lidocaine, Bupivacaine. Metabolized by liver (CYP450).
- Esters: Procaine, Cocaine. Metabolized by plasma pseudocholinesterase (PABA allergy risk).

⭐ Epinephrine co-administration causes vasoconstriction, prolonging duration & ↓ systemic toxicity. Avoid in end-arterial fields.

Lidocaine vs. Procaine: Amide and Ester Structures ⚠️ Bupivacaine has high cardiotoxicity.

💉 Management - Needles, Nerves, No Pain

Neuraxial Anesthesia:
- Spinal (Intrathecal): Single injection into CSF (L3/L4 or L4/L5). Rapid, dense block for lower abdominal/limb surgery. Uses fine-gauge needles (e.g., Quincke, Whitacre).
- Epidural: Catheter placed in epidural space for continuous infusion. Slower onset, titratable analgesia (e.g., labor, post-op pain). Uses Tuohy needle.
Peripheral Nerve Block (PNB):
- Ultrasound-guided injection near a nerve/plexus (e.g., brachial, femoral). Provides targeted anesthesia/analgesia for limb procedures.

⭐ Local Anesthetic Systemic Toxicity (LAST): A critical complication. Presents with CNS excitation (tinnitus, metallic taste, seizures) followed by cardiovascular collapse. Management: Intralipid emulsion therapy.

⚠️ Complications - When Blocks Go Wrong

Local Anesthetic Systemic Toxicity (LAST): Biphasic effects.
- CNS: Tinnitus, metallic taste, seizures → coma.
- CV: Bradycardia, hypotension → arrhythmia, cardiac arrest.
Nerve Injury: Persistent paresthesia or motor deficit post-block. Due to needle trauma, hematoma, or neurotoxicity.
Spinal/Epidural Hematoma: ⚠️ High risk with anticoagulation. Presents as new, progressive neurologic deficits.
Post-Dural Puncture Headache (PDPH): Positional headache after neuraxial procedures.

⭐ Treat LAST with 20% lipid emulsion therapy (Intralipid). Avoid vasopressin and calcium channel blockers in LAST-related cardiac arrest.

⚡ Biggest Takeaways

Spinal anesthesia (intrathecal) injects into CSF below L2; causes rapid block and sympathectomy-induced hypotension.

Epidural anesthesia is slower, uses larger volumes, and allows for continuous catheter analgesia.

Post-dural puncture headache (PDPH) is a major spinal risk; treat with an epidural blood patch.

Risk of epidural hematoma is high with anticoagulation-a major contraindication.

Bupivacaine is highly cardiotoxic; treat Local Anesthetic Systemic Toxicity (LAST) with lipid emulsion.

Interscalene blocks risk phrenic nerve palsy (ipsilateral diaphragmatic paralysis).

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