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Spinal Anesthesia - Complete MD Anaesthesiology Viva Question Bank

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SECTION 1: ANATOMY

1. Skin and subcutaneous tissue
2. Supraspinous ligament
3. Interspinous ligament
4. Ligamentum flavum
5. Epidural space
6. Dura mater
7. Subdural space (potential)
8. Arachnoid mater
9. Subarachnoid space (CSF obtained here)

• The intercristal (Tuffier's) line connecting the iliac crests corresponds to the L4-L5 interspace or the L4 spinous process.
• The L3-L4 interspace is just above this line.
• Midline approach: needle inserted in the midline between adjacent spinous processes.
• Paramedian (lateral) approach: needle inserted 1-1.5 cm lateral to midline at the lower edge of the superior spinous process, angled slightly medially and cephalad.

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SECTION 2: MECHANISM OF ACTION AND PHYSIOLOGY

1. B fibers (preganglionic sympathetic) - blocked first at lowest concentration
2. C fibers (pain, temperature, postganglionic sympathetic) - unmyelinated, slow pain
3. A-delta fibers (fast pain, temperature, touch)
4. A-gamma fibers (muscle spindle efferents)
5. A-beta fibers (touch, pressure, proprioception)
6. A-alpha fibers (motor, proprioception) - blocked last, highest concentration required

• Hypotension: Sympathetic blockade causes vasodilation (decreased SVR). Blocked cardioaccelerator fibers (T1-T4) reduce heart rate and cardiac output. Hypotension is more pronounced with higher blocks.
• Bradycardia: Blockade of T1-T4 cardioaccelerator fibers; also Bezold-Jarisch reflex (decreased venous return activates ventricular mechanoreceptors, causing reflex bradycardia).
• Cardiac arrest: Can occur with total spinal, particularly when high sympathetic block combined with deep sedation or hypoxemia causes sudden arrest in otherwise healthy young patients. Epinephrine should be administered promptly. (Barash, p. 2865)
• Decreased preload from venodilation contributes significantly to hypotension.

• Low and mid-thoracic blocks: minimal respiratory effect; patients may complain of "chest tightness" but spirometry is largely unchanged.
• High thoracic blocks: intercostal muscle paralysis impairs forced expiration and cough.
• Cervical blocks (C3-C5): diaphragmatic paralysis - patient can only whisper, requires immediate ventilatory support and intubation.
• Phrenic nerve (C3-C5) is usually spared in high thoracic spinals.
• The sensation of difficulty breathing is often more subjective (loss of chest wall proprioception) than objective in thoracic-level blocks.

• Liver: Decreased hepatic blood flow proportional to the fall in mean arterial pressure. Hepatic metabolism of drugs is reduced.
• Kidney: Decreased renal blood flow and GFR with hypotension. Urinary retention is a recognized complication due to sacral parasympathetic blockade (S2-S4), causing bladder detrusor relaxation and internal sphincter contraction. Duration of urinary retention correlates with the local anesthetic used.

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SECTION 3: DRUGS USED IN SPINAL ANESTHESIA

• Hyperbaric (density > CSF): spreads to dependent (gravity-dependent) regions. Made by adding dextrose (e.g., 8% glucose). Most predictable spread.
• Hypobaric (density < CSF): spreads to non-dependent regions. Made by adding sterile water.
• Isobaric (density = CSF): not significantly influenced by gravity/position.

• Baricity - most important
• Dose - most important
• Volume and concentration
• Temperature of solution
• Speed of injection (faster = slightly higher block)
• Addition of vasoconstrictors

• CSF volume (inversely proportional to block height)
• Age (elderly - higher block due to decreased CSF volume, increased neuronal sensitivity)
• Height (at extremes only)
• Weight/obesity (decreased CSF volume - higher blocks, especially hypobaric)
• Pregnancy (higher blocks - decreased CSF density, reduced CSF volume, progesterone-mediated sensitivity, lordosis)
• Sex (higher blocks in females - lower CSF density)
• Spinal anatomy (kyphosis, scoliosis)

• Patient position during and after injection
• Level of injection
• Needle bevel direction (bevel cephalad = slightly higher block)
• Speed and direction of injection

• Long duration (2-4 hours), allowing completion of most surgical procedures
• High protein binding (95%) and high lipid solubility - selective sensory blockade with less motor block at lower doses
• Available as hyperbaric preparation (0.5% in 8% dextrose) - predictable spread
• Isobaric preparation (0.5% in normal saline) also available
• Safe cardiac and neurological profile at spinal doses
• Well-established safety record
• Unlike lidocaine, no association with transient neurological symptoms (TNS) at clinical doses

• Levobupivacaine: The S(-) enantiomer of bupivacaine. Less cardiotoxic than racemic bupivacaine (R(+) isomer responsible for cardiotoxicity). Similar efficacy.
• Ropivacaine: Structurally related to bupivacaine; same pKa (8.1), slow onset, long duration. Potency is 0.6 that of bupivacaine. When given in equivalent doses to bupivacaine, produces slightly less motor block and earlier motor recovery. Greater motor-sensory differentiation.
• Practical caveat: both are only available as isobaric preparations; hyperbaric bupivacaine remains the most predictable.

• Pain or dysesthesia in the buttocks and/or lower extremities after spinal anesthesia
• Occurs within 24 hours of block resolution, resolves within 72 hours (usually)
• No objective neurological deficit
• Severity ranges from mild to severe
• Most strongly associated with lidocaine (especially 5% hyperbaric), incidence up to 30-40%
• Also reported with mepivacaine, procaine, and chloroprocaine
• Risk factors: outpatient/ambulatory setting, lithotomy position, obesity, early mobilization, knee arthroscopy
• Bupivacaine has minimal association with TNS
• Management: NSAIDs; opioids may be needed

• Morphine (hydrophilic): Slow onset (30-60 min), long duration (up to 24 h). Dose: 100-300 mcg. Mechanism: dorsal horn mu-receptor activation. Side effects: delayed respiratory depression (most serious - up to 12-24 h), pruritus, nausea/vomiting, urinary retention. Intrathecal:IV potency ratio = 200-300:1.
• Fentanyl (lipophilic): Rapid onset (10-15 min), short duration (3-4 h). Dose: 12.5-25 mcg. Less rostral spread due to high lipid solubility. Side effects: less delayed respiratory depression, pruritus, nausea. Potency ratio = 10-20:1.
• Sufentanil: 5-7.5 mcg. Similar to fentanyl but more potent.
• Diamorphine (UK only): Lipid-soluble prodrug, clearer from CSF faster than morphine.

• Clonidine: 15-45 mcg. Prolongs sensory and motor block by 2-3 h. Acts on alpha-2 receptors in dorsal horn (pre- and post-synaptic). Side effects: hypotension, bradycardia, sedation.
• Dexmedetomidine: More selective alpha-2 agonist. Dose: 3-10 mcg.

• Epinephrine (adrenaline): 0.1-0.2 mg. Prolongs block by vasoconstriction (decreased vascular uptake) + direct alpha-2 agonism. May cause TNS with lidocaine.
• Phenylephrine: Prolongs tetracaine block but increases TNS risk with lidocaine.

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SECTION 4: TECHNIQUE

1. Consent, IV access, monitoring (ECG, SpO2, NIBP), resuscitation equipment ready
2. Positioning: Sitting (best CSF identification, good for saddle block, hyperbaric solutions settle caudally for perineal surgery) or lateral decubitus (for unilateral block, preferred for hyperbaric solution)
3. Surface anatomy: Identify Tuffier's line (L4-L5 interspace)
4. Sterile preparation: Chlorhexidine 0.5% in alcohol (let dry), sterile drape
5. Local anesthesia: Infiltrate skin and interspinous ligament with 1% lidocaine
6. Needle insertion: Midline approach - insert introducer (for pencil-point needles), then spinal needle with bevel/opening oriented cephalad in midline between spinous processes. Paramedian approach if midline difficult.
7. Confirm subarachnoid placement: Free flow of clear CSF
8. Inject drug: Attach syringe, aspirate to confirm CSF, inject slowly (0.2 mL/s), re-aspirate at end to confirm still intrathecal
9. Position patient: According to baricity and desired block level
10. Monitor block onset: Cold sensation, pinprick, modified Bromage scale for motor block
11. Monitor cardiovascular response: Blood pressure and heart rate every 1-2 minutes for 10-15 minutes

• Cutting tip (Quincke-Babcock): Bevel cuts dural fibers - higher PDPH rate (up to 5-10%)
• Pencil-point (non-cutting): Separates dural fibers rather than cutting
  • Whitacre (solid tapered tip with lateral opening)
  • Sprotte (longer lateral opening)
  • Gertie Marx
  • Lower PDPH rate (0.5-1%)

• 25G, 26G, 27G pencil-point: lowest PDPH risk (<1%)
• 22G Quincke: PDPH risk ~3-5%

• Cold (temperature): Ethyl chloride spray or alcohol swab. C-fiber and A-delta testing. Highest (most cephalad) block level measured.
• Pinprick: Blunt needle; A-delta fibers. Level 2-3 segments lower than cold.
• Touch: A-beta fibers. Lowest block level measured.
• Motor block: Modified Bromage Scale
  • 0 = no block (full flexion of knees and feet)
  • 1 = inability to raise extended leg; can move knee and feet
  • 2 = inability to raise leg and move knee; can move feet
  • 3 = complete motor block

• Injecting a small dose of hyperbaric local anesthetic (e.g., hyperbaric bupivacaine 2.5-5 mg, or tetracaine 3-4 mg, or lidocaine 20-40 mg)
• With the patient sitting upright for 3-5 minutes after injection (gravity keeps hyperbaric solution in the sacral region)
• The patient is then placed in lithotomy with left uterine displacement

• Titrate block level precisely (small incremental doses)
• Extend duration of block
• Valuable in elderly and high-risk cardiac patients (slow titration minimizes hemodynamic changes)
• Useful for long operations

• Higher PDPH risk (large needle required)
• Cauda equina syndrome risk if microcatheters used (pooling of hyperbaric lidocaine)
• Infection risk
• Limited availability of appropriate catheters (microcatheters withdrawn from US market)

• Patient placed in lateral decubitus with operative side down
• Small dose of hyperbaric local anesthetic injected slowly
• Patient remains lateral for 15-20 minutes
• Slow injection (0.1 mL/s), small volumes, hypobaric solutions (with patient on non-operative side up)

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SECTION 5: CONTRAINDICATIONS

1. Patient refusal
2. Local infection at the site of injection
3. Septicemia/bacteremia
4. Coagulopathy or therapeutic anticoagulation within time limits (see ASRA guidelines)
5. Raised intracranial pressure (risk of cerebral herniation due to sudden CSF loss)
6. Hypovolemic shock (unresuscitated)
7. Allergy to local anesthetics

1. Pre-existing neurological disease (e.g., multiple sclerosis, peripheral neuropathy) - block may exacerbate, difficult to attribute new deficits
2. Aortic stenosis, severe fixed cardiac output states (hemodynamic compromise with sudden vasodilation)
3. Dementia/uncooperative patient
4. Fixed spinal deformity (technical difficulty)
5. Previous spinal surgery
6. Thrombocytopenia (platelet count <80,000 is generally a relative contraindication)
7. Tattoo over injection site (theoretical risk of tattoo ink injection)
8. Systemic sepsis without antibiotic coverage
9. Hypertrophic obstructive cardiomyopathy

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SECTION 6: COMPLICATIONS

• Hypotension (most common)
• Bradycardia
• Cardiac arrest (rare)

• High/total spinal (respiratory arrest)
• Hypoventilation with heavy sedation

• Post-dural puncture headache (PDPH)
• Transient neurological syndrome (TNS)
• Cauda equina syndrome
• Anterior spinal artery syndrome
• Direct needle trauma to nerve roots/cord
• Epidural/subdural hematoma
• Meningitis (bacterial, chemical)
• Arachnoiditis

• Local anesthetic systemic toxicity (LAST) - if inadvertent IV injection
• Allergic reaction

• Urinary retention
• Backache
• Nausea and vomiting (from hypotension)
• Failed block

1. CSF leaks through dural hole - CSF volume and pressure fall - brain sags - traction on pain-sensitive meningeal and vascular structures (veins, sinuses, dura) - headache
2. Compensatory intracranial vasodilation in response to decreased intracranial pressure

• Frontal or occipital headache (most common)
• Postural: worsens sitting/standing, relieved lying flat (pathognomonic)
• Associated: nausea, vomiting, neck stiffness, tinnitus, diplopia (VI nerve palsy), hearing loss, dizziness
• Onset: within 3 days in >90% cases; 66% within 48 hours
• Resolution: spontaneous in 72% by 7 days; 87% by 6 months
• Serious complications: cerebral venous thrombosis, subdural hematoma (aOR 19.0), bacterial meningitis (aOR 39.7)

• Young age (<40 years)
• Female sex
• Pregnancy
• Larger needle gauge
• Cutting needle tip
• Multiple puncture attempts
• Bevel perpendicular to dural fibers
• History of prior PDPH

• Small gauge (25G, 26G)
• Pencil-point needles
• Bevel parallel to spinal axis

• Conservative: Bed rest, oral/IV hydration, paracetamol, NSAIDs, caffeine (300-500 mg oral/IV), analgesics, abdominal binder
• Caffeine: 300-500 mg orally or IV. Works by cerebral vasoconstriction. Temporary relief.
• Epidural blood patch (EBP): Gold standard. 15-20 mL of autologous blood into epidural space at or below puncture site. Mechanism: tamponade effect, gelatinous clot seals dural hole, increases epidural/intrathecal pressure. Success rate: ~70-90% with first patch. Indicated when conservative treatment fails, for moderate-severe PDPH.
• Epidural saline/dextran: Temporary relief, less effective than blood patch.
• Cosyntropin (ACTH): May stimulate CSF production and endorphin release.
• Surgical repair: Very rare, for persistent leaks.

• Excessive dose
• Inadvertent intrathecal injection during intended epidural
• Hyperbaric solution in Trendelenburg
• Unrecognized dural puncture with epidural catheter dose
• Short stature, pregnancy, obesity

• Nausea and anxiety
• Hypotension (sympathetic block)
• Dyspnea, chest tightness (thoracic motor block - patient can feel but cannot breathe well)
• Handgrip weakness (cervical roots)
• Whispering voice (phrenic nerve compromise - C3-C5)
• Apnea (C3-C5 diaphragm block)
• Loss of consciousness (brainstem involvement, hypoperfusion)
• Cardiac arrest (sympathetic block + hypoxia)

• Call for help immediately
• Airway: Secure airway - intubate if block at C3-C5, patient whispers or cannot breathe
• Circulation: Aggressive fluid resuscitation; vasopressors (phenylephrine, ephedrine, norepinephrine); epinephrine for cardiac arrest - give early and aggressively
• Position: Supine. Do NOT use Trendelenburg (worsens hypotension, decreases cerebral perfusion). Avoid reverse Trendelenburg (decreases cerebral blood flow). Flex neck to limit further cephalad spread.
• Support: Continue IPPV as needed; bradycardia - atropine/epinephrine; reassure the patient
• Important: delayed epinephrine in subarachnoid-induced cardiac arrest leads to poor neurological outcomes (Barash, p. 2865)

• Perineal anesthesia/saddle anesthesia
• Bowel and bladder dysfunction (incontinence or retention)
• Variable lower extremity motor and sensory deficits
• Usually permanent

• Neurotoxicity of local anesthetics (concentrated lidocaine pooling around sacral roots)
• Associated with microcatheters for continuous spinal (now removed from US market)
• Repeated dosing through single-shot techniques when block inadequate
• Direct neural trauma

• Profound hypotension during spinal anesthesia
• Vasopressors causing extreme vasoconstriction
• Epidural hematoma compression
• Aortic surgery, atherosclerosis

1. Bacterial meningitis: From skin flora (commonest: Streptococcus viridans from the operator's oropharynx via droplet contamination), external contamination, hematogenous seeding from bacteremia. Strict aseptic technique, face mask wearing mandatory.
2. Aseptic (chemical) meningitis: From detergents, antiseptics, preservatives in local anesthetic preparations. Use preservative-free drugs.

• Strict asepsis (sterile gloves, mask, sterile field)
• No talking over the sterile field
• Chlorhexidine antisepsis (let dry completely before puncture)
• Use single-use, preservative-free local anesthetic preparations

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SECTION 7: SPECIAL CLINICAL SCENARIOS

• Preferred technique in elective and most urgent cesarean sections
• Level required: T4 (nipple line) - ensures block of uterine and peritoneal innervation
• Drug: Hyperbaric bupivacaine 0.5%, typically 10-12.5 mg + intrathecal fentanyl 12.5-25 mcg + intrathecal morphine 100-150 mcg (for postoperative analgesia)
• Positioning: Left lateral tilt (15 degrees) after positioning supine to prevent aortocaval compression
• Hypotension prophylaxis: Phenylephrine infusion is currently preferred over ephedrine for most patients (maintains uteroplacental blood flow better; ephedrine crosses placenta more, associated with fetal acidosis). Co-loading with 1-1.5 L crystalloid preferred over pre-loading.
• Height of block: Monitored by cold sensation; bilateral T4 confirmed before surgery starts
• Complications specific to obstetric setting: Aortocaval compression, failed block requiring GA with difficult airway, high spinal from spread in pregnant patients

• Reduced dose required - decreased CSF volume, increased neuronal sensitivity, increased spread
• Higher block levels with standard doses
• More pronounced cardiovascular effects (hypotension) - reduced cardiac reserve, inability to compensate
• Degenerative spinal changes may make identification and needle placement difficult - paramedian approach often preferred
• Calcified ligaments - more resistance felt
• Pre-existing neurological deficits must be documented before block
• Monitor for urinary retention

• Fixed cardiac output cannot compensate for sudden fall in SVR
• Acute severe hypotension can cause coronary ischemia, VF, circulatory collapse

• Co-loading with crystalloid or colloid (crystalloid is effective but requires larger volumes)
• Prophylactic vasopressor infusion: phenylephrine (preferred in obstetrics), norepinephrine
• Avoid excessive dose of local anesthetic, avoid Trendelenburg

• Lay patient supine; elevate legs
• IV fluid bolus (500-1000 mL crystalloid)
• Vasopressors: Ephedrine 5-10 mg IV bolus (mixed alpha and beta agonist; crosses placenta) or Phenylephrine 50-100 mcg IV bolus (pure alpha agonist; first-line in obstetrics)
• Severe/refractory: norepinephrine or epinephrine
• Bradycardia <50 bpm: atropine 0.6 mg IV; if severe: epinephrine 0.01-0.1 mg IV

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SECTION 8: COMPARISON AND ADVANCED TOPICS

• Rapid onset from spinal component
• Ability to extend/top up with epidural catheter (extending block duration, titrating for higher levels)
• Reduces total spinal LA dose
• Very popular for labor analgesia (low-dose spinal opioid + epidural catheter for ongoing labor)
• Cesarean section: initial spinal; catheter available for top-up if surgery prolonged or conversion needed

• More complex technique
• Epidural catheter may not be reliable (not tested before spinal)
• Higher risk of catheter migration or failure than standard epidural

1. Reduced dose requirements (20-30% less) due to:
   • Decreased lumbosacral CSF volume (dilated epidural veins from IVC compression, displacing CSF)
   • Reduced CSF density (lower by ~0.001 g/mL)
   • Progesterone-mediated increase in neuronal sensitivity
   • Increased spread due to lumbar lordosis
   • Aortocaval compression increasing extradural vascular engorgement
2. Risk of aortocaval compression in supine position
3. Increased risk of high block
4. Altered pharmacokinetics

• LA not in subarachnoid space (subdural injection, needle tip outside subarachnoid space)
• Drug error/empty syringe
• Inadequate dose

• Wait 15-20 minutes for full development
• If truly failed: reposition patient, supplemental IV analgesia/sedation for minor deficiencies
• Repeat spinal at different level with reduced dose (caution - total dose)
• Convert to epidural or general anesthesia
• Partial blocks: do not supplement with large epidural doses (risk of total spinal)

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SECTION 9: PHARMACOLOGY DEPTH

1. Distribute in CSF based on baricity, volume, dose, position
2. Bind to neural tissue (nerve roots, spinal cord) - pharmacologically active component
3. Absorbed into the epidural vasculature through arachnoid granulations and dural cuffs
4. Undergo redistribution and systemic metabolism
5. Amide LAs: hepatic metabolism (cytochrome P450)
6. Ester LAs: plasma pseudocholinesterase hydrolysis

• Significant toxicity: CNS stimulation, cardiovascular toxicity, addiction potential
• Narrow therapeutic index
• Cocaine inhibits reuptake of norepinephrine and dopamine - causing arrhythmias, hypertension, coronary spasm
• Procaine replaced it, then lidocaine replaced procaine

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SECTION 10: HISTORICAL, APPLIED, AND EXAMINER FAVORITES

• 1898: August Bier (German surgeon) first performed spinal anesthesia with cocaine on a patient and also performed it on himself (administered by his assistant Hildebrandt). Both experienced PDPH afterward.
• 1900s: Harvey Cushing and others in the US adopted the technique.
• Procaine replaced cocaine; lidocaine replaced procaine.
• Bupivacaine became standard in 1960s.
• Pencil-point needles developed to reduce PDPH.

• Intravascular injection: tachycardia (HR increase >20 bpm within 45 seconds from epinephrine)
• Intrathecal injection: rapid dense motor and sensory block within 3-5 minutes (from lidocaine dose)

• Systemic hypotension decreasing aqueous humor production
• Cardiovascular depression
• This effect is transient

• Complete sympathectomy of the lower body (splanchnic, renal, lumbar vasculature)
• Blockade of cardioaccelerator fibers (T1-T4) - loss of reflex tachycardia, bradycardia, decreased cardiac output
• Profound vasodilation (arterioles and venules)
• Reduced venous return (venodilation, venous pooling)
• Hypotension (decreased preload + decreased SVR)
• No compensatory tachycardia

• CSF density: 1.00059 g/mL at 37°C
• CSF specific gravity: 1.002-1.009

• Hyperbaric: density > 1.00059 (achieved by adding glucose)
• Hypobaric: density < 1.00059 (achieved by adding sterile water)
• Isobaric: density ≈ 1.00059

• Excellent postoperative analgesia (up to 24 hours with 100-300 mcg)
• Side effects: respiratory depression (early <2 h and late 6-24 h), pruritus (most common, 30-100%, histamine-independent, opioid receptor-mediated, responds to naloxone or low-dose naltrexone), nausea/vomiting, urinary retention

• Respiratory monitoring for at least 12-24 hours post-injection (due to risk of delayed respiratory depression)
• SpO2 monitoring recommended
• Reversal: naloxone 40-100 mcg IV (may need infusion); caution - reverses analgesia too

• Sympathetic block: extends 2-3 segments ABOVE the sensory block level
• Sensory block: clinical level tested with cold/pinprick
• Motor block: 2-3 segments BELOW the sensory block level

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SECTION 11: RAPID-FIRE / SHORT ANSWER VIVA QUESTIONS

• ~80,000/mm³ (80 × 10⁹/L) - institutional policies vary; some accept lower in certain obstetric contexts if trend is stable.

• Isobaric range: density within ±0.001 g/mL of CSF density (approximately 0.9990-1.0010 g/mL).

• Flex the neck (not Trendelenburg - this worsens hypotension). Some also suggest a slight head-up tilt for hyperbaric solutions.

• Doses >300 mcg are associated with increasing side effects without additional analgesic benefit. Most recommend keeping doses at 100-200 mcg for obstetrics and 200-300 mcg for major surgery.

• Approximately 0-1% (compared to ~3-5% with 22G Quincke).

• 8% dextrose (glucose). Commercial hyperbaric bupivacaine 0.5% is prepared in 8% dextrose.

• 15-20 mL. Injected slowly until headache relieves or back/buttock pressure felt.

• The cauda equina is the collection of lumbar and sacral nerve roots below the conus medullaris, resembling a horse's tail. The conus ends at L1-L2 in adults (range L1-L3).

• 24 hours.

• Morphine, fentanyl, clonidine (also: epinephrine, neostigmine, dexmedetomidine).

• Bradycardia; in severe cases - sinus arrest, AV block, asystole.

• Modified Bromage Scale (0-3).

• Backache (injection site soreness) - occurs in ~5-30% and is usually transient (resolves in days).

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