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Complications of Spinal Anesthesia

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Classification Overview

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1. Hypotension

• Mechanism: Sympathetic blockade (T1-L2) causes arterial vasodilation + venodilation, reducing preload and afterload
• Venodilation reduces venous return -> decreased cardiac output
• Bradycardia accompanies hypotension, especially if the cardioaccelerator fibers (T1-T4) are blocked
• Incidence: Up to 30% of patients; higher in elderly, hypovolemic patients, and with high spinal levels
• Treatment:
  • IV fluids (preload or coload)
  • Vasopressors: Phenylephrine (first-line in obstetrics, preserves uteroplacental flow), Ephedrine (preferred in non-obstetric patients, mixed alpha/beta action)
  • Epinephrine for refractory hypotension
  • Left uterine displacement in pregnant patients
• Prophylaxis: Adequate IV prehydration (crystalloid 500-1000 mL), avoid aortocaval compression

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2. High Neural Blockade / Total Spinal

• Occurs from excessive dermatomal spread of local anesthetic (inadvertent or from overdose)
• Risk factors: Elderly patients, obesity, pregnancy, very short stature, excessive dose, failure to reduce dose in high-risk patients
• Clinical features:
  • Dyspnea, weakness/numbness of upper extremities
  • Nausea (often precedes hypotension)
  • Severe hypotension, bradycardia
  • When block reaches cervical levels: Total spinal - unconsciousness, apnea, cardiovascular collapse
  • Cranial nerve involvement = total spinal
• Mechanism of apnea: More commonly due to medullary hypoperfusion from severe hypotension than phrenic nerve (C3-C5) paralysis
• Anterior spinal artery syndrome has been reported with prolonged severe hypotension + raised intraspinal pressure
• Treatment:
  • Reassurance + supplemental oxygen
  • Airway support: mask ventilation -> intubation and mechanical ventilation if apnea
  • Vasopressors (ephedrine/epinephrine) and rapid IV fluids for hypotension
  • Atropine for bradycardia

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3. Cardiac Arrest During Spinal Anesthesia

• Incidence: Up to 1:1500 patients (ASA Closed Claims data)
• Often preceded by bradycardia; can occur in young, healthy patients
• Many historic cases involved unrecognized hypoventilation/hypoxia from oversedation (pre-oximetry era)
• Treatment: Prompt treatment of hypovolemia, hypotension, and bradycardia is essential to prevent arrest
• Atropine + vasopressors; ACLS if cardiac arrest occurs

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4. Post-Dural Puncture Headache (PDPH)

• Pathophysiology (two theories):
  1. CSF leak through dural puncture -> loss of CSF cushioning -> traction on pain-sensitive intracranial structures as brain sags
  2. Loss of CSF -> compensatory intracranial vasodilation to offset reduced ICP (painful)
• Characteristic features:
  • Frontal or occipital headache, postural in nature (worse sitting/standing, relieved by lying supine)
  • Associated: nausea, vomiting, neck pain, dizziness, tinnitus, diplopia, hearing loss, cortical blindness, cranial nerve palsies, even seizures
• Onset: >90% begin within 3 days; 66% within 48 hours
• Resolution: Spontaneous in 72% within 7 days; 87% resolve by 6 months
• Serious associated risks: Substantially increased risk of cerebral venous thrombosis, subdural hematoma (aOR 19.0), and bacterial meningitis (aOR 39.7) - Miller's Anesthesia 10e
• Risk factors for PDPH:
  • Young age, female sex
  • Larger needle gauge (cutting > pencil-point)
  • Multiple puncture attempts
  • Needle bevel perpendicular to dural fibers
• Prevention:
  • Use pencil-point (Whitacre, Sprotte) needles - meta-analysis confirms lower PDPH rate vs. cutting needles
  • Orient cutting needle bevel parallel to the spinal axis (separates rather than cuts longitudinal dural fibers)
  • Smallest gauge needle possible (25G or 27G)
• Treatment:
  • Conservative: Bed rest, adequate hydration, oral analgesics (NSAIDs, paracetamol, caffeine)
  • Definitive: Epidural Blood Patch (EBP) - 15-20 mL autologous blood into epidural space; success rate ~80-90% with first patch, ~95% after second
  • Caffeine 300-500 mg PO/IV (causes cerebral vasoconstriction, raises CSF pressure)
  • ACTH/cosyntropin (increases CSF production)

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5. Urinary Retention

• Mechanism: Block of S2-S4 roots inhibits detrusor muscle tone and voiding reflex
• Can also occur with intrathecal/epidural opioids
• Especially common in males with benign prostatic hyperplasia
• Treatment: Bladder catheterization if not voiding within expected time after block regression

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6. Backache

• Caused by tissue trauma as needle passes through skin, subcutaneous tissue, muscle, and ligaments
• Paravertebral muscle spasm from ligamentous strain
• Usually transient - resolves within days
• More common with repeated attempts
• Can also occur from lithotomy position (stretching of lumbar ligaments and joints) - this is not unique to spinal anesthesia

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7. Post-Spinal Nausea and Vomiting (PONV)

• Multifactorial: hypotension, unblocked vagal tone (unopposed), opioid additives, patient anxiety
• Nausea often heralds hypotension - treat hypotension first
• Serotonin (5-HT3) antagonists (ondansetron), metoclopramide, or dexamethasone

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8. Transient Neurological Symptoms (TNS) / Transient Radicular Irritation (TRI)

• First described in 1993
• Definition: Back pain radiating to the legs WITHOUT sensory or motor deficits, beginning after resolution of spinal anesthesia, resolving spontaneously within several days
• Highest risk: Hyperbaric lidocaine (incidence up to 12%), lithotomy position, outpatients, males
• Also reported with: tetracaine (2%), bupivacaine (1%), mepivacaine, prilocaine, procaine, ropivacaine
• Risk factors: Lithotomy position > other positions; outpatients > inpatients
• Treatment: NSAIDs, opioids if severe; self-limiting within 72 hours

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9. Cauda Equina Syndrome

• Definition: Permanent neurological injury to the cauda equina roots - lower extremity weakness/paralysis, bowel/bladder dysfunction, saddle anesthesia
• Causes:
  • Maldistribution of hyperbaric local anesthetic in the subarachnoid space (pooling in sacral sac) - historically associated with microcatheters for continuous spinal anesthesia (lidocaine 5% hyperbaric)
  • Neurotoxicity of concentrated local anesthetics
  • Spinal cord ischemia
  • Direct needle trauma
• Key historical association: Small-bore (28G) microcatheters with repeated doses of 5% hyperbaric lidocaine -> concentrated pooling -> cauda equina syndrome -> withdrawal of continuous spinal microcatheters from market (1992)

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10. Neurological Complications - Nerve Injury & Spinal Cord Damage

• Direct trauma from needle or catheter: paresthesias, radiculopathy
• Spinal cord ischemia - rare; from prolonged severe hypotension, vasoconstrictors
• Epidural/spinal hematoma:
  • Risk factors: anticoagulation, thrombocytopenia, coagulopathy
  • ASRA guidelines give minimum intervals before neuraxial block after anticoagulants
  • Presentation: Back pain, new motor/sensory deficits, urinary/fecal retention
  • Treatment: Emergency surgical decompression within 8 hours for best outcome
• Anterior spinal artery syndrome - reported following neuraxial anesthesia with severe sustained hypotension
• Arachnoiditis - rare chronic inflammatory condition of the arachnoid mater; can lead to progressive neurological deficit

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11. Infection

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12. Subdural Block (Inadvertent)

• Injection into the potential space between dura and arachnoid
• Much rarer than intrathecal injection
• Features: Delayed onset (15-30 min), patchy and unpredictable block, can ascend higher than expected (extends intracranially)
• Treatment: supportive (airway + cardiovascular)

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13. Inadequate / Failed Spinal Anesthesia

• Low but measurable failure rate, inversely proportional to operator experience
• Even with CSF confirmed, failure can occur from:
  • Needle movement during injection
  • Incomplete entry of needle bevel into subarachnoid space
  • Subdural injection
  • Injection into nerve root sleeve
• Management: Convert to GA if surgery cannot be postponed; repeat block at different level

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Summary Table - Key Numbers for Exams

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ASA Closed Claims Data (Incidence per 40,640 Spinals)

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High-Yield Exam Points

1. Most common complication = Hypotension (sympathetic block T1-L2)
2. PDPH - postural headache; pencil-point needle prevents it; EBP treats it
3. Total spinal - apnea is usually from brainstem hypoperfusion, not phrenic nerve palsy
4. TNS - back pain to legs WITHOUT deficit; worst with hyperbaric lidocaine in lithotomy
5. Cauda equina - saddle anesthesia + bladder/bowel dysfunction; caused by concentrated hyperbaric LA pooling
6. Cardiac arrest - 1:1500; treat bradycardia and hypotension aggressively
7. Epidural blood patch - 15-20 mL autologous blood; gold standard for PDPH
8. Spinal hematoma - surgical emergency; decompress within 8 hours
9. Bacterial meningitis - from breach in asepsis; Streptococcus (operator's oral flora without mask)
10. Urinary retention - S2-S4 block; opioid additives worsen it

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Complications of Spinal Anesthesia

Classified as Early and Late Complications

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EARLY COMPLICATIONS

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1. Hypotension ⭐ (Most Common Complication)

• Time of onset: Within minutes of block
• Mechanism:
  • Sympathetic blockade (T1-L2) -> arterial vasodilation + venodilation
  • Reduced venous return -> decreased cardiac output -> hypotension
  • If T1-T4 (cardioaccelerator fibers) are blocked -> bradycardia compounds hypotension
• Incidence: Up to 30%; higher in elderly, pregnant, hypovolemic patients
• Clinical features: Nausea often precedes hypotension (imp. early warning sign)
• Treatment:
  • IV fluids (preload/coload with crystalloids 500-1000 mL)
  • Phenylephrine - first-line in obstetric patients (preserves uteroplacental blood flow)
  • Ephedrine - first-line in non-obstetric, bradycardic patients (mixed alpha/beta)
  • Epinephrine - refractory cases
  • Left uterine displacement in pregnant patients
• Prevention: Adequate IV hydration, avoid aortocaval compression

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2. High Spinal / Total Spinal Anesthesia

• Time of onset: Within minutes of injection
• Mechanism: Excessive cephalad spread of local anesthetic
• Risk factors: Elderly, obesity, pregnancy, short stature, excessive dose, failure to reduce dose
• Clinical features (progressive):

• Apnea mechanism: Primarily from medullary hypoperfusion due to severe hypotension - NOT phrenic nerve (C3-C5) paralysis
• Treatment:
  • Reassurance + O2 supplementation
  • Airway: mask ventilation -> intubation + IPPV if apnea
  • Vasopressors (ephedrine/epinephrine) for hypotension
  • Atropine for bradycardia
  • Rapid IV fluids

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3. Bradycardia

• Mechanism:
  • Block of cardioaccelerator fibers (T1-T4)
  • Bezold-Jarisch reflex: reduced venous return -> vagal activation -> bradycardia (especially in young, fit patients in sitting/reverse Trendelenburg position)
• Treatment: Atropine 0.6 mg IV; if severe, ephedrine/epinephrine

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4. Cardiac Arrest

• Incidence: Up to 1:1500 spinal anesthetics (ASA Closed Claims data)
• Often preceded by bradycardia; can occur in young, healthy patients
• Historically worsened by unrecognized hypoxia from oversedation (pre-oximetry era)
• Treatment: Aggressive treatment of hypotension and bradycardia; ACLS if arrest occurs

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5. Nausea and Vomiting

• Mechanism: Multifactorial:
  • Hypotension -> gut ischemia
  • Unblocked vagal tone (unopposed parasympathetics)
  • Opioid additives in spinal
  • Patient anxiety
• Nausea is often the first clinical sign of developing hypotension
• Treatment: Treat hypotension first; ondansetron, metoclopramide, dexamethasone

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6. Respiratory Depression / Apnea

• Causes:
  1. High/total spinal blocking phrenic nerve (C3-C5) and intercostal muscles
  2. Medullary hypoperfusion from severe hypotension
  3. Intrathecal/epidural opioid-induced respiratory depression (delayed - can be up to 12-24 h with morphine)
• Treatment: Supplemental O2, airway support, intubation; naloxone for opioid-related depression

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7. Inadequate / Failed Spinal Anesthesia

• Incidence: Low but definite; inversely proportional to operator experience
• Causes:
  • Needle movement during injection
  • Incomplete bevel entry into subarachnoid space
  • Subdural injection (misdirection)
  • Injection into a nerve root sleeve
  • Incorrect drug/dose
• Management: Convert to GA if needed; may repeat at a different interspace

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8. Urinary Retention

• Mechanism: Block of S2-S4 sacral roots -> decreased detrusor tone + inhibited voiding reflex
• Worsened by intrathecal/epidural opioids
• More common in males (BPH) and after long surgery
• Treatment: Urethral catheterization; resolves as block regresses

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9. Subdural Block (Inadvertent)

• Injection into the potential space between dura and arachnoid
• Features:
  • Delayed onset (15-30 min) unlike true spinal
  • Block is patchy and unpredictable
  • May ascend higher than expected (extends intracranially)
  • Can mimic high/total spinal
• Treatment: Supportive - airway management + cardiovascular support

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10. Local Anesthetic Systemic Toxicity (LAST)

• LAST from spinal dose alone is very rare (small volume used)
• More relevant if intravascular injection occurs during attempted epidural
• CNS signs: Tinnitus, circumoral numbness, metallic taste -> seizures -> unconsciousness
• CVS signs: Hypotension, arrhythmias, cardiac arrest
• Treatment:
  • Stop injection immediately
  • Lipid emulsion 20%: bolus 1.5 mL/kg IV, then infusion 0.25 mL/kg/min
  • Incremental epinephrine 1 mcg/kg (NOT large doses)
  • ACLS; cardiopulmonary bypass if refractory

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LATE COMPLICATIONS

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1. Post-Dural Puncture Headache (PDPH) ⭐

• Time of onset: 66% within 48 h; >90% within 3 days of procedure
• Pathophysiology (two theories):
  1. CSF leak -> brain loses buoyancy -> traction on pain-sensitive intracranial structures when upright
  2. CSF loss -> compensatory intracranial vasodilation to maintain ICP -> painful
• Classic features:
  • Postural headache - worse sitting/standing, relieved completely by lying supine (pathognomonic)
  • Location: frontal or occipital
  • Associated: nausea, vomiting, neck stiffness, tinnitus, diplopia, hearing loss, cortical blindness, cranial nerve palsies, even seizures
• Dangerous associations (Miller's 10e):
  • Cerebral venous thrombosis + subdural hematoma (aOR 19.0)
  • Bacterial meningitis (aOR 39.7)
• Resolution: Spontaneous in 72% within 7 days; 87% by 6 months
• Risk factors:
  • Young age, female, pregnant
  • Large gauge needle, cutting-tip needle
  • Multiple puncture attempts
  • Bevel perpendicular to dural fibers

• Treatment:
  • Conservative: Bed rest, oral hydration, NSAIDs, paracetamol
  • Caffeine: 300-500 mg PO/IV (cerebral vasoconstriction + raises ICP; short-term relief)
  • Epidural Blood Patch (EBP): Gold standard
    • 15-20 mL autologous blood into epidural space
    • Success: ~80-90% after first patch; ~95% after second patch
    • Mechanism: blood clots over dural tear + tamponade effect
  • ACTH/cosyntropin: increases CSF production

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2. Backache

• Time of onset: Hours to days
• Mechanism:
  • Needle trauma through skin, subcutaneous tissue, ligaments, paraspinal muscles
  • Ligamentous strain + muscle spasm
  • Relaxation of paraspinal muscles under anesthesia -> abnormal posture on OT table
  • Lithotomy position causes lumbar ligament stretch (not unique to spinal)
• Features: Localized back pain at puncture site; usually resolves within days
• Treatment: NSAIDs, local heat, reassurance

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3. Transient Neurological Symptoms (TNS) / Transient Radicular Irritation (TRI) ⭐

• First described: 1993
• Time of onset: After resolution of spinal block (hours later); resolves within 72 hours to several days
• Definition: Back pain radiating to buttocks/legs WITHOUT any sensory or motor deficit
• Key distinction from cauda equina: No neurological deficit in TNS
• Highest risk drug: Hyperbaric lidocaine - incidence up to 12%
• Incidence by drug:
  • Lidocaine: up to 12%
  • Tetracaine: 2%
  • Bupivacaine: 1%
  • Also: mepivacaine, prilocaine, procaine, ropivacaine
• Risk factors:
  • Lithotomy position > other positions
  • Outpatients > inpatients
  • Males > females
  • Knee arthroscopy (lithotomy equivalent)
• Treatment: NSAIDs, tramadol if severe; self-limiting

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4. Cauda Equina Syndrome ⭐

• Time of onset: Hours to days after spinal (may be delayed)
• Definition: Permanent lower motor neuron injury to sacral nerve roots
• Clinical features (3 cardinal features):
  1. Saddle anesthesia (perianal, perineal numbness)
  2. Bladder and bowel dysfunction (urinary retention/incontinence, fecal incontinence)
  3. Lower limb weakness/paralysis
• Causes:
  • Neurotoxicity from concentrated local anesthetics pooling in the sacral sac
  • Historical association: Microcatheters (28G) for continuous spinal + repeated doses of 5% hyperbaric lidocaine -> pooling in dependent sacral sac -> cauda equina syndrome (led to withdrawal of spinal microcatheters from the US market in 1992)
  • Direct needle trauma to nerve roots
  • Spinal cord ischemia
• Key distinction from TNS: Cauda equina syndrome has PERMANENT neurological deficits
• Treatment: No specific treatment; supportive; bladder management; physiotherapy

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5. Spinal/Epidural Hematoma

• Time of onset: Hours to days
• Risk factors: Anticoagulants (heparin, warfarin, NOACs, antiplatelets), thrombocytopenia, coagulopathy, traumatic needle insertion, vessel anomalies
• Clinical features:
  • Severe back pain (often described as excruciating)
  • New or worsening motor weakness
  • Sensory deficits
  • Urinary/fecal retention
• Diagnosis: Emergency MRI spine
• Treatment: Emergency surgical decompression - must be performed within 8 hours of symptom onset for best neurological recovery
• Prevention: Follow ASRA guidelines for anticoagulant-free intervals before neuraxial block

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6. Meningitis

• Time of onset: 24-72 hours
• Type: Can be bacterial or chemical (aseptic)
• Bacterial meningitis:
  • Most common organism: Streptococcus species (from operator's oropharyngeal flora - contamination via droplets when no mask worn)
  • Also: Staphylococcus, gram-negative organisms
  • Features: high fever, severe headache, neck stiffness, photophobia, Kernig/Brudzinski signs
  • Treatment: IV antibiotics (ceftriaxone + vancomycin empirically), dexamethasone
• Aseptic (chemical) meningitis:
  • From antiseptics, detergents, blood contamination
  • Less severe; self-limiting
• Prevention: Strict aseptic technique, face mask, chlorhexidine skin prep, sterile drapes

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7. Epidural Abscess

• Time of onset: Days to weeks
• Organism: Staphylococcus aureus most common
• Risk factors: Diabetes, immunocompromised, prolonged catheter, infection elsewhere
• Features: Back pain -> radiculopathy -> progressive paralysis (classic triad)
• Diagnosis: MRI spine with contrast
• Treatment: IV antibiotics + urgent surgical drainage; medical management alone only if no neurological deficit and early diagnosis

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8. Arachnoiditis

• Time of onset: Weeks to months (chronic)
• Mechanism: Chronic inflammatory reaction of the arachnoid mater
• Causes: Chemical irritants (detergents, antiseptics), blood in CSF, infection, multiple taps
• Features: Progressive, often irreversible neurological deficits; chronic pain
• Treatment: Supportive; pain management; no definitive cure

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9. Neurological Injury / Neuropathy (Direct)

• Time of onset: Evident after block resolution (hours to days)
• Mechanism:
  • Direct needle trauma to nerve root or spinal cord
  • Paresthesias during injection = warning sign
• Features: Persistent paresthesias, weakness, radiculopathy in dermatomal distribution
• Prognosis: Most resolve; permanent deficit is rare

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10. Anterior Spinal Artery Syndrome

• Time of onset: Hours after procedure
• Mechanism: Prolonged severe hypotension + raised intraspinal pressure -> ischemia of anterior 2/3 of spinal cord
• Features: Bilateral leg weakness/paralysis, loss of pain/temperature sensation, but preserved proprioception and vibration (posterior columns spared)
• Treatment: Supportive; maintain MAP; no proven treatment

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MASTER SUMMARY TABLE

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TOP HIGH-YIELD EXAM MNEMONICS

• TNS = No deficit, self-limiting, associated with lithotomy + lidocaine
• Cauda equina = Permanent saddle + bladder/bowel deficit

• MRI -> OR within 8 hours