Spinal anaesthesia

Surgical approach (where spinal anaesthesia is commonly used)

• Lower limb orthopaedics (e.g. hip/knee arthroplasty, fixation): positioning, limb exsanguination ± tourniquet, incision, bone work, cementing, closure
  • Tourniquet pain can occur despite adequate sensory level; may need sedation/analgesia or conversion
• Obstetrics (LSCS): Pfannenstiel incision, uterine entry, delivery, oxytocics, uterine repair, closure
  • High sympathetic block + aortocaval compression → profound hypotension risk
• Lower abdominal/urology (e.g. TURP, cystoscopy, hernia): lithotomy, irrigation fluids, resection/repair, catheterisation
  • Spinal allows early detection of TUR syndrome symptoms if patient awake

Anaesthetic management (typical)

• Type of anaesthesia: Regional (subarachnoid block) ± sedation; conversion to GA if inadequate/complications
• Airway: Usually none; oxygen via nasal cannulae/face mask; if heavy sedation or conversion → SGA/ETT as indicated
• Duration: single-shot spinal typically 1.5–3 hours depending on drug/dose/adjuvants; consider CSE/epidural/GA for longer cases
• How painful: intra-op should be painless below block; discomfort from positioning, traction, tourniquet, peritoneal traction (LSCS) may require sedation/analgesia
• Monitoring: standard AAGBI; frequent NIBP (e.g. 1–2 min initially), ECG, SpO2; consider invasive BP in high-risk patients

Definition and key principles

• Injection of local anaesthetic into CSF in the subarachnoid space to produce reversible block of nerve roots and spinal cord pathways
• Produces differential block: sympathetic > sensory > motor (onset and regression differ)
• Block height relates to baricity, dose, volume, patient position, pregnancy, spinal anatomy, and injection characteristics

Relevant anatomy

• Layers traversed (midline): skin → subcut tissue → supraspinous ligament → interspinous ligament → ligamentum flavum → epidural space → dura → arachnoid → subarachnoid space (CSF)
• Adult spinal cord ends ~L1 (range T12–L3); dural sac to ~S2; spinal performed below L2 (commonly L3/4 or L4/5)
• Tuffier’s line (iliac crests) approximates L4 spinous process / L4/5 interspace (variable)
• Dermatomes (useful targets): T4 nipple; T6 xiphisternum; T10 umbilicus; L1 inguinal; S2–4 perineum
  • LSCS typically requires sensory block to ~T4 (and adequate sacral spread)

Physiology of spinal block

• Sympathetic block (T1–L2) causes vasodilation (venous > arterial) → ↓ venous return and ↓ SVR → hypotension
  • Magnitude depends on block height, baseline tone (e.g. hypovolaemia), and aortocaval compression in pregnancy
• Bradycardia: blockade of cardioaccelerator fibres (T1–T4) and reduced venous return (Bezold–Jarisch reflex)
• Respiratory effects: usually minimal if block below T4; high block can impair intercostals; dyspnoea may be due to blocked chest wall sensation with preserved diaphragmatic function
  • Test phonation/ability to speak; consider EtCO2 if sedated
• GI/GU: increased gut motility; urinary retention common (sacral block)
• Thermoregulation: vasodilation and impaired shivering responses below block → hypothermia risk

Indications and advantages

• Lower limb surgery, pelvic surgery, perineal surgery, obstetrics (LSCS), urology (TURP), vascular (selected), analgesia for hip fracture (selected pathways)
• Advantages: avoids airway instrumentation; excellent analgesia; reduced blood loss in some surgeries; reduced thromboembolic risk; awake neurological monitoring; reduced PONV; good for high aspiration risk (if no sedation/GA)

Contraindications (absolute and relative)

• Absolute: patient refusal; infection at site; uncorrected severe hypovolaemia/shock; true LA allergy (rare); raised ICP due to mass lesion/obstructive hydrocephalus; coagulopathy/unsafe anticoagulation; inability to cooperate (context-dependent)
• Relative: sepsis/bacteraemia; fixed cardiac output lesions (e.g. severe AS); severe mitral stenosis; severe pulmonary hypertension; major spinal deformity/previous surgery; neurological disease (risk/benefit); thrombocytopenia (threshold depends on trend/cause); aortic stenosis is not absolute but requires senior planning and haemodynamic strategy

Anticoagulation/antiplatelets (high-yield principles)

• Neuraxial techniques require assessment of bleeding risk: drug, dose, timing, renal function, other agents, traumatic needle pass
• Aspirin alone is usually not a contraindication; dual antiplatelet therapy and recent P2Y12 inhibitors increase risk—follow local/ASRA/ESAIC guidance
• LMWH: avoid neuraxial puncture too close to dosing; ensure appropriate interval before and after; higher-dose regimens require longer intervals
• Warfarin: ensure INR acceptable; DOACs require adequate cessation based on agent/renal function

Local anaesthetic choices and baricity

• Common agent: bupivacaine (0.5%) as hyperbaric (in glucose) or isobaric; levobupivacaine/ropivacaine alternatives
• Baricity = density of solution / density of CSF (at 37°C): hyperbaric sinks, hypobaric rises, isobaric relatively position-independent
• Hyperbaric bupivacaine: more predictable spread with positioning; commonly used for LSCS and lower limb surgery
• Adjuvants: intrathecal opioids (fentanyl, diamorphine/morphine) improve analgesia; clonidine can prolong block but increases hypotension/sedation; preservative-free only
  • Intrathecal morphine/diamorphine: excellent prolonged analgesia but risk of pruritus, PONV, urinary retention, delayed respiratory depression

Technique (practical steps)

• Preparation: consent (including failure/GA conversion, PDPH, nerve injury, infection/bleeding); check anticoagulation; IV access; resus drugs ready; baseline observations
• Position: sitting or lateral; optimise flexion; maintain left uterine displacement in pregnancy
• Asepsis: hat/mask, sterile gloves, skin prep (chlorhexidine in alcohol—allow to dry), sterile drapes; avoid contamination of needle
• Landmark and approach: midline or paramedian; identify L3/4 or L4/5; infiltrate skin with LA
• Needle choice: pencil-point (Whitacre/Sprotte) reduces PDPH vs cutting (Quincke); introducer often used
• Confirm CSF flow (free flow); aspirate gently if needed; inject dose slowly; avoid repeated aspiration with very fine needles if traumatic
• Post-injection: position appropriately (esp hyperbaric); monitor BP closely; assess block (cold/light touch, motor Bromage); document level and haemodynamics

Assessment of block and adequacy

• Sensory testing: cold (A-delta) and light touch (A-beta); surgical anaesthesia correlates better with light touch than pinprick alone
• Motor: Bromage scale; note that motor block may be dense even if sacral sensory sparing exists
• For LSCS: aim T4 to light touch with stable haemodynamics; check ability to tolerate uterine exteriorisation/peritoneal traction (often needs opioid adjunct)

Haemodynamic management (core FRCA)

• Prevention: left uterine displacement (pregnancy), avoid aortocaval compression, judicious fluid loading (co-load often preferred), early vasopressors
• Treat hypotension promptly: vasopressor (phenylephrine or ephedrine depending on HR), fluids, reduce block height if possible (position), consider atropine for bradycardia
  • In obstetrics, phenylephrine is commonly first-line to maintain uteroplacental perfusion; ephedrine associated with more fetal acidosis in some studies
• Severe bradycardia/asystole: call for help, 100% O2, treat as peri-arrest; consider adrenaline early; consider high spinal as cause

Complications and management

• Failure/patchy block: wrong space, inadequate dose/spread, catheter/needle issues; options—wait/reassess, repeat spinal (caution), convert to GA, supplement with sedation/analgesia or peripheral blocks
• High/total spinal: hypotension, bradycardia, nausea, dyspnoea, upper limb tingling, loss of consciousness/apnoea
  • Management: call help; left uterine displacement if pregnant; airway support/ventilation; vasopressors (phenylephrine/ephedrine) and adrenaline if severe; IV fluids; treat bradycardia (atropine) and consider early intubation
• Local anaesthetic systemic toxicity (rare with spinal but possible with wrong drug/route): seizures, arrhythmias
  • Management: ABC, stop injection, intralipid per guidelines, treat seizures, ALS modifications
• Post-dural puncture headache (PDPH): postural headache ± neck stiffness, photophobia, tinnitus; risk reduced with pencil-point small gauge
  • Management: exclude other causes; hydration, simple analgesia, caffeine (selected), antiemetics; epidural blood patch for severe/persistent symptoms
• Neurological injury: transient neurological symptoms, nerve root trauma, cauda equina syndrome (rare), spinal cord injury (avoid high levels)
  • Red flags: progressive weakness, saddle anaesthesia, sphincter dysfunction—urgent MRI/neurosurgical input
• Spinal/epidural haematoma (rare, catastrophic): severe back pain, motor/sensory deficit, bladder/bowel dysfunction
  • Management: urgent MRI and decompression ideally within hours; treat as emergency
• Infection: meningitis, epidural abscess (rare); strict asepsis; investigate fever/back pain/neuro signs
• Hypothermia/shivering; nausea/vomiting (often hypotension-related); urinary retention

Special situations

• Obstetrics: reduced CSF volume and engorged epidural veins → higher spread; dose often reduced; prophylactic vasopressor strategy important
• Elderly: increased sensitivity and reduced physiological reserve; higher hypotension risk; consider lower dose and careful titration (CSE/epidural) for frail patients
• Aortic stenosis/fixed output: spinal may cause profound hypotension; if used, require senior plan, invasive monitoring, vasopressors ready, consider graded neuraxial (CSE/epidural) or GA
• Sepsis: relative contraindication; consider source control, haemodynamic stability, coagulation status; risk of hypotension and neuraxial infection