Spinal anaesthesia overview

What it is (definition) and what it does

• Spinal anaesthesia = injection of local anaesthetic (± opioid) into cerebrospinal fluid (CSF) in the subarachnoid space, usually in the lower back.
• Produces a dense, reliable block: loss of pain (sensory), weakness (motor), and sympathetic block (vasodilation → low blood pressure).
• Typically rapid onset (minutes) with a fixed duration (depends on drug/dose).
• Common uses: lower limb surgery, hip fracture surgery, caesarean section, some urology and lower abdominal procedures (depending on level needed).

How it differs from epidural (simple comparison)

• Spinal: into CSF, small volume, fast onset, dense block, single-shot most common.
• Epidural: outside dura, larger volume, slower onset, can top up via catheter, more titratable.
• A spinal is usually simpler and quicker, but less adjustable once given.

Indications (common first-time scenarios)

• Lower limb orthopaedics (e.g., hip fracture, knee arthroplasty) where regional is appropriate.
• Obstetrics: caesarean section (often with intrathecal opioid for postoperative analgesia).
• Urology: TURP/TURBT (allows early detection of symptoms and reduces GA exposure in some patients).
• Patients where avoiding airway instrumentation is beneficial (but only if spinal is appropriate and safe).

Contraindications (know the big ones)

• Patient refusal or inability to cooperate (absolute).
• Infection at injection site or systemic sepsis (relative/absolute depending on severity and local policy).
• Uncorrected hypovolaemia or severe haemodynamic instability (high risk of profound hypotension).
• Coagulopathy/anticoagulation: follow local neuraxial guidelines (timing of LMWH/DOACs/warfarin/antiplatelets).
• Raised intracranial pressure due to a mass lesion (risk of herniation).
• Severe aortic stenosis or other fixed-output states: spinal-induced vasodilation may be poorly tolerated (specialist discussion).
• Allergy to planned drugs (rare for amide local anaesthetics).

Pre-procedure checks (safe routine)

• Confirm: correct patient, procedure, side, consent for spinal (and discuss risks/benefits/alternatives).
• Review: anticoagulants/antiplatelets and last doses; check platelet count/coagulation if indicated; check for infection and neurological symptoms.
• Baseline observations and IV access (working cannula).
• Plan monitoring: ECG, NIBP, SpO2; set frequent BP cycling (e.g., every 1–2 min initially, then every 3–5 min).
• Prepare vasopressors and fluids before starting (e.g., metaraminol/phenylephrine/ephedrine per local practice).
• Position plan and airway backup: always be ready to convert to GA if needed.

Equipment and drugs (what you’ll typically need)

• Sterile pack: gloves, drapes, skin prep (chlorhexidine in alcohol if appropriate; allow to dry), gauze.
• Spinal needle (e.g., 25G–27G pencil-point if available to reduce PDPH; introducer needle often needed).
• Local anaesthetic for skin (e.g., lidocaine 1%).
• Intrathecal drug: commonly hyperbaric bupivacaine 0.5% (dose varies by context) ± opioid (e.g., fentanyl/diamorphine per local policy).
• Syringes, filter needle if required by local policy, labels, sharps bin.
• Resuscitation readiness: oxygen, suction, airway equipment, vasopressors, atropine, antiemetic.

Anatomy and landmarks (simple and practical)

• Aim below the end of the spinal cord (adult cord usually ends around L1; spinal is commonly performed at L3/4 or L4/5).
• Use iliac crests line (Tuffier’s line) roughly crosses L4 spinous process (approximate).
• Midline approach: through supraspinous ligament → interspinous ligament → ligamentum flavum → dura → CSF.
• Paramedian approach can help in older patients with difficult midline anatomy (ask for supervision early if unfamiliar).

Step-by-step technique (single-shot spinal)

• Position: sitting or lateral; aim for flexion (curved back) while keeping patient comfortable and stable.
• Asepsis: clean widely, allow antiseptic to dry, drape; maintain sterile field.
• Infiltrate skin with small amount of local anaesthetic.
• Insert introducer (if using) then spinal needle; advance slowly with control.
• Confirm free-flowing CSF (not just a flash): aspirate gently if needed; rotate needle if no flow.
• Inject intrathecal drug slowly; avoid moving needle during injection.
• Remove needle, apply dressing; position patient as planned (baricity and position affect spread).
• Start close haemodynamic monitoring immediately; treat hypotension early.

Assessing the block (don’t rush surgery)

• Sensory level: test with cold (ice/ethyl chloride) or light touch; document dermatome level on both sides.
• Motor block: e.g., straight leg raise / Bromage score (simple: can they lift legs?).
• Time: allow adequate onset; recheck before incision and after positioning.
• For caesarean section: typical target is around T4 sensory block (nipple line); confirm before knife-to-skin.
• If block is patchy or low: pause, reassess, consider time, position, dose, and whether conversion to GA is safer.

Physiology and haemodynamics (what to expect)

• Sympathetic block causes vasodilation → reduced venous return → hypotension; may also cause bradycardia (especially high block).
• Treat early: left uterine displacement in pregnancy, fluids as appropriate, vasopressors per local practice.
• Common symptoms: nausea, dizziness, feeling faint—often due to hypotension; treat the BP first.
• High/total spinal: severe hypotension, bradycardia, difficulty breathing, arm weakness, reduced consciousness—this is an emergency.

Common complications and immediate management

• Hypotension: check BP frequently; give vasopressor boluses/infusion per local protocol; consider fluid bolus; treat nausea with BP correction ± antiemetic.
• Bradycardia: treat promptly (e.g., atropine) and address hypotension; consider adrenaline in severe cases.
• High spinal: call for help, lay flat, support airway/ventilation, give vasopressors (may need adrenaline), prepare for intubation and GA.
• Failed/partial spinal: do not repeatedly re-attempt without a plan and senior input; consider alternative anaesthetic.
• Post-dural puncture headache (PDPH): postural headache days later; manage with hydration, simple analgesia, caffeine (local policy), and consider epidural blood patch via experienced clinician.
• Neurological injury/infection/haematoma: rare but serious; new weakness, numbness, severe back pain, bladder/bowel dysfunction—urgent senior review and escalation.

Aftercare and documentation (what to write down)

• Document: indication, consent, asepsis, level attempted, needle type/gauge, number of attempts, drugs and doses, patient position, sensory level achieved, haemodynamics and treatments.
• Handover: block level, intrathecal opioid given (and implications for monitoring), any complications, plan for analgesia and antiemetics.
• Post-op monitoring: observe for hypotension, urinary retention (procedure-dependent), pruritus/respiratory depression if intrathecal opioid used (follow local obstetric/acute pain guidance).