Continuous spinal anaesthesia

Surgical approach (if relevant)

• Not a surgical operation; technique used to provide neuraxial anaesthesia/analgesia for surgery.
• Typical procedures where CSA may be chosen: hip fracture fixation/hemiarthroplasty, major lower limb vascular surgery, lower abdominal surgery in high-risk patients, obstetrics (rare, selected cases).

Anaesthetic management (overview)

• Type of anaesthesia: neuraxial regional (continuous intrathecal local anaesthetic titration) ± light sedation; GA backup plan required.
• Airway: usually spontaneous ventilation with standard monitoring; have airway equipment ready. If conversion to GA: ETT or SGA depending on aspiration risk and surgical requirements.
• Duration: can be prolonged (hours) because block is titratable/extendable via intrathecal catheter; useful when duration uncertain.
• How painful: provides dense surgical anaesthesia; postoperative analgesia possible with low-dose intrathecal LA/opioid (practice varies; many use CSA primarily for intra-op anaesthesia).
• Key physiological issue: sympathectomy → hypotension/bradycardia; avoid large initial dose; incremental dosing and proactive haemodynamic strategy.

Definition and rationale

• CSA = placement of a catheter into the intrathecal space to allow incremental dosing of local anaesthetic (± opioid) to achieve and maintain a desired block height.
• Rationale: compared with single-shot spinal, CSA allows titration (smaller aliquots), potentially less abrupt sympathectomy, adjustable duration, and ability to manage unpredictable surgical duration.
• Distinguish from epidural: intrathecal doses are much smaller, onset is rapid, block is denser, and risk profile differs (e.g., PDPH, high spinal).

Indications (typical FRCA framing: when is CSA advantageous?)

• High-risk patients where avoiding GA is desirable and haemodynamic stability is critical: severe aortic stenosis (controversial; requires expert titration), severe LV dysfunction, severe respiratory disease.
  • Key point for viva: neuraxial techniques in fixed cardiac output lesions require extreme caution; CSA may be chosen by experts because it can be titrated, but it is not automatically “safe”.
• Elderly/frail with hip fracture where single-shot spinal may cause profound hypotension; CSA can be used to incrementally reach T10–T12 (or as required) with smaller doses.
• Surgery of uncertain duration where a dense neuraxial block is required and epidural may be unreliable/slow: complex lower limb/vascular procedures.
• When epidural is difficult or has failed but neuraxial is still desired (case-dependent).

Contraindications

• Same as other neuraxial techniques: patient refusal, infection at site, uncorrected hypovolaemia, raised ICP due to mass lesion, true LA allergy, inability to cooperate/position (relative).
• Anticoagulation/antiplatelets: follow current national guidance for neuraxial procedures; intrathecal catheter increases concern because removal is also a neuraxial intervention—plan insertion and removal timing.
  • Viva emphasis: always state you will check the latest guideline and document timing of last dose and planned catheter removal.
• Relative: severe aortic stenosis/fixed cardiac output lesions, severe pulmonary hypertension—requires senior decision-making, invasive monitoring consideration, and incremental dosing.

Equipment and set-up

• Standard neuraxial asepsis: hat/mask, sterile gown/gloves, chlorhexidine in alcohol (allow to dry), sterile drapes.
• CSA catheter options:
  • Microcatheter (very small-bore intrathecal catheter) inserted via spinal needle (historically associated with cauda equina syndrome when used with hyperbaric 5% lidocaine and maldistribution; rarely used in many settings).
  • Standard epidural catheter placed intrathecally via a Tuohy needle (intentional dural puncture) — easier to handle but larger dural hole → higher PDPH risk.
• Filters/connection: use a bacterial filter and secure, clearly label as INTRATHECAL to prevent wrong-route injection; minimise dead space and ensure staff awareness.
• Monitoring: standard AAGBI monitoring; consider arterial line for high-risk patients or anticipated haemodynamic lability.
• Resuscitation readiness: vasopressors drawn up (phenylephrine/metaraminol/ephedrine), atropine/glycopyrrolate, intralipid, airway/ventilation equipment.

Technique (stepwise)

• Consent: include neuraxial risks (failure, hypotension, high spinal, PDPH, infection, bleeding/haematoma, nerve injury) and CSA-specific issues (catheter misplacement, dosing errors, prolonged CSF leak).
• Position: sitting or lateral; identify interspace (often L3/4 or L4/5).
• Needle insertion and CSF confirmation; then advance catheter a short distance into intrathecal space.
  • Avoid excessive catheter advancement (aim minimal length intrathecally, e.g., ~2–3 cm) to reduce risk of nerve root irritation/knotting (practice varies by kit).
• Aspirate gently to confirm free-flowing CSF before each dose; inject incremental aliquots with time to assess effect (e.g., every 3–5 min).
• Secure catheter, label clearly, document drug concentrations and total intrathecal dose.

Drugs and dosing (principles + example regimens)

• Principle: use small intrathecal aliquots and titrate to effect; avoid a large initial bolus.
• Local anaesthetic choices: bupivacaine (common), levobupivacaine, ropivacaine; hyperbaric vs isobaric affects spread and predictability.
• Example incremental bupivacaine dosing (adult): 0.5% plain or heavy in 0.2–0.5 mL aliquots (1–2.5 mg) every 3–5 min until target block achieved; typical total dose often lower than single-shot spinal for similar surgery, but varies widely with patient and target height.
  • For hip surgery, a pragmatic target may be around T10 (variable by procedure); assess sensory level and motor block.
• Intrathecal opioid: fentanyl (e.g., 10–25 micrograms) may improve block quality and reduce LA requirement; morphine provides prolonged analgesia but increases risk of delayed respiratory depression and pruritus—use with appropriate monitoring and local policy.
• Test dose concept: because intrathecal placement is confirmed by CSF, a traditional epidural test dose is not required; however, a very small initial aliquot is effectively a functional test to avoid sudden high block.

Physiology and haemodynamic management

• Mechanism of hypotension: sympathetic blockade → venodilation (↓ venous return) ± arterial dilation (↓ SVR) → ↓ CO; bradycardia from cardioaccelerator fibre blockade (T1–T4) and reduced venous return (Bezold–Jarisch reflex).
• Prevention/management: incremental dosing, left uterine displacement if pregnant, judicious fluid (avoid overload in frail/heart failure), early vasopressors, treat bradycardia promptly.
  • Vasopressor choice: phenylephrine (SVR), metaraminol (SVR + some inotropy), ephedrine (HR/CO) depending on physiology and heart rate.
• High spinal recognition: rapid ascending sensory block, upper limb tingling/weakness, dyspnoea, hypotension, bradycardia, nausea, reduced consciousness; treat immediately.

Complications (CSA-specific emphasis)

• High/total spinal: risk increased if dosing errors or rapid boluses; manage with airway support, ventilation, vasopressors, atropine, and GA if required.
• PDPH: risk depends on dural hole size; potentially higher if using Tuohy with intrathecal epidural catheter. Manage with conservative measures and consider epidural blood patch when indicated.
• Neurological injury: direct trauma, neurotoxicity, cauda equina syndrome (historical association with microcatheters + concentrated lidocaine + maldistribution). Avoid high concentrations/large doses; use appropriate solutions and incremental dosing.
• Infection: meningitis/arachnoiditis—strict asepsis, minimise duration, monitor for fever/back pain/neurological symptoms.
• Intrathecal catheter issues: migration, kinking, knotting, breakage, difficult removal; manage with gentle traction, patient repositioning; seek senior help and follow local policy if resistance or breakage.
• Drug error/wrong-route injection: catastrophic if epidural doses given intrathecally; mitigate with labelling, dedicated line, restricted access, and team briefing.

Postoperative care

• Monitoring: haemodynamics until block regresses; motor/sensory checks; urinary retention risk.
• If intrathecal opioid used: respiratory rate/sedation monitoring per local policy (especially with morphine).
• Catheter removal: treat as neuraxial catheter removal—consider anticoagulation timing; document intact catheter tip; observe for neurological symptoms after removal.

Comparison with alternatives (useful in viva)

• Single-shot spinal: simple, rapid, reliable; but fixed dose/duration and potentially abrupt sympathectomy.
• Epidural: titratable and can provide postop analgesia; slower onset, less dense block, higher failure rate in some settings; larger doses and risk of systemic toxicity.
• CSE: combines rapid onset spinal with epidural top-ups; avoids intrathecal catheter but retains epidural catheter benefits; still has sympathectomy from spinal dose.
• Peripheral nerve blocks: avoid sympathectomy; may be preferable in severe cardiac disease; may not provide complete surgical anaesthesia for some operations and can be time-consuming.