Total Spinal Anaesthesia

Total spinal anaesthesia is complete cephalad spread of local anaesthetic in the subarachnoid space (or subdural space), causing apnoea, unconsciousness and profound hypotension within minutes. It is a life threatening complication.

Epidemiology. Rare (about 1 in 3,000 to 1 in 20,000 neuraxial blocks). It follows accidental intrathecal injection of an epidural dose (often 10 to 20 mL), subdural catheter placement or overdose of intrathecal drug.

Risk factors. Failed spinal followed by epidural, epidural top up through a catheter that has migrated intrathecally, large epidural volumes after dural puncture, obstetric patients, obesity and head down position.

Pathophysiology.

Local anaesthetic reaches the brainstem and cervical segments, blocking respiratory drive, sympathetic outflow and consciousness. Loss of sympathetic tone causes vasodilation and bradycardia.

Onset within 3 to 10 minutes: rapidly ascending numbness and weakness, dyspnoea, inability to speak, dilated pupils, bradycardia, severe hypotension, apnoea, loss of consciousness and asystole.

Red flags.

• Apnoea or inability to speak.
• Severe bradycardia or asystole.
• Fixed dilated pupils.

Clinical, in context of recent neuraxial injection. Aspirate catheters for cerebrospinal fluid before each top up, and give a test dose (3 mL of local anaesthetic with adrenaline).

Differential diagnosis.

• Local anaesthetic systemic toxicity.
• Intravascular injection.
• Anaphylaxis.
• Pulmonary embolism.
• Cardiac arrest from other cause.
• Subdural block.

Call for help, secure the airway with intubation, ventilate with 100% oxygen, and give vasopressors and fluids. Tilt left or displace the uterus in pregnancy.

• Atropine: 500 microgram to 1 mg IV, repeated every 3 to 5 minutes; maximum 3 mg; monitor heart rate.
• Adrenaline: 10 to 100 microgram IV, then 0.05 to 0.5 microgram/kg/min; titrate to blood pressure; monitor ECG and blood pressure; avoid excess in ischaemia. In arrest give 1 mg IV every 3 to 5 minutes with resuscitation.
• Phenylephrine or noradrenaline: noradrenaline 0.05 to 0.5 microgram/kg/min; titrate; monitor blood pressure; peripheral extravasation risk.
• Sedation after intubation: propofol 1 to 3 mg/kg/h IV (maximum 4 mg/kg/h for under 48 hours), to prevent awareness.

Fluids 1 to 2 L crystalloid. Perform delivery within 5 minutes of arrest in pregnancy. Consider cerebrospinal fluid drainage and lavage in selected severe cases when overdose is recognised early (specialist use). Support until the block resolves in 2 to 6 hours or longer with large volumes.

Prevention. Aspirate before injection, use test doses, fractionate epidural doses (3 to 5 mL boluses) and watch for sudden changes.

Monitoring. Continuous ECG, blood pressure, capnography and sedation depth until recovery. Neurological examination after the block resolves.

Referral and escalation. Critical care. Incident report and disclosure.