High Spinal Block

High spinal block is spread of subarachnoid local anaesthetic to a level higher than the expected dermatome, usually T1 to T4 or higher, causing cardiovascular and respiratory compromise. It lies on a continuum with total spinal block.

Epidemiology. It occurs in about 1 in 100 to 1 in 1,000 spinal anaesthetics, more often in obstetric patients, obese patients and with epidural top up after a failed spinal.

Risk factors. Pregnancy, obesity, short stature, older age, raised intra-abdominal pressure, hyperbaric solution with head down tilt, high dose, repeated dosing, epidural volume extension and accidental subdural or intrathecal catheter placement.

Pathophysiology.

Cephalad spread blocks sympathetic cardiac accelerator fibres (T1 to T4), causing bradycardia and hypotension. Blockade of cervical and thoracic motor roots (C3 to C5 for phrenic nerve, intercostals) impairs ventilation, and brainstem exposure causes loss of consciousness.

Numbness or weakness of the arms and hands, dyspnoea, difficulty speaking or coughing, nausea, anxiety, bradycardia, hypotension, Horner syndrome and loss of consciousness or apnoea at the extreme.

Red flags.

• Inability to speak or breathe.
• Bradycardia under 40/min.
• Loss of consciousness.
• Fixed dilated pupils.

Clinical. Test sensory level with cold or pinprick, and record motor power in the hands and respiratory effort. Exclude other causes of collapse.

Differential diagnosis.

• Local anaesthetic toxicity.
• Anaphylaxis.
• Amniotic fluid embolism.
• Haemorrhage.
• Vasovagal reaction.
• Subdural block.

Call for help, give 100% oxygen, lie the patient flat (with uterine displacement in pregnancy), and support ventilation. Intubate if the patient cannot breathe or loses consciousness. Sedate once airway is secured, because the patient may be aware.

• Atropine: 500 microgram IV, repeated every 3 to 5 minutes; maximum 3 mg; monitor heart rate; use caution in glaucoma and tachyarrhythmia.
• Ephedrine: 6 to 12 mg IV every 2 to 3 minutes for hypotension with bradycardia; maximum 50 mg; monitor blood pressure and heart rate; tachyphylaxis occurs.
• Phenylephrine: 50 to 100 microgram IV every 1 to 2 minutes, or infusion 25 to 50 microgram/min; maximum 200 microgram/min; monitor blood pressure and heart rate; may worsen bradycardia.
• Adrenaline: 10 to 50 microgram IV in severe hypotension, then 0.05 to 0.5 microgram/kg/min; titrate; monitor ECG; avoid excess in ischaemia.

Give IV fluid (500 to 1000 mL crystalloid), keep the patient supine, and start cardiopulmonary resuscitation for arrest. In pregnancy, perform delivery within 5 minutes of arrest.

Prevention. Reduce spinal dose in pregnancy, older adults and obesity, avoid epidural top up after spinal without monitoring, position carefully, and test levels regularly.

Monitoring. Continuous ECG, blood pressure every 1 to 2 minutes, saturation, sensory level and respiratory effort until block regresses (usually 2 to 4 hours).

Referral and escalation. Senior anaesthetic and critical care help. Paediatric team if delivery.