The baricity of a spinal anaesthetic solution determines its spread within the intrathecal space. A hyperbaric solution (e.g., heavy bupivacaine) is prepared by adding:

• A Normal saline
• B Distilled water (hypotonic)
• C Epinephrine
• D 8% dextrose in water ✓

Explanation

Baricity describes the density of a local anaesthetic solution relative to cerebrospinal fluid (CSF, density ~1.003–1.008 g/mL). Heavy (hyperbaric) bupivacaine is prepared by mixing bupivacaine with 8% glucose (dextrose), giving it a density greater than CSF so it sinks to dependent positions. The patient's posture is used to direct the block — sitting position concentrates the block in the perineum (saddle block) while Trendelenburg position can extend the block cephalad. Plain (isobaric) bupivacaine has similar density to CSF and spreads less predictably.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.