Hyperbaric bupivacaine 0.5% heavy is used for spinal anaesthesia in a patient undergoing LSCS. What makes this formulation 'hyperbaric' and how does baricity affect spread?

• A Adrenaline addition; vasoconstriction prolongs duration
• B NaCl addition; isobaric spread unaffected by position
• C Glucose removal; hypobaric solution rises regardless of position
• D Dextrose addition; heavy solution sinks, affecting spread by patient position ✓

Explanation

Hyperbaric bupivacaine 0.5% contains 8% dextrose, giving it a specific gravity higher than CSF (~1.026 vs CSF ~1.003). This means it sinks by gravity, so positioning (Trendelenburg, lateral tilt) determines spread — useful for unilateral spinal or saddle blocks. Isobaric solutions spread mainly by drug concentration gradients and volume injected. Hypobaric solutions float and are used in select positions (e.g., prone for anorectal surgery). For LSCS, the 15-degree left lateral tilt of the operating table is used after injection to promote bilateral spread and prevent aortocaval compression.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.