Isobaric ropivacaine 0.5% 3 mL is administered intrathecally for spinal anaesthesia. Compared to hyperbaric bupivacaine, the MOST important practical difference is:

• A Ropivacaine has more intense motor block than bupivacaine
• B Ropivacaine cannot be administered intrathecally due to neurotoxicity
• C Ropivacaine has a shorter duration than bupivacaine by at least 2 hours
• D Isobaric ropivacaine produces a block independent of patient position after intrathecal injection ✓

Explanation

Isobaric solutions (same density as CSF) are not affected by gravity and therefore spread in the intrathecal space independently of patient positioning after injection. This contrasts with hyperbaric solutions (heavier than CSF), which settle inferiorly and allow deliberate positioning to direct spread. For isobaric ropivacaine, once injected the block distribution is less predictably controllable by posture. Ropivacaine has intrinsically less motor-blocking potency than bupivacaine (differential block). There is no recognised clinical neurotoxicity concern for intrathecal ropivacaine.

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

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Written and medically reviewed by the StethoPrep medical team.