What volume of 0.75% hyperbaric bupivacaine (local anesthetic) should be used for an intrathecal bolus for hip arthroplasty in a patient who is 5 feet 9 inches tall?

Intrathecal Bupivacaine Dosing for Hip Arthroplasty

For a patient 5 feet 9 inches tall undergoing hip arthroplasty, use 2-3 mL of 0.75% hyperbaric bupivacaine (15-22.5 mg) intrathecally, with the lower end of this range (2 mL/15 mg) preferred to minimize hypotension while maintaining adequate surgical anesthesia.

Recommended Dosing Strategy

Primary Dose Selection

• The standard intrathecal dose is 15 mg bupivacaine (2 mL of 0.75% solution), which provides reliable surgical anesthesia with sensory blockade typically reaching T6-T8 within 15 minutes 1
• The American Society of Anesthesiologists recommends low-dose intrathecal bupivacaine (<10 mg) specifically for elderly patients to reduce hypotension risk, but for standard adult patients undergoing hip arthroplasty, 15 mg remains the established dose 2, 3
• For longer surgical procedures, 22.5 mg (3 mL of 0.75% solution) produces very long-lasting blockade with deep motor engagement, particularly suitable for hip surgery of extended duration 1

Patient Height Considerations

• At 5 feet 9 inches (175 cm), this patient falls within average adult height range
• The volume and concentration of 0.75% hyperbaric bupivacaine (rather than patient height alone) primarily determines spread, with hyperbaric solutions providing more predictable spread than isobaric formulations 4
• When 15 mg bupivacaine was administered in glucose-containing solutions, no difference in sensory blockade occurred regardless of volume (2 mL vs 3 mL), suggesting concentration matters more than total volume for standard patients 1

Administration Technique

Positioning and Injection

• Administer the injection with the patient in sitting position and maintain this position for 2 minutes post-injection to optimize spread 1
• After injection, position patient supine with left uterine displacement (if applicable) or neutral supine positioning
• Hyperbaric solutions produce more predictable spread and fewer high blocks compared to isobaric solutions 4

Adjuvant Considerations

• Add intrathecal morphine 0.1 mg (100 mcg) to the bupivacaine for superior postoperative analgesia without significantly increasing side effects 2, 5
• The 0.1 mg dose provides optimal balance between analgesic efficacy and side effect profile in patients undergoing hip arthroplasty, with 0.2 mg associated with significantly more pruritus (23% incidence) 6, 5
• Intrathecal morphine 0.1 mg reduces postoperative pain scores and morphine consumption for up to 24 hours postoperatively 4, 6

Monitoring and Safety

Hemodynamic Management

• Bupivacaine 0.75% in glucose solution (22.5 mg dose) produces more marked blood pressure effects than lower doses, requiring vigilant vasopressor support 1
• The 15 mg dose (2 mL) provides adequate anesthesia with less hemodynamic impact
• Avoid simultaneous administration of spinal and general anesthesia as this causes precipitous blood pressure drops 2, 3

Common Pitfalls to Avoid

• Do not use doses below 15 mg for hip arthroplasty, as inadequate surgical anesthesia may result, requiring conversion to general anesthesia
• Avoid exceeding 22.5 mg unless surgical duration is expected to be exceptionally long (>3 hours), as higher doses increase hypotension risk without improving block quality 1
• If using intrathecal morphine, monitor for respiratory depression for 24 hours postoperatively, though clinically significant depression is rare at the 0.1 mg dose 5

Clinical Context

The evidence strongly supports single-shot spinal anesthesia over epidural or general anesthesia for hip arthroplasty, as it avoids limb weakness, bladder dysfunction, and delayed mobilization associated with epidural techniques 4. The 0.75% concentration provides adequate density for predictable hyperbaric spread while the 2-3 mL volume range (15-22.5 mg) balances surgical requirements against hemodynamic stability 1.