PENG Block Dosing for 0.5% Bupivacaine
For a PENG block in adults, use 20 mL of 0.5% bupivacaine (100 mg total) without dilution with normal saline. This concentration and volume provides optimal postoperative analgesia with acceptable motor-sparing characteristics.
Evidence-Based Dosing
The most robust evidence comes from recent randomized controlled trials specifically evaluating PENG blocks:
0.5% bupivacaine at 20 mL volume demonstrated superior analgesic efficacy compared to lower concentrations (0.25% and 0.125%), with significantly lower pain scores and morphine consumption 1
No dilution is recommended - the evidence supports using 0.5% bupivacaine as-is rather than diluting it with normal saline. Studies comparing 0.5%, 0.375%, and 0.25% bupivacaine all used 20 mL volumes of the respective concentrations 2
Volume matters more than you might think - a recent non-inferiority trial showed 10 mL provided adequate analgesia, but 20 mL remains the standard studied volume with proven efficacy 3
Concentration-Specific Outcomes
The 0.5% concentration provides:
- Faster sensory block onset compared to 0.25% 2
- Longer time to first analgesic requirement (delayed rescue analgesia need)
- Reduced total opioid consumption in the first 24-48 hours 1
- Shorter hospital stays compared to control groups 1
Motor Block Considerations
Critical caveat: 0.5% bupivacaine causes significantly more quadriceps weakness at postoperative hour 0 compared to lower concentrations 1. This is transient but clinically relevant:
- Quadriceps weakness was significantly higher immediately post-surgery with 0.5% versus 0.25% or 0.125%
- This weakness typically resolves within 6-12 hours
- Does not delay ambulation in most patients when balanced against superior analgesia
Practical Application
Standard adult PENG block recipe:
- Draw up 20 mL of 0.5% bupivacaine (100 mg total dose)
- No dilution with normal saline needed
- Inject under ultrasound guidance between the psoas tendon and pubic ramus
- Maximum safe dose: 2.5 mg/kg for bupivacaine (well within limits for most adults) 4
Alternative Concentrations
If motor-sparing is paramount (e.g., early ambulation protocols, outpatient surgery):
- 0.25% bupivacaine at 20 mL provides good analgesia with minimal motor block 2
- Expect slightly longer onset time and potentially higher opioid requirements
- Still superior to placebo or no block
Pediatric Considerations
The provided guidelines are for pediatric peripheral nerve blocks and recommend 0.25% bupivacaine at 0.2-0.5 mL/kg for various lower extremity blocks 4. However, PENG blocks are not specifically addressed in pediatric guidelines, and the adult dosing above should not be extrapolated to children without institutional protocols.
What NOT to Do
- Don't dilute 0.5% bupivacaine with normal saline - there's no evidence supporting this practice for PENG blocks, and you'll reduce efficacy
- Don't use volumes <10 mL - insufficient spread to target nerves
- Don't exceed 20 mL - no additional benefit demonstrated, increases risk of systemic toxicity
- Don't use 0.5% if same-day discharge with immediate ambulation is planned - the motor block may delay discharge