Motor Sparing Lower Extremity Block
Recommended Techniques
- The American Society of Anesthesiologists recommends using low-dose local anesthetic concentrations (0.1-0.25% bupivacaine or ropivacaine) to minimize motor block while maintaining sensory analgesia 1
Monitoring and Assessment
- The Anaesthesia society recommends using straight-leg raising ability as a screening tool to assess motor function, with a strength of evidence level of high 2, 3
- The Anaesthesia society suggests implementing the Bromage scale to document the degree of motor block, with a moderate level of evidence 4
- Regular monitoring of motor function is recommended to detect any unexpected progression of block, with a high level of evidence 2
Important Considerations
- The Anaesthesia society emphasizes that motor sparing blocks are crucial when monitoring for compartment syndrome, as they allow for continued assessment of leg strength as a critical monitor of spinal cord health, with a high level of evidence 5
- For patients at risk of acute compartment syndrome, the ability to perform straight-leg raising serves as an important clinical indicator, with a moderate level of evidence 5, 6
Cautions and Pitfalls
- The American Society of Anesthesiologists advises against attributing prolonged motor block (>24 hours) solely to expected effects of local anesthetic, as this may delay diagnosis of serious complications, with a high level of evidence 1
- The Anaesthesia society recommends being vigilant for unexpected extensive block, which may indicate misplaced catheter or developing complications, with a moderate level of evidence 2, 4
- If a patient is unable to straight-leg raise at 4 hours post-block, escalation to anesthesiologist assessment is recommended immediately, with a high level of evidence 3
- The Anaesthesia society suggests considering adding adjuncts cautiously as they can increase the density and duration of blocks, with a moderate level of evidence 5