In a patient undergoing peripheral nerve block, which resolves first, motor or sensory function?

Resolution of Peripheral Nerve Block: Motor vs Sensory

Sensory function recovers before motor function after peripheral nerve block. 1

Physiological Basis for Differential Recovery

The FDA drug label for bupivacaine clearly establishes that the order of nerve function loss during block onset follows a specific sequence: (1) pain, (2) temperature, (3) touch, (4) proprioception, and (5) skeletal muscle tone. 1 This progression is directly related to nerve fiber diameter, myelination, and conduction velocity. 1

During block resolution, this sequence reverses—meaning motor function (skeletal muscle tone) returns last, after sensory modalities have already begun recovering. 1

Clinical Evidence of Recovery Patterns

Research directly measuring both sensory and motor recovery demonstrates that:

• Recovery of motor function occurs simultaneously with recovery of pinprick sensation when measured by quantitative methods (isometric muscle force testing). 2
• However, when assessed by the Bromage scale (the standard clinical tool), full motor recovery (Bromage scale = 0) was attained 1.5-2.5 hours later than when assessed by quantitative methods, indicating that complete motor function restoration lags behind sensory recovery. 2
• The Bromage scale only captures the first part of the regression phase, missing the final stages of motor recovery. 2

Practical Clinical Implications

Expected Recovery Timeline

• For intrathecal bupivacaine, sensorimotor block typically resolves in 2-3 hours. 3, 4
• For epidural administration, sensory block recovery takes 3-5 hours. 3, 4
• Patients should be tested for straight-leg raising ability at 4 hours after the last spinal/epidural dose as a screening tool. 3, 4

Assessment Protocol

• If a patient cannot perform straight-leg raising at 4 hours, an anesthesiologist must be called immediately for full neurological assessment. 3, 4
• The Bromage scale should be used for formal documentation when detailed motor block assessment is required. 4

Critical Safety Consideration

Motor block persisting beyond 24 hours should never be attributed solely to expected local anesthetic effects, as this may delay diagnosis of serious complications like epidural hematoma, which can cause irreversible neurological damage if not evacuated within 8-12 hours. 3, 5

Discharge Safety for Peripheral Nerve Blocks

Patients may be safely discharged home with residual sensory or motor blockade from peripheral nerve blocks, provided:

• The limb is protected. 6
• Appropriate support is available at home. 6
• The expected duration of blockade is explained. 6
• Written instructions are provided regarding conduct until normal power and sensation return. 6
• Oral analgesics are started before the local anesthesia begins wearing off. 6