Motor Activity Impaired During Supraclavicular Block
A supraclavicular brachial plexus block primarily impairs motor function of the entire upper extremity, including the shoulder, arm, forearm, and hand, with inability to move the fingers, flex the elbow, and abduct the shoulder being the most significant motor impairments.
Anatomical Basis and Motor Impairment
The supraclavicular block targets the brachial plexus at the level of the trunks and divisions, which affects motor function in the following ways:
Complete motor block (Bromage scale 1): Unable to move feet or knees in neuraxial blocks, but in supraclavicular blocks, this translates to complete inability to move the fingers, wrist, elbow, and shoulder 1
Motor function affected includes:
- Finger flexion and extension
- Wrist movement
- Elbow flexion and extension
- Shoulder movement (particularly abduction)
Assessment of Motor Block
The degree of motor impairment can be assessed using standardized methods:
For upper limb blocks: Assessment of finger movement, wrist flexion/extension, elbow flexion/extension, and shoulder movement 1
Motor block progression: Typically begins distally with finger weakness and progresses proximally to affect the entire limb 1
Clinical Implications
Understanding the motor impairment pattern has important clinical implications:
Surgical applications: Supraclavicular blocks provide excellent anesthesia for procedures on the entire upper extremity, with a success rate of 95.23% compared to 80.95% for axillary approach 2
Respiratory considerations: Supraclavicular blocks may affect the phrenic nerve, potentially impairing diaphragmatic function, which is more pronounced with larger volumes of local anesthetic (30 mL vs. 20 mL) 3
Block selection: When respiratory function is a concern, axillary or infraclavicular blocks may be preferred over supraclavicular blocks to minimize respiratory effects 1
Monitoring and Safety
Proper monitoring of motor function is essential:
Block assessment: Motor function should be assessed before discharge, especially in day surgery settings 1
Patient education: Patients must receive clear instructions about the expected duration of motor impairment and precautions to take while the limb is blocked 1
Protection of limb: The anesthetized limb should be protected until motor function returns, as patients cannot feel or control the affected extremity 1
Potential Complications
Phrenic nerve involvement: May cause diaphragmatic paralysis, which can be assessed by measuring forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) 3
Prolonged block: Motor function typically returns within 6-8 hours, but may occasionally be prolonged 4
Respiratory compromise: More likely with bilateral blocks, which should only be performed with caution and appropriate monitoring 5
Technique Optimization
Ultrasound guidance: Improves block quality and reduces execution time (5.0 min vs. 9.8 min) compared to anatomical landmark techniques 6
Volume considerations: Lower volumes (20 mL vs. 30 mL) of local anesthetic can provide effective blocks while reducing phrenic nerve involvement and preserving pulmonary function 3
Nerve stimulator settings: When using nerve stimulation, eliciting finger movement at 0.9 mA is as effective as reducing to 0.5 mA for successful blocks 7
Understanding the pattern and extent of motor impairment during supraclavicular blocks is crucial for appropriate patient selection, monitoring, and post-procedure care to ensure optimal outcomes and patient safety.