What is the most commonly injured nerve under general anesthesia?

The Ulnar Nerve is the Most Commonly Injured Nerve Under General Anesthesia

The ulnar nerve is the most commonly injured nerve under general anesthesia (answer b), accounting for 28% of all anesthesia-related nerve injuries according to closed claims analysis 1.

Epidemiology and Risk Factors of Perioperative Nerve Injuries

• Ulnar nerve injuries represent the largest proportion (28%) of all anesthesia-related nerve injuries, followed by brachial plexus (20%), lumbosacral nerve root (16%), and spinal cord (13%) 1
• Ulnar nerve injuries occur predominantly in male patients (75%) and frequently have a delayed onset of symptoms (62%) compared to other nerve injuries 1
• 85% of ulnar nerve injuries are associated with general anesthesia rather than regional techniques 1
• Elderly patients are at higher risk of preventable peripheral nerve injuries during prolonged surgery, particularly affecting the ulnar nerve when in supine position 2

Mechanism of Ulnar Nerve Injury

• The ulnar nerve is particularly vulnerable at the elbow where it passes through the cubital tunnel, making it susceptible to compression and stretch injuries 3
• Mechanical factors caused by malpositioning of the arm during anesthesia and operation result in direct compressive nerve injury 4
• The ulnar nerve demonstrates greater sensitivity to ischemia compared to median and radial nerves, showing earlier and more significant decreases in signal amplitude during brachial artery occlusion 5
• Hypermobility of the nerve is a predisposing local factor for injury 4

Prevention Strategies

• Every operating theatre should be equipped with quantitative neuromuscular monitoring devices to monitor nerve function throughout anesthesia 2
• The ulnar nerve is the most useful site for neuromuscular monitoring, but readings may be unreliable if thumb movement is impeded 2
• Padded armboards may decrease the risk of upper extremity neuropathies during positioning 2
• Specific padding (e.g., foam or gel pads) at the elbow may decrease the risk of ulnar neuropathy 2
• Avoid positions that place direct pressure on the ulnar nerve at the elbow or extreme elbow flexion for prolonged periods 4
• Perform a simple postoperative assessment of extremity nerve function for early recognition of peripheral neuropathies 2

Special Considerations

• In some circumstances, the use of padding may paradoxically increase the risk of peripheral neuropathies if applied incorrectly 2
• Adequate perfusion of the upper extremities should be ensured during anesthesia, as the ulnar nerve shows particular sensitivity to decreased blood supply 5
• The mechanism for most ulnar nerve injuries remains unclear despite their prevalence, making prevention strategies challenging 1
• Documentation of specific perioperative positioning actions is recommended for continuous improvement processes 2

Monitoring and Early Detection

• Quantitative neuromuscular monitoring is essential and should be used throughout all phases of anesthesia 2
• Probable sites of nerve injury should be comprehensively padded before surgery and assessed routinely every 30 minutes throughout the procedure 2
• Monitoring should be applied after induction of general anesthesia but before neuromuscular blockade 2
• Adequacy of recovery should be demonstrated and documented before patient awakening and extubation 2