RAPID ONSET OF ULNAR NERVE DYSFUNCTION DURING TRANSIENT OCCLUSION OF THE BRACHIAL-ARTERY

Perioperative ulnar neuropathy is a complication that occurs even in p atients who seem to be appropriately padded and positioned. The dispro portionately high incidence of postoperative ulnar nerve injury compar ed with the median and radial nerves has largely been attributed to it s vulnerability to compression or stretch at the cubital tunnel. Some clinical and laboratory evidence suggests that compromise of perfusion to the upper extremity may also play a role in this complication. To determine whether the ulnar nerve is more sensitive to ischemia of the upper extremity, we studied 10 men during general anesthesia. Somatos ensory evoked potentials of the radial, median, and ulnar nerves were simultaneously recorded during general anesthesia with the brachial ar tery occluded proximal to the cubital fossa. All three nerves showed r apid changes in signal amplitude in response to occlusion of the brach ial artery, but the amplitude of the ulnar nerve was affected earlier and to a greater degree. Compared with the median nerve, the change in ulnar nerve signal amplitude during ischemia was significantly greate r after 4 min (P = 0.002). This trend persisted at 6 and 8 min (P = 0. 008). At 4, 6, and 8 min of ischemia, the ulnar nerve likewise showed a greater decrease in amplitude compared with the radial nerve, with c orresponding P values of 0.015, 0.008, and 0.008. We conclude that the ulnar nerve is more sensitive to ischemia of the upper extremity comp ared with the radial and median nerves. In addition to its increased v ulnerability at the elbow, compromise of arterial flow may contribute to some cases of postoperative ulnar neuropathy. Implications: Postope rative ulnar neuropathy is thought to result from compression or stret ch of the ulnar nerve at the elbow. However, patients may sustain this complication despite careful padding and positioning. This study sugg ests that the ulnar nerve may also be unusually sensitive to decreases in blood supply to the arm. Care should not only to properly position and pad the elbows, but also to ensure adequate perfusion of the uppe r extremities.