Wrist hyperextension leads to median nerve conduction block: implications for intra-arterial catheter placement

It is common practice to hyperextend the wrist to facilitate insertion of a radial intra-arterial catheter. This position may be maintained for prolonged periods. Although there has been much discussion about optimal patient management to protect the ulnar nerve and brachial plexus, little attention has been paid to the median nerve during wrist hyperextension. The authors report the effects of wrist hyperextension on conduction in the median nerve.

Median nerve conduction was studied in 12 awake, healthy volunteers using standard nerve conduction tests consisting of the measurement of compound sensory and motor action potentials, as well as their amplitudes and latencies. With the contralateral hand as a control, the right wrist was placed in hyperextension (angled between 65 and 80 degrees), and compound action potentials were recorded to determine the onset and magnitude of effects. Subsequently, the hand was released from hyperextension and recovery was recorded.

In 83% of subjects, hyperextension resulted in a significant decrease in compound sensory action potential amplitudes, sufficient to qualify as conduction block (16.6% of baseline). The average time to conduction block was 43 +/- 13.2 min. All subjects who manifested conduction block showed marked improvement 5 min after release from hyperextension.

Wrist hyperextension for arterial line placement and stabilization is likely to result in profound impairment of median nerve function. Although the effects were transient in this study, the results suggest that prolonged hyperextension may be associated with significant changes in median nerve conduction. To minimize the chance for nerve injury, the authors recommend that wrists be returned promptly to the neutral position following arterial line placement.