Nerve puncture and apparent intraneural injection during ultrasound-guided axillary block does not invariably result in neurologic injury

Ultrasound controlled nerve stimulation in the elbow region: high currents and short distances needed to obtain motor responses

BACKGROUND

Electrical nerve stimulation is commonly used to perform peripheral nerve blocks. The purpose of this study was to investigate the relation between stimulating currents and the distance between the needle-tip and stimulated nerves.

METHODS

In 18 volunteers the radial and ulnar nerves were stimulated in the elbow region from opposite directions. Needle-to-nerve distances were measured by high-frequency ultrasound when motor responses to electrical stimulation were elicited with currents of 5, 2, 1 and 0.5 mA and impulse widths of 0.1 ms. Additionally, current thresholds for nerve stimulation were identified when the needle-tip was in contact with the nerve.

RESULTS

The ulnar nerves responded to electrical stimulation from a significantly greater distance than the radial nerves. Threshold levels at needle-to-nerve contact ranged from 0.4 to 4.5 mA for the radial nerve and from 0.32 to 2.0 mA for the ulnar nerve. They were significantly lower for the ulnar nerve than for the radial nerve. Currents required to obtain neuromuscular responses often exceeded the recommended current levels for nerve stimulation.

CONCLUSIONS

Our results show significant differences in the ease of stimulation between the radial and ulnar nerves. High current thresholds and short nerve-to-needle distances were often needed to obtain neuromuscular responses in two nerves in the elbow region.

Ultraschallgezielte Anästhesie peripherer Nerven

Ultrasound-guided anaesthesia of peripheral nerves is a new challenge for anaesthesiologists. The number of ultrasound users in this field has increased over the last 10 years because of improved high frequency ultrasound technology and increased mobility of machines. There have been many publications on blocking procedures but many questions still remain unanswered on the practical aspects of ultrasound-guided techniques. Basic knowledge in ultrasound technology and image characteristics and a defined approach to blocking procedures to ensure sterile working conditions are necessary to guarantee optimal safety of patients. Furthermore economic questions and the implementation of a standardised education program are very important.

Ultrasound-Guided Regional Anesthesia: Current Concepts and Future Trends

The scope of ultrasound imaging guidance for regional anesthesia is growing rapidly. Preliminary data, although limited, suggest that ultrasound can improve block success rate and decrease complications. In this review, we describe the basic principles of ultrasound scanning and needling techniques for nerve blocks, highlight some of the data on clinical outcome, discuss specific limitations of ultrasound for regional anesthesia, and speculate on the future direction for physician training and competency assessment with this technology.