Abstract ID: A9

Abstract Title: Finding Optimal Position for Ultrasound-Guided Nerve Blocks in the Forearm

Authors: McCartney C¹, Xu D², Constantinescu C³, Chan V⁴
Toronto Western Hospital Toronto ON Canada
Poster Type: Discussion

ABSTRACT BODY

Introduction:
Current techniques for performing median, radial, ulnar blocks in the forearm are restricted to landmark, paresthesia and nerve stimulation endpoints at the elbow or wrist. These areas whilst optimizing surface landmark recognition are limited because of proximity to structures that may lead to vascular or neurological injury. Blocks at the wrist may also miss terminal branches of nerves that arise proximal to the site of injection.
The aim of the present study was to determine by ultrasound the consistency of anatomical location of the median, radial and ulnar nerves in the forearm and to locate a best position that optimizes locating the nerve and placing local anesthetic whilst reducing possibility of neurological or vascular injury.

Materials and Methods:
After research ethics board approval and informed consent 10 ASA I or II adult volunteers were recruited to this observational study. The scans were performed using a Philips HDL5000 ultrasound machine with a 5-12MHz probe in the transverse plane. Wrist and elbow level were marked and then mid-forearm measured and two points at one-third and two thirds distance distal to the elbow were marked and labeled proximal and distal forearm respectively. The median and ulnar nerves were visualized at the elbow, mid-forearm, wrist and at the proximal and distal forearm. The deep and superficial branches of the radial nerve were identified at the elbow and followed proximally to a point 5cm above the elbow. The nerve was then followed distally down past the elbow and as far distal as possible towards the radial styloid.
At each point the distance from skin to nerve was calculated and data is presented as mean (+/-SD). Variations in normal anatomy were also noted. For each nerve a point was chosen that combined ease of visualization, proximity to skin and as far as possible from vascular structures or from areas where the nerve could be exposed to pressure injury (for example when adjacent to bony structures).

Results:
Five males and five females were recruited. Seven volunteers had both forearms scanned and three had one scanned to give a total of 17 forearm scans. The distance from skin to nerve at each location is given in Table 1. Nerves were located in a consistent location apart from one volunteer where the median nerve was lateral to the brachial artery at the elbow. The superficial radial nerve could only be followed past the elbow in 76% of cases but could be followed to the distal forearm in 47% of cases.

Discussion:
The median, radial and ulnar nerves can be consistently visualized using ultrasound in the forearm with minimal anatomical variation. Due to ease of location, distance from vascular structures and location of branching nerves the distal 1/3 of forearm is the most logical location to anesthetize the median (figure 1) and the proximal 1/3 for the ulnar (figure 2) nerves using ultrasound guidance. The radial nerve is most easily seen deep to brachioradialis at the elbow (figure 3) but in order to spare motor function it may be beneficial to block the superficial radial nerve only, where possible, distal to the elbow (figure 4).

ATTACHED FILES

A9_ASRA abstract table.doc

A9_ASRA abstract figures.doc

Reg Anesth Pain Med 2005; 30(3):A9