A new rule for femoral nerve blocks

Acupuncture points are described by use of a proportional system that is based on the width of the thumb at the level of the distal interphalangeal joint, defined as 1 CUN. Our study tested first the correlation between the CUN and weight and height in 500 Americans and second the hypothesis that the CUN system is superior to the conventional landmarks to localize the femoral nerve 1 or 2 cm lateral to the artery in a prospective, double-blinded, randomized study.

Sixty-two patients were randomized to receive a femoral nerve block by a needle entry point either 1 CUN lateral, 1 cm lateral, or 2 cm lateral to the femoral artery at the level of the inguinal crease. The time from needle entry to injection of local anesthetic was measured by an investigator blind to the technique, who also counted the frequency of needle repositioning, graded the ease of the block and its success, and registered complications.

Good correlation occurred between weight and CUN (r = 0.79) and height and CUN (r = 0.83), which indicates that the CUN of a normal person (predefined as 175 cm tall and 70 kg weight) is 18.7 +/- 1 mm. In the CUN group, the femoral block was achieved significantly faster (P < .01) with fewer attempts (P < .003). The success rate was the same and complications did not differ significantly between the groups.

A needle insertion point 1 CUN lateral to the midpoint of the palpated femoral artery at the level of the inguinal crease makes femoral nerve blocks faster and easier compared with conventional landmark 1 cm to 2 cm lateral to the artery.