Abstract ID: A1

Abstract Title: INTRANEURAL ELECTRICAL STIMULATION AND ULTRASOUND DETECTION OF INTRANEURAL INJECTION

Authors: Brull R1, Chan V2, Shannon P3
         Toronto Western Hospital Toronto Ontario Canada1, Toronto Western Hospital Toronto Ontario Canada2, Mount Sinai Hospital Toronto Ontario Canada3
Poster Type: Either


ABSTRACT BODY

INTRODUCTION: Inadvertent intraneural injection of local anesthetic during peripheral nerve blockade can cause nerve injury. Surrogate indicators of intraneural injection, including pain and high pressure on injection, can be misleading. The dual objectives of this animal study are to determine the minimum stimulating current associated with intraneural needle placement and to characterize the sonographic appearance of intraneural injection.
MATERIALS AND METHODS: Following general endotracheal anesthesia, 5 pigs underwent surgical dissection to expose the brachial plexus at the upper chest bilaterally. A 22 gauge insulated needle (Stimuplex®, B. Braun) was inserted lengthwise 2 cm intraneurally under direct vision at the midpoint of each exposed nerve (28 total) and then stimulated at 1 Hz and 100 μsec duration using a nerve stimulator (Stimuplex® HNS11, B. Braun). The minimum stimulating current required to elicit a distal muscle twitch was recorded in triplicate by a blinded research assistant. Under ultrasound imaging (15 MHz scan head, Phillips HDI 5000 System), 2.5 mL dextrose 5% combined with 2.5 mL India Ink stain (total 5 mL) was injected intraneurally over 30 seconds and the images were video recorded to determine the change in nerve diameter before and after injection. Each of the 28 nerves was subsequently harvested for histological examination and the pigs were sacrificed under general anesthesia.
RESULTS: The median minimum current required to elicit a distal twitch with intraneural needle placement was 0.43 mA (range: 0.02 - 5.0 mA). Isolated nerve expansion (figures 1 and 2) was visualized by ultrasound during intraneural injection in 24 of 28 nerves. The mean difference in nerve diameter between pre- and post-intraneural injection as measured by ultrasound image was 0.28 cm (SD: 0.15 cm). Gross examination of nerve stain distribution was consistent with ultrasound findings and revealed complete absence of intraneural injectate in 3 specimens and minimal intraneural injectate in 1 specimen. Histological examination revealed injectate penetration of the epineurium in 24 of 28 specimens with penetration of the perineurium in 2 of 28 specimens.
DISCUSSION: This preliminary animal study suggests that ultrasound is a useful and reliable technique to detect intraneural injection under the study conditions described. Further, our data suggest that a muscle twitch achieved above the conventional stimulating threshold of 0.5 mA may not exclude intraneural needle placement.

ATTACHED FILES

A1_Figure 1.ppt

A1_Figure 2.ppt



Reg Anesth Pain Med 2005; 30(3):A1