N. Herman et al., NO ADDITIONAL METAL-PARTICLE FORMATION USING THE NEEDLE-THROUGH-NEEDLE COMBINED EPIDURAL SPINAL TECHNIQUE, Acta anaesthesiologica Scandinavica, 40(2), 1996, pp. 227-231
Background. Combined epidural/spinal analgesia utilizing a needle-thro
ugh-needle technique has become very popular in anesthesia. However, f
indings of concave deformities at the orifice of Tuohy needles after s
pinal needle passage have raised concerns that metal fragments might b
e deposited within the epidural space. This study was proposed to inve
stigate whether the needle-through-needle technique does produce metal
lic flecks. Methods. Ten unused Tuohy and Hustead epidural needles wer
e inspected microscopically and photomicrographed prior to flushing sa
line through each into a single tissue culture well. After drying, a s
ingle pass was made with a 120 mm 24-gauge Sprotte needle through each
epidural needle to maximal extension while the orifice was within ano
ther tissue culture well. Each needle was again flushed into a third w
ell before reexamination and photomicroscopy. Each of the wells was in
spected for metallic particles by microscopy. Additional freshly unpac
kaged Tuohy needles were microscopically examined after exposure to a
magnetic field. Results. Comparison of micrographs before and after ne
edle experiments revealed concave deformities at the orifice of all th
e Tuohy and Hustead needles. No particles were observed in either of t
he two saline-flushed wells or within the well in which the needle-thr
ough-needle passes were made. Inspection of unused Tuohy needles expos
ed to a magnetic field revealed metal filings ''standing up'' along th
e bevel of every needle examined. Conclusions. Metallic particles are
not produced by the needle-through-needle technique. However, metal pa
rticles are an apparent contaminant of all epidural needles and are pr
obably routinely introduced into patients when the needle is placed.