NO ADDITIONAL METAL-PARTICLE FORMATION USING THE NEEDLE-THROUGH-NEEDLE COMBINED EPIDURAL SPINAL TECHNIQUE

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.