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A study of the characteristics of single-injection insulated block needles in a biologic model
  1. Anand M. Sardesai, F.R.C.A.,
  2. Nicholas M. Denny, F.R.C.A.,
  3. Martin J. Herrick, F.R.C.A.,
  4. Andy Lynch, Ph.D. and
  5. William A. Harrop-Griffiths, F.R.C.A.
  1. From the Department of Anaesthesia, Norfolk and Norwich University Hospital, Norwich, United Kingdom (A.M.S.)
  2. Department of Anaesthesia, Queen Elizabeth Hospital, King's Lynn, United Kingdom (N.M.D.)
  3. Department of Anaesthesia, Addenbrooke's Hospital, Cambridge, United Kingdom (M.J.H.)
  4. the Centre for Applied Medical Statistics, Department of Public Health and Primary Care, University of Cambridge, Cambridge, United Kingdom (A.L.)
  5. Department of Anaesthesia, St Mary's Hospital, London, United Kingdom (A.W.H.-G.).
  1. Reprint requests: A. M. Sardesai, F.R.C.A., Specialist Registrar in Anaesthetics, Norfolk and Norwich University Hospital, Colney Lane, Norwich, Norfolk, NR4 7UY, UK. E-mail: Sardesai1{at}


Background and objectives Single-injection block needles are manufactured in many different lengths, diameters, and tip designs, but the literature contains no reports of methods to assess clinical characteristics of regional-block needles. A novel animal model for the assessment of the characteristics of single-injection regional anesthesia needles is described.

Methods Nine different needles designed for peripheral nerve blocks that were fitted with identical hubs were used. Pork bellies were used as the biologic model. The bellies were mounted such that the needles passed from inside to outside. The last layer to be penetrated was the skin. Ten experienced and blinded anesthesiologists scored the feel, resistance, and usability of the 9 needles during their passage through similarly prepared pork bellies. Two identical (index) needles were included in the study to assess the internal validity of the study.

Results The overall scoring was acceptably consistent and repeatable and showed statistically significant differences between the needles tested. The needles that were judged the most usable were those with a moderate resistance to passage through the tissue and a high degree of feel, which was defined as the ability to appreciate the passage of the needle through the tissue planes. Needles with very high or very low resistances and those with poor feel scored poorly on the usability scale. Differences in individuals' assessment of the index needles suggested some within-subject variability during the study.

Conclusions This type of biologic model can be used for the quantifiable and repeatable assessment of different needle tip designs. Needles with moderate resistance and high feel were preferred.

  • Biologic models
  • Needles
  • Conduction anesthesia

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  • Dr. N. M. Denny is a paid consultant to B Braun, Melsungen, Germany.