title: The effect of needle dimensions and infusion rates on injection pressures in regional anaesthesia needles: a bench-top study.
abstract: Animal studies have shown that injection pressures > 75 kPa indicate probable intrafascicular needle tip position. This study describes the flow/pressure characteristics of seven common needle systems. A syringe pump delivered flow rates of 5, 6.67, 10, 13.3, 15 and 20 ml.min(-1) through these needle systems, while keeping the needle tips open to atmosphere. A pressure transducer connected between the syringe and needle provided a real-time graphical display for analysis. Mean plateau pressures increased linearly with flow and with decreasing needle diameter (2.7-92 kPa). Flow rates > 17 ml.min(-1) and needle sizes 22 G and smaller produced mean plateau pressures > 75 kPa. Pressure monitors upstream from the needle may produce false-positive alarms at high flow rates due to needle resistance, and unreliable readings due to non-laminar flow. We recommend injection rates ≤ 15 ml.min(-1) (0.25 ml.s(-1) ) to reduce the effect of factors upstream from the needle tip as a cause of high pressure readings.
authors.affiliation: Department of Anaesthesia and Intensive Care, Airedale General Hospital, Steeton, UK.
authors.forename: J J
authors.initials: JJ
authors.lastname: Patil
authors.forename: S
authors.initials: S
authors.lastname: Ford
authors.forename: C
authors.initials: C
authors.lastname: Egeler
authors.forename: D J
authors.initials: DJ
authors.lastname: Williams
mesh_terms: D000765:Anesthesia, Conduction / Q000295:instrumentation*; D004867:Equipment Design; D007260:Infusion Pumps / Q000706:statistics & numerical data; D007267:Injections / Q000295:instrumentation / Q000706:statistics & numerical data; D009339:Needles / Q000145:classification* / Q000706:statistics & numerical data*; D011312:Pressure; D012212:Rheology / Q000379:methods / Q000706:statistics & numerical data; D013594:Syringes / Q000706:statistics & numerical data