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Reduced Injection Pressures Using a Compressed Air Injection Technique (CAIT): An In Vitro Study
  1. Ban C.H. Tsui, M.Sc., M.D., F.R.C.P.C.,
  2. Mark P. Knezevich, M.D. and
  3. Jennifer J. Pillay, B.Sc.
  1. Department of Anesthesiology and Pain Medicine, University of Alberta, Edmonton, Alberta, Canada.


Background and Objectives: High injection pressures have been associated with intraneural injection and persistent neurological injury in animals. Our objective was to test whether a reported simple compressed air injection technique (CAIT) would limit the generation of injection pressures to below a suggested 1,034 mm Hg limit in an in vitro model.

Methods: After ethics board approval, 30 consenting anesthesiologists injected saline into a semiclosed system. Injection pressures using 30 mL syringes connected to a 22 gauge needle and containing 20 mL of saline were measured for 60 seconds using: (1) a typical “syringe feel” method, and (2) CAIT, thereby drawing 10 mL of air above the saline and compressing this to 5 mL prior to and during injections. All anesthesiologists performed the syringe feel method before introduction and demonstration of CAIT.

Results: Using CAIT, no anesthesiologist generated pressures above 1,034 mm Hg, while 29 of 30 produced pressures above this limit at some time using the syringe feel method. The mean pressure using CAIT was lower (636 ± 71 vs. 1378 ± 194 mm Hg, P = .025), and the syringe feel method resulted in higher peak pressures (1,875 ± 206 vs. 715 ± 104 mm Hg, P = .000).

Conclusions: This study demonstrated that CAIT can effectively keep injection pressures under 1,034 mm Hg in this in vitro model. Animal and clinical studies will be needed to determine whether CAIT will allow objective, real-time pressure monitoring. If high pressure injections are proven to contribute to nerve injury in humans, this technique may have the potential to improve the safety of peripheral nerve blocks.

  • Injection pressure
  • Intraneural injection
  • Nerve block techniques
  • Nerve injury

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  • Reprint requests: Ban C.H. Tsui, M.Sc., M.D., F.R.C.P.C., Department of Anesthesiology and Pain Medicine, 8-120 Clinical Sciences Building, University of Alberta, Edmonton, Alberta T6G 2G3, Canada. E-mail: btsui{at}

  • Supported in part by a Clinical Investigatorship Award, Alberta Heritage Foundation for Medical Research, Alberta, Canada. This work was presented, in part, as a resident's abstract at the Canadian Anesthesiologists' Society annual meeting, June 16-20, 2006.