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Injection line pressure - inaccurate but still useful?

Last post 05 Feb 2019, 12:01 PM by Michael Lim. 0 replies.
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  •  05 Feb 2019, 12:01 PM 2729

    Injection line pressure - inaccurate but still useful?

    Barrington and Lirk [1] and Saporito et al [2] make many valid arguments with regard to pressure monitoring during regional anaesthesia. However, I would like to dispel the implicit assumption that because injection line pressure is not an accurate reflection of needle-tip pressure, it is not useful. Being a positive pressure system, in-line pressure is equal or higher than the needle-tip pressure. If we are guided by in-line pressure, we err on the side of lower and therefore, safer needle-tip pressure.

    There is one scenario where in-line pressure is equal to needle-tip pressure and that is when there is no flow, assuming a patent fluid system. The in-line pressure at which flow starts, that is, the "opening pressure", will then be a reasonably accurate (if safer) reflection of needle-tip pressure.  

    As one of the authors of a paper [3] cited in the editorial [1], I regularly use the clinically improvised pressure gauge we described, which is a three-way tap with an air-filled 1 ml syringe inserted between the needle and the syringe, in my practice as an orthopaedic anaesthetist. I apply the principles described above, with the added bonuses of high availability, low cost and quick construction.  

    M. Lim

    Cardiff and Vale University Health Board,

    Cardiff, Wales.


    No external funding and no conflicts of interest declared.


    1. Barrington MJ, Lirk P. Reducing the risk of neurological complications after peripheral nerve block: what is the role of pressure monitoring? Anaesthesia 2019; 74: 9-12.  

    2. Saporito A, Quadri C, Kloth N, Capdevila X. The effect of rate of injection on injection pressure profiles measured using in‐line and needle‐tip sensors: an in‐vitro study. Anaesthesia 2019; 74: 64–8.

    3. Patil J, Ankireddy H, Wilkes A, Williams D, Lim M. An improvised pressure gauge for regional nerve blockade/anesthesia injections: an initial studyJournal of Clinical Monitoring and Computing 201529: 673–9.

    Dr Michael Lim
    Consultant Anaesthetist
    Cardiff and Vale University Health Board
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