Real‐time continuous monitoring of injection pressure at the needle tip for peripheral nerve blocks: description of a new method

Abstract

The measurement of injection pressure during the performance of peripheral nerve blocks can be pivotal to detect intraneural placement of the needle tip and thus avoid intrafascicular injection. However, injection pressure can only be measured along the injection line (tubing), which is influenced by several factors. The primary aim of this feasibility study was to describe and validate the principle of a novel nerve-block needle conceived for real-time continuous monitoring of injection pressures at the needle tip. Our secondary aim was to provide measurements and compare injection pressure values at the needle tip and in the injection line. Four porcine lower limb anatomic models were prepared and extraneural injections were performed with fractioned boluses of 2 ml saline at a controlled infusion rate of 10 ml.min (0.16 ml.s ). Injection pressure at the needle tip was monitored and compared with the pressure in the injection line. The system proved to be reliable. Thirty injections were successfully performed without technical failures. The mean (95%CI) difference between pressures at the needle tip and the injection line varied substantially from 14.33 (12.58-16.08) kPa at 0.5 ml injected volume to 41.56 (39.66-43.45) kPa at the end of the injection. This study demonstrates that the described system allows for real-time continuous monitoring of injection pressure at the needle tip. Moreover, this study shows that injection pressure values measured in the injection line cannot be assumed to be a reliable indicator of the injection pressure at the needle tip.

The effect of rate of injection on injection pressure profiles measured using in‐line and needle‐tip sensors: an in‐vitro study

“…Even if the rationale underpinning these studies is sound, the methodology of many of them has one major pitfall: the measurement of injection pressure is along the injection line, assuming that this value reflects the pressure measured at the needle tip. This assumption is incorrect as the pressure along the injection line is influenced by various parameters of the injection system including rate of injection, size of the needle (internal diameter and length) and size and compliance of the injection line (connection tubing) .…”

“…Δp is the pressure created by flow resistance within the needle and injection line and it follows the Hagen–Poiseuille law for laminar flow ; for the needles typically used in regional anaesthesia procedures, the flow is laminar at an injection rate < 30 ml.min −1 (0.5 ml.s −1 ) :…”

The ability of a real‐time injection pressure monitoring system to discriminate between perineural and intraneural injection of the sciatic nerve in fresh cadavers

“…An exact measurement of injection pressure at the needle tip is essential in order to understand the flow dynamics at the injection site . Measurement of injection pressure is considered to be a pivotal element in the detection of intraneural placement of a peripheral nerve block needle in order to reduce the risk of nerve damage .…”

“…Measurement and, consequently, limitation of injection pressure during a nerve block procedure may be of value in reducing the risk of nerve damage . There is only one device currently available that measures injection pressures along the injection line (BSmart™, B.Braun Melsungen AG, Melsungen, Germany) but the accuracy of in‐line pressure measurement has been questioned as this is influenced by several factors including speed of injection and dimensions of the needle and connecting injectate lines . Moreover, the system only measures initial opening injection pressure and does not allow continuous monitoring of pressure throughout the period of infiltration.…”

“…We have shown in a previous in‐vitro study that precise continuous monitoring of injection pressure at the needle tip can be achieved with a sensing needle consisting of an optical fibre pressure sensor embedded within the shaft of standard nerve block needle (Lightsens Medical SA, Bellinzona, Switzerland). The sensor consists of a Fabry–Pérot optical cavity bonded to the tip of an optical fibre.…”