An improvised pressure gauge for regional nerve blockade/anesthesia injections: an initial study

Abstract

High injection pressure is one of the warning signs of intraneural injection, with animal models suggesting pressures higher than 69 or 176 kPa as high risk, and is normally detected subjectively and inaccurately. We describe a system improvised from common clinical components that uses Boyle's law to objectively measure injection pressure. The objectives of the study were to (1) Validate our improvised pressure gauge (IPG) by comparing the injection pressure as calculated by Boyle's law against the measured pressure and (2) Use the IPG to measure the range of injection pressures by two groups of anesthetic professionals using the "syringe feel" technique. Our IPG system consists of an extended 1 ml syringe attached to a 3-way stopcock, inserted between the syringe containing the local anesthetic injectate and the needle. The IPG was validated against a pressure calibration reference. 20 anesthesiologists and 20 anesthetic assistants were recruited to apply pressure to the 20 ml syringe in vitro while blinded to the attached IPG. The pressures were measured on three separate occasions for each participant. There was good agreement (<8 percent difference) between the measured and theoretical pressure values. Anesthesiologists exceeded the threshold of 69 kPa in 18 of a total of 60 attempts whereas anesthetic assistants exceeded the threshold in 30 attempts out of 60 attempts. Anesthetic assistants exerted a higher overall pressure of 80 kPa compared to 51 kPa for anesthesiologists-this was statistically significant (p = 0.027). Our improvised system is easily and rapidly assembled from common clinical equipment and shows promise as a monitor for inadvertent intraneural injection.

Advances of Techniques in Deep Regional Blocks

“…The concept of “half-the-air” to keep injection pressure below 15 psi derives from the reliability of compressed air injection technique [ 22 , 23 ], and the facility-independent half-the-air setting helps popularize injection pressure monitoring in clinical practice by the advantages of low cost, easy assembling, and incorporating a test syringe (ensuring the total mass of local anesthetic to be delivered) and a long (200 cm) extension tube (facilitating the operation for the assistant, thus physical ergonomics) with a low dead space (1.4 mL) [ 9 ]. Thereafter, another improvised pressure gauge was proposed using the fluid meniscus level in the 1 ml syringe in place of D5W syringe as the passive indirect in-line manometer [ 24 ]. However, as with the drawback of the commercial in-line manometer, this improvised pressure gauge lacks a pop-off valve to limit the injection pressure and/or eliminate the initial high peak pressure [ 20 , 24 ].…”

“…Thereafter, another improvised pressure gauge was proposed using the fluid meniscus level in the 1 ml syringe in place of D5W syringe as the passive indirect in-line manometer [ 24 ]. However, as with the drawback of the commercial in-line manometer, this improvised pressure gauge lacks a pop-off valve to limit the injection pressure and/or eliminate the initial high peak pressure [ 20 , 24 ]. In other words, with the in-line manometer only as a monitor, “syringe feel” is still performed at the very beginning of injection.…”

“Knowing It Before Blocking It,” the ABCD of the Peripheral Nerves: Part C (Prevention of Nerve Injuries)

“…Apart from providing enhanced safety of PNBs, the BSmart offers some advantages such as objective monitoring of injection pressure, warning of high injection pressure, prevention of too forceful and rapid injections, consistent monitoring of resistance to injection regardless of who performs the actual injection, and standardized and objective documentation of injection pressure information. However, such assembly may produce false-positive readings during higher injection flow rates [ 48 ] due to changed injectate flow characteristics from laminar to turbulent flow during rapid injection or the inherent resistance to flow from the needle shaft [ 48 ]. Since this manometer is disposable, it is unknown if its accuracy will degrade with repeated use or if the piston will become less free to move with multiple injections.…”

Reducing the risk of neurological complications after peripheral nerve block: what is the role of pressure monitoring?

“…In humans, injection pressure monitoring has been shown to give a positive (pathological) signal upon needle‐nerve contact injection against fascial planes , or injection at high speed , suggesting good sensitivity but low specificity for intraneural injection. Following a review of factors associated with the risk of nerve injury after peripheral nerve block, Sondekoppam et al concluded that there is inadequate evidence (low quality) supporting the use of injection pressure monitoring for preventing nerve injury .…”

“…The experimental setups by Claudio et al and Patil et al which seemed to suggest that physicians are bad at detecting high injection pressures cannot be simply translated to the clinical situation, where dynamic sonographic information on needle‐tip localisation is combined with visual and tactile information during incremental injection of small fluid volumes to confirm needle‐tip location. Whether active measurement of injection pressure curves (or opening injection pressure ) has the potential to elevate patient safety above the level provided by expert use of ultrasound guidance combined with tactile cues and situational awareness (hopefully today's scenario) remains unclear.…”