CLINICAL PROBLEM

A successful ultrasound-guided peripheral nerve block (PNB) procedure consists of injecting the local anesthetic (LA) perineurally, i.e. extraneurally, as close as possible to the nerve, so that the LA spreads properly around the nerve with a minimal volume injected.

The problem is that, due to the limitations of ultrasound imaging, its resolution prevents detailed visualization of millimeter anatomical structures, and the image may be misinterpreted. In many cases, structures and especially nerve boundaries are not clearly visible. In addition, an involuntary millimeter displacement of the needle tip may occur during injection without being noticed.

Clinical reality tells us that, when injecting close to the nerve, it is not uncommon to inadvertently inject intraneurally, which you want to avoid because it can cause serious consequences.

Recent evidence still reports an incidence of inadvertent intraneural injection of around 16%–17% in the hands of experienced practitioners.1,2

Rates of residual paresthesia and/or numbness after ultrasound-guided peripheral nerve blocks has been estimated to be as high as 0.18 to 0.4%.1,3 Other reports suggest that the incidence of transient neurological symptoms can be as high as 2.6 to 16%.4,5 The most feared complication is permanent paralysis.

There is a need to reduce at minimum the incidence of these complications due to inadvertent intraneural injections that can have a devastating impact on patients’ life with associated social implications and costs.

UNMET NEED

Monitoring the injection pressure can be pivotal to safely and effectively perform a perineural injection in close proximity to the nerve, and to be able to stop an inadvertent intraneural injection as soon as possible, since injection into a low-compliance structure such as a nerve causes a sudden increase in pressure.

High injection pressures during intraneural injection may be indicative of intrafascicular injection and may predict the development of neurologic injury. Kapur6 found nerve lesions with intraneural injections > 20 psi, Hadzic7 with intraneural injections > 25 psi, and Hasanbegovic8 with intraneural injections > 15.9 psi.

Avoiding excessive injection pressures during PNB procedure reduce the risk of neurological complications. The widely recognized safety guideline recommends injecting at a pressure below 15 psi.9

With injection pressure monitoring, the anesthesiologist can immediately stop the injection if there is a sudden increase in pressure caused by an inadvertent intraneural needle position, reposition the needle, and start again, always maintaining a low injection pressure profile.

THE SMART NEEDLE SOLUTION

The Smart Needle is a disposable sensing needle that provides accurate, objective, and easily understandable real-time continuous monitoring of the injection pressure at the needle tip, the real pressure in the tissues.

Monitoring the injection pressure right at the needle tip (instead of along the injection line) is essential to have a reliable and reproducible measurement of the real pressure in the tissues, but also to have a measurement that is not affected by the injection system and its parameters, i.e. injection speed, needle and connecting tube size, and connecting tube compliance.

  1. Liu SS, YaDeau JT, Shaw PM, Wilfred S, Shetty T, Gordon M. Incidence of unintentional intraneural injection and postoperative neurological complications with ultrasound-guided interscalene and supraclavicular nerve blocks. Anaesthesia 2011;66:168-74.
  2. Hara K, Sakura S, Yokokawa N, et al. Incidence and effects of unintentional intraneural injection during ultrasound-guided subgluteal sciatic nerve block. Reg Anesth Pain Med 2012;37:289–93.
  3. Sites BD, Taenzer AH, Herrick MD, Gilloon C, Antonakakis J, Richins J, Beach ML. Incidence of local anesthetic systemic toxicity and postoperative neurologic symptoms associated with 12,668 ultrasound-guided nerve blocks: An analysis from a prospective clinical registry. Reg Anesth Pain Med 2012;37:478-82.
  4. Bilbao AA, Sabaté A, Porteiro L, Ibanez B, Koo M, Pi A. Neurological complications associated with ultrasound-guided interscalene and supraclavicular block in elective surgery of the shoulder and arm. Prospective observational study in a university hospital. Rev Esp Anestesiol Reanim 2013;60:384-91.
  5. Widmer B, Lustig S, Scoles CJ, Molloy A, Leo SP, Coolican MR, Parker DA. Incidence of severity of complications due to femoral nerve blocks performed for knee surgery. Knee 2013;20:181-5.
  6. Kapur E, Vuckovic I, Dilberovic F, Zaciragic A, Cosovic E, Dinanivic K-A,Mornjakovic Z, Babic M, Borgeat A, Thys DM, Hadzic A. Neurologic and histologic outcome after intraneural injections of lidocaine in canine sciatic nerves. Acta Anaesthesiol Scand 2007;51:101–7.
  7. Hadzic A, Dilberovic F, Shah S, Kulenovic A, Kapur E, Zaciragic A, Cosovic E, Vuckovic I, Divanovic K-A, Mornjakovic Z, Thys D, Santos AC. Combination of Intraneural Injection and High Injection Pressure Leads to Fascicular Injury and Neurologic Deficits in Dogs. RAPM 2004;29:417-23.
  8. Hasanbegovic I, Kulenovic A, Hasanovic S. Effects of intraneural and perineural injection and concentration of ropivacaine on nerve injury during peripheral nerve block in wistar rats. Journal of Health Science 2013; 3:243-49.
  9. Carassiti, M., et al., Injection pressures measuring for a safe peripheral nerve block. Minerva Anestesiologica 2019;85:1003-13.
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