P002: NEEDLE TIP RECOIL FOLLOWING NEEDLE ADVANCE: A POSSIBLE MECHANISM FOR FALSE LOSS OF RESISTANCE?
Samsun Lampotang, PhD, Brandon Lopez, MD, Andre Bigos, David Lizdas, BSME, Anthony DeStephens, MSME, Terrie Vasilopoulos, PhD, Nikolaus Gravenstein, MD, Michael Cometa, MD; University of Florida
Introduction: Loss of resistance (LOR) is the most common technique to identify the epidural space. However, when using fluoroscopy to confirm the accuracy of needle placement within the epidural space, incidence of false LOR can be high, e.g., 74.7% during cervical interlaminar epidural injections at C7-T1. To distinguish true LOR from false LOR, techniques like applying pressure with two fingers at the needle entry point have been devised (bi-digital pressure test; BiP Test). We made an incidental observation (needle tip recoil) during a simulator-based study that may be a potential mechanism for false LOR.
Methods: After IRB approval and informed consent, we studied three LOR techniques on a custom-built mixed reality simulator with 45 providers: Incremental needle advancement, with Intermittent LOR assessment (II); Continuous needle advancement, with high-frequency Intermittent LOR assessment (CI); and Continuous needle advancement, with Continuous LOR assessment (CC). Participants pushed a needle tracked with a magnetic sensor (sub-millimeter resolution) near its tip into gel simulating human tissue. LOR is simulated by allowing the plunger to slide forward if tapped and can be felt only when the needle tip position is past a virtual LOR plane. Each provider identified LOR using each technique 5 times with LOR set at random depths in the simulator software. To assess differences among the 3 LOR techniques in occurrence of false LOR, Cochran’s Q test was used, which is a repeated measures analysis for dichotomous outcomes. This accounts for potential within-participant correlations among the techniques. We replaced the gel block with a lower spine of a freshly slaughtered pig with a fat layer of ~20 mm to determine if needle recoil is present in animal tissue as well.
Results: We unexpectedly observed needle recoil with all 3 techniques: II, CI, and CC, averaging 2.5 to 3.5 and as high as 5 mm (Fig. 1). Needle recoil when releasing pressure on the syringe can cause the needle tip to retract behind the virtual LOR plane after initially obtaining LOR, thus creating a false LOR position (Fig. 1). There was a higher likelihood of the final overshoot position retaining LOR with the II technique versus CC or CI (χ2=7.9, df=2, P=0.019; Fig 2). We obtained similar magnitudes (average ~3 mm, as high as 5 mm) of needle tip recoil in animal tissue (Fig. 1) if the needle initially traversed the fat layer, as those obtained in gel.
Figure 1. Needle advancement over time for various advancement techniques in ballistics gel and pig tissue medium.
Figure 2. Percentage of participants who retained LOR at final needle depth.
Conclusion: If our simulator and pig needle tip recoil data are representative of what occurs in actual patients, our findings suggest a potential new mechanism for explaining false LOR and new ways to clinically address false LOR. Our data seem to support performing a second LOR assessment before advancing the catheter to verify if the initial LOR is still present, especially with a continuous needle advancement technique. Our data requires verification in a clinical study with actual patients.