Real-time needle-tracking ultrasound facilitates needle placement in a phantom gel model

Editor, Visualisation of the needle and especially of the needle-tip using ultrasound in regional anaesthesia can be difficult and requires clinical training and profound skills. Improvements attributed to modern navigation techniques may facilitate needle placement during regional anaesthesia. In this randomised crossover study (Ethical approval No. 13/303; German Clinical Trials Register: DRKS00005581), we evaluated the impact of a novel ultrasound needle guidance system (UltrasonixGPS, Richmond, British Columbia, Canada) for needle placement in a phantom gel model. The primary endpoint was time to needle placement utilising a guidance positioning system (GPS) compared with conventional ultrasound (CON). To analyse efficacy and safety of GPS in comparison to CON, secondary endpoints included the needle to target distances and the incidence of accidental target puncture in the simulated nerve structures. Forty-four anaesthetists in various phases of clinical training were included and allocated into the following categories: junior residents (1 to 18 months of experience; 12/44), advanced residents (19 to 36 months; 7/44), senior residents (37 to 60 months; 10/44) and certified anaesthetists (15/44). All participants performed four needle placements: Once each they used the in-plane GPS, in-plane CON, out-of-plane GPS and out-of-plane CON technique. The sequence was randomised and distributed among study participants to eliminate training errors. Participants were instructed to place the needle in close proximity to a simulated nerve structure without touching or penetrating. Time from the beginning of needle insertion into the gel model until final position announced by the participants was recorded as the time to needle placement. Procedures were considered a failure if simulated nerve structures were penetrated or the needle to target distance was greater than 5 mm. Investigations were monitored by a single instructor (D.S.). Due to immediate time and distance measurements during the investigation process, blinding of the instructor was not possible. Blinding of the participants was impossible due to the red silhouette that indicated the needle position thereby revealing the use of the GPS technique. The SonixTouchGPS Ultrasound System with the proprietary 8 cm 19-gauge GPS needle was used for all attempts. The GPS was turned on and off on the basis of the randomised technique. The GPS provided an on-screen needle representation in relation to the transducer. A red silhouette indicated the real-time needle position, while the projected path was outlined in green. Simulation of nerve structures was achieved using a gel model (Blue Phantom, Redmond, Washington, USA) containing deep and superficial nerve structures and simulated vessels filled with red dye.1 Calculating 44 individuals, there was a medium effect size δ/σ = 0.43 using a paired t-test (significance level 5%, power 80%, calculation with G*Power 3.1.7). Using a novel simulation model, a power calculation based on existing published data could not be performed. Statistical analysis was performed with SPSS (IBM SPSS 22.0; IBM Corp., New York, USA). The Wilcoxon signed-rank test for paired observations was used to compare time to needle placement and needle to target distances. Accidental target puncture rates of the simulated nerve structures in the gel model were compared using the McNemar test. Performance time for needle placement was significantly decreased for the in-plane and the out-of-plane approach using the GPS when compared with CON without GPS guidance. Needle to target distance in terms of more precise needle-tip placement was reduced using GPS guidance in the out-of-plane technique. No significant difference was seen in the in-plane position. In contrast, the incidence of accidental target puncture of the simulated nerve structures was significantly reduced when using GPS in the in-plane technique. No statistical differences were observed comparing GPS and CON in the out-of-plane technique. Detailed analyses are summarised in Table 1.Table 1: Performance time, needle to target distance and accidental target punctureRegarding a reduced severity level in the phantom gel model, a cut-off point at 5 mm between needle-tip and simulated nerve structures was set. This cut-off was fulfilled in 81.8% attempts in the CON technique and 97.2% using the GPS technique. Different levels of experience among anaesthetists had no influence on the time to needle placement, final needle to target distances or accidental target puncture rates (data not shown). The safety and efficacy of peripheral nerve blocks is increased using ultrasound guidance.2,3 The most common error using CON is caused by failure of needle visualisation during needle advancement and unintentional probe movement particularly in the in-plane approach.4 Therefore, a needle guidance system indicates the needle outline and its trajectory might be challenging. Previously published trials investigated ultrasound-guided nerve approaches on gel models using the puncture of target structures.5,6 In contrast, we created a simulation situation adapting the proceedings into clinical practice. Participants were instructed to simulate a nerve block with needle-tip placement in close proximity to the simulated nerve structure without penetration. These instructions ensured a realistic regional anaesthesia simulation to measure accidental punctures of the simulated structures in the phantom gel model. Our study has several limitations including a small sample size, especially in subgroup analyses. Due to a possible influence of outliers, cautious interpretation of data is required. Performance on a gel model differs from clinical practice in structure complexity, anatomical variations and ultrasonographical appearance. In conclusion, this randomised controlled trial indicates that the use of GPS-navigated ultrasound improves performance times and needle placement when compared with CON in a phantom gel model. Whether these findings can be transferred to regional anaesthesia in a clinical setting warrants further clinical studies in order to improve patients’ safety and comfort. Acknowledgements relating to this article Assistance with the study: none. Financial support and sponsorship: this work was supported by the Department of Anaesthesiology and Intensive Care Medicine, University Hospital of Cologne, Germany. R Schier received the Clinical Research Award 2011 research grant by the German Society of Anaesthesiology and Intensive Care Medicine. Conflicts of interest: none.

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