Needle Angle Matters: An Investigation of the Effect of Needle Angle on Hemodialysis Cannulation Skill

KEY POINTS: Three metrics that quantify cannulation skill on the basis of needle angle are introduced. All three needle angle metrics were demonstrated to be useful in predicting cannulation outcomes on the simulator. BACKGROUND: Cannulation is critical for maintaining a functional vascular access for patients on hemodialysis. However, relatively little is known about the quantitative aspects of needle insertion dynamics required for skilled cannulation. In this article, we introduce three kinds of metrics that quantify needle insertion angle—recognized as important for safe and effective cannulation—during cannulation on an instrumented simulator for skill assessment. Three questions were examined in this study: (1) Are simulator-based needle angle metrics related to cannulation success? (2) Are needle angle metrics related to simulated blood flashback quality? and (3) Can needle angle metrics be used to distinguish between high and low skill levels? METHODS: Fifty-one cannulators with varying degrees of clinical experience performed cannulation on the instrumented simulator. Each participant cannulated 16 times on different fistulas with varying geometries. During each trial, needle angle along with other sensor data was obtained through a motion sensor placed inside the needle. Data analysis was conducted by relating needle angle over time with our previously validated simulator-based cannulation outcome metrics. RESULTS: The results revealed that all three types of needle angle metrics were useful in predicting the probability of cannulation success. In addition, they were also correlated with flashback quality metrics. Furthermore, these metrics successfully distinguished between high and low performers regardless of whether they were classified using subjective ratings or objective scores. These results indicate that needle insertion angle is an important component of cannulation skill. CONCLUSIONS: The simulator-based metrics for needle insertion angle presented in this work measure a key aspect of skilled cannulation. As such, if implemented in a structured way, these metrics could lead to competency-based skill assessment and training for cannulation in the future. Raising the bar of cannulation skill of our clinicians can have a tangible effect on patient outcomes.