Learning Curve of Medical Students in Ultrasound-guided Simulated Nerve Block

Background: Good hand-eye coordination is a prerequisite for safe ultrasound-guided peripheral nerve blocks. However, new skills have to be acquired when compared to the traditional nerve stimulation technique. We tested and mathematically described the learning curve of these skills in inexperienced ultrasound users employing a simple phantom of a peripheral nerve.

Methods: A simple phantom made from a piece of spaghetti to simulate a nerve, within a starch core and embedded in gelatine was used for ultrasound-guided simulation of a peripheral nerve block. Eighteen medical students who were novices to ultrasound were enrolled. Serial time to successful injection was measured. Quality of injection was rated by two independent observers.

Results: Time to successful injection improved from a median of 66.5 s (49.5-90) for the first trial to 37 s (23.5-53.5) for the 11th trial. A plateau of 30 s was reached for t 1/2 after 2.7 trials and 4 × t 1/2 after 7.8 trials when described as first-order exponential decay. Time to successful injection was significantly shortened after 5 trials. Quality of injection with numbers of trials followed a sigmoidal shape with 50 % of maximum quality after 3.6 trials and a plateau after 8.5 trials. Likewise, a significant improved quality of injection was reached after 5 trials.

Conclusion: Based on our mathematical analyses of the learning curve, inexperienced ultrasound users can improve their hand-eye coordination within 5 subsequent trials in a simple model of a peripheral nerve block.