CUSUM method for construction of trainee spinal ultrasound learning curves following standardised teaching

Spinal ultrasonography is a promising aid for epidural insertion. We aimed to determine the learning curve of spinal ultrasonography tasks and the number of training scans required to reach competency after undergoing standardised step-wise teaching. Trainees were required to complete a minimum of 60 assessed scans on selected non-pregnant models following attendance at two training sessions, with feedback from an expert after each scan. Learning curves were plotted using the non-risk cumulative summation technique and an acceptable failure rate of 20%. Five trainees completed between 65 and 75 scans each. All trainees were competent at identifying a randomly assigned intervertebral space after a median of five scans (range one to nine) and at measuring the depth from skin to the posterior complex after a median of 10 scans (range 1 to 42). Two trainees were competent at marking an ideal needle insertion point after 55 scans, while three trainees did not attain competency. All trainees were competent after 60 scans if the tolerance was changed from five to eight millimetre for marking the needle insertion point. The average time taken to complete a scan was 163 seconds. Our study showed that after a standardised educational intervention, anaesthetic trainees are able to identify a lumbar interlaminar space easily and can measure the depth to the posterior complex after a reasonable number of additional practice scans, but experienced difficulty accurately marking the needle insertion point whilst using spinal ultrasonography. We confirmed that it was hard to achieve competency in all aspects of spinal ultrasonography, based on assessment using our predefined competency criteria.