Excision of vestibular schwannomas – is there a learning curve and how best to demonstrate it?

Abstract

Objective. To demonstrate the existence of a learning curve in a consultant neurosurgeon's performance in excising vestibular schwannomas by plotting the cumulative sum (CUSUM) chart. Also, to evaluate the influence of new technology in the form of the facial nerve monitor (FNM) and the KTP-532 Laser on surgical performance.

Method. Analysis was carried out on a prospectively collected data series of 102 consecutive cases of vestibular schwannomas excisions between 1986 and 2000 by a single neurosurgeon using the retrosigmoid approach. The CUSUM score chart of the surgical outcomes across the series was plotted for all and large tumour sizes separately. The changes in CUSUM scores were assessed using statistical change-point analysis. Using the multivariate logistic regression analysis, we inspected the association between use of FNM and laser on outcome.

Results. After the first 27 cases and coinciding with the introduction of the FNM there was a clear change in the direction of the slope of the CUSUM chart, showing a clear improving trend in performance (p = 0.09). The same phenomenon was also seen when plotting the CUSUM chart for large tumours only, although this was not statistically significant. The use of FNM reduces the risk of bad House Brakmann-score by approximately 90% for all tumours (risk of bad outcome with FNM = 3.2% and without FNM = 26.7%, odds ratio = 0.10 and 95% confidence interval (0.02–0.61), p = 0.013) after adjusting for age at operation, but no significant association was seen with the use of laser.

Conclusion. There appears to be a learning curve in the performance of a neurosurgeon. Compared to previous reports of sequential block analysis, the CUSUM method is less arbitrary and more transparent. The CUSUM is most useful as an audit tool that can help spare patients from undesirable learning curves, and help to demonstrate good standards in appraisal and revalidation.

Key words:

• Cumulative sum (CUSUM)
• facial nerve monitor
• KTP-532 laser
• learning curve
• revalidation
• vestibular schwannoma

Acknowledgement

The authors thank Dr. Doug Cochrane (Chairman of the British Columbia patient safety and quality council) for his encouragement and guidance in the preparation of this article.