Cusum analysis of trends in operative selection and conversion rates for laparoscopic cholecystectomy

Laparoscopic cholecystectomy (LC) requires a high degree of technical ability, spatial resolution and dexterity. Assessing trainees and competent operators is an important aspect of quality assurance in patient care. Most institutions quote mean conversion rate as a method of comparing operators' performance. The purpose of the present study was to use the technique of cumulative sum (cusum) analysis to determine whether a learning curve phenomenon exists in operators performing LC.

Data were obtained retrospectively by reviewing the operative records of all patients undergoing elective and acute cholecystectomy for a 30-month period coinciding with the commencement of LC at North Shore Hospital. Patients' age and gender, date and type of operative procedure, duration of operation, and name of operator were recorded. Mean and cusum-transformed data were derived for all operations as well as for four individual operators' performances.

Over the study period a total of 614 cholecystectomies was performed, with 85% attempted laparoscopically. A total of 9.8% required conversion to the open technique. Time trend analysis with the cusum technique for all surgeons revealed an inverse relationship between selection rate and conversion rate. Analysis of four individual surgeons revealed three different time trend profiles.

There was a direct inverse relationship between conversion rate and selection rate, in that careful selection is associated with a low conversion rate. Comparison of individual surgeons' performance showed wide variation, with only one surgeon exhibiting the phenomenon of a learning curve. Contrary to other reports, we found that performance on LC was not always related to operative experience. This highlights the need for a more objective method to analyse operator competence than operator experience alone.