Complex sentence: Once a trainee has been the primary perfusionist in 150 clinical procedures they must undertake a practical exam, in which they will be observed by two external examiners whilst building and priming a cardiopulmonary circuit, then using it during a surgical operation.
Split into simpler sentences: Once a trainee has been the primary perfusionist in 150 clinical procedures, they must undertake a practical exam. For this exam, the candidate is observed by two external examiners whilst building and priming a cardiopulmonary circuit, then using it during a surgical operation.