Following discussion with statisticians and viewing the sample sizes of previous related studies, it was suggested that minimum 200 patients will be required for phase I. This was based on the availability of data in a similar aspects of the study. But incidentally there has been no known study looking specifically at delirium and post traumatic stress symptoms in cardiac surgery patients. So the researcher aims to enrol at least 400 patients but may not be able to achieve this number by the end of data collection phase.