What can be done to reduce the risk of cross contamination while performing cpr?

To reduce the risks of cross contamination when performing cpr, we should try, as far as possible, and if conditions permit, practice cpr in a clean environment of any chemical or physical waste, that the person who is performing the procedure doesn´t have any respiratory disease that can make the situation worse, having clean hands not to contaminate the patient, keep other people away so fresh air can flow freely.

You should never redesign your experiment. try and see what in your experiment you made a mistake on or try and test your experimemt with somebody else. see if they get the right results.