This clinician-initiated project will establish whether or not selective digestive decontamination (SDD) reduces the risk of dying in hospital for patients who require life support with a breathing machine in an Intensive Care Unit (ICU). SDD consists of a short course of antibiotic and antifungal treatment given to reduce the risk of developing hospital-acquired infection. This is a 'cluster randomised trial' in which 100 ICUs in four countries, including three ICUs in NZ, will be assigned to use either SDD or standard therapy. As well as establishing whether SDD saves lives, this study will also establish whether SDD changes the numbers of antibiotic-resistant bacteria in the ICU. If the potential benefits of this treatment are realised, the results of this study will have global impact in terms of lives saved and infections prevented as well as potentially allowing large savings in health care spending.