Haibo Zhang1,2,3,4
and Arthur S Slutsky1,2,5 
1Keenan Research Centre at the Li Ka Shing Knowledge Institute of St Michael's Hospital, Bond Street, Toronto, ON, Canada
2Interdepartmental Division of Critical Care Medicine, Division of Respirology, Department of Medicine, University of Toronto, 1 King's College Circle, Toronto, ON, Canada
3Department of Anaesthesia, University of Toronto, 1 King's College Circle, Toronto, ON, Canada
4Department of Physiology, University of Toronto, 1 King's College Circle, Toronto, ON, Canada
5King Saud University, BOX 2454, Riyadh 11451, Kingdom of Saudi Arabia