[1] Univ British Columbia, Dept Crit Care Med, Royal Columbian Hosp, Vancouver, BC V5Z 1M9, Canada
[2] Univ Toronto, Sunnybrook Hlth Sci Ctr, Dept Crit Care Med, Toronto, ON, Canada
[3] Univ Toronto, Interdept Div Crit Care Med, Toronto, ON, Canada
[4] St Michaels Hosp, Interdep Div Crit Care Med, Toronto, ON M5B 1W8, Canada
[5] St Michaels Hosp, Li Ka Shing Knowledge Inst, Toronto, ON M5B 1W8, Canada
[6] Queens Univ, Dept Med, Kingston, ON K7L 3N6, Canada
[7] Kingston Gen Hosp, Kingston, ON K7L 2V7, Canada
[8] Univ Alberta, Div Crit Care Med, Edmonton, AB, Canada
[9] Univ Toronto, Mt Sinai Hosp, Dept Med, Toronto, ON M5G 1X5, Canada
[10] Univ Toronto, Mt Sinai Hosp, Interdept Div Crit Care Med, Toronto, ON M5G 1X5, Canada
[11] McMaster Univ, Dept Med, Hamilton, ON, Canada
[12] Univ British Columbia, Dept Med, Vancouver, BC, Canada
[13] Sunnybrook Res Inst, Toronto, ON, Canada
[14] McMaster Univ, Dept Clin Epidemiol & Biostat, Hamilton, ON, Canada
[15] Royal Inland Hosp, Dept Resp Therapy, Kamloops, BC, Canada
[16] St Pauls Hosp, Div Crit Care Med, Vancouver, BC V6Z 1Y6, Canada
[17] Queen Elizabeth 2 Hlth Sci Ctr, Div Respirol, Halifax, NS, Canada
[18] Dalhousie Univ, Halifax, NS, Canada
[19] McGill Univ, Sir Mortimer B Davis Jewish Gen Hosp, Montreal, PQ, Canada
[20] McGill Univ, Resp Epidemiol & Clin Res Unit, Montreal Chest Inst, Montreal, PQ, Canada
[21] Univ Calgary, Dept Crit Care Med, Calgary, AB, Canada
[22] N York Hosp, Dept Med, Toronto, ON, Canada
[23] St Pauls Hosp, Dept Med, Div Crit Care Med, Vancouver, BC V6Z 1Y6, Canada
[24] St Michaels Hosp, Keenan Res Ctr, Toronto, ON M5B 1W8, Canada