Participants
We included all mechanically ventilated patients admitted directly from the emergency department (ED) to our ICU from August 2011 to December 2013, who also developed shock within the first 24 h of ICU stay. We chose to include only mechanically ventilated patients because these patients routinely received arterial cannulation and invasive blood pressure monitoring. Only the first ED to ICU admission was used in patients with multiple encounters during the study period. Patients with onset of shock beyond 24 h of ICU stay were excluded.