- Time-to-event outcome measures was period of time between the arrival at the ICU after cardiac surgery and before spontaneous breathing on mechanical ventilation. The event (hypotension) was defined as systolic arterial pressure under 90mmHg,less than 40mmHg, mean arterial pressure under 70mmHg, tachycardia upper 100 beats/min, presence of skin mottling, low cardiac output or previous blood loss.