Ventilator-free days (VFDs) is defined as the number of days from randomization to Day 28 after achieving unassisted breathing for patients who maintained unassisted breathing for at least two consecutive calendar days. If a patient achieved unassisted breathing, subsequently required additional assisted breathing, and once again achieved unassisted breathing, we counted only the VFDs after beginning the final period of unassisted breathing. Patients who died before Day 28 were assigned zero VFDs.

All the intent to treat patients were analyzed. Data was available on all subjects for the primary analysis only.

Success for this efficacy variable was defined as being alive on study day 60 or having been discharged alive off mechanical ventilation from the study hospital (or subsequent hospital) to the subject's original place of residence. Those subjects alive in hospital at day 60 were considered to have survived.

Intent to treat population.

Success for this efficacy variable was defined as being alive on study day 90 or having been discharged alive off mechanical ventilation from the study hospital (or subsequent hospital) to the subject's original place of residence. Those participants who still remained in the hospital at 90 days after randomization were considered to have survived.

Intent to treat.

ICU (intensive care unit)-free days was defined as the number of days a subject was out of the ICU during study hospitalization from date of randomization up to study day 28. All incidences of ICU admission and discharge during the study hospitalization were captured. Any portion of a calendar day that a subject was in the ICU was counted as an ICU day.

Intent to treat.

Subjects were followed for development of organ failures from date of randomization to hospital discharge or study day 28, whichever was first. Organ failure was defined as present on any calendar day when the most abnormal vital signs or clinically available lab value met the definition of clinically significant organ failure according to the Brussels Organ Failure Table. Each day a patient was alive and free of a given clinically significant organ failure was scored as a failure-free day. The worst value for a calendar day was captured (lowest systolic BP, platelet count and highest creatinine and bilirubin values). Specific definitions of organ failure were: cardiovascular-systolic BP less than or equal to 90 mmHg or on a vasopressor; coagulation-platelet count less than or equal to 80 x 1000/mm3; Renal-creatinine less than or equal to 2.0 mg/dL; Hepatic-bilirubin less than or equal to 2.0 mg/dL.

Intent to treat.

Difference in the main outcome Ventilator Free Days to study day 28 was calculated for the subset of patients with ARDS (defined as a PaO2/FiO2 ratio of less than or equal to 200). P/F ratio is an index of the effectiveness of arterial oxygenation that corresponds to the ratio of partial pressure of arterial O2 to the fraction of inspired O2. VFD to Day 28 is defined as the number of days from the end of ventilation to day 28 in patients who maintained unassisted breathing for at least two consecutive calendar days. Patients who died before day 28 were assigned a VFD count of zero. If a patient returned to assisted breathing, subsequently required assisted breathing, and once again achieved unassisted breathing, only the VFDs after beginning the final period of unassisted breathing were counted. An increase in the number of VFDs was considered a positive result.

Patients meeting the criteria for ARDS (pre-randomization PaO2/FiO2 ratio less than or equal to 200) were selected for this subset.

Difference in the main outcome mortality to study day 60 was calculated for the subset of patients with ARDS (defined as a PaO2/FiO2 ratio of less than or equal to 200) prior to randomization. P/F ratio is an index of the effectiveness of arterial oxygenation that corresponds to the ratio of partial pressure of arterial O2 to the fraction of inspired O2.

Patients meeting the criteria for ARDS (pre-randomization PaO2/FiO2 ratio less than or equal to 200) were selected for this subset.

Difference in the main outcome Ventilator Free Days to study day 28 was calculated for the subset of patients who were in shock at the time of randomization. Shock was defined as mean arterial pressure<60 or the need for vasopressors (except dopamine <6 ug/kg/min).

Patients with protocol defined shock (mean arterial pressure<60 or need for vasopressors except dopamine < 6ug/kg/min) at the time of study entry.

Difference in the main outcome hospital mortality to study day 60 was calculated for the subset of patients who were in shock at the time of randomization. Shock was defined as mean arterial pressure<60 or the need for vasopressors (except dopamine <6 ug/kg/min).

Patients with protocol defined shock (mean arterial pressure<60 or need for vasopressors except dopamine < 6ug/kg/min) at the time of study entry.

Biologic end-points were selected that would provide mechanistic insight into how albuterol improved lung function. Concentrations of two proinflammatory cytokines, interleukin 6 and 8 (IL-6 and IL-8), were measured. Plasma was collected and cytokine levels were measured at baseline and 3 days after randomization. IL-6 and IL-8 levels were normalized using log transformation. Wilcoxon's test was used to compare mean log-transformed interleukin levels per day and a mixed-effects model was fit to compare the slopes.

Not all subjects had available data for secondary analyses and therefor the numbers will be less than the 152 (active) and 130 (placebo) arms.