Outcome of acute respiratory distress syndrome in university and non-university hospitals in Germany

Table 3 Control for confounding and sensitivity analyses with a further multivariable model including only potential confounders at ARDS onset

	Odds ratio for hospital mortality of ARDS patients in non-university hospitals vs university hospitals
	n ^a	Odds ratio multivariable	p value
Multivariable analysis with all potential confounders	128	2.8 (1.1–7.1)	0.035
Excluding SAPS II	137	2.7 (1.1–6.6)	0.032
Excluding BMI	142	3.5 (1.5–8.4)	0.004
Excluding compliance	151	2.4 (1.1–5.5)	0.037
Excluding SAPS II, BMI	151	3.4 (1.5–7.7)	0.005
Excluding compliance, SAPS II	164	2.4 (1.1–5.4)	0.028
Excluding compliance, BMI	174	3.5 (1.7–7.6)	0.001
Excluding compliance, SAPS II, BMI	189	3.3 (1.6–6.7)	0.001

The consistency of results of these sensitivity analyses indicates that this multivariable model including only potential confounders was robust with respect to alterations of included variables or to the corresponding changes of the study group
To control for confounding only potential confounders were considered in this further multivariate model, including factors that differ between ARDS patients in university and non-university hospitals at onset of ARDS and also including those factors that did not differ significantly but only numerically between groups (Table 1): age, BMI, SAPS II, main problem (medical/surgical), ARDS origin (pulmonary/extrapulmonary), day of ARDS onset, dynamic compliance at ARDS onset, reason for initiation of mechanical ventilation, (postoperative acute respiratory failure (ARF), ARF after aspiration, ARF after multiple trauma), and comorbidities or complications present until onset of ARDS (sepsis, pneumonia, cardiovascular failure, coagulation failure, liver failure, metabolic acidosis)
ARDS acute respiratory distress syndrome, SAPS II Severe Acute Physiology Score II, BMI body mass index
^aNumber of ARDS patients included in the respective multivariable analysis after excluding factors or various combinations of factors with missing values (SAPS II 5% missing values, BMI 7%, compliance 12%) (all ARDS patients n = 198, eight patients without outcome variable, one patient without age)