Study objectives: To determine whether the widely accepted concept of using lower tidal volume (Vt) values in patients with ARDS or obstructive lung disease has affected the pattern of ventilator settings in mechanically ventilated patients who do not have one of these conditions.
Design and patients: We performed a retrospective chart review of all patients who had experienced out-of-hospital cardiac arrest and had received ventilatory support for ≥ 1 day at a university-affiliated county hospital during the years 1990, 1991, 1992, 1995, 1998, 1999, and 2000.
Results: In 139 such patients, the mean final Vt values used on the first day of mechanical ventilation were 11.7, 12.4, 11.3, 9.6, 9.7, 9.2, and 9.8 mL/kg in those years, respectively. Multivariate analysis revealed that increasing year (β-coefficient = −0.24; p = 0.001) and the presence of pulmonary edema (β-coefficient = −1.2; p = 0.001) were independent predictors of the use of lower Vt values. Patients managed with a low Vt (ie, < 10 mL/kg; mean [± SD] Vt, 8.4 ± 1.3 mL/kg) had a significantly higher incidence of atelectasis than the patients who were managed with traditional, larger Vt values (ie, ≥ 10 mL/kg; mean Vt, 11.8 ± 1.5 mL/kg) [61.1% vs 36.7%, respectively; p = 0.02]. Multivariate analysis revealed that the mean Vt used on days 1, 2, and 3 (<10 mL/kg or ≥ 10 mL/kg) was the only predictor of the development of atelectasis during the first 3 days of mechanical ventilation (odds ratio, 0.33; p = 0.015). There was no difference in the incidence of pneumonia, the number of days spent receiving mechanical ventilation, Pao2/fraction of inspired oxygen ratio, or respiratory system compliance between the low Vt group and the traditional Vt group.
Conclusion: Currently, physicians at our hospital use lower Vt values than they have in the past. This is associated with the increase in the incidence of atelectasis in the patients who received ventilation using low Vt values.