Objective: In a cohort of mechanically ventilated patients to compare the automatic tidal volume (VT)-respiratory rate (RR) combination generated by adaptive support ventilation (ASV) for various lung conditions.
Design and setting: Prospective observational cohort study in the 11-bed medicosurgical ICU of a general hospital.
Patients: 243 patients receiving 1327 days of invasive ventilation on ASV.
Measurements: Daily collection of ventilator settings, breathing pattern, arterial blood gases, and underlying clinical respiratory conditions categorized as: normal lungs, ALI/ARDS, COPD, chest wall stiffness, or acute respiratory failure.
Results: Overall the respiratory mechanics differed significantly with the underlying conditions. In passive patients ASV delivered different VT-RR combinations based on the underlying condition, providing higher VT and lower RR in COPD than in ALI/ARDS: 9.3ml/kg (8.2-10.8) predicted body weight (PBW) and 13 breaths/min (11-16) vs. 7.6ml/kg (6.7-8.8) PBW and 18 breaths/min (16-22). In patients actively triggering the ventilator the VT-RR combinations did not differ between COPD, ALI/ARDS, and normal lungs.
Conclusions: ASV selects different VT-RR combinations based on respiratory mechanics in passive, mechanically ventilated patients.