Early Changes in respiratory mechanics in acute respiratory failure

Abstract

The purpose of this study was to investigate early changes in respiratory mechanics in mechanically ventilated patients with acute respiratory failure (ARF), using modern ventilators equipped with operational and measuring devices. To this end, 24 patients with ARF related to acute exacerbation of chronic airway obstruction (CAO, 8 patients) or pulmonary edema, both cardiogenic (8 patients) and noncardiogenic (8 patients with ARDS adult respiratory distress syndrome), were examined within 24 hours of the onset of mechanical ventilation. We found that: 1. patients with CAO were characterized by high ‘intrinsic’ PEEP (PEEPi), mean 13.6(6.7) cm H2O, relatively low compliance, increased respiratory resistance, both maximum and minimum, with marked frequency-dependence of resistance; 2. in pulmonary edema PEEPi was present, amounting, on average, to 3.8 and 3.0 cm H2O in non-cardiogenic and cardiogenic pulmonary edema respectively, and respiratory resistance was increased, though exhibiting a significant frequency-dependence only in the non-cardiogenic type of edema; 3. early ARDS was characterized by low compliance, mean 0.035(0.005) L/cm H2O, and frequency-dependence of resistance. We conclude that changes in respiratory mechanics in the mechanically ventilated patient with ARF should be assessed to gain a better understanding of the patient’s condition, and that noninvasive study can be easily performed with modern operational and measuring ventilators.