[High frequency ventilation with a conventional respiratory following heart surgery interventions]

This study was designed to compare the effects of Continuous Positive-Pressure Ventilation (CPPV) and, by using the same unmodified conventional ventilator, High-Frequency Positive-Pressure Ventilation (HFPPVkonv). First, CPPV and HFPPVkonv were studied in a lung model with both normal (R = 5 mbar/1/second) and elevated (R = 20 mbar/1/second) resistance. Our results indicate that in HFPPVkonv the large compressible volume of the conventional ventilator did not influence lung model ventilation at normal resistance. The adjusted (300 ml) tidal volume (VT) and the measured volume of actual expiration (270 ml) were about the same (Fig. 1). However, with elevated resistance air trapping occurred. The large compressible volume influenced model ventilation during both CPPV and HFPPVkonv (Fig. 2). As a second step we evaluated the effects of HFPPVkonv on gas exchange, airway pressure, and hemodynamics in 12 patients (aged 43-69) postoperatively after elective cardiac surgery. After a period of stabilization at the intensive care unit every patient was first ventilated with CPPV. The ventilator settings were: VT = 10-12 ml/kg, inspiratory: expiratory ratio (I:E) = 1:2, frequency (F) = 12/min, V = 60 1/min, PEEP = 5 cm, FiO2 = 40%. After 20 min of CPPV baseline measurements were made (series I). Then the initial ventilator settings of CPPV were switched to HFPPVkonv, the conventional ventilator remaining unmodified. The settings were changed as follows: I:E = 1:3, F = 60/min, V = 120 1/min, PEEP = 5 cm, FiO2 = 40%. During 60 min of HFPPVkonv variables were measured first after 20 min (series II) and again after another 40 min (series III). Minute volume had to be doubled after changing from CPPV to HPFFVkonv to achieve eucapnia. As a result of the new ventilatory settings, VT and hold showed a significant decrease (P less than 0.01) (Table 2).(ABSTRACT TRUNCATED AT 250 WORDS)