Imposed work of breathing during high-frequency oscillatory ventilation: a bench study

Introduction The ventilator and the endotracheal tube impose additional workload in mechanically ventilated patients breathing spontaneously. The total work of breathing (WOB) includes elastic and resistive work. In a bench test we assessed the imposed WOB using 3100 A/3100 B SensorMedics high-frequency oscillatory ventilators. Methods A computer-controlled piston-driven test lung was used to simulate a spontaneously breathing patient. The test lung was connected to a high-frequency oscillatory ventilation (HFOV) ventilator by an endotracheal tube. The inspiratory and expiratory airway flows and pressures at various places were sampled. The spontaneous breath rate and volume, tube size and ventilator settings were simulated as representative of the newborn to adult range. The fresh gas flow rate was set at a low and a high level. The imposed WOB was calculated using the Campbell diagram. Results In the simulations for newborns ( assumed body weight 3.5 kg) and infants ( assumed body weight 10 kg) the imposed WOB ( mean +/- standard deviation) was 0.22 +/- 0.07 and 0.87 +/- 0.25 J/l, respectively. Comparison of the imposed WOB in low and high fresh gas flow rate measurements yielded values of 1.63 +/- 0.32 and 0.96 +/- 0.24 J/ l ( P = 0.01) in small children ( assumed body weight 25 kg), of 1.81 +/- 0.30 and 1.10 +/- 0.27 J/ l ( P <0.001) in large children ( assumed body weight 40 kg), and of 1.95 +/- 0.31 and 1.12 +/- 0.34 J/ l ( P