Fig. 2.

Pressure tracings and ventilator recordings (I:E ratio 1:2, 7 mm ID ETT). a Effects of altered trigger sensitivity on peak and end-expiratory model airway pressures (blue tracings, P_{PEAK MA} and P_{EEP MA}) are shown during bronchoscope insertion (16 Fr) through a 7 mm ID ETT and with suction pressure −765 cm H₂O (−75 kPa). Note (both circles) that the pressures, which are measured distal to the obstruction, fall as the bronchoscope is inserted and drop below zero when suctioning is performed. b Details of the most and least sensitive triggers with their corresponding ventilator circuit pressures (grey lines; P_{PEAK VENT} and P_{EEP VENT}). The total effect of suction compared to normal ventilation (prior to scope insertion) is shown as Δ P_{PEAK MA} and Δ P_{EEP MA}. VF = ventilator frequency. Note that ventilator peak pressures, which are measured in the ventilator circuit, are much higher than the actual pressures distal to the obstruction for as long as the bronchoscope is inserted. Ventilator end-expiratory pressures are also much higher than model end-expiratory pressures during suctioning. c Details of the same trigger settings during VCV mode, shown as in panel B. Note that for both modes, triggering of new inspirations during suctioning increases the ventilation rate and prevents further reduction of P_{EEP MA}