[The effects of endotracheal suction on gas exchange and respiratory mechanics in mechanically ventilated patients under pressure-controlled or volume-controlled ventilation].

OBJECTIVE: To compare the effects of endotracheal suction on gas exchange and respiratory mechanics in mechanically ventilated patients receiving pressure-controlled ventilation (PCV) or volume-controlled ventilation (VCV).

METHODS: A randomized cross-over study was conducted. Twenty-three mechanically ventilated patients were randomly assigned to ventilation with either PCV or VCV at first, and then the other. Endotracheal suction was performed with an open suction system. Changes in gas exchange and respiratory mechanics after suctions under the two modes were compared.

RESULTS: With PCV, the tidal volume (VT) and the compliance were (6.60+/-1.95) ml/kg and (18+/-7) ml/cm H2O (1 cm H2O=0.098 kPa) respectively at 30 minutes after suction, as compared to (9.05+/-0.22) ml/kg and (24+/-6) ml/cm H2O respectively at baseline; the difference being significant (F=8.47, 8.01, all P<0.05). PaO2 and PaCO2 were (87+/-13) mm Hg (1 mm Hg=0.133 kPa) and (53+/-11) mm Hg respectively at 30 minutes after suction, as compared to (113+/-22) mm Hg and (41+/-10) mm Hg respectively at 0 minute; the difference being significant (F=6.18, 9.13, all P<0.05). With VCV, the compliance, the plateau pressure and the peak inspiratory pressure were (18+/-7) ml/cm H2O, (27+/-8) cm H2O and (33+/-8) cm H2O respectively at 30 minutes after suction, as compared to (23+/-7) ml/cm H2O, (22+/-5) cm H2O, and (27+/-8) cm H2O respectively at baseline; the difference being significant (F=6.83, 6.97, 7.08, all P<0.05). PaO2 and PaCO2 were (105+/-26) mm Hg and (38+/-11) mm Hg respectively at 30 minutes after suction, as compared to (109+/-21) mm Hg and (37+/-14) mm Hg respectively at 0 minute; but the difference was not significant (F=1.88, 1.32, all P>0.05). With PCV, the heart rate (HR) and the mean systemic arterial pressure (MAP) were (109+/-20) beats/min and (89+/-10) mm Hg respectively at 5 minutes after suction, as compared to (97+/-17) beats/min and (83+/-12) mm Hg respectively at baseline; the difference being significant (F=5.86, 9.49, all P<0.05). With VCV, HR and MAP were (110+/-17) beats/min and (87+/-11) mm Hg respectively at 5 minutes after suction, as compared to (96+/-17) beats/min and (79+/-11) mm Hg respectively at baseline; the difference being significant (F=7.33, 7.96, all P<0.05).

CONCLUSION: Endotracheal suction causes lung collapse leading to impairment of gas exchange and decreased compliance both under PCV and VCV, but the effect on gas exchange was more severe and persistent under PCV than under VCV.