| ObjectivePatients dependent on mechanical ventilation often need to have mucus suctioned from their airways. But open endotracheal suction may create the negative pressure that can lead to serious complications. We designed this study to compare the effects of open endotracheal suction on gas exchange and respiratory mechanics in mechanically ventilated patients in pressure-controlled ventilation (PCV) with volume-controlled ventilation (VCV).MethodsA randomized cross-over study was conducted in a 15-bed emergency intensive care unit of the first affiliated hospital of China Medical University. From April to September 2006, thirty mechanically ventilated patients were included. They were randomly assigned to be ventilated with either PCV or VCV at first, then the other. Endotracheal suction was performed with an open suction system when it is necessary. In order to standardize lung volume history, a recruitment maneuver was performed before suction: Paw was increased for 20s to 10 cm HO( 1 cm HO=0．098 kPa) above plateau pressure in VCV or above inspiration pressure level in PCV. No changes in individual ventilator settings were made when ventilation mode changed from PCV to VCV except tidal volume ( V ) was either set to 9 ml/kg in VCV or inspiration pressure level was set to achieve V of 9 ml/kg in PCV. Supplementary oxygenation was not used before or after endotracheal suction. A bolus injection of 10 mg of valium was administered (?) before each suction. During the suction procedure, the catheter was inserted into the endotracheal tube and suction with a-150mmHg (1 mm Hg=0．133 kPa) vacuum was performed for 15s. Changes in gas exchange and respiratory mechanics after suctions in two modes were compared.ResultsIn PCV, V and compliance were (6．6(?)1．9) ml/kg , (18．1(?)7．2) ml/ cm HO, respectively, at thirty minutes after suction; And they were (9．0(?)0．2) ml/kg, (24．4(?)6．4) ml/cm HO, respectively, at baseline .There were significant differences between thirty minutes and baseline (F=8．47, 8．01, P<0．05) . PaO and PaCO were (86．7(?)13．4) mmHg, (53．4(?)10．7) mmHg, respectively, at thirty minutes after suction; And they were(112．9(?)21．6) mm Hg, (41．3(?)9．6) mm Hg, respectively, at 0 minute . There were significant differences between thirty minutes and 0 minute (F=6．18,9．13, P<0．05) . In VCV , compliance , plateau pressure and peak inspiratory pressure were (17．7(?)7．3) ml/cm HO, (26．5(?)8．1) cmHO, (32．6(?)7．7) cm HO, respectively, at thirty minutes after suction; And they were (22．5(?)7．1) ml/cm HO, (21．6(?)5．4) cm HO, (27．0(?)8．2) cmHO, respectively, at baseline .There were significant differences between thirty minutes and baseline(F=6．83,6．97,7．08, P<0．05) . PaO and PaCO were( 105．1(?)26．4) mm Hg, (37．9(?)11．2) mm Hg, respectively, at thirty minutes after suction; And they were (109．2(?)20．6) mmHg, (36．9(?)13．6) mm Hg, respectively, at 0 minute .But there were no significant differences between thirty minutes and 0 minute (F=1．88,1．32, P> 0．05) .In PCV, heart rate (HR) and mean systemic arterial pressure (MAP) were(109(?)20) beats/min, (89(?)10) mm Hg, respectively, at five minutes after suction; And they were (97(?)17) beats /min, (83(?)12) mm Hg, respectively, at baseline .There were significant differences between five minutes and baseline (F=5．86, 9．49, P<0．05) . In VCV , HR and MAP were (110(?)17) beats /min, (87(?)11) mm Hg, respectively, at five minutes after suction; And they were(96(?)17) beats /min, (79(?)11) mm Hg, respectively, at baseline .There were also significant differences between five minutes and baseline (F=7．33,7．96,P<0．05) .ConclusionsThese results suggest that endotracheal suction causes lung collapse leading to impairment of gas exchange and compliance decreased both in PCV and VCV, but the effect on gas exchange is more severe and persistent in PCV than in VCV. Preventing the periodic alveolar derecruitment induced by open endotracheal suctioning could be more clinically relevant than its reversal in mechanically ventilated patients.
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