不同通气模式下吸痰对呼吸力学和气体交换的影响

目的比较在压力控制通气（PCV）与容量控制通气（VCV）模式下吸痰对患者气体交换和呼吸力学的影响。方法采取自身交叉对照的方法，在PCV和VCV模式下分别对23例机械通气患者进行开放式吸痰，比较不同时间点气体交换、呼吸力学及血流动力学等指标的变化。结果在PCV模式下，吸痰后30min潮气量、顺应性分别为（6．60±1．95）mL／kg、（18±7）ml／cmH2O（1cmH2O=0．098kPa），与基础水平[（9．05±0．22）mL／kg、（24±6）ml／cmH2O]比较差异有统计学意义（F值分别为8．47、8．01，P均〈0．05）；而30min时动脉血氧分压（PaO2）、动脉血二氧化碳分压（PaCO2）分别为[（87±13）mmHg（1mmHg=0．133kPa）、（53±11）mmHg]，与0min[（113±22）mmHg、（41±10）mmHg]比较差异有统计学意义（，值分别为6．18、9．13，P均〈0．05）；在VCV模式下，吸痰后30min顺应性、气道平台压、气道峰压分别为[（18±7）ml／cmH2O、（27±8）cmH2O、（33±8）cmH2O]，与基础水平[（23±7）ml／cmH2O、（22±5）cmH2O、（27±8）cmH2O]比较差异有统计学意义（，值分别为6．83、6．97、7．08，P均〈0．05）；而30min时PaO2、PaCO2分别为（105±26）mmHg、（38±11）mmHg，与0min[（109±21）mmHg、（37±14）mmHg]比较差异无统计学意义（F值分别为1．88、1．32，P均〉0．05）；在PCV模式下，吸痰后5min心率、平均动脉压（MAP）分别为（109±20）次／min、（89±10）mmHg，与基础水平[（97±17）次／min、（83±12）mmHg]比较差异有统计学意义（F值分别为5．86、9．49，P均〈0．05）。在VCV模式下，吸痰后5min心率、MAP分别为（110±17）次／min、（87±11）mmHg，与基础水平[（96±17）次／min、（79±11）mmHg]比较差异有统计学意义（F值分别为7．33、7．96，P均〈0．05）。结论吸痰在PCV和VCV模式下均引起患者气体交换受损和顺应性下降，但对气体交换的影响在PCV模式下比VCV更严重和持久。

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.