Imanaka H, Nishimura M, Takeuchi M, Kimball W R, Yahagi N, Kumon K
Surgical Intensive Care Unit, National Cardiovascular Center, Osaka, Japan.
Crit Care Med. 2000 Feb;28(2):402-7. doi: 10.1097/00003246-200002000-00019.
We noticed that in some patients after cardiac surgery, when flow triggering was used, cardiogenic oscillation might be autotriggering the ventilatory support. In a prospective study, we evaluated the degree of cardiogenic oscillation and the frequency rate of autotriggering. We suspected that autotriggering caused by cardiogenic oscillation was more common than clinically appreciated.
Prospective, nonrandomized, clinical study.
Surgical intensive care unit in a national heart institute.
A total of 104 adult patients were enrolled after cardiac surgery.
During the study period, patients were paralyzed and ventilated with intermittent mandatory ventilation at a rate of 10 breaths/min, pressure support of 10 cm H2O, and flow triggering with a sensitivity of 1 L/min.
Because the patients would not be able to breathe spontaneously, we counted pressure-support (PS) breaths as instances of autotriggering. Then, we classified the patients into two groups according to the number of PS breaths: an "AT group" (PS breaths of >5/min) and a "non-AT group" (PS breaths of < or =5/min). If autotriggering occurred, we decreased the sensitivity so autotriggering disappeared (threshold triggering sensitivity). The intensity of cardiogenic oscillation was assessed as the flow and airway pressure at the airway opening. A total of 23 patients (22%) demonstrated more than five autotriggered breaths/min. During mechanical ventilation, the inspiratory flow fluctuation caused by cardiogenic oscillation was significantly greater in the AT group than in the non-AT group (4.67+/-1.26 L/min vs. 2.03+/-0.86 L/min; p<.01). The AT group also showed larger cardiac output, higher ventricular filling pressures, larger heart size, and lower respiratory system resistance than the non-AT group. As the inspiratory flow fluctuation caused by cardiogenic oscillation increased, the level of triggering sensitivity also was increased to avoid autotriggering. In the AT group with 1 L/min of sensitivity, the respiratory rate increased (19.9+/-2.7 vs. 10+/-0 breaths/min, p<.01), Paco2 decreased (30.8+/-4.0 torr [4.11+/-0.36 kPa] vs. 37.6+/-4.3 torr [5.01+/-0.57 kPa]; p < .01), and mean esophageal pressure increased (7.7+/-3.0 vs. 6.9+/-3.0 cm H2O; p<.01) compared with the threshold triggering sensitivity.
Autotriggering caused by cardiogenic oscillation is common in postcardiac surgery patients when flow triggering is used. Autotriggering occurred more often in patients with more dynamic circulation. Autotriggering caused respiratory alkalosis and hyperinflation of the lungs.
我们注意到在一些心脏手术后的患者中，当使用流量触发时，心源性振荡可能会自动触发通气支持。在一项前瞻性研究中，我们评估了心源性振荡的程度以及自动触发的频率。我们怀疑由心源性振荡引起的自动触发比临床上认识到的更为常见。
前瞻性、非随机临床研究。
一家国立心脏研究所的外科重症监护病房。
共有104名成年心脏手术后患者入组。
在研究期间，患者接受肌肉松弛并采用间歇强制通气，通气频率为每分钟10次呼吸，压力支持为10 cm H₂O，流量触发敏感度为1 L/min。
由于患者无法自主呼吸，我们将压力支持（PS）呼吸计为自动触发的实例。然后，我们根据PS呼吸次数将患者分为两组：“AT组”（PS呼吸次数>5次/分钟）和“非AT组”（PS呼吸次数≤5次/分钟）。如果发生自动触发，我们降低敏感度以使自动触发消失（阈值触发敏感度）。心源性振荡的强度通过气道开口处的流量和气道压力进行评估。共有23名患者（22%）表现出每分钟超过5次的自动触发呼吸。在机械通气期间，AT组由心源性振荡引起的吸气流量波动明显大于非AT组（4.67±1.26 L/min对2.03±0.86 L/min；p<0.01）。AT组还显示出比非AT组更大的心输出量、更高的心室充盈压、更大的心脏尺寸和更低的呼吸系统阻力。随着由心源性振荡引起的吸气流量波动增加，触发敏感度水平也会升高以避免自动触发。在敏感度为1 L/min的AT组中，与阈值触发敏感度相比，呼吸频率增加（19.9±2.7对10±0次/分钟，p<0.01），动脉血二氧化碳分压降低（30.8±4.0托[4.11±0.36千帕]对37.6±4.3托[5.01±0.57千帕]；p<0.01），平均食管压力升高（7.7±3.0对6.9±3.0 cm H₂O；p<0.01）。
当使用流量触发时，心源性振荡引起的自动触发在心脏手术后患者中很常见。自动触发在循环更活跃的患者中更常发生。自动触发导致呼吸性碱中毒和肺过度充气。
