Autotriggering caused by cardiogenic oscillation during flow-triggered mechanical ventilation

Objectives: We noticed that in some patients after cardiac surgery, when fl ow triggering was used, cardiogenic oscillation might be autotriggering the ventilatory support. In a prospective study, we evaluated the degree of ca rdiogenic oscillation and the frequency rate of autotriggering. We suspecte d that autotriggering caused by cardiogenic oscillation was more common tha n clinically appreciated. Design: Prospective, nonrandomized, clinical study. Setting: Surgical intensive care unit in a national heart institute. Patien ts: A total of 104 adult patients were enrolled after cardiac surgery. Interventions: During the study period, patients were paralyzed and ventila ted with intermittent mandatory ventilation at a rate of 10 breaths/min, pr essure support of 10 cm H2O, and flow triggering with a sensitivity of 1 L/ min. Measurements and Main Results: Because the patients would not he able to br eathe spontaneously, we counted pressure-support (PS) breaths as instances of autotriggering. Then, we classified the patients into two groups accordi ng to the number of PS breaths: an "AT group" (PS breaths of >5/min) and a "non-AT group" (PS breaths of less than or equal to 5/min). If autotriggeri ng occurred, we decreased the sensitivity so autotriggering disappeared (th reshold triggering sensitivity). The intensity of cardiogenic oscillation w as 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 t he 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 pre ssures, larger heart size, and lower respiratory system resistance than the non-AT group. As the inspiratory flow fluctuation caused by cardiogenic os cillation 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) , Pace, decreased (30.8 +/- 4.0 torr [4.11 +/- 0.36 kPa] vs. 37.6 +/- 4.3 t orr [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 tr iggering sensitivity. Conclusions: Autotriggering caused by cardiogenic oscillation is common in postcardiac surgery patients when flow triggering is used. Autotriggering o ccurred more often in patients with more dynamic circulation. Autotriggerin g caused respiratory alkalosis and hyperinflation of the lungs.