The Science Journal of the American Association for Respiratory Care

1998 OPEN FORUM Abstracts

AUTOTRIGGERING DUE TO CARDIOGENIC OSCILLATION DURING FLOW-TRIGGERED MECHANICAL VENTILATION AFTER CARDIAC SURGERY.

Muneyuki Takeuchi, MD, Hideaki Imanaka, MD, Masaji Nishimura, MD*, Naoki Yahagi, MD, Kumon Kumon, MD, ICU, National Cardiovascular Center and Osaka University Hospital*, Osaka, JAPAN.

Flow-triggering (FT) sensitively detects the patient's inspiratory effort. We noticed in some patients after cardiac surgery when FT was used that cardiogenic oscillation was liable to trigger the ventilator as autotriggering. In a prospective study we evaluated the incidence and factors associated with autotriggering.

Methods: One hundred and four consecutive adult patients were enrolled. All patients underwent cardiac surgery: 50 had acquired valve disease, 44 had coronary artery disease, and 10 had atrial septal defect. They were paralyzed and ventilated with SIMV at a rate of 10 breaths/min, pressure support (PS) of 10 cm H_{2}O, and FT with a sensitivity of 1 L/min. After 15 min of the ventilation, blood gases, cardiac output, and flow were measured. Because there should have been no PS, we separated the patients into 2 groups according to the number of PS breaths observed during a 2-min measurement: an " AT group" when PS breaths > 10 and " non- AT group" when < = 10. If PS breaths occurred, we decreased the sensitivity until PS disappeared. Then the intensity of cardiogenic oscillation was assessed as the peak inspiratory flow fluctuation at end expiration.

Results: Twenty-three patients (22%) showed > 10 autotriggered breaths. The AT group showed larger inspiratory flow fluctuation, cardiac output, higher central venous pressure (CVP), larger heart size on chest X-ray, lower respiratory system resistance (Rrs), and hyperventilation than the non-AT group.

AT group (23) non-AT group (81)

Peak inspiratory flow 4.67 ± 1.26 2.03 ± 0.86 *

fluctuation (L/min)

Cardiac output (L/min) 5.47 ± 1.49 4.18 ± 0.91 *

CVP (mm Hg) 9.2 ± 2.8 7.2 ± 2.9 *

Cardiothoracic ratio (%) 61.4 ± 6.1 57.8 ± 4.6 #

Rrs (cm H_{2}O*s*L^{-1}) 8.5 ± 2.1 10.0 ± 2.8 *

Respiratory rate (/min) 19.9 ± 2.7 10.3 ± 0.8 *

Minute ventilation (L/min) 8.54 ± 1.46 5.79 ± 0.99 *

PaCO_{2} (mmHg) 30.8 ± 4.0 37.6 ± 4.4 *

(* p < 0.01, # p < 0.05)

Conclusions: Autotriggering due to cardiogenic oscillation is common in post cardiac surgery patients when flow-triggering is applied. Autotriggering occurred more often in patients with hyperdynamic states.

The 44th International Respiratory Congress Abstracts-On-Disk®, November 7 - 10, 1998, Atlanta, Georgia.

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