Exhaled tidal volume overestimation in mechanically ventilated patients with large cardiogenic oscillation.
OBJECTIVE
In postcardiac surgery patients, we often noticed that monitored tidal volumes exceeded the ventilator settings. We investigated whether cardiogenic oscillation causes overestimation of tidal volume.


METHODS
Prospective, observational, clinical study.


METHODS
Surgical intensive care unit in a national heart institute.


METHODS
Eight postcardiac surgery patients (age 13-70).


METHODS
Patients were paralyzed and received flow-triggered volume-controlled ventilation with a tidal volume of 10 mL/kg. In random order, two types of ventilator (Bird 8400 STi and Servo-300) and two respiratory rates (5 and 10 breaths/min) were applied to each patient via a disposal ventilatory circuit and heat-and-moisture exchanger. For each ventilator, we adjusted the flow-triggering sensitivity to prevent autotriggering due to cardiogenic oscillation: 10 L/min for the Bird 8400 STi and green zone for the Servo-300.


RESULTS
The magnitude of cardiogenic oscillation during mechanical ventilation was defined as peak expiratory flow fluctuation at end-expiration. We recorded tidal volume using the monitoring devices on the ventilators and calculated the discrepancy from the set tidal volume. Cardiogenic oscillation was significantly greater with the Bird 8400STi (4.0 +/- 1.8 L/min) than with the Servo-300 (1.7 +/- 0.8 L/min). With the Bird 8400 STi, the discrepancy between monitored tidal volume and set tidal volume ranged from 15 to 260 mL when the respiratory rate was 5 breaths/min and from -9 to 75 mL at 10 breaths/min; there was a linear correlation between the overestimation of tidal volume and the magnitude of cardiogenic oscillation. In contrast, with the Servo-300, the discrepancy was relatively small (-36 to 14 mL).


CONCLUSIONS
In mechanically ventilated patients with large cardiogenic oscillation, exhaled tidal volume is overestimated on at least one model of ventilator.
Imanaka
Hideaki
H
Surgical Intensive Care Unit, National Cardiovascular Center, Osaka, Japan.
Takeuchi
Muneyuki
M
Tachibana
Kazuya
K
Nishimura
Masaji
M
D000293:Adolescent; D000328:Adult; D000368:Aged; D001784:Blood Gas Analysis; D005260:Female; D006331:Heart Diseases / Q000601:surgery; D006801:Humans; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000009:adverse effects / Q000379:methods*; D013990:Tidal Volume