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Crit Care Med. 2004 Jul;32(7):1546-9.

Exhaled tidal volume overestimation in mechanically ventilated patients with large cardiogenic oscillation.

Author information

1
Surgical Intensive Care Unit, National Cardiovascular Center, Osaka, Japan.

Abstract

OBJECTIVES:

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.

DESIGN:

Prospective, observational, clinical study.

SETTING:

Surgical intensive care unit in a national heart institute.

PATIENTS:

Eight postcardiac surgery patients (age 13-70).

INTERVENTIONS:

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.

MEASUREMENTS AND MAIN 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.

[Indexed for MEDLINE]

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