Determination of cardiac output during mechanical ventilation by electrical bioimpedance or thermodilution in patients with acute lung injury: effects of positive end-expiratory pressure.

OBJECTIVE

To evaluate the usefulness of transthoracic electrical bioimpedance in sedated and paralyzed patients with acute lung injury during mechanical ventilation with and without early application of positive end-expiratory pressure (PEEP).

DESIGN

Prospective, repeated-measures study.

SETTING

University-affiliated intensive care center.

PATIENTS

Ten patients with acute lung injury.

INTERVENTIONS

Simultaneous, three-paired cardiac output (CO) measurements by transthoracic electrical bioimpedance (TEB) and thermodilution (TD) were made at 0 and 15 cm H2O of PEEP.

MEASUREMENTS AND MAIN RESULTS

The average of the TD-CO measurements was 7.22 +/- 2.12 (SD) L/min during 0 cm H2O of positive end-expiratory pressure (ZEEP), and 6.91 +/- 1.72 L/min during PEEP (NS). The average of the TEB-CO measurements was 4.48 +/- 1.37 L/min during ZEEP, and 6.03 +/- 2.03 L/min during PEEP (p < .05). For each level of PEEP, bias and precision between methods were calculated. Bias calculations between TD-CO and TEB-CO ranged from -1.54 +/- 7.02 L/min at ZEEP to -2.52 +/- 4.28 L/ min at PEEP, and -2.47 +/- 6.09 L/min for mixed data at ZEEP and PEEP. There was no significant correlation between the percent change with PEEP in TEB-CO and TD-CO (r2 =.05, NS).

CONCLUSIONS

In patients with acute lung injury: a) the agreement between TEB-CO and TD-CO measurements is poor; b) agreement is not clinically improved by application of PEEP; and c) TEB cannot monitor trends in CO.