Effect of positive end-expiratory pressure on regional ventilation monitored by electrical impedance tomography in mechanically ventilated ICU patients

Introduction

The optimal positive end-expiratory pressure (PEEP) is a balance between the prevention of overdistention in the nondependent part and alveolar collapse in the dependent part. Electrical impedance tomography (EIT) has been introduced to monitor regional change of ventilation at the bedside. We evaluated the effect of changes in PEEP on regional ventilation in mechanically ventilated patients with or without lung disorders.

Methods

Functional EIT (fEIT) images were obtained in 14 patients on pressure-controlled ventilation with constant driving pressure at four PEEP levels (15, 10, 5 and 0 cmH₂O). fEIT images made before each reduction in PEEP were subtracted from those recorded after each PEEP step to evaluate the regional increase/decrease in tidal impedance in each EIT pixel.

Results

The response of regional tidal impedance to PEEP showed a significant difference from 15 to 10 cmH₂O (P = 0.002) and from 10 to 5 cmH₂O (P = 0.001) between patients with and without lung disorders (Figure 1). During the decrease in PEEP from 15 to 10 cmH₂O, tidal impedance increased in the ventral parts in both groups, but decreased markedly in the dorsal parts in the patients with lung disorders. From PEEP 10 to 5 cmH₂O, tidal impedance increased in the ventral parts and decreased in the dorsal parts in patients without lung disorders, whereas in patients with lung disorders tidal impedance decreased in both regions. Lowering the PEEP from 5 to 0 cmH₂O decreased tidal impedance in both regions in both groups.

Figure 1

abstract

Conclusion

During a decremental PEEP trial, EIT can visualize improvement or loss of ventilation in dependent and nondependent parts, indicating lung collapse or decreased overdistention.