Functional residual capacity measurements during mechanical ventilation in ICU patients

Introduction

The level of positive end-expiratory pressure (PEEP) is important to avoid ventilator-induced lung injury (VILI) by preventing alveolar collapse and alveolar overdistension. One of the mechanisms of application of optimal PEEP could be measurement of the functional residual capacity or end-expiratory lung volume (EELV) in mechanically ventilated patients. Recently, GE Healthcare introduced a multibreath open-circuit nitrogen technique to measure the EELV during mechanical ventilation. The aim of this study was to measure the EELV levels at three different PEEP levels in ventilated patients with different diseases.

Methods

We examined 45 sedated mechanically ventilated patients in a mixed ICU of a university hospital. Patients were divided into three groups: normal pulmonary function (group N), respiratory failure due to primary lung disorders (group P) and respiratory failure due to secondary lung disorders (group S). In all patients the EELV measurements were performed at three PEEP levels (15 cmH₂O, 10 cmH₂O, 5 cmH₂O). Arterial blood gases were also obtained at each PEEP level.

Results

Figures 1 and 2 show the EELV data and PaO₂/FiO₂ (PF) ratio data, respectively.

Figure 1

Figure 2

Conclusion

We conclude that the EELV values decreased significantly after stepwise reduction of the PEEP levels from 15 to 5 cmH₂O, whereas the PaO₂/FiO₂ ratio did not change. This indicates that monitoring a patient's lung function could be a prerequisite to find the optimal PEEP in order to prevent VILI.