Beneficial effects of CT scan guided protective ventilation: multislice thoracic CT analysis

Introduction

Recruitment maneuvers (RM) to open the lungs and PEEP titration to keep the lungs opened are believed to be an important component of a lung protective strategy in ARDS. There are scarce data assessing the occurrence of tidal recruitment (TR) and the gas distribution throughout the lung parenchyma by thoracic CT scan before and after maximal recruitment.

Objectives

To analyze the occurrence of TR before and after stepwise recruitment maneuver (SRM) and PEEP titration by thoracic CT scan. To analyze the effects of the proposed maneuver on gas distribution throughout the lung parenchyma.

Methods

Ten ARDS patients under mechanical ventilation were transported to the CT room and sequences of CT scans at expiratory and inspiratory pauses were performed before and after a SRM. The SRM consisted of 2-min steps of tidal ventilation with a fixed delta pressure PCV = 15 cmH₂O and progressive PEEP levels (10, 20, 25, 35, 45, 25, 20, 15, 10 cmH₂O), RR = 10, I:E 1:1, and FiO2 1.0. At equivalent PEEP levels, the amount of collapsed tissue as well as the difference of collapsed tissue between inspiration and expiration (TR) were compared (before versus after maximal SRM). The amount of air content (ml) at end expiration – functional residual capacity (FRC) – was calculated and compared before maximal recruitment at PEEP of 20 cmH₂O and after maximal SRM at PEEP of 25 cmH₂O.

Results

See Figs 1 and 2. The TR difference is statistically significant at PEEP 25 cmH₂O (Wilcoxon P < 0.015). There was a significant decrease of gas at FRC at non-dependent regions (Wilcoxon P < 0.008) and a significant increment of gas at the most dependent region with PEEP 25 cmH₂O after maximal recruitment (Wilcoxon P < 0.008).

Figure 1

Figure 2

Conclusion

The TR decreased significantly only under PEEP of 25 cmH₂O after the SRM (P < 0.0003), suggesting that the application of SRM might be effective when accompanied by sufficient PEEP levels. Aeration of dependent portions of the lung after maximal SRM with maintenance of sufficient PEEP levels to keep the lungs opened (Wilcoxon P < 0.008) was associated with deflation of non-dependent regions, rendering the gas distribution more homogeneous.