CT-scan lung morphology predicts the response to a recruitment maneuver in acute respiratory distress syndrome patients

Introduction

CT-scan lung morphology (lobar or nonlobar) is the main determinant of positive end-expiratory pressure (PEEP) response. Repartition of gas and tissue probably influences the response to a recruitment maneuver (RM), but to date there is no proof. The aim of this study was to assess RM-induced changes in lung morphology and gas exchange during and after RM in acute respiratory distress syndrome (ARDS) patients.

Methods

Nineteen patients with ARDS were included in the study. Patients were ventilated with volume control ventilation (Gallileo; Hamilton Medical, Bonaduz, Switzerland) with Vt = 6 ml/kg (ideal body weight) and respiratory rate to keep PaCO₂ >55 mmHg without intrinsic PEEP. After a first CT scan in zero end-expiratory pressure conditions, a pressure–volume curve was performed and the PEEP was set above the lower inflection point. After a stabilisation period, a second CT scan (in PEEP) was performed. Then a RM was performed, using continuous positive airway pressure 40 cmH₂O for 40 seconds. At the end of the RM (between 35 and 39 s) a third CT scan was performed. Five minutes after the RM, a fourth CT scan was performed in PEEP conditions (same level of PEEP). Blood gas analysis was sampled at each step of the study. CT-scan analysis was performed using specific volumetric software (IRMA).

Results

Ten men and nine women, 63 ± 11 years old, were included in the study. SAPS II was 44 ± 8. Nine presented a nonlobar CT-scan attenuation and eight a focal loss of aeration. All patients presented early ARDS (onset between ARDS diagnostic and study inclusion was 18 ± 11 hours). Setting PEEP 2 cmH₂O above the lower inflection point increased PaO₂/FiO₂ from 167 ± 110 to 205 ± 72 mmHg (P < 0.001), and 265 ± 80 mmHg after the RM (P < 0.005 vs. PEEP) and 273 ± 96, 5 minutes after the RM. The RM-induced recruited volume at the same level of PEEP was 8 ± 45 ml in the case of lobar CT-scan attenuation versus 96 ± 63 ml in nonlobar CT-scan attenuation (P < 0.005). The overinflated lung volume after RM was 121 ± 170 ml in the case of lobar attenuation versus 18 ± 22 ml in diffuse (P < 0.005). During the RM, the overinflated lung volume was over 50% in the case of lobar CT-scan attenuation.

Conclusion

As for PEEP, lung morphology predicts the response to a RM. In the case of lobar loss of aeration, RM induced overinflation more than the recruited volume and should be avoided.