Respiratory effects of different recruitment maneuvers in acute respiratory distress syndrome

Abstract

Introduction: Alveolar derecruitment may occur during low tidal volume ventilation and may be prevented by recruitment maneuvers (RMs). The aim of this study was to compare two RMs in acute respiratory distress syndrome (ARDS) patients.

Methods: Nineteen patients with ARDS and protective ventilation were included in a randomized crossover study. Both RMs were applied in each patient, beginning with either continuous positive airway pressure (CPAP) with 40 cm H2O for 40 seconds or extended sigh (eSigh) consisting of a positive end-expiratory pressure maintained at 10 cm H2O above the lower inflection point of the pressure-volume curve for 15 minutes. Recruited volume, arterial partial pressure of oxygen/fraction of inspired oxygen (PaO2/FiO2), and hemodynamic parameters were recorded before (baseline) and 5 and 60 minutes after RM. All patients had a lung computed tomography (CT) scan before study inclusion.

Results: Before RM, PaO2/FiO2 was 151 +/- 61 mm Hg. Both RMs increased oxygenation, but the increase in PaO2/FiO2 was significantly higher with eSigh than CPAP at 5 minutes (73% +/- 25% versus 44% +/- 28%; P < 0.001) and 60 minutes (68% +/- 23% versus 35% +/- 22%; P < 0.001). Only eSigh significantly increased recruited volume at 5 and 60 minutes (21% +/- 22% and 21% +/- 25%; P = 0.0003 and P = 0.001, respectively). The only difference between responders and non-responders was CT lung morphology. Eleven patients were considered as recruiters with eSigh (10 with diffuse loss of aeration) and 6 with CPAP (5 with diffuse loss of aeration). During CPAP, 2 patients needed interruption of RM due to a drop in systolic arterial pressure.

Conclusion: Both RMs effectively increase oxygenation, but CPAP failed to increase recruited volume. When the lung is recruited with an eSigh adapted for each patient, alveolar recruitment and oxygenation are superior to those observed with CPAP.

Figure 1

Illustration of the time course of the study. Nineteen patients ventilated with protective lung strategy first had a washout period of 5 minutes of zero end-expiratory pressure ventilation. After 15 minutes of stabilization in positive end-expiratory pressure (PEEP) ventilation, baseline measures (M) were obtained. Then, patients were randomly asssigned to benefit from one of the two recruitment maneuvers (RMs): RM1 or RM2 (that is, continuous positive airway pressure or extended sigh). At 5 and 60 minutes after RM, measurements were obtained. After this first part of the study, a second washout period was performed followed by 15 minutes of ventilation in PEEP and the second RM was performed. The same measurements were performed at baseline and at 5 and 60 minutes after RM. M indicates blood gas analysis, recruited volume by pressure-volume curve method, hemodynamics, and respiratory parameters. LIP, lower inflection point.

Figure 2

Pressure-time and flow-time curves of a representative patient with a lower inflection point at 11 cm H₂O and an upper inflection point (UIP) at 39 cm H₂O. This patient was randomly assigned to benefit from extended sigh (eSigh) first. Initially, positive end-expiratory pressure (PEEP) was set at 14 cm H₂O and tidal volume (V_T) at 480 mL. During eSigh, PEEP was increased to 21 cm H₂O. Plateau pressure was higher than UIP, so V_T was decreased to 390 mL for 15 minutes. After an 80-minute period (Figure 1), the second recruitment maneuver (RM) (continuous positive airway pressure [CPAP]) was performed at 40 cm H₂O for 40 seconds. After this second RM, PEEP was set at 14 cm H₂O. On the flow-time curve, we can see two large expiratory cycles after both RMs corresponding to RM-induced changes in end-expiratory lung volume.

Figure 3

Both recruitment maneuvers increased oxygenation. Extended sigh (eSigh) induced a significantly higher increase in arterial partial pressure of oxygen (PaO₂) than continuous positive airway pressure (CPAP) at 5 and 60 minutes after the recruitment maneuver. * significant versus baseline, † significant versus CPAP.

Figure 4

Recruited volume in responders and non-responders according to recruitment maneuver method. Eight patients were non-responders for extended sigh (eSigh) and 13 for continuous positive airway pressure (CPAP). Changes in recruited volume were significantly higher at 5 and 60 minutes with eSigh only.

Figure 5

Correlation between recruitment maneuver-induced changes in recruited volume and changes in arterial partial pressure of oxygen (PaO₂) for extended sigh (full circles) and continuous positive airway pressure (empty circles).