Different patterns of lung recruitment maneuvers in primary acute respiratory distress syndrome: effects on oxygenation and central hemodynamics.

BACKGROUND

The aim of this study was to test if different recruitment maneuver (RM) patterns, that achieve the same maximum pressure for the same length of time in humans, have a similar efficacy on alveolar recruitment, intrathoracic vascular pressures and flows, and on cardiac function and ventricular filling.

METHODS

Forty patients were randomly allocated to undergo different RM patterns: sustained inflation (SI) or pressure controlled ventilation (PCV). The RM methods tested are as follows: SI was achieved by raising peak inspiratory pressure to 45 cmH(2)O and sustaining it for 40 seconds. The PCV was set to obtain a 45 cmH(2)O peak inspiratory pressure for 2 minutes, I:E 1:2, PEEP 16 RR 8/min. During the study period, patients were mechanically ventilated to obtain a volume of 6 mL/kg, FiO(2) 0.7, PEEP 14, RR 14, Pplateau < or =30 cmH(2)O according to the ARDSnet trial. All patients were sedated and paralyzed during the study period. All patients were given i.v. norepinephrine. Heart rate, pulse oxymetry, blood pressure, pulmonary artery catheter data (C.I., PVRI, MPAP, PAOP, SvO(2), CVP), and arterial and right heart side venous blood gas analysis data (ph, PaO(2), PaCO(2), SatO(2), HCO(3)(-), SvO(2)) were recorded before and immediately after the lung recruitment maneuver. The static compliance of the respiratory system (CRS) was recorded. Echocardiographic spot evaluations before and after RM were obtained in all cases.

RESULTS

Central venous pressure increased during RM. Mean pulmonary artery pressure, pulmonary capillary wedge pressure and pulmonary vascular resistance index were reduced during PCV RM compared to SI RM (P<0.05). The right ventricle stroke work index decreased to a major extent during PCV RM (P<0.05). The P/F ratio was significantly increased after PCV RM compared to SI RM (P<0.05). PaCO(2) levels were similar in the two groups. Compared to baseline, the Qs/Qt decreased significantly after the PCV recruitment maneuver. Ventricular end-diastolic and end-systolic areas decreased during both RM protocols, but they were decreased to a greater extent after SI RM than after PCV RM (P<0.05). The eccentricity index increased from baseline after the SI RM (P<0.05).

CONCLUSION

Given its comparable, or even superior, performance over the SI RM, we favor the PCV technique over the time-honored SI maneuver.