Interventions performed to maintain vital parameters within preset limits.

PaO2 = arterial partial pressure of oxygen, FiO2 = inspired fraction of oxygen, PEEP = positive end expiratory pressure, MAP = mean arterial pressure, CI = cardiac index, MPAP = mean pulmonary arterial pressure.
aPEEP was increased stepwise until a peak pressure of 35 cm H2O was reached. At this point, an inspiratory hold was performed for 10 s. Thereafter, the PEEP was stepwise decreased to the PEEP defined by the protocol. If MAP decreased to the level of the MPAP, the recruitment maneuver was aborted.