Comparison of Three Methods of PEEP Titration During One Lung Ventilation in Prone Position

Constant PEEP of 5 cm H2O will be applied and maintained throughout one-lung ventilation.

PEEP titration will be started at 5 cmH2O and then increased in 1 cmH2O interval to 10 cmH2O. After 10 breath cycles will maintained, Driving pressure (ΔP) will be measured at each PEEP level at the last cycle. The PEEP indicating the lowest ΔP will be selected if multiple levels of PEEP showed the same lowest ΔP, the lowest PEEP will be selected. Driving pressure will be calculated as plateau pressure minus PEEP. Titration will stopped if peak inspiratory pressure of 50 cm H2O, or plateau pressure of 40 cm H2O reached, or hypotension will be observed.

PEEP titration will be started from 5 cmH2O and increase of 1 cmH2O every 4 min with fixed driving pressure that will result in delivery of a fixed tidal volume (TV) of 6ml/kg ideal body weight (IBW). Optimal PEEP will be defined as the PEEP below which PaO2 /FIO2 falls by at least 20%. If at least 20% PaO2 /FIO2 decrement is not obtained, then PEEP that will result in the highest PaO2 will be selected.