METHODS	Arterial blood gas analysis with measurements of partial pressure of arterial oxygen/fraction of inspired oxygen ( PaO2 / FiO2 ) , and physiologic dead space-to-tidal volume ratio ( VD / VT ) was performed 15 min after anaesthetic induction ( T1 ) , and 30 ( T2 ) and 60 min ( T3 ) after onset of CO2 insufflation .\