Controlled ventilation of O2/air mixture (FiO2 0.5-0.6) is performed with following setting of anesthesia ventilator (ADU™, Datex-Ohmeda, Finland): tidal volume of 7 ml/ideal body weight (calculated by obsolete formulas), respiratory rate maintain normocarbia (end-tidal CO2 tension 35-40 mmHg) and inspiratory:expiratory ratio of 1:2.