The authors describe the advantages and disadvantages, the indications and benefits on gas exchange as a result of mechanical ventilation during anaesthesia. The two models of ventilation most commonly used have been analyzed: pressure ventilators and volume preset ventilators. The former are used only in cases of short-term anaesthesia or when volume ventilators are not available. Both the most appropriate settings and ventilatory modes have been discussed regarding different paediatric ages. Particular attention has been given to the oxygen concentration in the ventilated gases (oxygen toxicity > 40%) and to barotrauma connected with high peak pressure (> 30 cm H2O). The authors suggest the type and caliber of endotracheal tube and the tidal volume for paediatric ages.