Controlled respiration and mechanical ventilation have long been part of anaesthetic practice. Modern surgery, anaesthetic techniques, and new agents require a reappraisal of this established habit. In many circumstances the adverse effects of mechanical ventilation can be avoided by the use of the laryngeal mask and allowing spontaneous ventilation. In addition to the more prominent advantages, such as less sore throat, reliable assessment of anaesthetic depth, and good recovery, there may be more subtle advantages such as improved cardiopulmonary interaction, better distribution of ventilation, and reduced mechanically induced lung damage. Some of these advantages may be also applied during mechanical ventilation, by allowing continued muscle activity or continuously varying the size of the tidal breaths.Mechanical ventilation is often unnecessary and may be harmful
