Spontaneous versus positive pressure ventilation with the laryngeal mask airway: a review

Over the last 10 years,the Laryngeal Mask Airway (LMA) has gained widesprea d acceptance as a general purpose airway for routine anaesthesia. Published data from large studies and reports have confirmed the safety and efficacy of the device for spontaneous and controlled ventilation during routine us e. The initial experience with the LMA should ideally be confined to short cases requiring the patient to remain sponta neously ventilating. With expe rience, it will be found that less anesthetic agent is required during anes thesia with the LMA and patient recovery should be improved as a result. Sp ontaneous breathing is the chosen mode of ventilation in approximately 60% of LMA uses in the UK During spontaneous breathing a minimal inspiratory pr essure support will help with higher endtidal carbon dioxide levels. The an aesthetist should be experienced with using the LMA in spontaneously ventil ating patients before using it with positive pressure ventilation. Several large scale studies have failed to show any link between positive pressure ventilation and pulmonary aspiration or gastric insufflation. The main disa dvantage of the LMB is that it does not protect against aspiration. From a practical point of view, most fasted patients with normal lung compliance m ay be mechanically ventilated through the LMA to airway pressures of approx imately 20 cmH(2)O. The low pressure seal implies that tidal volumes should be approximately 6-8 ml*kg(-1) and the inspiratory flow rates should be re duced to achieve adequate and safe ventilation.