The risk of aspiration if regurgitation occurs

This risk is often overstated. Published large series and analyses of literature suggest an incidence of clinically apparent pulmonary aspiration during elective anaesthesia with the cLMA of around 1 in 4000-11 000 cases. While this may be an underestimate, it is very similar to the rate of aspiration in elective anaesthesia with a tracheal tube.

Poor case selection will dramatically increase risk. Both poor insertion technique and poor intra-operative care will increase risk.

There is no robust evidence that the cLMA adversely affects oesophageal sphincter pressure, or that it directs regurgitant material towards the larynx.

There is evidence from cadaver work that the correctly positioned cLMA provides some protection against aspiration when compared to the native airway. This protection is considerably lower than that afforded by the ProSeal LMA.

Inadequate ventilation due to airway leak

This may occur during positive pressure ventilation, with most of the gas leaking out through the mouth.

The airway seal provided by the cLMA is low (about 16-20 cmH₂O). This is similar to the tone of the upper oesophageal sphincter (cricopharyngeus muscle).

Increasing airway pressure above 20 cmH₂O is likely to lead to loss of ventilating gas by leakage, and cannot be recommended. Increasing airway pressure leads to:

• An increase in the proportion of gas lost to leakage, which risks hypoventilation
• An increase in gas leaking into the oesophagus and stomach. This risks gastric distension, which may splint the diaphragm, thereby reducing lung compliance and so increasing airway pressure, and thus creating a vicious circle of increasing airway leak and raised airway pressure. Gastric inflation also increases the risk of regurgitation