To assess the ease of insertion of airway devices you must examine a patient's mouth opening. A patient should be able to open more than three of their fingers breadths.

If mouth opening is more than three fingers there is sufficient room for a laryngoscope or an LMA.

If mouth opening is between 2 cm and 2.5 cm then there is no room for a laryngoscope and LMA placement may be difficult.

If mouth opening is less than 2 cm it will be impossible to use a laryngoscope or an LMA.