OSCE Station #16 for the Primary

• First generation laryngeal mask airway (invented by Dr Archie Brain in 1988 - no extra marks for this information)
• Can be single use or reusable - the image shows a single use version
• Used for ventilation in low risk elective anaesthesia in fasted patients with no significant reflux
• Also used as a rescue airway device in an unanticipated difficult airway
• Can be used to facilitate intubation, either blind or under bronchoscopy, depending on whether the airway tube has bars at the patient end

• Standard
• Reinforced or flexible
• Intubating
• Second generation - LMA ProSeal

• Convenience
• Sterilisation doesn't inactivate prions

• Flexible large diameter plastic airway tubing to conduct fresh gas flow and expired gases at low resistance
• 15 mm connector for connection to breathing system
• Inflatable elliptical pharyngeal cuff designed to create a seal to faciliate ventilation and provide a degree of airway protection from secretions
• Pilot balloon with self-sealing valve to inflate cuff with 20-40mL of air

• Deflate the cuff and lubricate the back of the mask
• Push the mask posteriorly along the contour of the hard palate
• Use index finger to guide the mask down posterior pharynx
• Continue inserting until resistance met
• Remove finger and inflate cuff - the solid line on the tube should be in the centre

• Easy to insert
• No need for muscle relaxation
• Much less stimulating than intubation
• Can transfer to recovery before extubation (hospital policy dependent)
• Generally works very well

• Doesn't properly protect the airway
• Can cause laryngospasm
• No bite block
• Doesn't always form a reliable seal
• Low ventilatory pressure limit of around 20cmH2O

HIGHLY UNLIKELY EXAM QUESTION

This is more just for interest, because nobody can seem to agree.

The theory is as follows:

• Normal spontaneous breathing in an awake patient produces around 5cmH2O of PEEP as a result of the elasticity of the lungs and the action of the adductor muscles of the vocal cords
• When you intubate someone, you lose the adductor action and its associated PEEP
• However with an LMA in a non-paralysed patient, theoretically this is maintained
• Many argue that the low-pressure airway seal is at risk of leaking and gastric insufflation if PEEP is applied
• Others argue - logically - that if you're applying a driving pressure to ventilate the patient already, the PEEP isn't going to add any more risk of a leak

Take home:

• Use second-generation LMA (LMA ProSeal, IGEL) with better seals if you're planning on using PEEP
• Use low PEEP (3-5 cmH2O) to improve recruitment and gas exchange
• Avoid high PEEP >5 cmH₂O unless you've got a very good seal
• Beware in lighter planes of anaesthesia – increased pressures may provoke coughing or laryngospasm