The Optimal Time to Put Laryngeal Mask Airway in the Mouth Under General Anesthesia

This is a randomized, controlled, blinded trial. Midazolam, 2 mg and fentanyl 1.0 µg/kg, would be given prior to induction with propofol, 2.5 mg/kg.

The investigator who does the induction of general anesthesia will also be responsible for the timekeeping. For this reason, it is not possible for this investigator to be blinded to randomization. The induction would conclude after loss of eyelash reflex (LER). At that point insertion of the LMA (#4 for females, #5 for males) will occur 0, 60 and 90 seconds after LER. The LMA will be lubricated with a water soluble gel and will be inserted with a deflated cuff according to the technique described by Brain.

The investigator who inserts the LMA (Inv1) will be in the operating room and blinded to randomization groups by not seeing the induction of general anesthesia. This investigator will insert the LMA only when called by the investigator who induces general anesthesia (Inv2). Inv1 will also grade ease of LMA insertion.

The primary outcome is Jaw opening at the time of LMA insertion, defined as full 1, partial 2, and nil 3.

Secondary outcomes include:

• Insertion of LMA (easy, difficult, impossible)
• Coughing or gagging (none, some, significant)
• Head or body movement (none, some, significant)
• Laryngospasm or airway obstruction (none, partial, total)

Inclusion criteria

• subjects 18 years or older
• ASA status 1-3

Exclusion criteria

• high risk of aspiration
• anticipated difficult airway
• use of sedative drugs
• patient refusal