Methoxyflurane analgesia during local anaesthetics injections.

Methoxyflurane will be given orally to participants before and during injection of local anaesthetic Ropivacaine. Methoxyflurane is self-administered by inhalation through a hand-held whistle shaped inhaler marketed as Penthrox 'Registered Trademark'. All patients are assessed by an anesthesiologist before commencement of the study. Patients are instructed how to use Penthrox 'Registered Trademark' with advice to occlude the aerating hole if they felt they required more analgesia. Pulse oximetry is used throughout the procedure. The anesthesiologist charges the whistle by emptying the entire contents of the bottle of methoxyflurane provided (3 mL) into the bottom of the whistle. Patients are instructed to take some slow easy breaths of the vapour and when they were comfortable with the aroma, take 10 large full breaths, inhaling and exhaling through the whistle. The injection of LA lasts 1 minute and commences after the second breath on Penthrox 'Registered Trademark'. Participants can inhale through the Penthrox 'Registered Trademark' more than 10 times if they feel the need.