Comparison Study of Two Supraglottic Airway Devices Used for Patients Under General Anesthesia

First of all, we will record the following demographic variables: age, sex, height, weight, BMI, surgery planned, American Society of Anesthesiology (ASA) status, dental state (good, bad, edentulous), tobacco use (none, ceased, active) and packs year, Mallampati score, thyromental distance and whether or not there is trauma on the tongue, teeth or lips prior to surgery.

Induction of anesthesia will be standardized with Fentanyl 1-3 mcg/kiloGram(kG) and Propofol 1-3,5 mg/kG. The use of myorelaxant will be mandatory, but either succinylcholine or rocuronium will be used as long as complete disappearance of T1 is observed before attempting supraglottic airway insertion.

Prior to insertion, ease of ventilation (yes/no) will be noted.

The two airway devices will be used according to manufacturers instructions. The sizes of the devices will be chosen according to weight:

I-Gel: 50-90 kG: #4 and 90 Kg and up: #5 LMA Supreme: 50-70 Kg: #4 and 70-100 Kg: #5.

Patients will be randomized in either I-Gel or LMA Supreme group. Two insertions with the same device will be allowed before a crossover to the other device. If the third attempt fails, a standard endotracheal tube will be put in the trachea and blood in the oral cavity will be sought. After each failed attempt (no thoracic expansion, no carbon dioxide (CO2) square wave or leak at standardized volume. Blood on the devices will also be recorded.

Since the LMA Supreme has a cuff, we will inflate it to 25 mL and then by intervals of 5 mL of air (max 45 mL) we will inflate it at a volume where no audible leak is heard at a standardized ventilation scheme of volume controlled 8 mL/kg X 10 breaths per minute.

Once fixed with tape, we will measure peak and mean airway pressure for three breaths after 30 seconds of volume controlled breathing. Then the fresh gas flow will be fixed at 3 L/min of 50-50 air-oxygen blend and the Adjustable Pressure Limiting valve will be closed. We will look either for a plateau pressure at which a leak equal to the fresh gas flow or a pressure of 40 cm of water.

We will sought adverse effect like bronchospasm, cough, regurgitation, desaturation, aspiration and deglutition movement.

Ease of insertion will be score on a scale of 1 to 4. 1 being very easy and 4 being very hard.

Endoscopic evaluation will take place afterwards. First in the ventilation tube. Scoring for laryngeal view:

• Vocal cords all visible;
• Partial view of the cords including arytenoids;
• View of the epiglottis only;
• Other (LMA or pharynx).

Downfolding of the epiglottis will be sought.

Then we will go through the oesophageal port and see if the oesophageal mucosa il visible.

During surgery, we will check if airway manipulation and/or withdrawal was necessary and why.

If traces of blood on the devices are present at the end of the intervention it will be noted.

Two interviews will take place one at the post anesthesia care unit and another the following day by phone if the patient was having ambulatory surgery. Sore throat, cough, dysphagia and dysphonia will be asked to be graded: absent, mild, moderate or severe.

Pulse and arterial pressure with the operating room's sphygmomanometer and oximeter will be written before induction, after induction before insertion and at 1 and 2 minutes post insertion.

Inclusion criteria

• Weight more than 50 kg;
• Body Mass Index less than 30;
• ASA I to III.

Exclusion criteria

• Symptomatic gastro oesophageal reflux disease (GERD);
• Non fasted patients;
• Nasogastric tube in place;
• Intestinal obstruction;
• Ear, nose and throat surgery in the past or deformation of the airway;
• Known difficult airway (Cormack-Lehane grade 3-4);
• Oral cavity opening less than 3 cm;
• Pregnancy.