Three Inflation Methods of the Laryngeal Mask Airway Ambú Auraonce™ and Its Pharyngolaryngeal Adverse Effects

This is a prospective randomized controlled trial. The study was approved by the Ethics Committee of University Hospital of La Paz, Madrid. Written informed consent will be obtained from each patient before the procedure. We plan to include 210 patients scheduled for a fibrobronchoscopy with EBUS-transbronchial needle aspiration (TBNA) procedures under general anesthesia using a LMA. Patients will be allocated randomly to one of three groups of cuff inflating methods according to computer-generated randomization. The size of LMA will be chosen according to body weight, following the manufacturer recommendations (LMA size 3 for patients of 30-50 kg, LMA size 4 for patients of 50-70 kg and LMA size 5 for patients with a weight >70 kg). After standard monitoring with electrocardiography, noninvasive blood pressure device and pulse oximeter were applied, general anesthesia will be induced with Propofol 2.5 mg.kg-1 and fentanyl 1 mcg.kg-1 intravenously Face mask ventilation with 100% oxygen will be used after patients have lost eyelash reflex. Then, the assigned LMA will be inserted, after appropriate conditions for insertion are obtained. LMA Insertion will be performed with standard maneuver according to LMA practice manual by the same experienced anesthesiologist (> 1-year use experience). The initial position of LMA will be assessed by visualization of bilateral chest movement when positive pressure ventilation will be performed and the square capnography waveform is observed on the monitor screen.

If the LMA is not in the proper position at the first attempt, we will use an "up and down" maneuver to adjust and reposition LMA to attain satisfactory ventilation. If this maneuver fails, LMA will be withdrawn from the mouth of the patients and a second attempt will be authorized to acquire a correct position. If the proper position of LMA cannot be achieved after two attempts, the airway will be controlled with another device or a tracheal intubation will be performed and the patients will be excluded from the trial.

The patient´s lungs will be ventilated with the anesthesia machine in controlled volume mode, using the following parameters: Tidal volume, 8 ml/kg; frequency, 12-14 per min; the ratio of inspiratory and expiratory, (I: E) = 1:2; and positive end expiratory pressure, 5 cmH20.

After the LMA will be fixed with adhesive tape and the vital signs will be stable, the LMA cuff will be connected with a closed system manometer composed of a three-way stopcock, a 5 ml syringe and a manometer. Intracuff pressure will be measured and recorded, if it exceeds of 60 cmH20 we will deflate the cuff 1 mL by 1 mL with the syringe until intracuff pressure reaches 60 cmH20. The deflated volume and the final intracuff pressure will be recorded. We will measure the inspiratory peak airway pressure, the volume difference of inspiratory and expiratory tidal volume under the positive pressure ventilation. The plateau pressure, medium pressure and Compliance will also be recorded at the corresponding cuff inflating volume, before and after measuring OLP. The OLP will be measured simultaneously at the corresponding cuff inflating volume, by setting the airway pressure relief valve (APL) of the breathing circuit to 40 cmH20 at a fixed gas flow rate of 4 L/ min and reading the airway pressure on manometer at which equilibrium of airway pressure will be established or at the pressure the air leakage will be heard.

Fiberoptic visibility scores will be recorded on a scale of 1 to 4 (4: only vocal cords visible, 3: vocal cords plus posterior epiglottis visible, 2: vocal cords plus anterior epiglottis visible, 1: vocal cords not seen). A score of 1 will be considered the worst and a score of 4 was considered the best.