Three Inflation Methods of the Ambú Auraonce™ and Its Adverse Effects

Overview

Laryngeal mask airway device (LMA) is a common device used in the daily practice for airway management. Consecutive generations have permitted an expansion of its use, probably because of a rapid increase of ambulatory surgical procedures and also due to the development of procedures in areas away from the operating room. The cuff inflating volume is not standardized and it is common practice to inflate the LMA cuff according to the manufacturer's recommendations, without using a manometer. A hyperinflation of the LMA cuff was associated with complications ranging from sore throat, or dysphagia and dysphonia, to more serious complications such as paralysis of the vocal cord, arytenoid cartilages dislocation, recurrent laryngeal nerve injury and hypoglossal nerve injury. Also, the excess of volume or pressure is related to poor ventilation and increase the risk of gastric insufflation. The aim of this study is to evaluate the best cuff inflation method, in order to limit the intracuff pressure beyond the recommended maximum pressure (PM \< 60 cmH2O) and to allows decrease the pharyngo-laryngeal complications. The Primary outcome is to compare three different cuff inflating methods using AuraOnce™ LMA during fibrobronchoscopy and endobronchial ultrasound (EBUS) procedures, and to control the intracuff pressure, and the effect on pharyngo-laryngeal complications. The three different cuff inflating methods are: 1) residual volume group (RV group) 2) half of the maximum volume group (MV group) 3) unchanged volume group (NVgroup)

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. Any adverse events (i.e., desaturation (pulse oximetry\< 90%), aspiration/regurgitation, bronchospasm, airway obstruction, coughing, gagging or vomiting) and corresponding interventions will be recorded. After the procedure, all patients will be transferred to the recovery unit and observed for at least 1 hour. Observed adverse effects, such as sore throat, hoarseness, aphasia, nausea and vomiting will be recorded in the recovery room period. At 24h, a home telephone interview will record these parameters, as well as patient satisfaction scores using visual analog scales.