A Study Comparing the Laryngeal Mask Airway Supreme With the Laryngeal Mask Airway Protector In the Ambulatory Surgery Unit

Overview

The Laryngeal Mask Airway is a supraglottic airway device that has been used in anesthesia for decades. Now the third generation (LMA Supreme) is commonly used. Recently the LMA Protector is manufactured. The primary hypothesis of this study is: the oropharyngeal leak pressure of the LMA Protector is 5 cmH2O higher than the oropharyngeal leak pressure of the LMA Supreme. Secondary outcome measures are: ease of insertion, fibreoptic position, ease of gastric tube placement. Differences between LMA Supreme and LMA Protector are: the LMA protector has a dual gastric drainage channel, LMA supreme one. For LMA protector, airway tube and cuff are 100% silicone, in LMA supreme the cuff is polivinylchloride. Silicone cuffs have shown to reduce risk of sore throat and achieve higher seal pressures. There are no aperture bars in the LMA protector (2 in LMA supreme). The tube of LMA protector is more flexible. An integrated cuff pressure indicator for single use airway management devices that enables continuous cuff pressure monitoring only in the LMA protector.

1. Outpatients planned for elective minor surgery, routinely done with LMA, will be asked to participate in the study. 2. The patient is preoxygenated for 3 min. Anaesthesia is induced with 0.15 mcg/kg sufentanil and 1 - 4 mg/kg propofol. Routine monitoring is used together with BIS-monitoring. No neuromuscular relaxing agent is used. Patients lungs will be ventilated with a face mask for 3 min and then the LMA will be inserted while the neck of the patient is flexed, the head extended. LMA cuff is completely deflated. The LMA is inserted using a single-handed rotational technique. Failed insertion is defined as: failed passage in the pharynx, malposition (air leak) and ineffective ventilation (expired tidal volume\<25% of administered volume). The time between picking up the LMA and successful placement is recorded. When failed on the first attempt the LMA will be inserted with a digital guided technique. A Third attempt will be a gum-elastic-bougie guided technique. 3. Oropharyngeal leak pressure is determined at 0-40ml cuff volume in 10 ml increments. The expiratory valve of the circle system is closed at a fixed gas flow of 3 l/min and noting the airway pressure at equilibrium (max allowed 40 cmH2O) 4. Fiber optic position: 4=only vocal cords visible, 3=vocal cords + posterior epiglottis, 2=vocal cords + anterior epiglottis, 1=vocal cords not seen. Fiber optic position will only be evaluated if available at the moment of the study. 5. Cuff pressure is set at 65 cmH2O using a manometer and patients lungs are ventilated at a tidal volume of 10 ml/kg, at a respiratory rate of 12/min. Presence of air leak is detected by listening over the mouth, gastric air leak (stethoscope over epigastrium, larynx, drain tube air leaks (lubricant over proximal end) or end-tidal CO2 \> 45 mmHg. Respiratory settings are changed at the discretion of the anesthesiologist after successful placement. 6. Correct gastric tube placement is assessed by suction of fluid. Cardiorespiratory data are collected: bradycardia \>100/min, tachycardia \>, hypotension, hypoxaemia 7. Upon removal of the LMA at the end of the procedure the device will be checked for blood staining. 8. At discharge from day surgery unit patients will be asked for presence of sore throat.