This study showed that the LMA-Protector™ provides a better airway sealing effect than the i-gel™, however, the LMA-Protector™ required a longer insertion time, provided a worse fiberoptic view of the vocal cords, and caused more mucosal injury.
In the present study, the mean airway leak pressure was higher with the LMA-Protector™ (31 cmH2O) than with the i-gel™ (27 cmH2O), consistent with the results of the previous studies showing values of 23–29 cmH2O for the i-gel™ [5, 9, 10, 12]. The oropharyngeal airway seal, quantified by the airway leak pressure, is essential for the prevention of aspiration and ventilator efficiency. Higher airway leak pressure results from the closer contact between the cuff and the adjacent soft tissues. The LMA-Protector™ cuff, made of medical-grade silicone, may provide a more individualized fit in the pharynx and hypopharynx. According to a preliminary evaluation, the median pharyngeal seal pressure of the LMA-Protector™ was 34 cmH2O . In another preliminary assessment in non-paralyzed female patients with the LMA-Protector™ size three , median oropharyngeal leak pressure was 25.2 cmH2O. In the present study, we used the different sized devices (size three, four or five) according to the manufacturer’s recommendation based on the patient’s weight in paralyzed males and females. Several factors such as the use of neuromuscular blockade and the size of the device, may have affected the airway leak pressure.
In the present study, the mean airway leak pressure was slightly higher with the LMA-Protector™ than with the i-gel™, which might be clinically insignificant. However, this result should not be ignored because it may also suggest that the LMA-Protector™ can be a choice in some clinical situations where a higher airway leak pressure is required such as laparoscopic surgery, although it was not evaluated in this study.
The success rate of the device insertion at the first attempt (91% vs. 93%, LMA-Protector™ vs. i-gel™, respectively), and ease of insertion were not different between the two devices, but the insertion time was longer with the LMA-Protector™ than with the i-gel™. The i-gel™ has a non-inflatable cuff, whereas the LMA-Protector™ has a longer and larger inflatable cuff, therefore, it might take more time to introduce the larger cuff into the oropharyngeal space and inflate it. Moreover, anesthesiologists had more familiarity with the i-gel™ than the LMA-Protector™, which may influence insertion time.
The i-gel™ and LMA-Protector™ can be used as an intubation conduit, and proper alignment of the ventilation pathway with the vocal cords is crucial for successful tracheal intubation. In the present study, ventilation was adequate in all patients, but the i-gel™ had a better fiberoptic view of the glottis with less epiglottic down-folding than the LMA-Protector™. This finding was consistent with previous studies in which the i-gel™ provided an acceptable fiberoptic view of the vocal cords in more than 80% of subjects [5, 10]. The i-gel™ has an epiglottic rest preventing the epiglottis from down-folding or obstructing the distal opening the airway , whereas the LMA-Protector™ has no component to prevent epiglottic down-folding, such as the epiglottic elevating bar in the LMA-Fastrach™ [13, 14].
The i-gel™ has one gastric channel, similar to other pre-existing supraglottic airway devices. The newly developed LMA-Protector™ distinctively contains two gastric channels, a suction port and a drainage port, which emerge proximally as separate ports, entered a chamber located behind the cuff bowl, and communicates distally with the upper esophageal sphincter (Fig. 1). The gastric fluid can be removed by attaching suction to the suction port or by inserting a gastric tube through the drainage port to the stomach. The internal volume of the drainage pathway in the LMA-Protector™ (31 mL for size three; 41 mL for size four; 42 mL for size five)  is much larger than that of the i-gel™. Thus, the LMA-Protector™ may be more efficient at reducing the risk of pulmonary aspiration of gastric contents. Nevertheless, in the present study, the gastric tube insertion was more difficult through the LMA-Protector™ than through the i-gel™ despite of adequate ventilation in all patients. We failed to insert the gastric tube in nine patients through the LMA-Protector™ and one patient through the i-gel™. This finding might be associated with the size of the gastric tube used with the LMA-Protector™. According to the instructions for use of each device, the recommended maximum size of the gastric tube was 12 or 14 Fr for the i-gel™ (12 Fr for sizes three and four; 14 Fr for size five) and 16 or 18 Fr for the LMA-Protector™ (16 Fr for size three; 18 Fr for sizes four and five) [1, 6]. In the present study, we used the gastric tube size 12 Fr for the i-gel™ and size 14 Fr for the LMA-Protector™. The selection of the 14 Fr gastric tube for the LMA-Protector™ was based on a preliminary study using the LMA-Protector™ size three in female patients in which the 14 Fr gastric tube was successfully inserted in 24 of 25 patients . In this study, we inserted the 14 Fr gastric tube through the size three, four or five LMA-Protector™, and considered that it was difficult to introduce the relatively thin and flexible gastric tube within the large drainage pathway. Thus, the use of a larger sized gastric tube might facilitate the passage through the gastric channel of the LMA-Protector™ although it was not evaluated in this study. Moreover, the LMA-Protector™ has a large gastric pathway, which may provide a potential advantage at risk of pulmonary aspiration. Thus, a further study is required regarding the protective effect of the LMA-Protector™ against pulmonary aspiration.
In the present study, blood staining indicative of mucosal injury was more frequent with the LMA-Protector™ (24%) than with the i-gel™ (7%). In some previous studies, blood staining was observed in 0–13% of patients with the i-gel™ [9, 15,16,17]. The i-gel™ has a non-inflatable cuff made of a soft, gel-like medical-grade thermoplastic elastomer, potentially reducing the oropharyngeal tissue injury . Although the LMA-Protector™ is made of flexible medical-grade silicone, it has a strongly tapered leading tip and a longer and larger inflatable cuff compared to the i-gel™, which may cause more mucosal injury. The incidence and severity of postoperative sore throat, however, were not different between the two devices.
This study had several limitations. First, the investigators who inserted the supraglottic airway device were not blinded to the group assignment due to the nature of the study. They followed the standardized and detailed study protocol. The investigators that evaluated postoperative sore throat, and all patients were blinded to the group allocation. Yet, there is still the potential for bias. Second, the investigators who inserted the supraglottic airway device had more experience with the i-gel™ (more than 100 insertions) than with the LMA-Protector™ (more than 30 insertions). They did have experience with more than 50 insertions of the LMA-Supreme™ which has a similar insertion method to the LMA-Protector™. However, a conscious (or unconscious) bias against the newer device, LMA-Protector™, might affect the results. Furthermore, the difference in experience with the two devices, especially less experience with the newer device, may be a possible source of bias. Third, this study was performed in anesthetized and paralyzed patients with normal airways. Thus, our results cannot be generalized to non-paralyzed patients, patients during spontaneous ventilation, and patients with difficult airways. Fourth, this study was conducted in patients with a mean body mass index of 24 kg/m2, not in obese patients, and our results may not be applicable to obese patients.