A comparison of the Laryngeal Tube S and the LMA ProSeal laryngeal mask airway

Abstract

Because the laryngeal mask technique is so essential to our specialty, we are frequently surprised by lack of appreciation for the newer LMA ProSeal™ (Laryngeal Mask Company, Henley-on-Thames, UK) [1]. We credit Dr Brimacombe and colleagues for describing an important malposition of the LMA ProSeal in 2001 [2]. They described how the LMA ProSeal can ‘fold over backwards’. In this position ventilation may be adequate and the practitioner gains a false sense of security that the position is satisfactory. The drain tube is also folded backward however, and cannot function as intended because it does not enter the oesophageal inlet. While folded backward, the LMA ProSeal does not provide any protection from the risk of regurgitation. A folded over LMA ProSeal may, in fact, act as a hypopharyngeal spring and pry open the upper oesophageal sphincter. We were surprised, therefore, by the publication of a study where the definition of ‘successful insertion attempt’ of the LMA ProSeal consisted simply of checking airway patency [3]. Among the 74 ‘successful’ insertions there were 12 patients in whom it was impossible to insert the orogastric tube. Evidently in these 12 patients the LMA ProSeal was folded backward. The purpose of the LMA ProSeal is to expand use of laryngeal mask technology to encompass patients at increased risk for aspiration. When the device is folded backward, as occurred in these 12 patients, this enhanced capability is completely defeated. The only proven technique to insert the LMA ProSeal into the oesophageal inlet with near complete success is by using a bougie-guided insertion method pioneered by Brimacombe and colleagues [4]. Another technique to verify correct positioning behind the larynx is to pass a well-lubricated orogastric tube through the drain tube and suction gastric fluid. A semiqualitative technique to test for foldover is the suprasternal notch test [5, 6]. This involves placing a membrane of children's bubble solution on the drain tube port. Tapping the suprasternal notch causes the membrane to bounce up and down when the LMA ProSeal is behind the cricoid cartilage (normal). If the membrane remains stationary, it can be assumed that the LMA ProSeal is folded backward. The device should be removed and reinserted. After using the suprasternal notch test to screen for foldover in over 3000 patients, we have always been able to pass an orogastric tube. However, there has been no prospective study to verify this simple and inexpensive test. In summary, just as it is automatic and prudent to exclude oesophageal intubation following every insertion of a tracheal tube, it should be automatic to exclude foldover following every insertion of the LMA ProSeal.