Discussion

 

 

In this clinical study, we evaluated a new insertion technique for the ProSeal Laryngeal Mask Airway (PLMA) recently communicated by Micaglio and co-workers (14). The technique involves priming the esophageal drain tube (DT) of the PLMA with a gastric tube (GT), placing the GT into the esophagus under video laryngoscopic view [using the GlideScope Video Laryngoscope (GVL)], and inserting the PLMA (using the GT as guide) into the hypopharynx. The main results were that insertion of the PLMA into the correct position (allowing only one insertion attempt) was easy and performance of the PLMA as an effective and reliable airway device for ventilation was successful in all patients. These findings are in accordance with the results from two previously published studies using a gum elastic bougie as guide for PLMA insertion performed by extremely experienced users of this device (2, 9). In a recent survey of PLMA performance (6), the success rate of PLMA insertion at the first attempt (mainly using the standard digital technique) was about 87 percent (ranging from 76 to 100 percent). 

 

The operators of this study were less experienced in the use of the PLMA. The learning curve with the new PLMA insertion technique was not evaluated, because all operators were already familiar and confident with the technique [after prior hands-on training on a suitable airway model (15)] when performing the procedure on patients. The number for obtaining acceptable clinical performance and competence with this technique, estimated by the instructor, remained within 10 applications for all operators, far less than for the standard digital insertion technique suggested by Cook (6).

 

The GVL provided a panoramic view of anatomical structures with visualization of at least parts of the laryngeal aperture and the hypopharynx; only gentle lifting force on the GVL blade was required as experienced in a recently published study using the lower-profile GVL for orotracheal intubation (13). The potential advantage of video laryngoscopy prior to PLMA insertion is that this procedure allows for the identification of unexpected oropharyngeal pathology excluding the use of the PLMA.

 

The cuff of the PLMA is bulkier and less rigid than that of the reusable LMA. There are two important PLMA misplacements: folding over of the distal cuff and incomplete insertion with the distal cuff being directed into the laryngeal aperture rather than the hypopharynx (3, 6). Using the GT-guided PLMA insertion technique, there is usually no need for tests to show that the distal cuff is correctly positioned. The PLMA was in the correct position in all patients, additionally assessed by flexible laryngoscopic view grading through the airway tube (AT).

 

In this study, the flexible laryngoscopic views through the AT of the PLMA (with visualization of the laryngeal aperture in 100 percent) were superior compared to those identified in a recent survey of PLMA performance (6) with visualization of the laryngeal aperture in only about 85 percent; the operators in these studies mainly used the standard digital insertion technique and up to a maximum of three insertion attempts were provided by the study designs. The lowest-rated laryngeal views obtained were published by Kihara and co-workers (12); they visualized the laryngeal aperture (standard digital insertion technique, provision of a maximum three attempts, and successful performance in all patients) in 56 percent (133/237 patients). The best results were obtained by Cook and Cranshaw (5), experienced users of the PLMA; the laryngeal aperture was visible through the airway tube of the PLMA in all 32 investigated patients (introducer insertion technique and provision of a maximum of two insertion attempts).

 

With the spirometry-monitored technique of cuff inflation, far less cuff volumes were required to obtain an air-tight seal than recommended by the manufacturer and used by others (6). The cuff volumes required (and the cuff pressures measured) were in the range to exert minimum pharyngeal mucosal pressures with less-reduced pharyngeal mucosal perfusion (11); this may have implications on for the incidence of pharyngolaryngeal morbidity with the use of the PLMA.

 

Whether the GT should be left in place or further advanced (to enable gastric drainage) or removed (to enable the DT to act as vent and drain) was not examined; this decision depended on the clinical situation. In this study, further GT advancement for gastric drainage was occasionally performed; correct gastric placement of the GT was confirmed in all of these patients.

 

We now prefer the GVL-assisted and GT-guided technique of PLMA insertion in routine clinical practice. We speculate, that less-experienced users of the PLMA may have a higher primary success rate of PLMA insertion when using this technique evaluated in this study.

 

 

References