To the Editor:— We read the recent case report by Kleine-Brueggeney et al. with interest.1This report raises several questions. Details as to the patient's head position, height and weight, depth of device insertion, cuff inflation volume, and use of any of the known maneuvers to detect device malposition are critical for problem-solving in supraglottic airway management.
The Laryngeal Mask Airway ProSeal ™ (LMA-P ™) and Laryngeal Mask Airway Supreme ™ (LMA-S ™) were compared in two recent studies.2,3In a series of 93 anesthetized, paralyzed, adult female patients, Eschertzhuber et al. 2concluded that ease of insertion, gastric tube placement, and fiberoptic position are similar for the LMA-P ™ and LMA-S ™, but oropharyngeal leak pressure and intracuff pressure are slightly higher for the LMA-P ™. A prospective, randomized crossover study comparing the LMA-P ™ and LMA-S ™ in 36 fasted female patients by Verghese found similar results.3These studies suggest that many of the previously published findings regarding the performance of the LMA-P ™ may apply to the LMA-S ™.
Kleine-Brueggeney et al. chose a size 5 LMA-S ™ for their patient. Airway obstruction developed immediately after cuff inflation. This clinical finding suggests several possible etiologies.
A recent study by Xue et al. found that head flexion impaired the passage of an orogastric tube via the drain tube of the LMA-P ™.4Patient head position was not specified by the authors.
The authors do not specify the patient's height and weight, only the body mass index of 30.2 kg/m2. The reader must assume that the authors chose to insert a size 5 LMA-S ™ based on the manufacturer's recommended weight-based guidelines (size 5 LMA-S ™ for patients weighing 70–100 kg).
Goldman et al. recently presented a study in which correct LMA-S ™ size was chosen by correlating the patient's Guedel oral airway size. Guedel oral airway size was judged by aligning its tip with the angle of the jaw and its proximal end with the corner of the patient's mouth. This maneuver was done next to the patient's head just before anesthetic induction. In a series of 100 patients, 77% of women required a size 3 LMA-S ™ using an 80-mm, size 3 oral airway, while 77% percent of men required a size 4 LMA-S ™ using a 90-mm, size 4 oral airway as a size guide. The remaining patients required the next-largest size LMA-S ™. Appropriate size of the LMA-S ™ was accurate using this method, regardless of the patient's body weight.
Other clinical findings that confirm appropriate LMA-S ™ size include insertion of more than 50% of the bite block at the level of the teeth/gums.5The issue of acute airway obstruction may have resolved entirely if the authors had chosen to downsize to a size 4 LMA-S ™, rather than to reinsert the size 5 LMA-S ™.
The authors do not specify the amount of air used to inflate the cuff or its resulting pressure. Manufacturer's guidelines indicate that the cuff inflation volume should not exceed 45 ml for a size 5 LMA-S ™. Clinically, overinflation of the cuff could lead to narrowing of the glottic inlet as a result of extrinsic compression. The combination of inappropriate size and cuff overinflation can cause the events described.
Finally, five types of LMA-P ™ malposition have been described after insertion.6The incidence of LMA-P ™ malposition is approximately 5–15%. Three percent of LMA-P ™ malpositions occur with the distal cuff of the device in the glottic inlet, severe epiglottic downfolding occurs in < 0.5%, and glottic compression occurs in 0.3%. These types of LMA-P ™ malposition are associated with airway obstruction as diagnosed in table 1.6
The esophageal drain tube is designed to aid the clinician in detecting malposition.7Free passage of a gastric tube via the drain tube provides information about the position and patency of the drain tube of the LMA-P ™ or LMA-S ™. The “bubble test” described by O'Connor and Stix8detects misalignment of the distal tip of the LMA-P ™ or LMA-S ™ with the glottic inlet. Reseating the LMA-P ™/LMA-S ™ with a jaw thrust maneuver may be helpful.6
The challenge of attaining expertise and facility with any new airway device remains the clinical problem to solve. This depends, in part, on review of the existing scientific literature as well as ongoing clinical experience. Kleine-Brueggeney et al. should be commended for initiating a clinical dialogue about the LMA-S ™, a new but potentially useful advancement in airway management.
*Mount Sinai School of Medicine, New York, New York. email@example.com