Materials and Methods

 

 

Legal and Ethical Considerations. The study was approved by the Institutional Review Board. Informed patient consent was obtained for the planned strategy of airway management (AM) and the anonymous use of patient data for scientific purposes.

 

Patient Selection. The study was performed at a community hospital. Adult patients with American Society of Anesthesiologists physical status classification 1, 2, or 3 not requiring tracheal intubation for elective general surgical or urological operative procedures (performed in the supine or lithotomy position) were included in this investigation, provided that the GlideScope Video Laryngoscope (GVL) and the flexible fiberoptic laryngoscope (FFL) used for this study were available. Therefore, this clinical report represents data of a prospective, but non-consecutive observational study. Patients with limited mouth opening (of less than 25 mm), gastroesophageal reflux disease, known or suspected oropharyngeal and esophageal pathology, and those with difficult face-mask ventilation experienced during induction of general anesthesia were excluded from the study. 

 

Participating Operators. The operators (voluntary staff anesthetists, anesthesia residents, and qualified anesthesia nurses could participate in the study) were experienced users of the GVL and the standard laryngeal mask airway (LMA), but had less experience with the use of the ProSeal Laryngeal Mask Airway (PLMA). They first received formal hands-on training on an airway model (AirSim Multi, TruCorp, Belfast, United Kingdom), suitable particularly for training insertion of LMAs (15), and were then instructed during the first 10 applications of the new PLMA insertion technique on patients (the number for obtaining acceptable clinical performance and competence estimated by the instructor). The study design provided successful PLMA insertions attempts on a maximum of 20 patients.

 

Experienced Instructor. The instructor (the corresponding author of this clinical report) first searched the literature (main findings: 2, 6, 7, 9, 14). He then performed an evaluation process testing the various recommended PLMA insertion techniques on an airway model (AirSim Multi). After acquiring clinical experience with the selected PLMA insertion technique on more than 20 patients, he initiated the stepwise introduction of this AM technique into clinical practice at his department by formal instruction.

        

Anesthetic Technique. Patient monitoring and anesthetic care were provided by the S/5 Anesthesia Delivery Unit (Datex-Ohmeda, Instrumentarium Corporation, Helsinki, Finland). Glycopyrrolate 0.2 to 0.4 mg was given 3 min before induction of anesthesia. Following preoxygenation, general anesthesia was induced with 2.5 to 3.5 mg.kg^-1 propofol supplemented by 1.5 to 3.0 µg.kg^-1 fentanyl. After confirmation of effective face-mask ventilation with oxygen, muscle relaxation was achieved using 0.6 mg.kg^-1 rocuronium. During AM, intermittent boluses of propofol were occasionally given on the discretion of the instructor/independent observer for maintaining an adequate depth of anesthesia.

 

Description of Video Laryngoscope. The lower-profile GVL blade (the Lo Pro Adult GlideScope Video Laryngoscope) was exclusively used during this study. It is made from medical-grade plastic material and similar to the Macintosh laryngoscope, but the blade has a pronounced 60-degree upward angulation; the maximum thickness of this blade is 14 mm. A high-resolution, fog-resistant video camera is situated on the inferior aspect of the blade at its inflection point. The view obtained is oriented anteriorly and the video camera is sufficiently remote from the laryngeal aperture to provide a wide visual field. Three light emitting diodes adjacent to the video camera provide adjustable illumination. A power cord/video cable, emerging from the handle, attaches to a dedicated, light-weight liquid crystal display monitor (the GlideScope Video Intubation System, mounted on a mobile stand) where the resulting color image is displayed.

 

Video Laryngoscopy. After complete neuromuscular blockade [judged by neuromuscular transmission (S/5 Neuromuscular Transmission Module and Mechanosensor, with the electrodes placed over the ulnar nerve using the train-of-four mode)], laryngoscopy with the GVL was performed. Positioning of the patient regarding elevation of the head and extension of the neck [particularly using the ramped head-elevated laryngoscopy position in obese patients (4)] was at the discretion of the operator when staff anesthetist, otherwise at the discretion of the instructor. The GVL was inserted in the midline into the oral cavity; early identification of the uvula centered on the monitor was used as the first landmark to ensure that the blade was in the midline and correctly orientated. The blade was then slided around the tongue into the posterior pharynx; optimum depth of insertion was determined by the vallecula. The blade was slightly elevated against the dorsal face of the tongue with minimum upward pressure for indirectly lifting the epiglottis. 

 

Video Laryngoscopic View Grading. The laryngeal views obtained with the GVL were evaluated without external laryngeal manipulation; the 5-grade modification of the original classification of laryngoscopic views by Cormack and Lehane was used for video laryngoscopic view grading (16). In addition, visualization of the esophageal lumen was also evaluated.

 

Description of the Laryngeal Mask Airway. The PLMA is a reusable LMA (manufactured from medical-grade silicone) with a larger, wedge-shaped cuff (and a second cuff attached to the dorsal surface of the mask) to improve the seal with the laryngeal aperture and an esophageal drain tube (DT; forming a seal with and opening into the esophageal lumen) to prevent aspiration and gastric insufflation (3). The bowl of the mask is open without mask aperture bars, as the DT functions as a solitary mask aperture bar for the accessory vent and the deeper bowl makes epiglottic occlusion of the distal laryngeal aperture less likely. The airway tube (AT) and DT section is flexible (wire-reinforced) and both tubes have a common built-in bite block.

 

Preparation of the Laryngeal Mask Airway. The cuff of the mask was first tested for cuff leakage and then fully deflated. The DT of the PLMA was first filled with some amount of a water-soluble lubricant and then primed with a simple gastric tube [GT; made of plastic material, with an outer diameter of about 5.5 mm and a length of 110 cm, manufactured by Unomedical, Berkeroed, Denmark]; the introducer (a stiffening device inside the GT for easier insertion) was retracted for about 4 to 6 cm to soften the distal end (for atraumatic insertion). The posterior surface of the mask was also lubricated with a water-soluble lubricant.  

 

Insertion and Performance of the Laryngeal Mask Airway. PLMA sizes 4 and 5 were used in small and large adults, respectively; the decision of PLMA size selection was at the discretion of the operator when staff anesthetist, otherwise at the discretion of the instructor. Under videolaryngoscopic view, the GT was first placed gently into the esophagus and advanced for approximately 8 to10 cm. The GVL was removed and the PLMA was then inserted, holding the tubes at the proximal end, around the back of the oropharynx into the hypopharynx (along the GT as guide) until resistance was felt; during manipulation of the PLMA, the proximal end of the GT was stabilzied by an assistant to prevent further penetration into the esophagus. Correct position of the appropriately sized PLMA was assumed when at least 50 percent of the bite block disappeared beyond the upper incisors (or the gums in toothless patients). After insertion of the PLMA into the hypopharynx, the cuff of the PLMA was inflated with air (up to the maximum volume recommended by the manufacturer: 30 ml for size 4 and 40 ml for size 5) until an effective air-tight seal was obtained [judged by spirometry (S/5 Compact Airway Module, with the flow sensors and gas sample line attached to the common connector close to the patient)]; an effective air-tight seal was confirmed when the expiratory tidal volume equaled the inspiratory tidal volume (delivered with mechanical ventilation maintaining normocapnia) and an uninterupted pressure-volume curve appeared on the screen. The PLMA cuff pressure was measured using a cuff pressure manometer (Control Inflator, VBM Medizintechnik, Sulz am Neckar, Germany).

 

Description and Preparation of the Flexible Laryngoscope. A FFL (model LF-2, Olympus Europe, Hamburg, Germany) with an insertion cord diameter of 3.8 mm and a diameter of the working channel of 1.5 mm was used throughout the study. Before its use, the distal end of the insertion cord was first placed in warm sterile destillated water (to prevent fogging of the optical system); then the insertion cord was lubricated with a water-soluble lubricant, an antifogging solution was applied on the optical system, and the FFL was attached to an appropriate light source (EVIS LUCERA CLV-260 Light Source, Olympus Europe) and a suctioning device. Finally, the operator adjusted the diopter ring to ensure a clear and focused view.

 

Flexible Laryngoscopic View Grading through the Airway Tube. When the FFL just passed the distal end of the AT, flexible laryngoscopic view grading was performed. A classification system for laryngoscopic views through LMAs evaluated by Keller and co-workers (11) was used in reverse order: grade 1, visualization of the laryngeal aperture; grade 2, visualization of the laryngeal aperture and the posterior epiglottis; grade 3, visualization of the laryngeal aperture and the anterior epiglottis; and grade 4, visualization of the laryngeal aperture not obtained. The PLMA was then fixed by taping the tubes over the chin.

 

Gastric Tube Advancement for Gastric Drainage. The decision of further GT advancement through the DT for gastric drainage was at the discretion of the operator when staff anesthetist, otherwise at the discretion of the instructor; when gastric drainage was not considered, the GT was removed. Correct gastric positioning of the GT was confirmed by epigastric auscultation under insufflation of air through the GT.

 

Procedure after Failed Insertion and Performance of the Laryngeal Mask Airway. The study design allowed only one PLMA insertion attempt (maximum duration of PLMA insertion: 60 seconds); patients, in which insertion of the GT or the PLMA failed, or an effective airway could not be obtained with the PLMA, were excluded from the study. Further AM was at the discretion of the operator when staff anesthetist, otherwise at the discretion of the instructor. Between the subsequent attempt(s) of securing the airway, the patients received face-mask ventilation with oxygen to ensure adequate oxygenation.

 

Hygienic Reprocessing of the Reusable Airway Management Devices. An automatic endoscopy washing and disinfection unit (EDTplus2, Olympus Europe) was used for reliable hygienic reprocessing of the GVL and the FFL. The PLMA was first manually cleaned immediately after removal, then cleaned and disinfected [using the Washer-Disinfector G 7736 CD, Miele, Guetersloh, Germany (dedicated for anesthesia equipment)], and later sterilized (placed in a pouche, with the manual vent of the cuff left open) by steam autoclaving [Steam Sterilizer MST-H, Belimed Infection Control, Ballwill, Muehldorf, and Sulge, Switzerland (following the standard procedure for porous loads)] at the central sterilization division of our institution.     

 

Severe Complaints and Injuries Associated with Airway Management. Severe complaints and injuries (to oropharyngeal, laryngeal, and/or esophageal structures) associated with AM were evaluated at the postanesthesia care unit and during the postanesthesia visit on the first postoperative day at the normal ward.   

 

Independent Observer. The instructor was also independent observer during the entire study. He documented the video and flexible laryngoscopic views obtained (rated by himself); furthermore, he documented minor problems and difficulties and failures during AM, the procedure(s) applied after failed insertion and performance of the PLMA, and severe complaints and injuries associated with AM.

 

Statistics. Statistical analysis was performed using a statistical software program (SAS, version 8.20, SAS Institute Incorporated, Cary, North Carolina, United States). After passing normality test, one way analysis of variance was performed; multiple comparison using the Tukey test followed if the one way analysis of variance showed significance. Results were considered significant at p-values less than 0.05.

 

 

Results