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 with a reference center for the management of thyroid diseases; the institutional department of general surgery performs more than 1200 thyroid surgical procedures a year. Adult patients with American Society of Anesthesiologists physical status classification 1, 2, or 3 requiring orotracheal intubation for elective thyroid surgery were investigated. Patients with gastroesophageal reflux disease and those with difficult face-mask ventilation experienced during induction of general anesthesia were excluded from the study. Patients with previously experienced difficult conventional tracheal intubation, anatomic features predictive for difficult conventional laryngoscopy and tracheal intubation [such as limited mouth opening (but not less than 20 mm), restrictions in forward movement of the jaw, reduced thyromental distance, and/or limitations in head and neck movement], and/or obesity were given preferential enrollment into the study. Therefore, this clinical investigation represents data of a prospective, but non-consecutive observational study.

 

Participating Operators. The operators (voluntary staff anesthetists, anesthesia residents, and qualified anesthesia nurses could participate in the study) had no experience with laryngoscopy and tracheal intubation using the Airtraq Optical Laryngoscope (AOL). They first received formal hands-on training on a suitable airway model (AirSim Multi, TruCorp, Belfast, Northern Irland) for acquisition of sufficient skills in handling the AOL and passing the tracheal tube (TT) through the laryngeal aperture into a midtracheal position, and were then instructed during the first 10 applications on patients (the number for obtaining acceptable clinical performance and competence estimated by the instructor). Residents and qualified anesthesia nurses were supervised during all performances on patients The study design provided successful AOL-assisted laryngoscopies and tracheal intubations on a maximum of 20 patients.

 

Experienced Instructor. The instructor (the corresponding author of this clinical investigation) first searched the literature (main findings: 2, 5, 6, 8, 9, 10); in addition, he had personal contact with the inventor of the AOL (Pedro A. Gandarias, Vizcaya, Spain) at a meeting and workshop for AM. He then evaluated and trained AOL-assisted laryngoscopy and tracheal intubation on a suitable airway model (AirSim Multi), before performing the technique on selected patients. After acquiring experience with the AOL and performing an evaluation process, testing the efficacy and safety of the AOL in easy and later in difficult tracheal intubation situations including more than 20 patients, he initiated the stepwise introduction of the AOL into clinical practice by formal instruction of novice users.

                   

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 at the discretion of the instructor for maintaining an adequate depth of anesthesia.

 

Conventional 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)], conventional laryngoscopic view grading (CLV) was performed using direct laryngoscopy with a standard Macintosh laryngoscope for fiberoptic battery handles (Karl Storz Endoscopy, Tuttlingen, Germany; blade sizes 3 and 4 in small and large adults, respectively. The depth of blade insertion was determined by the vallecula; gentle lifting force on the blade was applied and the laryngeal view was evaluated without external laryngeal manipulation. 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 (1)] was at the discretion of the operator when staff anesthetist, otherwise at the discretion of the instructor.

 

Conventional Laryngoscopic View Grading. The 5-grade modification of the original classification of laryngoscopic views by Cormack and Lehane was used for CLV (10): grade 1, visualization of the entire laryngeal aperture; grade 2, visualization of just the posterior portion of the laryngeal aperture; grade 3, visualization of only the arytenoids; grade 4, visualization of only the epiglottis; and grade 5, visualization of just the soft palate. Laryngoscopy and tracheal intubation with the AOL were then attempted after a short period of face-mask ventilation with oxygen.

 

Description of the Optical Laryngoscope. The AOL is a disposable device made from medical-grade plastic material. The blade is anatomically shaped and contains a series of lenses, prisms, and mirrors that transfer the image from the illuminated tip of the blade to the view finder at the proximal end of the AOL providing a wide visual field. The blade incorporates a tube-guide channel on the right side to guide the tracheal tube (TT). Light is supplied by alkaline batteries included in the main body of the AOL. The Regular AOL (the blue-coded size 3 model) was used throughout this study; the maximum thickness of the blade is 18 mm and the tube-guide channel may be loaded with TTs up to 8.5 mm inner diameter.

 

Preparation of the Optical Laryngoscope. The AOL was activated 30 seconds before use by pressing the button located on the left side of the viewfinder which turns on the light and warms up the distal optical system to prevent fogging; the light stops blinking when the anti-fogging mechanism is fully activated. The selected TT (tested for cuff leakage and lubricated with a water-solule lubricant) was then placed into the tube-guide channel aligning the tip of the tube with the distal optical system. The upper surface of the blade was also lubricated without contacting the optical system. 

 

Optical Laryngoscopy. The AOL was inserted in the midline into the oral cavity. The blade was then slided around the tongue into the posterior pharynx; optimum depth of insertion was determined by the vallecula. Before the AOL main body reached the vertical plane, visualization of laryngeal structures was attempted. The blade was slightly elevated against the dorsal face of the tongue with minimum upward pressure for indirectly lifting the epiglottis.

 

Tracheal Intubation Technique. For AOL-assisted tracheal intubation, positioning of the patient (as selected for CLV) remained unchanged. Standard TTs (Lo-Contour Murphy, Mallinckrodt Medical, Athlone, Ireland) with inner diameters of 7.5 and 8.0 mm were used in small and large adults, respectively. When the laryngeal aperture was in the center of the view finder, the TT was gently advanced from the position in the tube-guide channel through the laryngeal aperture (under continued view). When the TT impinged on laryngeal structures (the arytenoids or the interarytenoid area), the blade was slightly withdrawn, elevated, and/or turned to the right or left side, and TT advancement was repeated. After visual confirmation of correct placement, the TT was secured at the proximal end and disengaged from the tube-guide channel, and the AOL was removed by rotating the unit forward back and gently lifting it out of the oral cavity.

 

Procedure after Failed Tracheal Intubation. When tracheal intubation failed after two separate attempts (duration more than 120 seconds and/or desaturation with oxygen saturations of less than 95 percent), further AM (and the tracheal intubation technique applied) was at the discretion of the operator when staff anesthetist, otherwise at the discretion of the instructor. Between the tracheal intubation attempts, the patients received face-mask ventilation with oxygen to ensure adequate oxygenation.

 

Disposal of the Optical Laryngoscope. The AOL and the containing alkaline batteries were separately disposed. The view finder was separated from the main body of the AOL and the alkaline batteries were removed by pulling the battery cover away from the main body.  

 

Severe Complaints and Injuries Associated with Airway Management. Severe complaints and injuries to oropharyngeal, laryngeal, and/or tracheal structures associated with AM were evaluated by the instructor 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 laryngeal views obtained with CL and the AOL (both rated by the operator) obtained; furthermore, he documented minor problems and difficulties and failures during AM, the procedure(s) applied after failed tracheal intubation, 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