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) were experienced users of video laryngoscopes. The study design provided laryngoscopy and tracheal intubation attempts with the McGrath Portable Video Laryngoscope (MVL) on a maximum of 20 patients.

                   

Anesthetic Technique. General anesthesia was induced with the patients placed in a high-level air-conditioned operating room. 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 independent observer/supervisor for maintainig 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 independent observer/supervisor.

 

Conventional Laryngoscopic View Grading. The 5-grade modification of the original classification of laryngoscopic views by Cormack and Lehane was used for CLV (7): 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 MVL were then attempted after a short period of face-mask ventilation with oxygen.

 

Description of the Video Laryngoscope. The MVL is a self-contained device powered by a single alkaline battery (giving usually one hour of non-continuous use when fully charged) included in the laryngoscope handle. The miniaturized color liquid crystal video screen mounted on the proximal end of the laryngoscope handle is movable and allows viewing of anatomical structures and the tracheal intubation process. The core of the laryngoscope blade is the robust camera stick (CS; adjustable by up to 34 mm) with a high-intensity light emitting diode fiber and a small digital camera at the distal end. The light and the point of view from the digital camera are realigned anteriorly and to the left by lenses within a dedicated disposable laryngoscope blade (DLB; similarly shaped as standard Macintosh blades, made of medical-grade optical polymer, and packaged sterile). The DLB (with a maximum thickness of 12 mm) entirely covers the CS. The digital signal is processed within the CS and transmitted to the video screen via contacts within the clamp at the bottom of the laryngoscope handle. The recently released MVL model series 5 was used throughout this study.

 

Preparation of the Video Laryngoscope. The CS was first assembled on the laryngoscope handle; the adjustable length of the CS was adapted to the size of the standard Macintosh laryngoscope used for CLV. The DLB was then mounted on the CS and the device was powered-up by pushing the button at the top of the laryngoscope handle. 

 

Video Laryngoscopy. The MVL was inserted in the midline into the oral cavity; early identification of the uvula centered on the video screen 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. Positioning of the patient (as selected for CLV) remained unchanged. The laryngeal views obtained with the MVL were evaluated with the same 5-grade classification as used for CLV using gentle lifting force without external laryngeal manipulation.

   

Description of the Directional Tracheal Tube Stylet. The Schroeder directional tracheal tube stylet (DS) is a single-use device available in four sizes; for the study, the recently modified Flex 7580 (dedicated for TTs with inner diameters of 7.5 and 8.0 mm) was used. The DS consists of two polyethylene members joined at their distal ends and a proximal thumb button and flange. Activation of the thumb button against the flange induces an articulating action in the DS and a variable curvature in the surrounding TT, particularly in the distal area. The members of the stylet were positioned in the posterior slot of the flange without using the locking mechanism.

 

Tracheal Intubation Technique. MVL-assisted tracheal intubation was attempted when laryngeal structures were visible. The usual level of the operating table was lowered to ease manipulation of the styletted TT. 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. The selected TT (after testing for cuff leakage) was fitted with the DS and preferably introduced midline beneath the phalange of the MVL blade; occasionally (in patients with limited mouth opening and/or restricted pharyngeal space), the TT was introduced from the right lateral side. The thumb action on the DS allowed to remotely adjust the curvature of the TT during the tracheal intubation process. After advancing the tip of the TT through the laryngeal aperture, the DS was withdrawn by about 4 cm; this usually straightens the tip of the TT and eases advancement of the TT. When further advancement of the TT was impeded (by impinging on the anterior wall of the thyroid cartilage or the anterior trachea), the DS was completely withdrawn and the TT was rotated 90 degree or more to the right to facilitate passage into a midtracheal position. After visual confirmation of correct placement, the TT was secured at its proximal end and the MVL 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 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 independent observer/supervisor. Between the tracheal intubation attempts, the patients received face-mask ventilation with oxygen to ensure adequate oxygenation.

 

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 independent observer/supervisor at the postanesthesia care unit and during the postanesthesia visit on the first postoperative day at the normal ward.   

 

Independent Observer. The corresponding author of this clinical report was independent observer/supervisor during the entire study. He documented the conventional laryngeal views (rated by the operator) and the videolaryngoscopic views (rated by himself); 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