This study was approved by the University of Washington Minimal Risk Institutional Review Board (Seattle, WA) without the need for informed consent, and conducted from March 1, 2011 through April 1, 2011 at the Harborview Medical Center (HMC, Seattle, WA), a 413-bed municipal medical center affiliated with the University of Washington, having 28 dedicated operating rooms, staffed by attending anesthesiologists, either working solo or supervising anesthesiology trainees and/or nurse anesthetists. Additionally, the operating rooms are a primary airway management training location for a number of nonanesthesia trained providers, including local emergency medical services personnel, flight nurses, and emergency and internal medicine trainees.
The GSD was made available for any case for which the primary anesthesia team was planning to use direct laryngoscopy with a Macintosh blade as the initial technique for tracheal intubation. Patient selection, therefore, was nonrandom and only of convenience. Once the primary team requested the GSD, one of the authors (DV, AMJ) made themselves available to briefly explain the design and functionality of the device. The primary laryngoscopist was instructed to perform direct laryngoscopy as usual using the GSD and described pertinent airway structures as the blade was advanced into the airway. The AVL monitor was kept turned to the attending anesthesiologist at all times, unless the described CL grade by the primary laryngoscopist was >3. Under these conditions and at the discretion of the attending anesthesiologist, the laryngoscopist was given access to the AVL monitor view, and indirect laryngoscopy could be attempted. Alternatively, another technique, such as use of the GlideScope GVL, could be performed.
As per routine practice, all patients were brought to the operating room after intravenous access was achieved and standard monitors, including continuous surface electrocardiography, pulse oximetry, and an automated blood pressure cuff, were applied. The patient was preoxygenated with 100% oxygen and general anesthesia was instituted with standard intravenous induction drugs and dosages given by the attending anesthesiologist. All intubation attempts were then performed under general anesthesia. A second spare blade was available to overbridge time for sterilization after use, which was performed using a Steris System 1 tabletop machine per manufacturer recommendations.
Data was collected by one of the study authors in an anonymous format using a paper-based data collection form contemporaneously with airway management. Medical records were not accessed directly at any time. Demographic and airway exam variables collected included age, gender, height (cm), weight (kg), body mass index (kg·m−2), ASA physical status, Mallampati class, interincisor distance, thyromental distance, cervical mobility, and upper lip bite test. Trainee type and experience level, including prior intubation experience and number of intubation attempts, CL grade as reported by the primary laryngoscopist, and subjective assessment of overall airway management difficulty were also recorded. Additional, data collected during laryngoscopy included, conversion to instructor level airway management, CL grade as observed on the video monitor, and any remarks that instructors or trainees had about the device.
Data were entered into an electronic spreadsheet (Excel, Microsoft, Redmond, WA) and descriptively expressed as number (%) unless otherwise noted. For the purposes of analysis, a novice laryngoscopist was one who had performed <30 direct laryngoscopies, while an experienced laryngoscopist was considered one who had performed ≥30 laryngoscopies. Reinsertion of the blade of the device into the mouth or reinsertion of the tracheal tube into the mouth once it had been viewed on the video screen defined an “attempt” at direct and indirect laryngoscopy, respectively. Risk factors for difficult laryngoscopy and subsequent intubation were defined by the presence of one or more of the following: a Mallampati class >
3 airway, thyromental distance <6
cm, interincisor gap <3
cm, reduced cervical spine motion, an inability to bite any part of upper lip, or history of difficult intubation documented by a prior anesthetic record or by patient self-report.