Hyperangulated Versus Standard Geometry Laryngoscope Blade Trial

Overview

The Hyperangulated versus Standard Geometry Laryngoscope Blade (ANGLE) Trial is a multi-center, non-blinded, parallel-group, randomized clinical trial evaluating the effect of use of a hyperangulated video laryngoscope blade versus use of a standard geometry video laryngoscope blade. Critically ill adults undergoing tracheal intubation in participating EDs and ICUs who meet eligibility criteria will be enrolled and randomly assigned in a 1:1 ratio to either intubation using a hyperangulated video laryngoscope blade or a standard geometry video laryngoscope blade. The primary outcome is the incidence of successful intubation on the first attempt. The secondary outcome is incidence of hypoxemia during the interval between induction and 2 minutes after tracheal intubation.

Clinicians frequently perform tracheal intubation of critically ill patients in the emergency department (ED) or intensive care unit (ICU). In 10-20% of emergency tracheal intubations, clinicians are unable to intubate the trachea on the first attempt, which increases the risk of complications during intubation. To intubate the trachea, clinicians use a device called a laryngoscope, which consists of a handle with an attached blade. Clinicians intubate by holding the laryngoscope handle and inserting the blade into the patient's mouth to (1) visualize the opening to the trachea (the larynx) and (2) create a pathway through which an endotracheal tube can be advanced through the oropharynx and larynx and into the trachea. Video laryngoscopes use a camera embedded in the laryngoscope blade to transmit images of the airway to a screen that can be viewed in real time by the clinician to aid endotracheal tube placement. Video laryngoscopes have been shown to improve the ability of clinicians to view the larynx and increase the likelihood of successful intubation on the first attempt, compared to direct laryngoscopes, which do not have a camera or a screen. A recent multicenter randomized trial found that, among 1,417 adults undergoing tracheal intubation in an ED or ICU, the incidence of successful intubation on the first attempt was 85% with a video laryngoscope and 70% with a direct laryngoscope (absolute difference, 14.3; 95% CI, 9.9 to 18.7). Use of a video laryngoscope is now standard of care for tracheal intubation in many EDs and ICUs and is recommended in international guidelines. Two types of laryngoscope blades are available for use with video laryngoscopes in clinical care. Standard geometry video laryngoscope blades were designed to approximate the shape of Macintosh direct laryngoscopes, the preferred tool before the advent of video laryngoscopy. When using a standard geometry laryngoscope blade, the clinician inserts the blade into the mouth, displaces the tongue, and lifts up and away from the operator to elevate the epiglottis and expose the vocal cords. Because this approach creates a direct line-of-site view of the vocal cords, the clinician may view the vocal cords directly (with the naked eye) or indirectly on the video screen. Creating this line-of-site view of the vocal cords with a standard angulation blade may require more effort than with a hyperangulated blade, but it creates a direct pathway for passage of an endotracheal tube through the mouth and into the trachea. Because use of a standard geometry laryngoscope blade includes creation of a direct pathway for passage of an endotracheal tube, some experts have hypothesized that use of a standard geometry laryngoscope blade could increase the incidence of successful intubation on the first attempt, compared to use of hyperangulated blades. Hyperangulated video laryngoscope blades were designed to have a more acute angle that more closely matches the natural curvature of the airway, allowing a view of the vocal cords with less manipulation of the airway. Because use of a hyperangulated blade does not include creation of a direct, line-of-sight view of the vocal cords, it is only used for indirect laryngoscopy with a video laryngoscope. When using a hyperangulated video laryngoscope blade, the clinician inserts the hyperangulated blade into the mouth, displaces the tongue, and then gently tilts the blade to view the vocal cords. While use of a hyperangulated blade may make it easier to obtain a view of the vocal cords, the pathway for passage of an endotracheal tube through the mouth and into the trachea may be less direct than with a standard geometry video laryngoscope blade. Some experts have hypothesized that, by making it easier to obtain a view of the vocal cords, use of a hyperangulated video laryngoscope blade may increase the incidence of successful intubation on the first attempt, compared to use of a standard geometry video laryngoscope blade. Two randomized controlled trials among adults intubated by anesthesiologists during elective tracheal intubation in the operating room reported different effects of use of a hyperangulated versus standard geometry video laryngoscope blade on the incidence of successful intubation on the first attempt. Köhl et al reported a 30% increase in the incidence of successful intubation on the first attempt with use of a hyperangulated video laryngoscope blade (97% vs 67%; p=0.002) in patients with anticipated difficult airways. In contrast, Zhang et al reported a non-significant increase in the incidence of successful intubation on the first attempt with use of a standard geometry video laryngoscope blade (79% vs 71%; p=0.26) in patients in cervical immobilization. Emergency tracheal intubation in the ED and ICU differs significantly from elective tracheal intubation in the operating room. Patients are more likely to have difficult airway characteristics that might make it more challenging to obtain a complete view of the larynx (e.g., cervical spine immobilization during trauma), rates of failure on the first attempt and complications during intubation are significantly higher, and clinicians performing intubation have less prior experience performing intubation, on average. No prior randomized trials have compared hyperangulated blades to standard geometry blades during intubation using a video laryngoscope in the ED or ICU. To determine the effect of use of a hyperangulated video laryngoscope blade versus a standard geometry video laryngoscope blade on the incidence of successful intubation on the first attempt among critically ill adults undergoing intubation in the ED or ICU, a randomized trial is needed.