Hyperangulated vs Standard Videolaryngoscopy vs Direct Laryngoscopy for Double-Lumen Endobronchial Tube Intubation

Background and Rationale:

Double-lumen endobronchial tubes (DLTs) are the primary airway device for one-lung ventilation (OLV) in intrathoracic surgery. Their use enables lung isolation, which is essential for surgical exposure in procedures such as lobectomy, pneumonectomy, esophagectomy, and thoracoscopic interventions. Despite their widespread use, DLT placement is technically more demanding than standard single-lumen endotracheal intubation due to the tube's larger outer diameter, greater length, increased rigidity, and the presence of a distal bronchial cuff. These structural characteristics make laryngoscopy and tube advancement through the glottis considerably more challenging and are associated with a higher incidence of oropharyngeal, laryngeal, and tracheobronchial trauma compared to standard intubation.

Airway injuries related to DLT placement span a wide spectrum, ranging from minor mucosal lacerations of the lips, tongue, and pharynx to temporary or permanent vocal cord damage. In rare but serious cases, tracheobronchial perforation has been reported, a potentially life-threatening complication. The increased structural difficulty of DLT intubation translates into a higher likelihood of multiple intubation attempts, each of which independently increases the risk of airway trauma, hemodynamic instability due to prolonged laryngoscopy, and desaturation. Minimizing the number of attempts and the total intubation time is therefore of direct clinical importance in this patient population.

Videolaryngoscopy (VL) has become increasingly integrated into routine and difficult airway management over the past two decades. By providing an indirect, magnified view of the glottis transmitted via a camera mounted at the tip of the blade, VL improves glottic visualization compared to direct laryngoscopy (DL), particularly in patients with anticipated or unanticipated difficult airways. Multiple meta-analyses and randomized controlled trials have demonstrated the superiority of VL over DL in terms of first-attempt success rate, Cormack-Lehane grade, and rate of esophageal intubation in both routine and difficult airway scenarios.

The Storz C-MAC system is one of the most widely studied videolaryngoscopes and is available in two blade configurations relevant to this study: the Macintosh-geometry blade (C-MAC M-blade), which allows both direct and indirect laryngoscopy and preserves familiar hand mechanics, and the hyperangulated D-blade (C-MAC D-blade), which provides a more acute viewing angle and is specifically designed for cases where standard geometry blades fail to achieve adequate glottic exposure. Both blades transmit a high-resolution image to an external monitor, and the C-MAC system has been shown to improve first-attempt success rates and glottic visualization in a range of clinical settings.

In the context of DLT intubation, the choice of laryngoscope blade is further complicated by the need to shape the DLT stylet to match the blade curvature. A hyperangulated blade requires a correspondingly acute stylet bend, which may facilitate or hinder tube advancement depending on the operator's experience and the patient's anatomy. While several studies have compared videolaryngoscopy systems with direct laryngoscopy for DLT placement - including the GlideScope, C-MAC, and other platforms - the existing literature remains limited in volume and inconsistent in its conclusions. No adequately powered prospective randomized trial has directly compared the C-MAC D-blade, C-MAC M-blade, and standard direct Macintosh laryngoscopy head-to-head for DLT intubation in thoracic surgery patients. The present study is designed to address this gap.

Objectives and Hypotheses:

The primary objective of this study is to compare three laryngoscopy techniques for DLT intubation - (i) C-MAC hyperangulated D-blade videolaryngoscopy (HCMAC), (ii) C-MAC Macintosh blade videolaryngoscopy (MCMAC), and (iii) direct Macintosh laryngoscopy (DL) - with respect to intubation time, glottic visualization quality, procedural difficulty, and intubation-related complications in adult patients undergoing elective thoracic surgery requiring one-lung ventilation.

The secondary objective is to provide prospective, randomized clinical evidence to guide the selection of the most appropriate laryngoscopy method for DLT intubation in routine thoracic anesthesia practice and to contribute to standardization of airway management in this surgical context.

Primary hypothesis: Total DLT placement time is shorter with videolaryngoscopy, particularly with the C-MAC hyperangulated D-blade, compared to direct Macintosh laryngoscopy.

Secondary hypotheses: (1) Videolaryngoscopy groups will demonstrate superior glottic visualization as measured by POGO score and Cormack-Lehane grade. (2) Intubation difficulty as assessed by the Intubation Difficulty Scale (IDS) and the need for auxiliary maneuvers will be lower in videolaryngoscopy groups. (3) The overall incidence of intubation-related complications, including mucosal trauma, dental or lip injury, and hemodynamic perturbations associated with laryngoscopy, will be lower in videolaryngoscopy groups compared to direct laryngoscopy.

Study Design:

This is a prospective, randomized, single-center, three-arm, open-label, low-risk medical device clinical study. The study is conducted at the Department of Anesthesiology and Reanimation, Trakya University Medical Faculty, Trakya University Health Research and Application Center Hospital, Edirne, Turkey. The study is classified as a low-risk medical device clinical investigation, as all procedures are performed within the scope of routine clinical care and no additional investigational drugs or invasive interventions beyond standard practice are introduced.

Patients fulfilling eligibility criteria are randomized in a 1:1:1 ratio to one of three study arms (HCMAC, MCMAC, or DL) using a computer-generated block randomization sequence. Allocation concealment is maintained using sequentially numbered, opaque, sealed envelopes that are opened in the operating room immediately prior to the intubation attempt.

Eligibility Criteria:

Inclusion criteria: age ≥18 years; written informed consent obtained prior to surgery; ASA physical status class I, II, or III; scheduled for elective thoracic surgery requiring one-lung ventilation and double-lumen endobronchial intubation.

Exclusion criteria: age \<18 years; refusal or inability to provide informed consent; ASA physical status class IV or above; emergency surgery; anticipated difficult airway defined by any of the following - Mallampati score 4, thyromental distance \<6.5 cm, restricted mouth opening, or BMI >30 kg/m²; history of upper airway surgery; significant upper airway obstruction or stridor; pregnancy.

Interventions and Procedures:

All patients receive standard intraoperative monitoring per ASA guidelines, including continuous ECG, peripheral oxygen saturation (SpO₂), and non-invasive blood pressure (NIBP). Following induction of general anesthesia, mask ventilation is performed until conditions for intubation are achieved. DLT size is selected according to a validated sex- and height-based sizing scale. The intubation is then performed using the laryngoscopy device assigned by randomization.

Glottic visualization is assessed by the operator immediately upon laryngoscope insertion and recorded as Cormack-Lehane grade and POGO score. Intubation time is defined as the interval from cessation of mask ventilation to fiberoptic bronchoscopic confirmation of correct DLT positioning, and is recorded in seconds. The number of intubation attempts and any auxiliary maneuvers employed - including BURP (backward-upward-rightward pressure), Sellick maneuver, shoulder elevation, 90° or 270° tube rotation during bronchial advancement, and external tracheal pressure - are documented. Where applicable, the number of tube size changes, the sizes attempted, and the size ultimately used for successful placement are recorded.

Correct DLT placement is defined as positioning of the tube in the target bronchus without proximal or distal migration, confirmed by fiberoptic bronchoscopy. Malposition is classified as: deep bronchial migration, contralateral bronchial placement, or proximal (tracheal) positioning, and is corrected under fiberoptic guidance. If three intubation attempts fail, the institution's established difficult airway management algorithm is activated and the case is classified as intubation failure. All devices used in this study are CE-marked and are used strictly in accordance with their intended purpose as specified by the manufacturer.

Hemodynamic parameters (SpO₂, heart rate, NIBP) are recorded at baseline, immediately before intubation, and at 0, 1, 3, 5, and 10 minutes after intubation. Where available, subglottic diameter and left main bronchial diameter are measured from preoperative CT imaging and recorded. Postoperative assessment includes evaluation for sore throat, dysphagia, and dysphonia at 1, 6, and 24 hours after surgery, as well as documentation of any signs of airway trauma observed intraoperatively or in the postoperative care unit.

Sample Size and Statistical Analysis:

Sample size was estimated based on a power analysis using data from previous reference studies (linked at "references" section). Cohen's effect size f was calculated as 0.235. With 80% statistical power and a two-sided type I error rate of 5%, a minimum of 60 patients per group is required, yielding a total enrollment target of 180 patients across three groups.

Normality of continuous variables will be assessed using the Shapiro-Wilk test. For normally distributed variables, between-group comparisons will be performed using one-way analysis of variance (ANOVA); for non-normally distributed variables, the Kruskal-Wallis test will be used. Relationships between categorical variables will be analyzed using chi-square tests. Correlations between continuous variables will be assessed using Pearson or Spearman correlation analysis as appropriate. Continuous variables will be reported as mean ± standard deviation or median (interquartile range) according to distribution; categorical variables will be reported as frequency and percentage. The threshold for statistical significance is set at p \< 0.05 for all analyses.