What are the different types of laryngoscopes, their historical development, clinical uses, and the recommended next step if direct laryngoscopy is unsuccessful?

Laryngoscope Types, Historical Development, and Clinical Uses

Historical Evolution of Laryngoscopy

Laryngoscopy has evolved from indirect visualization in the 1700s to direct laryngoscopy in the late 19th century, culminating in modern videolaryngoscopy in the 21st century. 1

• Indirect laryngoscopy was the first technique developed, providing only an indirect view of the glottis 1
• Direct laryngoscopy emerged in the late 1800s, allowing direct visualization of the vocal cords 1
• The Macintosh and Miller blades appeared in the 1940s and became the standard for direct laryngoscopy 2
• Videolaryngoscopy represents a return to indirect visualization but with superior technology, rapidly gaining popularity since the early 2000s 3, 1

Types of Laryngoscopes

Direct Laryngoscopes

Metal blades should be used for direct laryngoscopy in ICU and difficult airway scenarios, as plastic disposable blades are not recommended when difficult intubation is anticipated. 4

Rigid Blade Designs:

• Macintosh blade (curved): The most popular device for first attempts, with the English-Macintosh #4 providing superior larynx exposition at all insertion depths between 5-14 cm 5
• Miller blade (straight): Provides nearly ideal view line but reduces space for the tongue behind the mandible 5
• Curved blades demonstrate significantly higher success rates than straight blades in prehospital settings: 86% vs 73% first-attempt success (13% difference, 95% CI: 9-17) and 96% vs 81% overall success (15% difference, 95% CI: 12-18) 6

Levering Blade Designs:

• McCoy blade: Features a tip that can be elevated, though maximal elevation provides limited view 5
• Flexiblade: Functions as a multiblade device with three basic positions (straight, neutral, maximally curved), suitable for both routine and difficult intubations 5

Videolaryngoscopes (VL)

Videolaryngoscopes should be used either initially or after failed direct laryngoscopy to limit intubation failures, with preference for first-line use when difficulty is predicted (MACOCHA score ≥3). 4, 7

Classification by Design:

Channel-guided devices (with guide channel for endotracheal tube): 4

• Airtraq
• KingVision
• Pentax AW Scope

Non-channel-guided devices (allowing direct viewing with endoscopic optimization): 4

• GlideScope
• C-MAC
• McGrath MAC

Optical stylets: 4

• Bonfils
• Sensascope
• RIFL

Blade Geometry Selection:

Standard geometry (Macintosh-style) blades are recommended for patients with 0-1 difficulty predictors because they allow gentle stylet curvature and straightforward tube passage. 8

Hyperangulated blades should be reserved for patients with ≥2 difficulty predictors, as they create a more acute pharyngo-glotto-tracheal angle that can paradoxically make tube delivery more difficult despite excellent visualization in non-difficult airways. 8

• Standard geometry requires only gentle stylet curvature 8
• Hyperangulated blades require a 60° stylet curve 8
• Achieving a perfect Grade 1 view may paradoxically make tube passage more difficult by creating a more acute insertion angle; withdrawing the blade slightly can facilitate tube delivery 8

Flexible Intubation Scopes

• Fiberoptic bronchoscopes remain essential for difficult airway management, with 94% of British ICUs having immediate access 4
• Flexible scopes can be combined with supraglottic airways, airway exchange catheters, or retrograde intubation 4

Clinical Uses and Performance

Evidence for Videolaryngoscopy Superiority

The 2017 Cochrane Review demonstrated statistically significantly fewer failed intubations with VL, particularly in those with an anticipated difficult airway. 7

• C-MAC trial (n=300) showed reduced need for adjuncts: 24% with VL vs 37% with direct laryngoscopy (P=0.020) 7
• 2025 meta-analysis (15 RCTs, 4,582 intubations) confirmed reduced esophageal intubation (RR 0.44; 95% CI: 0.26-0.75) and reduced poor glottic visualization 7
• ICU meta-analysis (1,066 patients) demonstrated increased first-attempt success (OR 2.07; 95% CI 1.35-3.16; P<0.001) and reduced esophageal intubation (OR 0.14; 95% CI 0.02-0.81; P=0.03) 4

Specific Clinical Scenarios

Cervical Spine Injury:

Videolaryngoscopy should be used for tracheal intubation in patients with suspected or confirmed cervical spine injury (Grade A recommendation). 4, 7

• VL produces significantly less vertebral body displacement than Macintosh blade at all levels C1-C5 4
• VL achieved 100% success vs only 1 of 16 attempts with Macintosh blade in severe cervical instability models 4
• Multiple systematic reviews confirm VL superiority with cervical spine immobilization 4, 7

ICU and Emergency Settings:

• VL preferred as first-line when MACOCHA score ≥3 predicts difficulty 4, 7
• McGrath MAC is the best validated VL for ICU use, showing superiority in laryngoscopy quality, intubation success, and specifically in MACOCHA ≥3 patients 4
• C-MAC increased first-attempt success from 55% to 79% and decreased Cormack-Lehane Grades III-IV from 20% to 7% in ICU patients 4

Recommended Next Steps After Failed Direct Laryngoscopy

If direct laryngoscopy is unsuccessful, the immediate next step is to use videolaryngoscopy (if not already attempted), followed by combination techniques if VL fails. 4

Algorithmic Approach:

1. After failed direct laryngoscopy with adequate face mask ventilation: 4

   • Switch to videolaryngoscopy with appropriate blade geometry
   • Consider adjuncts: bougie, stylet, or optimal external laryngeal manipulation

2. Combination techniques if VL fails: 4

   • VL with supraglottic airway
   • VL with bougie
   • VL with optical stylet
   • VL with flexible intubation scope
   • VL with airway exchange catheter

3. Alternative advanced techniques: 4

   • Flexible intubation scope (awake or asleep)
   • Optical stylet/lighted stylet
   • Supraglottic airway as rescue device

4. Cannot intubate, cannot oxygenate scenario: 4

   • Emergency front-of-neck access (cricothyrotomy)

Critical Adjuncts to Maximize Success:

• Call for help immediately 4
• Maximize oxygenation: nasal oxygen during intubation attempts, high-flow nasal cannula, expiratory ventilation assistance 4
• Use cognitive aids to guide decision-making 4
• Shape stylet appropriately: gentle curve for standard geometry blades, 60° curve for hyperangulated blades 8
• Adopt "patient-screen-patient" approach rather than fixating solely on screen view 4, 8

Critical Limitations and Pitfalls

When Videolaryngoscopy May Be Limited:

Active upper GI bleeding with blood, secretions, or vomitus obscures the camera lens and makes VL less reliable; consider direct laryngoscopy with immediate suction availability or awake fiberoptic intubation instead. 9, 7

• Both VL and fiberoptic visualization are hampered by airway contamination 9
• VL relies entirely on camera view, making it less effective than direct laryngoscopy in contaminated airways 9

Absolute Contraindications for Both Blade Types:

• Mouth opening <2.5 cm 8, 7
• Cervical spine fixed in flexion 8, 7

Technical Pitfalls to Avoid:

• Do not use hyperangulated blades routinely in non-difficult airways as they complicate tube delivery without benefit 8
• Do not fixate on achieving Grade 1 view at the expense of practical tube insertion angle 8
• Risk of airway trauma with stylets—exercise caution when advancing the endotracheal tube 7
• VL may increase intubation time, which is problematic in aspiration-risk patients 8
• Cricoid pressure (Sellick maneuver) degrades glottic view and lowers VL success rates in full-stomach patients 8

Training and Competence Requirements:

All anaesthetists should be trained to use and have immediate access to a videolaryngoscope, with regular practice required to develop and retain proficiency. 4

• Experience and competence with any device are critical for successful use 2
• Departments should choose one VL system to allow trainees and consultants to develop expertise rather than having multiple devices 4
• Proficiency requires frequent rather than exceptional use 4