Direct laryngoscopy (DL) remains an important skill because many of the most successful modern intubation devices allow simultaneous DL and video laryngoscopy (VL). These devices, VL devices with a Macintosh-shaped blade, may be the best choice for optimizing first-pass intubation success in difficult setting, because VL can be used to overcome anatomic difficulty and DL can be used when the VL camera becomes soiled with secretions, blood, or vomitus. DL also remains relevant because 80% of ICU intubations in current clinical care worldwide are performed with DL,¹ and DL equipment is inexpensive and ubiquitous.

Current evidence shows that DL/VL devices are superior to hyperangulated VL blades for ease of endotracheal tube (ETT) placement.² In a randomized DL/VL (Storz C-MAC) study of bougie versus stylet for ETT delivery, the bougie group had the highest first-pass intubation success (98%).³ In this study the Storz C-MAC was utilized and it was the operator’s choice whether to visualize directly or use the VL monitor, and 58% of the patients in the bougie group were intubated under direct vision (the operator not viewing the C-MAC monitor at any point during the procedure), which may have contributed to the very high first-pass success rate. The benefit of DL/VL devices is that they allow the possibility of both DL and VL during the same intubation attempt, which may be important for optimizing first-pass success, especially in the unpredictable setting of critical care airway management.

DL skills are difficult to teach using traditional equipment because the instructor cannot see what the learner is seeing. Using traditional DL equipment, a minimum of 50 intubations is required to gain proficiency in elective settings,⁴ and this number is much higher in critical care settings. Teaching DL with a traditional laryngoscope in the critical care setting can be challenging for both trainees and the instructors because only one person can view the airway directly.⁵ The rate of complications increases dramatically when there are multiple intubation attempts, so the intubator should have a goal to intubate successfully on the first attempt regardless of their training level.^6,7

For this reason, the best way to learn DL is to use a device that allows simultaneous DL and VL. These devices allow the instructor to see what the learner is seeing, which results in more effective real-time teaching and improved first-pass success. VL increases intubation success even in difficult airways; however, hyperangulated VL devices do not recreate DL mechanics.^8,9,10 Thus, a standard Macintosh geometry blade is required for using VL to teach DL. Several devices allow simultaneous DL and VL for both adult and pediatric patients.^11,12,13

This method of learning DL has been shown to lead to more rapid skill acquisition of both direct and video laryngoscopy skills and it is safer for patients. There is subjective and objective evidence that these devices shorten the learning curve for DL.^11,12,13,14 In a small randomized trial of 198 patients intubated with either standard geometry VL (C-MAC) or DL, first-attempt success was higher with VL (92% vs. 86%), although the small sample size prevented this from being statistically significant.¹⁵ Eight patients (8%) failed DL intubation on the first attempt, and all were successfully intubated using VL on the second attempt. Interestingly, the residents involved in this study learned DL using the C-MAC, which demonstrates the effectiveness of learning and performing DL with a Macintosh-shaped VL device.

The concept of DL is simple: create a straight line of sight from the mouth to the larynx in order to visualize the vocal cords. The tongue is the greatest obstacle to creating this line of sight. The laryngoscope is used to control the tongue and displace it, allowing direct vision of the airway.

A laryngoscope consists of a handle, a blade, and a light source. It is used as a left-handed instrument regardless of the operator’s handedness. In general, DL blades are either curved (Macintosh) or straight (Miller) (Fig. 23.1). Both blades come in a variety of sizes, from newborn to large adult, with sizes 3 and 4 commonly used in adults. Macintosh blades have a gentle curve, a vertical flange for displacing the tongue, and a relatively wide square tip capped with a small knob. Variations of the original Macintosh blade design, which include a smaller vertical flange and a shorter light-to-tip distance, have also been manufactured. The vertical flange height of the size 3 and 4 blades is similar, making it reasonable to start with the longer size 4 blade in most adults. Curved blades are intended to be advanced into the vallecula, and when the knob on the tip makes contact and depresses the midline vallecular fold (and the underlying hyoepiglottic ligament), the epiglottis elevates, exposing the vocal cords (Fig. 23.2).

Miller blades, the most common straight blades available, have a narrower and shorter flange and a slightly curved tip without a knob. The smaller flange may be advantageous when there is less mouth opening but makes tongue control more difficult and decreases the area of displacement for visualization and tube placement. Size 3 and 4 Miller blades are identical except for length, so it may be reasonable to start with the (longer) size 4 blade in most adults. Miller blades are intended to be passed beyond (posterior) to the epiglottis, to lift it directly to expose the vocal cords (Fig. 23.3).

Many operators prefer the curved Macintosh blade because it is wider and allows better control of the tongue; however, the straight Miller blade may provide better visualization of the glottis in difficult airway scenarios such as a narrow interincisoral gap, limited mouth opening, or a large and floppy epiglottis. For these reasons, it is important to master both curved and straight-blade DL techniques.

Tracheal intubation is accomplished by passing the ETT through the vocal cords after visualization with laryngoscopy. Recognition of anatomic landmarks is critical to DL success. The most important landmarks are the epiglottis, vallecula, posterior arytenoid cartilages, interarytenoid notch, and vocal cords. Success is more likely if the vocal cords are well visualized and success is nearly certain if a full view is obtained with a direct laryngoscope (Fig. 23.4A). Successful intubation, however, does not always require visualization of the vocal cords. If only the posterior cartilages are visible, the tube can be passed anterior to these structures in the midline and will usually enter the trachea (Fig. 23.4B). Furthermore, intubation can even be accomplished when the only visible structure is the epiglottis (Fig. 23.4C), especially if a bougie (ETT introducer) is used. This makes identification of the epiglottis a pivotal step in laryngoscopy. If the epiglottis cannot be identified, the likelihood of successful tracheal intubation is essentially nil (Fig. 23.4D).

An important anatomic structure is the midline vallecular fold (median glossoepiglottic fold), which overlies the hyoepiglottic ligament. Although not as well visualized with DL compared with VL, this anatomic structure is critical to curved blade laryngoscopy. Applying gentle pressure to this structure with the tip of the laryngoscope blade has been shown to symmetrically lift the epiglottis and improve laryngeal visualization (Fig. 23.5). When there is poor glottic exposure during Macintosh laryngoscopy owing to a low-hanging epiglottis, it is often because of failure of or limited engagement with the hyoepiglottic ligament.

Before using a direct laryngoscope for intubation, the following equipment must be available (vascular access, patient monitors, and medications for rapid sequence intubation [RSI] are discussed separately).

The assistant should be prepared to do any of the following:

Preintubation assessment of the patient’s airway, as discussed in Chapter 5, ‘Airway evaluation for anatomic difficulty’, is essential and must be performed on every patient before administration of neuromuscular blocking agents. The selected laryngoscopy blade must be wide and long enough to capture the tongue during laryngoscopy, sweep it leftward and then forward into the mandibular space out of the visual field, and permit direct visualization of the airway. The larger flange of the curved Macintosh blade typically provides better tongue control than the thinner blade of the straight Miller blade. Many operators prefer a size 4 Macintosh blade for most emergency airways to ensure adequate blade length. However, choice of a laryngoscope blade and the technique used to facilitate intubation is best guided by the operator’s bedside assessment, personal choice, and skill.

The laryngoscope should be held low on the handle so the proximal end of the blade pushes into the thenar or hypothenar eminence of the left hand. This grip will encourage lifting from the shoulder, keeping the elbow low, and keeping the wrist stiff during laryngoscopy. The operator should be in an upright position, with their arms and hands at a comfortable working height, rather than stooping or straining to reach the patient. When possible, the patient’s bed should be elevated to an optimal position for the intubator (waist height or higher). The intubator should step back from the patient so that their back is relatively straight during laryngoscopy.

Cormack and Lehane devised the most widely accepted system of categorizing the view of the larynx achieved with an orally placed laryngoscope.¹⁶ Optimal head and neck positioning for DL is often described as the “sniffing position”: lower cervical flexion and atlanto-occipital extension. The sniffing position attempts to align the oral, pharyngeal, and laryngeal axes of the upper airway (Fig. 23.6A-C) and the best Cormack and Lehane view. The sniffing position (head extension and neck flexion) has been widely accepted as the optimum position for orotracheal intubation. However, there is conflicting evidence that increased head elevation (increased neck flexion) or just simple extension (head extension and neck extension) may be better than the sniffing position.^17,18 Absent contraindications, alignment of the airway axes is important for optimizing the laryngoscopic view. The optimal degree of lower cervical flexion brings the external auditory meatus to the level of the sternal notch or anterior surface of the shoulder. In adult patients of normal body habitus, a 4- to 6-cm pad beneath the occiput usually suffices for this purpose. Alternatively, the operator can extend and lift the head with their right hand during laryngoscopy to determine the optimal position empirically. The head can then be supported by folded towels or an assistant standing on the right side of the patient while the operator intubates or performs OELM. In morbidly obese patients, optimal positioning will often require a ramp to be constructed from linens or pads placed beneath the upper torso, shoulders, neck, and occiput in order to align the ear canal with the sternal notch (see Chapter 19).^19,20,21 Airway ramps are also commercially available for this purpose. In small children with a protuberant occiput, the torso may need to be raised to allow the external meatus to fall back to the desired plane. Because of individual variations in anatomy, the optimal head and neck position is often unpredictable and may require empiric adjustment during the intubation attempt. It is critically important that some means of adjusting the patient’s position be available before initiating the procedure. Understanding optimal head and neck positioning will help operators appreciate the difficulty of performing DL on trauma patients and others who must be intubated in a fixed position.