Limitations in mouth opening impede the ability of the laryngoscopist to visualize pharyngeal or laryngeal structures. Ideally, mouth opening should exceed 6 cm or 3 fingerbreadths (Fig. 15-1).

Direct laryngoscopy requires that the tongue be forced into the floor of the mouth to permit the laryngoscopist to view the glottis. The larger the tongue, the more difficult this becomes, contributing to poor laryngoscopy grades. The disproportionally large tongue is usually evident when the Mallampati class is evaluated (Fig. 15-2).

Large, protruding teeth, or teeth lying at odd angles may complicate attempts to place the laryngoscope in the mouth, visualize the laryngeal orifice, or place an endotracheal tube (ETT). They may also be at higher risk for tooth damage during direct laryngoscopy, as well as ETT cuff damage during intubation (Figs. 15-3 and 15-4).

Patients with short, thick necks may present difficulty in achieving normal extension and frequently have worse laryngoscopy grades at direct laryngoscopy than patients with long, thin necks. Positioning in these patients can greatly improve laryngoscopy success (Fig. 15-5).

A small mandible, or receding chin, adversely affects the ability to visualize the glottis making the grade of laryngoscopy worse (Fig. 15-6).

Occasionally, the elongated epiglottis is difficult to elevate sufficiently with the curved blade, and a straight blade must be used to lift it directly out of the way (Fig. 15-7).

Prominent or protuberant nasal turbinates may create an obstruction to passage of nasopharyngeal airways or nasal ETTs leading to trauma and epistaxis, which can be severe, especially if the patient is in an anticoagulated state (Fig. 15-8).

Bushy beards or goatees may complicate attempts to make a face mask seal, resulting in difficult mask ventilation (Fig. 15-9).

Some congenital abnormalities result in enlargement of the tongue (macroglossia). This is commonly seen in Down syndrome, Beckwith-Wiedmann syndrome, as well as other chromosomal abnormalities. Macroglossia can also be seen with mucopolysaccharidosis, hypothyroidism, alpha-mannosidosis and aspartylglucosaminidase deficiency (Fig. 15-10).

Airway stenosis may be a congenital condition, or may be associated with prolonged intubation, making passing an ETT difficult (Fig. 15-11).

Cervical spine skeletal anomalies may complicate attempts to manage the airway by conventional means, due to either decreased range of motion (making axis alignment difficult), or to ligamentous instability (Fig. 15-12).