**3. Airway assessment**

Preanesthetic assessment of the airway should be performed, when possible, to detect the potential of difficulty airway [2, 3, 28, 29]. Preanesthetic assessment should consist of history taking and physical [3]. Any history of difficult airway management is vital in preanesthetic airway assessment [30]. Presence of pathological conditions associated with a difficult airway should also be noted, including snoring, which may make mask ventilation more difficult [31, 32]. A complete physical examination should always be performed to detect the physical characteristics associated with difficult airway. There are five specific components of the airway exam that should be evaluated: overall inspection of the face and neck, oropharyngeal and dental anatomy, neck anatomy and range of motion, mandibular protrusion ability, and submandibular space [3].

The overall inspection of face and neck is necessary to detect any pathological states involving the face or neck, such as massive face deformities, facial burns,

retrognathia, tumor involving the face or neck, thick or short neck, or large goiter [3]. In the setting of pregnancy and trauma, the presence of a cervical collar has been shown to interfere with mask ventilation and direct laryngoscopy [33].

There are two important components in oropharyngeal and dental examination that should be evaluated: maximum voluntary mouth opening and Mallampati score [3]. Measurement of maximum mouth opening is achieved by measuring the interincisor distance when the patient voluntarily opens the mouth as wide as possible [3, 34, 35]. Inter-incisor distance of less than 3 cm, or 2 fingerbreadths, is associated with difficult intubation [34]. Some studies even suggest that a distance of less than 4–4.5 cm can increase the risk of a difficult airway [35]. In 1983, Mallampati et al. described a clinical sign to determine the difficulty of direct laryngoscopy and tracheal intubation, based on the size and position of the tongue relative to the pharyngeal size. To assess the Mallampati classification, the patient should be in an upright sitting position with the head in a neutral position, the mouth wide open, and the tongue protruding as far as possible without phonation. Higher scores on the Mallampati classification indicate more difficult laryngoscopy and tracheal intubation, because the tongue is large enough to obscure oropharyngeal view. The original version of Mallampati classification consisted of a three-point scale [36]. However, Samsoon and Young further modified the Mallampati classification into a four-point scale (see **Table 1**) [9].

The dental condition of the patient has also been shown to affect airway management [34]. To prevent trauma and tooth aspiration, it is recommended to extract very loose teeth prior to laryngoscopy. Although the edentulous patient is almost always associated with easy tracheal intubation, face mask ventilation is often difficult [37].

A thick neck (neck circumference greater than 43 cm) has been shown to increase the risk of difficult tracheal intubation [33, 38]. In addition, neck mobility is also essential in airway examination as it is necessary to have an ideal neck position when doing laryngoscopy and intubation. The ideal intubating position is achieved by the extension of the atlantooccipital joint, in what is called the sniffing position, with the alignment of the oral, pharyngeal, and laryngeal axes. Normal atlantooccipital joint extension should be greater than 35° [39, 40]. Moreover, the sternomental distance can also be used to quantitatively assess neck mobility. The sternomental distance is the distance between the chin point and the sternal notch, measured when the head is in extension and the mouth is closed. Distance less than 12.5 cm has shown to increase the risk of difficult intubation [41]. Overall neck range of motion also can be used to predict the risk of difficult intubation. The assessment is performed by measuring the angle between forehead and neck when fully flexed and extended. An angle of less than 80° is associated with difficult intubation [42].

The mandibular protrusion test has been shown to have strong predictive value in determining a difficult laryngoscopy. It is performed by instructing the patient to


**Table 1.** *Modified Mallampati classification [9].*

*Difficult Airway in Obstetric Patients DOI: http://dx.doi.org/10.5772/intechopen.108341*


#### **Table 2.**

*The upper lip bite test classification [44].*

extend the mandible as far as possible and then assessing the location of the mandibular teeth in comparison to the maxillary teeth. When the mandibular teeth can extend beyond the maxillary teeth, it is predictive of easy laryngoscopy [43]. Similar to mandibular protrusion test, the upper lip bite test (ULBT) is also shown to have predictive value in determining the likelihood of difficult airway, with higher specificity than the Mallampati classification. In the ULBT, the patient is instructed to bite their upper lip. The ability of biting the upper lip is then classified into three classes (see **Table 2**). The higher the class, the more difficult it is to laryngoscope and intubate [44, 45].

Evaluation of submandibular space is essential in determining the risk of difficult laryngoscopy and intubation. During direct laryngoscopy, the blade of the laryngoscope displaces the tongue into the submandibular space. A small submandibular space will cause inadequate visualization of the glottis. The submandibular space can be estimated by measuring the thyromental distance. It is measured from the lower border of the mentum to the thyroid cartilage notch. A distance of less than 6.5 cm or 3 fingerbreadths suggests an increased risk of difficult intubation [46, 47].

In pregnant women, a recent study found that the modified Mallampati test was shown to have better predictive value compared with ULBT, thyromental distance, and sternomental distance. In addition, this study also showed that the best cutoff point for the thyroid distance was 5 cm and for the sternomental distance was 15 cm. However, combining these various tests suggested to have a better diagnostic accuracy [48]. Moreover, several new modalities such as bedside endoscopy, point-of-care ultrasonography (POCUS), virtual laryngoscopy/bronchoscopy, or three-dimensional printing can be used to further evaluate the risk of airway difficulty, especially in patients with complex airway pathology [28].
