Upper Airways the Maxilar-Jaw Effect

Abstract

The pharynx is divided into three sections: the nasopharynx, oropharynx, and laryngopharynx.

The nasopharynx is a part of the respiratory system as the posterior portion of the nasal cavity. The nasopharynx communicates with the oropharynx through the soft palate and posterior wall of the pharynx. The oropharynx extends from the soft palate to the superior border of the epiglottis, and it communicates anteriorly with the oral cavity by the soft palate and tongue (O’rahilly et al., Basic Human Anatomy. A Regional Study of Human Structure, Chapter 53. Saunders, Philadelphia, 1983).

The reduction in the pharyngeal airway space causes difficulties in both nasal and mouth breathing, thus affecting the morphology of the entire face, including the mandible (Dunn et al., Angle Orthod 43:129–35, 1973). As a result, both sleep quality and facial development during childhood might be affected. Moreover, acute infections of the sinuses might occur. Repeated anatomic partial collapse or obstruction of this region causes cessation of airflow along with persistent respiratory effort, defined as obstructive sleep apnea (Prisant et al., J Clin Hypertens (Greenwich) 8:746–50, 2006).

Several studies have investigated the relationship between breathing patterns and craniofacial morphology (Katyal et al., Am J Orthod Dentofacial Orthop. 143:20–30.e3, 2013). However, these connections are not still completely clarified. The possible correlation between airway obstructions and the frequency of malocclusions remains under investigation (Leech, Dent Pract 9:57–68, 1958).

Maintenance of upper airway patency during anesthesia is of vital importance, as upper airway muscle activity becomes significantly compromised with the loss of consciousness. In such cases, mechanical upper airway properties predominate in control of overall collapsibility of the airway. Hence, improving the mechanical characteristics of the upper airway during anesthesia is crucial in the maintenance of airway patency. Positional changes of the mandible, such as avoiding opening of the mouth (jaw closure), are known to play an important role in the maintenance of upper airway patency during anesthesia. Establishment of jaw closure with approximately 6 cm head elevation, achieved by lying on a table with a 6-cm-high pillow, helps maintain upper airway patency in normal healthy subjects (Ayuse et al., J Dent Res 83:718:22; Kobayashi et al., Anesthesiology 115:273–81, 2011).

Performing bedside testing for identifying a potential difficult airway before general anesthesia is part of routine clinical practice. Most commonly used tests include:

• The Mallampati test (usually in its modified form, including a Class 4)

• Wilson risk score

• Thyromental distance

• Sternomental distance

• Mouth opening

• The upper lip bite test

These tests are regarded as screening tests that are very sensitive in identifying all potential cases of difficult airway but have a lower specificity to identify those without a difficult airway.

Obstructive processes of morphologic, physiologic, or pathologic nature of the visceral skull, such as hypertrophy of adenoids and tonsils, chronic and allergic rhinitis, irritant environmental factors, infections, congenital nasal deformities, nasal traumas, polyps, and tumors, are predisposing factors to a blocked upper airway. Techniques that allow the precise diagnosis of changes in the upper airway considering their morphology and volume are fundamental to ensure normal development of the craniofacial complex in growing subjects and the choice of an adequate treatment plan (Roth et al., Anaesthesia 161:e390–e399).