Nasotracheal Intubation

Anatomy and Physiology

Performing NTI properly requires knowledge of the anatomy of the nasal vestibule, nasal cavity, nasopharynx, oropharynx, hypopharynx, and larynx.

Nasal Cavity

The nasal cavity begins at the nares and ends at the posterior end of the nasal septum, where it channels into the nasopharynx via the posterior nasal apertures (choanae). The nasal cavity sits above the oral cavity and hard palate and rests below the skull base.

Hard Palate

The hard palate constitutes the cavity floor that runs horizontally behind the nares. The ethmoid bone, with the cribriform plate at its center, forms the ceiling of the nasal cavity. Lastly, the left and right lateral walls comprise the medial walls of the orbit superiorly and the maxillary sinus inferiorly.

Lateral Nasal Walls

The lateral nasal walls contain the turbinates, which project into the nasal passages as ridges of bone covered by soft tissue and mucosa; these are responsible for maintaining humidity and warmth in the nasal cavity.

Inferior Turbinate

The inferior turbinate is the largest of the three and projects along the lateral nasal wall. The inferior turbinates often obstruct nasal airflow when enlarged or inflamed. The middle turbinate projects into the superior and posterior central nasal cavity to the inferior turbinate's anterior face or head. The superior turbinate, ordinarily the smallest of the three, attaches to the skull base superiorly and the nasal wall laterally. In some cases, patients may have a fourth pair of turbinates located superior to the superior ones; these structures are known as supreme turbinates but have minimal clinical significance. The middle, superior, and supreme turbinates are all processes of the ethmoid bone. In contrast, the inferior conchae are separate bones that articulate with the maxillae and the palatine, lacrimal, and ethmoid bones.

Nasal Septum

The nasal cavity is separated by a nasal septum consisting of a cartilaginous part that sits anteriorly (the quadrangular cartilage) and a bony portion located posterosuperiorly (the vomer and perpendicular plate of the ethmoid bone). This septum separates the nasal passages into left and right sides; the two cavities eventually coalesce to form a single continuous cavity in the back of the nose (the nasopharynx).

Respiratory Mucosa

The nasal cavity is lined by respiratory mucosa, histologically described as ciliated pseudostratified columnar epithelium, lying on a highly vascular stroma. These cells produce serous secretions that aid in the humidification of inspired air. The cilia help to prevent unwanted debris from entering the lungs.[6]

Due to the high vascularity of the nasal cavity, minor trauma to any part of the tissue can cause bleeding (epistaxis). The anterior nasal septum is particularly susceptible to developing epistaxis due to the arterial plexus's superficial location. This confluence is known as Kiesselbach’s plexus and is supplied by branches of the anterior and posterior ethmoid, superior labial, sphenopalatine, and greater palatine arteries.[7][8]

While considering normal nasal cavity anatomy, it is important to understand that anomalies often exist. Septal deviation is the most common abnormality involving the nasal septum. The deviation is most often due to trauma but can also be congenital or iatrogenic. Other anatomical variations include conditions that result in unilateral obstruction, such as nasal polyps, concha bullosa, septal spurs, stenosis, and choanal atresia. It is important to consider these possibilities during pre-anesthetic evaluation to minimize complications, as most of these variations result in changes to airflow dynamics inside the nasal cavity. Nasal polyps or spurs may be unilateral, dictating which side of the nose is more amenable to NTI.[9][10][11]

Indications

Indications for NTI include, but are not limited to, the following:

• Impending airway compromise
  • In this case, NTI is typically performed on the awake patient to avoid loss of airway protection reflexes during the intubation process.
  • NTI causes less gagging and is better tolerated in awake patients than oral intubation.
• Intraoral and oropharyngeal surgery
• Complex intraoral procedures involving mandibular reconstruction
• Rigid laryngoscopy 
• Dental surgery
• Maxillofacial or orthognathic surgery

Contraindications

Absolute contraindications include:

• Suspected epiglottitis
• Midface instability 
• Previous history of old or recent skull base fractures
• Any known bleeding disorder that could predispose the patient to severe epistaxis
• Choanal atresia
• Anterior skull base fractures, which may result in passage of the tube intracranially [12]

Relative contraindications include:

• Obstruction of the nasal airway (large nasal polyps, foreign bodies)
• Recent nasal surgery
• History of frequent episodes of epistaxis

Equipment

Some of the necessary equipment needed to perform nasotracheal intubation includes the following (see Image. Equipment for Endotracheal Intubation): 

• Endotracheal tube (nasal RAE or standard endotracheal tube)
• Lidocaine jelly or a water-soluble lubricant
• Magill forceps 
• Intubating laryngoscope 
• Vasoconstricting nasal spray (oxymetazoline 0.05% or phenylephrine nose drops 0.25% to 1%)
• Syringe to inflate the cuff
• Video laryngoscope

Personnel

Although the anesthesia provider is primarily responsible for performing NTI, a nurse can help to pass instruments (such as the Magill forceps), apply pressure to the cricoid cartilage, or remove the endotracheal tube's stylet should be present. A second anesthesiologist can be very helpful in prophylactic nasotracheal intubation to prevent airway compromise, such as evolving angioedema. An otolaryngologist may also assist by passing a fiberoptic scope through the nose or even providing a surgical airway should attempts at NTI fail while the patient is in extremis.

Preparation

A pre-anesthetic evaluation must be performed for each patient undergoing general anesthesia, focusing on identifying potential risks or complications related to the upcoming procedure and composing an individualized plan for patient care. Often, the patient can relay important information regarding unilateral restriction or congestion in the nasal airway and give some direction as to which naris should be used for the NTI. If the patient interview does not yield information related to the relative patency of one side versus the other, physical examination may guide the laterality of intubation.

Anterior rhinoscopy may be performed (this is not a common practice), allowing the anesthesia provider to visualize the anterior portion of each nasal cavity. The main limitation of anterior rhinoscopy is the inability to provide information regarding the posterior nasal cavity. A flexible fiber-optic nasopharyngoscope or bronchoscope may be passed into the nasopharynx to assess the pathway fully.[13][14]

Technique or Treatment

Once the choice of laterality is determined, NTI may proceed. The first step to performing an NTI is a generous application of vasoconstricting spray bilaterally. A topical anesthetic may be applied via spray or a lubricant mixed with a local anesthetic. Common options include oxymetazoline hydrochloride 0.05%, phenylephrine hydrochloride 1%, and cocaine 4%. Only the latter has a topical anesthetic effect; therefore, using the former two should ideally be accompanied by administering 2 to 4% topical lidocaine.

After applying a topical anesthetic and a vasoconstrictor, some anesthesiologists advocate using a device to dilate the nasal cavity, commonly a nasopharyngeal trumpet airway. The necessity of dilation before intubation is a topic of debate in the anesthesiology community. No PubMed-indexed papers show benefits from this practice, only increased complications from repeated instrumentation of delicate structures. As of the time of this article, dilation is not a recommended practice.

Before intubation, the patient should be pre-oxygenated with a FiO2 of 1.0 and ventilation assessed before the muscle relaxant is administered.

It is important to lubricate the distal end of the nasotracheal tube, with the most common lubricants being lidocaine or a plain, non-medicated water-soluble jelly. Adequate topical anesthesia and vasoconstriction are particularly important when NTI is performed on an awake patient, such as a patient with developing edema from a blunt laryngeal injury. Topical anesthetic sprayed onto the vocal cords and regional anesthesia of the larynx can also be beneficial. Sensation to the supraglottis is provided by the superior laryngeal nerves, which can be blocked with local anesthetic injections between the greater cornu of the hyoid bone and the superior cornu of the thyroid cartilage.[15] In awake NTI, the endotracheal tube (ETT) is typically passed over a flexible fiberoptic bronchoscope; glycopyrrolate reduces secretions and facilitates visualization. In these cases, keeping the patient sitting somewhat upright during intubation can help the patient maintain their airway protection reflexes and avoid the collapse of pharyngeal soft tissue into the airway, which would, in turn, obstruct the view through the bronchoscope.

After insertion into the naris, gentle pressure should be applied to advance the tube, with the force vector directed posteriorly towards the nasopharynx and the operating room table. Some manipulation is required while passing the tube through the nasal cavity, and resistance will be encountered.

If the amount of resistance felt is significant, the tube may be repositioned before attempting to advance farther. A smaller-sized ETT may be needed if the anatomy cannot accommodate passage of a standard-size tube, as determined by the patient's age and sex. It is important to remember that for a nasal RAE tube, the diameter is proportional to the length of the tube. For this reason, if a tube with a narrow diameter is chosen, it may not be able to advance far enough into the trachea for the balloon to be situated completely in the subglottis. In this case, options include switching to a standard ETT, considering orotracheal intubation, or changing sides and approaching the contralateral nostril.

When the ETT has reached the posterior nasopharynx and passed the soft palate into the oropharynx, transoral direct laryngoscopy is performed, and Magill forceps are used to advance the tube between the vocal cords and into the trachea. Once the ETT cuff has passed the vocal cords and is inflated, the chest should be auscultated and end-tidal PCO2 verified to confirm that the end of the tube is positioned in the trachea.

The position of the patient's head should be noted during and after intubation to determine the depth of the ETT insertion. Flexion may advance the tube deeper into the trachea, which is usually of little clinical significance when using a nasal RAE, as the likelihood of endobronchial intubation is low with an appropriately sized tube. Perhaps more likely is the tube withdrawal with extension of the neck. If a narrow nasal passage necessitates using a relatively small tube, an extension of the neck can force the balloon against the vocal cords. It may lead to injury, balloon herniation, or extubation.

Complications

The most common complication of nasotracheal intubation is epistaxis, which occurs to some degree with nearly every NTI. Other complications include bacteremia (introducing bacteria from the nasal cavity into the body due to trauma from the tube) and risk of perforation (retropharyngeal perforation, soft palate perforation, or perforation of a piriform sinus). It is best to avoid NTI in patients who have sustained high-speed trauma or isolated facial trauma due to the potential for loss of skull base integrity and inadvertent placement of the ETT intracranially.

Clinical Significance

Nasotracheal intubation is a useful technique for securing the airway in preparation for intraoral surgery; it has proven very safe and effective when used correctly. Knowledge of the anatomy, indications, contraindications, and complications is critical for anesthesia providers.

Enhancing Healthcare Team Outcomes

Anesthesiologists and nurse anesthetists commonly perform nasotracheal intubation. The technique requires in-depth knowledge of upper airway anatomy. NTI is a useful technique for intubation when the oral cavity is unavailable. Patients must be closely monitored during the procedure; auscultation of the lungs and end-tidal PCO2 confirmation is essential to ensure the tube is in the trachea. Unlike oral ETTs, nasotracheal tubes can be dislodged easily. Therefore, the patient's head must be stable throughout the intubation, particularly during head and neck surgery.[16]