Advances in the application of nasopharyngeal airways during general anesthesia

A nasopharyngeal airway, also known as a nasopharyngeal tube, is a simple and cost-effective airway device primarily used to relieve upper airway obstruction caused by conditions such as posterior tongue displacement. Traditional nasopharyngeal airways resemble endotracheal tubes in shape, with a short, rounded, beveled tip at the pharyngeal end to minimize irritation to the pharynx; the nasal end has a flange to prevent it from falling into the nasal cavity.The nasopharyngeal airway is made of medical-grade polyvinyl chloride material, which is neither too soft nor too hard. This reduces damage to the nasal mucosa and prevents twisting or kinking within the body, thus avoiding lumen narrowing. Compared to other supraglottic airway devices with similar functions (such as oropharyngeal airways), patients tolerate the nasopharyngeal airway better and experience more stable hemodynamics.

Currently, nasopharyngeal airways are widely used as a common airway adjunct in various clinical departments. This article provides a review of their application in general anesthesia.

The size of a nasopharyngeal airway is related to its inner diameter and length, and is usually indicated by the inner diameter in millimeters. Choosing the correct size is crucial; only by inserting a nasopharyngeal airway of the appropriate diameter to the correct depth can the posterior pharyngeal wall be supported, thereby relieving upper airway obstruction and maintaining airway patency. Therefore, the suitability of the nasopharyngeal airway size for the patient determines whether the device will be effective.The ideal placement for a nasopharyngeal airway is when, after insertion through the patient's nasal cavity into the pharynx, the pharyngeal end is located within 3 cm above the epiglottis. Current consensus suggests that the length of the nasopharyngeal airway is more important than its diameter; therefore, the selection of nasopharyngeal airway size in clinical practice is primarily based on its length, i.e., the intended insertion depth.

In recent years, clinicians have become dissatisfied with the traditional nasopharyngeal airway's function in relieving upper airway obstruction. An increasing number of modified NPAs have been invented, developed, and applied clinically, including improvements in both function and appearance. We will categorize general anesthesia into three types: inhalational anesthesia, endotracheal intubation intravenous anesthesia, and non-endotracheal intubation intravenous anesthesia, and describe the application of nasopharyngeal airways in general anesthesia.

1.The application of nasopharyngeal airways in inhalational anesthesia.
The airway tube of the nasopharyngeal airway extends from the nostril directly to the upper part of the epiglottis, forming a nearly closed circuit that delivers gas to the glottis, and can be used for administering inhalational anesthetics. Studies have shown that a modified nasopharyngeal airway can be used as a routine airway and a channel for administering sevoflurane during upper gastrointestinal endoscopy in children.

2.The use of nasopharyngeal airway during tracheal intubation under intravenous anesthesia.
- A nasopharyngeal airway is pre-inserted before tracheal intubation. Acute upper airway obstruction is one of the main complications during tracheal intubation or extubation, especially in cases of difficult intubation. The use of a nasopharyngeal airway to alleviate acute upper airway obstruction has been clinically applied, but it is often used only after symptoms appear, which can delay rescue efforts and worsen the patient's hypoxia.Studies have shown that pre-inserting a nasopharyngeal airway can improve difficult airways and is a non-invasive method for preventing and resolving acute upper airway obstruction during tracheal intubation or extubation in adult patients with difficult airways undergoing general anesthesia. It is simple to perform, effective, and well-tolerated. Selecting an appropriately sized nasopharyngeal airway as an aid for nasal tracheal intubation is safe and effective, and can reduce the time required for laryngeal visualization and tracheal intubation.

- After extubation, a nasopharyngeal airway was inserted. Following extubation, due to the incomplete metabolism of anesthetic drugs in the body, tongue prolapse can easily occur, leading to airway obstruction. Experimental results showed that inserting an NPA during the recovery period from anesthesia in neurosurgical patients better maintained upper airway patency, had fewer circulatory effects, was well-tolerated, and resulted in fewer complications.

3.The application of nasopharyngeal airways in non-intubated intravenous anesthesia.
In non-intubated intravenous anesthesia, nasopharyngeal airways are primarily used in outpatient procedures such as painless gastroscopy and colonoscopy, and painless induced abortion. Outpatient procedures are short in duration, and international guidelines recommend propofol intravenous injection for anesthesia induction due to its rapid onset, short duration of action, rapid recovery, few adverse effects, and good patient tolerance. However, propofol can cause respiratory depression, airway obstruction, and hemodynamic instability, making prevention of airway obstruction, effective oxygen delivery, and prevention of hypoxia particularly important. Studies have shown that NPAs can reduce the incidence of hypoxemia during propofol-induced anesthesia.

Nasopharyngeal airway insertion is simple, provides good ventilation, maintains hemodynamic stability, is well-tolerated, inexpensive, and readily available, leading to its increasing use in anesthesiology and other departments. However, healthcare professionals should be aware of potential complications such as nausea, vomiting, aspiration, and nasal mucosal injury. While proper placement and fixation of the nasopharyngeal airway can reduce the incidence of nausea, vomiting, and aspiration, nasal mucosal injury is unavoidable.Even when inserted by skilled operators, nasopharyngeal airways can still cause nasal mucosal damage in 4.7% of patients. Furthermore, it cannot be guaranteed that every operator in clinical practice will possess this level of skill, meaning the actual incidence of nasal mucosal damage is likely to be even higher. While nasal mucosal damage is not life-threatening, it increases the risk of infection and reduces patient satisfaction.Therefore, we believe that improvements to nasopharyngeal airways should focus on reducing complications. Improving performance, optimizing structure, reducing complications, and simplifying operation are the future directions for the development of improved nasopharyngeal airways, and the clinical effectiveness of these improved airways still requires further clinical trials for verification.