A nasopharyngeal airway (NPA) is a soft, flexible tube designed to be inserted through the nose to ensure the upper airway remains open. This device is frequently used in emergency and pre-hospital settings to bypass obstructions caused by the tongue or soft palate collapsing backward in a patient with a reduced level of consciousness. The NPA is often favored over an oropharyngeal airway when a patient retains an intact gag reflex, which could be stimulated by an oral device. Selecting the correct size is essential before insertion, as an improperly sized airway can negate its purpose and potentially lead to serious complications.
The Criticality of Correct Fit
Selecting an incorrect size for a nasopharyngeal airway carries significant risks that undermine the goal of maintaining a clear breathing passage. When the NPA is too short, its tip does not extend far enough into the pharynx to bypass the soft tissue obstruction. This renders the airway adjunct ineffective, leaving the patient vulnerable to continued low oxygen levels due to the persistent collapse of the pharyngeal structures.
Conversely, an NPA that is too long poses dangers related to over-insertion into the lower airway. An excessively long tube may advance into the hypopharynx, causing its tip to press against the epiglottis or the posterior pharyngeal wall. This improper placement can stimulate the gag reflex, triggering vomiting and subsequently increasing the risk of aspirating stomach contents into the lungs. The stimulation of the posterior pharynx can also excite the vagus nerve, potentially leading to laryngospasm or a dangerous slowing of the heart rate.
In patients with undiagnosed or suspected basal skull fractures, an NPA that is too long or forced into place could risk penetrating the cribriform plate. The more common danger from a long NPA is trauma to the vocal cords or the epiglottis, which can itself cause an airway obstruction. Precise measurement is a fundamental safety measure to prevent iatrogenic harm.
Determining Appropriate Length
The primary objective of sizing the NPA length is to ensure the distal tip rests in the correct anatomical location, positioned just above the epiglottis, allowing for unobstructed airflow. The gold standard technique for estimating the correct length before insertion involves external anatomical landmark measurement. This procedure measures the distance from the tip of the patient’s nose, specifically the opening of the nares, to the tragus of the ear on the same side of the face.
To perform this measurement, a clinician should hold the NPA next to the patient’s face. The flared or trumpet end of the NPA, which prevents the device from disappearing into the nasal cavity, must be aligned with the naris opening. The tube is then extended along the cheek toward the ear.
The point where the distal tip of the NPA aligns with the tragus—the small cartilage flap protecting the ear canal—approximates the correct length to position the tip just behind the tongue base and in front of the epiglottis. Some clinicians may use the earlobe or the angle of the jaw as an alternative endpoint, but the nose-to-tragus method remains the most widely taught standard. Utilizing a spare NPA or a measuring tape for this external assessment prevents the need for repeated, traumatic internal adjustments. After confirming the measurement, the length selected must allow the NPA’s flange to sit securely against the nostril opening without applying excessive pressure. This careful external measurement is critical since the internal length of the airway path is not visually accessible during the emergency procedure.
Selecting the Correct Diameter
The diameter, or width, of the nasopharyngeal airway is the second factor that must be correctly selected, measured in French units (Fr) or the internal diameter in millimeters (mm). The French scale is most commonly used for sizing these tubes. The primary concern with diameter is finding a size that maximizes airflow without causing trauma to the delicate nasal mucosa.
A diameter that is too wide significantly increases the risk of complications during insertion, including nasal trauma and bleeding, known as epistaxis. The nasal passage contains a rich blood supply, and forcing a large tube through can cause substantial hemorrhage, which can lead to aspiration or simply make the airway management procedure more difficult. Excessive pressure from an oversized tube over a prolonged period can also cause localized pressure necrosis or ulceration of the nasal tissues.
Conversely, an NPA that is too narrow will substantially increase airway resistance. This restriction of airflow can negate the benefits of the adjunct. The flow of air through a tube is exponentially reduced as the radius decreases, meaning a small reduction in diameter can lead to a disproportionately large increase in breathing effort.
A common, though less precise, method for estimating the diameter is to select a size that approximates the width of the patient’s small finger. A more practical approach is to use age- or weight-based charts, with typical adult NPA diameters ranging from 26 French (6.0 mm) to 36 French (9.0 mm). For adult males, sizes around 32 Fr to 36 Fr are often appropriate, while adult females commonly use 28 Fr to 32 Fr. The final selection should be the largest diameter that can be inserted through the nares with minimal resistance and without causing blanching or excessive pressure on the nostril tissues.