Page 49 - JSOM Winter 2024

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placement may be more difficult. A medic will need to evaluate of the NPA in anesthetized adults. Stoneham identified that
benefits and disadvantages of the recovery position and adjust the NPA’s ideal placement length is 10mm above the epiglottis.
as appropriate. This may include placing a patient temporarily If significantly shorter, the device will fail to separate the soft
in the supine position to re-evaluate or perform a procedure, palate and tongue from the oropharynx wall. If too long, the
before placing the patient back into the recovery position. NPA can stimulate a gag reflex and lodge itself in the vallecula
Level of Evidence: B-NR evidence (nonrandomized studies and or the esophagus.
observational data)
Stoneham identified that the NPA length, not the outside di-
How should patients be positioned to protect ameter or inside diameter, is the most influential sizing mea-
their airway? surement for proper placement. The nares-epiglottis (N-E)
length is the critical measurement when determining proper
Medics should continue to advocate for the conscious patient NPA sizing. Stoneham attempted to correlate the N-E length
to self-manage their airway by assuming the best tactically rel- to different external patient landmarks and found the only
evant position to maintain a patent airway. Allowing a patient significant correlation of N-E length was to the patient’s
to manage their own airway encourages self-ventilation and height. Of note, nares-tragus length (t=1.79, P=.08) did not
does not degrade cardiac output. Positive pressure ventilations produce a significant correlation, although was the next clos-
increase intrathoracic pressure resulting in reduced cardiac est correlated landmark. Stoneham created the following for-
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preload. Therefore, it is important for the battlefield medic mula for determining a patient’s N-E length, based on patient
to recognize and allow a hemorrhagic compromised patient to height:
continue to maintain their own airway if possible.
NE(mm) = -5.38 + 0.915 x HEIGHT(cm) (r = 0.478. p = 0.0002).
Evidence supports the continuing use of the recovery position The formula below adapts Stoneham’s formula to find the pa-
while incorporating chin away from chest principles to ensure tient’s ideal NPA size:
the airway remains patent. Prehospital providers should con-
tinue to place unconscious patients without traumatic airway NPA length(mm) = (Patient Height (in) × 2.3241) – 15.38
obstructions in the recovery position as first-line treatment, if
the patient is unable to manage their own airway. The head Using reasonably-sized NPAs, Stoneham noted a 42% ob-
should be extended (chin away from chest) to minimize airway struction rate with NPAs (120 patients), indicated by patient
occlusion. Additionally, providers should continue to allow the distress such as see-sawing of the chest abdomen, rib recession,
conscious patient to self-manage their airway by assuming the and tracheal tug. Three of those patients (2.5%) experienced
best tactically relevant position. complete airway obstruction, and the NPA was found to be
Level of Evidence: B-NR and C-LD evidence (nonrandomized compressed in the nasopharynx in 15.8% of patients. While
studies and observational data and limited data) Stoneham noted that obstruction rates for this study are likely
to be artificially high due to occlusion of the patient’s other
nostril and mouth, the design method did eliminate additional
What are the limitations of the nasopharyngeal airway?
variables to singularly assess the NPA’s efficacy. Additionally,
The NPA’s purpose is to separate the soft palate and tongue Stoneham found a secondary finding of a 7% incidence of
from the posterior oropharynx wall. The device is normally moderate to severe bleeding from NPA insertion.
tolerated in conscious or semi-conscious patients, easy train-
able, inexpensive, and takes up minimal aid bag weight and Stoneham’s research found that a 150-mm long NPA would
space. There is, however, a surprising lack of published data adequately fit most males. Despite this length recommendation,
concerning the use of the NPA in the prehospital setting. Stoneham noted a 30.5% airway obstruction rate (36 patients)
for this size of device in his own study. While Stoneham’s re-
The airway in an unconscious patient has three physiological search is regarded as the most comprehensive, two Asia-based
mechanisms that can drive airway occlusion. In a study ob- studies conflict with Stoneham’s measurement assessment and
serving deeply anesthetized adults, Boidin observed that the provide alternate anatomical landmark proposals for deter-
tongue is not the sole anatomic structure which may cause mining N-E length. 23,24 Hwang et al. found NPA lengths rang-
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airway occlusion. The epiglottis and soft palate also play ing from 132 to 154mm are most appropriate and found an
significant roles in upper airway patency. Boidin removed N-E correlation between nares and mandibular angle length
tongues from cadaver models and still observed complete air- (P<.004, r=0.324). Tseng et al. found N-E statistically cor-
way occlusion, solely caused by the falling of the epiglottis. If related to a complex formula, including a combination of body
properly placed and sized, the NPA may be able to secure the weight, body height, nares to tragus, philtrum-to- mandibular
tongue and soft palate but is not designed to secure the epi- angle, philtrum-to-tragus, and nares-to-tragus distances. While
glottis and if inserted too deep, will likely cause a pharyngeal not statistically significant, Tseng et al. contended the phil-
reflex in the patient unless deeply unconscious. NPA evidence trum-to-tragus length was a good predictor of the optimal
and considerations are outlined in the following questions. insertion depth as it differed from the statistically significant
Level of Evidence: B-NR and C-LD (Nonrandomized and Lim- formula by less than 1cm in most patients.
ited Data)
Stoneham argued that the most important NPA metric is the
How does the length and sizing of NPAs affect length of the device, but NPA sizes are marketed and labeled in
their effectiveness? French (FR) sizing—a measurement of the catheter’s diameter.
NPA catheter lengths do not relate or correspond to French
The preponderance of non-obstructive sleep apnea NPA data sizing, and length measurements regularly do not appear on
is provided by Stoneham’s 1993 study assessing the patency distributors’ websites, nor do they appear on the NPA catheter

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