Page 49 - JSOM Fall 2021

optimal NPA insertion length (1cm above the epiglottis, i.e., female patients. Age, body weight, and height of all patients
nares-to-epiglottis distance –1cm) with various external facial were recorded. The nares-to-vocal cords distance measured
measures. Their goal was to estimate the optimal tube length 18.3 ± 0.8cm in males and 16.3 ± 0.7cm in females. A statis-
by clinically testing possible correlations to six variables. tically significant correlation to body height was determined,
Measurements were completed using a fiberoptic broncho- consistent with all other studies on the subect. These findings
scope. The philtrum-to-ear tragus distance showed the least also indicated a statistically significant correlation between the
difference from nares-to-epiglottis distance –1cm. The authors nares-to-vocal cords and the nares-to-ear tragus distances. The
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concluded that the optimal length and insertion depth of the correlations of Han et al. are included in Table 2.
NPA tube could be predicted by the philtrum-to-ear tragus
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distance. Table 1 lists their variables and the variable correla- Watanabe et al. examined the optimal length of the NPA by
tions to nares-to-epiglottis distance. measuring three distances according to their classification of
clinical importance. All 26 of their patients were under general
A study conducted by Vamadevan et al. in 2008 evaluated anesthesia for elective surgery. Distance A, the distance allow-
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the relation of the NPA length to body height in 50 patients ing the release of airway obstruction, was 12.73 ± 0.85cm in
undergoing surgery with nasal intubation without visual opti- males and 11.70 ± 0.75cm in females. Distance B, the disance
mization. Upon withdrawing the endotracheal tubes, the au- to provide the most effective ventilation, was 14.55 ± 0.96cm
thors checked the tube withdrawal to compare it to the distal in males and 13.93 ± 1.12cm in females. Distance C, the
placement of an NPA tube. They found that to maintain good nares-to-arytenoid cartilage distance, was 18.84 ± 0.90cm in
ventilation with NPA placement, male patients had a mean males and 17.40 ± 0.97cm in females. The authors concluded
distance of 14cm and females, of 12.4cm. There was a cor- that most commercially provided NPAs are too short; they
relation between patient height and NPA positioning perfor- found distance B to be approximately 2cm longer than distance
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mance, as noted in Table 1. A, making it necessary to advance the NPA about 2cm farther
to provide the most effective ventilation in airway-obstructed
Studies That Specifically Referenced patients. Finding no correlation between height and weight,
Nares-to-Vocal Cords Distance to Anatomic Landmarks they concluded that using external body parameters to predict
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With the intent to measure the nares-to-vocal cords distance, optimal length of the NPA tube is difficult. Their finding of
compared with six external body meaurements, Sareen et al. no correlation to body height is presented in Table 2.
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used fiberoptic nasal intubation in their 2015 study. This study
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included 50 males and 50 females. The nares-to-vocal cords dis- Kawamura et al. in 2003 measured the length of the na-
tances were a mean of 18.5 ± 1.5cm in males and 15.9 ± 1.1cm res-to-vocal cords distance by fiberoptic laryngoscope using
in females. When combining both gender groups, the authors NPA tubes in 54 patients. Their study showed that the distance
were able to correlate three of the six anatomic landmarks to the of the nares to the vocal cords was dependent on patient gen-
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nares-to-vocal cords distance. Table 2 reflects their findings. der and did correlate with body height. The measured length
in males was 20.2 ± 1.0cm and in females, 17.3 ± 1.1cm.
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TABLE 2 Overview of Studies Referencing Nares-to-Vocal Cords Table 2 provides their correlation findings.
Distance to Anatomic Landmarks and the Extracted Correlations to
Anatomic Adult Landmarks
Nares-to-Vocal Total Discussion
Cords Distance Number Number of The goal of our literature search was to discover (1) whether
Related to: of Studies n = Correlations there are study references that can provide valid guideline mea-
Height 4 5,10,12,13 95 (Han et al. ) 3 5,12,13 surements to determine the optimal NPA tube length in adults,
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100 and (2) whether the often-cited guidelines recommending the
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(Sareen et al. ) measurement of tube length to the nose-tip-to-earlobe distance
26 0 10 are correct. None of the articles provided a clear definition
(Watanabe et al. ) of the differentiation between nose-tip and nares. However,
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54 (Kawamura
et al. ) what must be recognized is that in many patients, based on
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Sternal length 1 12 100 1 12 their facial features, there is potentially a difference of a few
(Sareen et al. ) millimeters in these two starting reference points.
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Arm span 1 12 100 1 12
(Sareen et al. ) The articles we reviewed had a total of 12 variables—external
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Nares-to-ear tragus 2 5,12 95 (Han et al. ) 1 5 body measurements—correlated to one or both of the follow-
distance 100 0 12 ing: nares-to-epiglottis distance and/or nares-to-vocal cords
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(Sareen et al. ) distance. Tables 1 and 2 list these variables and the studies
Nares-to-mandibular 1 12 100 0 12 that included each of these. Overall, the study designs, their
angle (Sareen et al. ) correlated distances, and the different measurements of the
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Nose tip-to- 1 5 95 (Han et al. ) 0 5 included studies were very heterogeneous. Many of the listed
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mandibular angle results indicate a strong correlation between the patients’
Nares-to- 1 12 100 0 12 height and both the nares-to-epiglottis distance and the nares-
thyromental distance (Sareen et al. ) to- vocal cords distance. 1-3,5,8,11-13 Therefore, a patient’s height
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Body weight 1 5 95 (Han et al. ) 0 5 might be one of the most important variables in choosing the
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optimal tube length.
Han et al. in 2005 fiberoptically examined the distance be-
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tween the nares and the vocal cords, then compared this dis- The current and most common method to estimate the correct
tance to two external facial measurements in 50 male and 45 length of an NPA tube is to measure the distance between the
Correct Length of Nasopharyngeal Airways in Adults | 47