Aust. Radiol. (1975), 19, 161

The Length of the Upper Airway in Infants and Neonates A STUDY TO DETERMlNE THE OPTIMAL LENGTH FOR ENDOTRACHEAL TUBES By JOHNE. CURRAN, M.D., BRUCED. DOUST, M.B., B.S., AND VIVIENNE L. DOUST, M.B.,B.S. The Department of Radiology, University of Michigan, Wayne County General Hospital, Eloise,Michigan 48132 INTRODUCTION Tracheal intubation is frequently necessary during resuscitation of neonates and small infants, particularly those with hyaline rnembrane disease. Malposition of the endotracheal tube adds considerably to the patient’s already substantial respiratory problem. A review of chest films in neonatal patients at Wayne County General Hospital suggested that malposition of the tube is not uncommon. This study was undertaken to determine the frequency and type of malpositioning of endotracheal tubes in neonates and infants under 5000 grams body weight and to determine if there is an optimal length for endotracheal tubes which would minimize the problem. METHODS AND MATERIALS The chest x-rays of 250 neonates and infants under 5000 grams body weight were reviewed. In more than two-thirds of these the x-ray beam was collimated too tightly to provide an image of the mouth, pharynx and larynx on the chest film, or the radiographic density of the overlying shoulders precluded adequate visualization of the upper airway. In 77 patients, however, the entire upper airway was adequately demonstrated on at least one film. This was usually a lateral projection. in those patients in whom a suitable lateral projection W a s not available, an AP with the head turned we11to One side was used. A piece of string was laid along the tine of the trachea and over the tongue to the alveolar marpin, and over the soft palate to the external nares. The distances from the alveolar margin and the external nares to the carina and to the vocal cords were then measured. (Figure 1 ) In many patients, visualization of the

FIGURE]-Diagram of the upper airway. Distances from the carina and vocal folds to the maxillary alveolar margin or to the external narcs were measured by laying a picce of string along the airway as shown (-) or The c a k a , vocal f,,Ids, externat nares and maxillary alveolar margin are marked (I) 1.

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KEYWORDS Airway Length. Neonates. Intubation, endotracheal. Malposition.

laryngeal ventricle allowed accurate identification of the cords. In all other patients, the position of the vocal cords was identified by following the aryepiglottic folds to their bases. each patient the presence of an end* tracheal tube was noted and the nature of any misplacement recorded. There were two separate groups of studies in this series. Neonates were examined using

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JOHN E. CURRAN. BRUCE D. DOUSTAND VIVIENNE L. Dousr a mobile x-ray unit with a focus-film distance of 40 inches. Older children were examined in the Department of Radiology using a focus-film distance of 72 inches. In both types of study the patient was in direct contact with the film cassette. The airway is separated from the film by a variable distance depending on the size of the child, so that the x-ray image of the airway is magnified. For the computation of the degree of magnification both the focus-film distance and the object-film distance must be known. For the AP roentgenograms, the object-film distance was taken as the distance from the trachea to the skin of the posterior chest wall at the level of the sternal notch. This distance was measured from the corresponding lateral view. For the lateral roentgenograms the object-film distance was taken as the distance from the trachea to the lateral chest wall at the level of the sternal notch, that is, 50% of the transverse diameter of the thorax at the level of the sternal notch, as measured on the AP view. (This procedure avoided error when rotated AP views had to be used.) Magnification was then calculated using the formulaTrue length = length of image X (focus-film distanceMobiect-film distance) focus-film distance

film distances that occur when a small patient is in direct contact with an x-ray film cassette. From Figures 2 and 3 it can be seen that the tip of an endotracheal tube introduced through the mouth and advanced 7 cm beyond the alveolar margin would fall somewhere within the trachea in all infants between 800 grams and 4500 grams body weight. Similarly, the tip of a tube introduced through the nose and advanced 8 cm beyond the external nares would lie within the trachea in all infants in this weight range.

DISCUSSION Several techniques have been described to avoid malposition of endotracheal tubes. These

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FIGURE 2-Distances from the maxillary alveolar margin to the vocal folds ( * ) and to the carina ( o ) plotted against body weight in 77 patients weighing between 750 grn and 5000 gm. In RO case is the distance to the carina greater than 7 cm. The distance to the vocal cords is never less than 7 cm.

RESULTS Of the 77 patients, 22 were intubated at some time during their hospital course. In 1 1 of these, that is 50%, the endotracheal tube was in some way misplaced. In one, the tube tip was in the pharynx; in another, the tube tip was in the esophagus. In the remaining nine patients the tube tip was in the right main bronchus. In three patients the endotracheal tube was misplaced on more than one occasion. The distances from the alveolar margin to the larynx and from the alveolar margin to the carina are presented in graphic form in Figure 2. The distances from the external nares to the larynx and to the carina are presented in graphic form in Figure 3. All measurements have been corrected for magnification. Magnification averaged about 3 %, varying from a little over 4% to about 2%. This was true of both AP and lateral films taken with a film distance of 40 inches and for AP and lateral films taken with a tube film distance of 72 inches. The small magnification factor reflects the short object-

FiCURE 3-Distances from the external nares to the vocal folds ( ) and to the carina ( o ) plotted against body weight in 77 patients weighing between 750 gm and 5000 gm. In no case is the distance to the carina greater than 8 cm. The distance to the vocal folds is never less thin 8 cm.

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Australasian Radiology, Vol. X I X , No. 2, June, 1975

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THELENGTH OF THE UPPER AIRWAY IN INFANTS AND NEONATES include use of nomograms correlating crownheel length, body weight, head circumference, etc., with optimum tube length(*),@),measurement of the distance from the tip of the nose to the earlobe as a measure of the most suitable length for a nasotracheal tube@) and multiplication of crown-heel length by O.21(3). The high frequency with which tubes are misplaced suggests that these methods are either not used, or are ineffective. Even though a method has been described at the University of Michigan(5) it does not appear to have reduced our incidence of malposition of endotracheal tubes (50% ) in the last three years. This suggests that something simpler than a nomogram is required if the method is to be clinically useful. From our results it appears that if an endotracheal tube marked 7 cm and 8 cm from the tip is introduced through the mouth to the 7 cm mark or through the nose to the 8 cm mark, the tip will fall somewhere in the trachea in all infants between weights of 800 and 4500 grams. This does not guarantee an ideal position for the tube tip, nor does it eliminate the need for x-rays to check the tube position, but it is likely to diminish the incidence of intubation of the right main bronchus, which may occur in spite of careful auscultation of the chest(@.

vocal folds were measured from chest roentgenograms in 77 patients weighing between 7.50 gm and 5000 gm. The tip of an endotracheal tube introduced 7 cm beyond the alveoIar margin, or 8 cm beyond the external nares, would fall somewhere in the trachea in all patients in this series weighing between 800 gm and 4500 gm. The incidence of misplacement of endotracheal tubes is high (5’0% in this series). Introduction (or subsequent displacement) of the tube beyond 7 cm (if in the mouth) of 8 cm (if in the nose) should arouse suspicion of misplacement of the tube tip in the right mainstem bronchus.

REFERENCES

ABSTRACT The distances from the maxillary alveolar margin and external nares to the canna and the

‘Meredith, W. J., and Massey, I. B. (1972): “Fundamental Physics of Radiology,” Ed. 2. Baltimore: Williams and Wilkins Co., 205. ‘Mattila, M. A. K., Heikel, P. E., Suutarinen, T., and Lindfors, E. L. (1971): “Estimation of a suitable nasotracheal tube length for infants and children.” Acta Anaesthesiol. Scand., 15, 239. Coldiron, I. S . (1968): “Estimation of nasotracheal tube length in neonates.” Pcdiorrics, 41, 823. ‘Leigh, M. D., and Belton, M. K. (1960): Pediatric anaesthesia, Ed, 2. New York: Macmillan Co., 208. ‘Kuhns, L. R., and Poznanski, A. K. (1971): “Endotracheal tube position in the infant.” J . Pediatr., 78, 991. ‘Hamilton, W. K., and Stevens, W. C. (1964): “Malpositioning of endotracheal catheters.” I . A .M.A ., 198,1113.

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The length of the upper airway in infants and neonates.

Aust. Radiol. (1975), 19, 161 The Length of the Upper Airway in Infants and Neonates A STUDY TO DETERMlNE THE OPTIMAL LENGTH FOR ENDOTRACHEAL TUBES B...
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