To the Editor:
We read with great interest the article by Litman1 concerning the problems surrounding the choice of cuffed and uncuffed tracheal tubes in anesthesia and pediatric intensive care. Although the issue has been on debate for many years and now there is a general belief that cuffed tubes can also be safely used in children, I think it is important to make some reflections on the strict geometrical relationship between tracheal tubes and the anatomy of the cricoid and trachea. Both Litman and Weiss2,3 have frequently reported and demonstrated that the cricoid lumen is not circular but rather of an ellipsoidal shape. By performing investigations with nuclear magnetic resonance, Litman has shown that the cricoid ring in its cross section is narrower than the anteroposterior section. This finding is, in our opinion, of considerable clinical importance and should not be overlooked. Considering that the orotracheal tubes have a perfectly circular shape, they are ill-adapted within an ellipsoidal structure. If we try to draw a circle inside an ellipse, imagining that the circle represents the tube and the ellipse is the cricoid, we can easily demonstrate that the tracheal tube, even if the proper size, can apply excessive pressure on cricoid structures along the minor axis of its elliptical shape. At the same time, the tube would not adhere well to the lateral areas of the cricoid corresponding to the major axis of the ellipse. This circumstance, in the presence of uncuffed tubes, creates the condition for an imperfect seal in the tube airway system with an increased risk of micro-inhalation, loss of gas, requiring repeated adjustments of mechanical ventilation parameters. Another risk present is the excessive movement of the tube and its tip with consequent laryngotracheal mucosal microtrauma. On the contrary, the cuffed tubes can better adapt, thanks to the latest generation in cuff design, the ellipsoidal geometry airway and, contrary to what history has always claimed, they represent a considerable advantage in terms of efficacy and safety in pediatric patients as compared with the uncuffed tubes.
However, another important aspect should be taken into consideration regarding the variability of the geometry and morphology of the airways that is observed in neonates affected with a congenital disorder or after some operations where the geometric relationship between the endotracheal tube and airway may change dramatically, accentuating the problems described using uncuffed tubes. In his study, Fayoux4 reported postnatal tracheal changes after in utero fetoscopic balloon tracheal occlusion in seven consecutive newborn infants with severe congenital diaphragmatic hernia. On careful examination of the bronchoscopic images reported by Fayoux in his article, a significant change is observed in the tracheal diameter indicating a more evident tendency to collapse during the expiratory phase, followed by a progressive dilatation of the trachea during the inspiratory phase, and a greater expansion of the upper part of the trachea compared with the lower similar to tracheomalacia. The geometric appearance taken, which one can observe, is exactly that of an ellipsoid. In this circumstance, or in clinical circumstances similar to the one just described, in a newborn inadequately adapted to the mechanical ventilator, the tracheal mucosa would produce repeated movements toward and away from the surface of a tube not fitted with a cuff causing micro-lesions in the mucosa and, moreover, no guarantee of an adequate seal for gas exchange. Even in these cases, the uncuffed tubes may not represent an advantage for children. Another disadvantage of uncuffed tracheal tubes is related to the geometric variation of the airways in relation to the progressive deepening of anesthesia over the course of its entire duration. In the initial stages of anesthesia, the tracheal tube may be adequate in size and seal without gas leakage. In the later stages, as a result of the deepening of the neuromuscular block and the incremental administration of anesthetic drugs and associated movements of the head and neck, the airway caliber is modified, and the presence of uncuffed tubes does not guarantee an adequate seal of the gas with consequent losses from the breathing circuit, inadequate ETCO2 and capnography readings, and lung hypoventilation. With the cuffed tubes, this problem does not exist because the cuff ensures a greater seal and immobilization of the tube also with respect to the movements of the neck even when using tubes of underestimated size. In conclusion, we cannot fail to agree on the safety of using cuffed tubes in children. But at the same time, we should not underestimate the variations and changes in the geometry and anatomy of the airways, particularly in newborns, at various stages of pediatric development and in some comorbidities. Regarding technological innovations and new ideas for study, the analysis of the relationship between the cuffed/uncuffed tracheal tubes and laryngotracheal morphology with ultrasound-guided technique can be, in our opinion, a valuable additional tool for noninvasive real-time investigation especially in cases in which it is necessary to monitor the consequences of prolonged intubation.5