In Reply:
We greatly appreciate Dr Bellini's interest in our study1 and would like to address his concerns. We agree that the first or second thoracic vertebra (ie, T1 or T2) has been described in several studies as the reference point for mid-tracheal endotracheal tube (ETT) positioning.2,3 The definition of the correct ETT location in our study was “the tip of the ETT below the thoracic inlet and above the carina.” The carina is located at T4 in 85% of infants, with a range of T3–T5 as given by Blayney and Logan.2 The “at approximately thoracic vertebrae 2 or 3” in our methods is for reassuring the reader that we considered the location of the carina in our estimates without specifically defining mid-trachea.
Respiratory movement and head and neck position affect the position of the ETT, and the ETT may move as much as 5-8 mm.4 The trachea is shortened during head flexion and during expiration, thus the ETT is pushed toward the carina, whereas the opposite occurs during extension of the head and inspiration. We noted in our paper that “we were unable to determine if there was any neck flexion,” without making any other assumptions regarding patient positioning. We respectfully note that, in the study by Bellini et al,5 only 12 neonates weighed < 750 g, whereas the mean weight of the 131 subjects in our study was 729 ± 140 g.1,5 Given the difference in the populations enrolled in each study and that fact that subjects in the study by Bellini et al5 were nasally intubated, it is difficult to compare our results. The determination of ETT depth is challenging in infants with a birth weight < 750 g, and medical practitioners have a tendency to insert the ETT deeper than T2 to avoid the risk of extubation.6 Any extension of the infant's head, whether due to the infant's movements, tension from the ventilator circuit, ETT movement due to the securement method, could dislodge the ETT in smaller infants.1 This is why the standard practice in our unit is to consider the proper ETT position to be at T2 or T3, which allows a margin of safety.
Our study was a retrospective analysis and included only infants < 1 kg born at a tertiary center, in a controlled setting, with experienced clinical teams and radiographic evaluation available at all times, and we did not include any intubations done outside our unit or during transport to our hospital, and no infants with a birth weight > 1,000 g. We agree with and recommend clinical evaluation postintubation, including, but not limited to, symmetrical chest rise, equal breath sounds bilaterally, equal response in heart rate and oxygen saturation, and the use of reference nomograms. Based on the available data from our study and others,7,8 weight-based methods for determining initial ETT depth may provide a starting point, but ETT depth should be adjusted based on clinical assessment, and chest radiography should be performed as quickly as possible.
Footnotes
Dr Miller has disclosed a relationship with VOCSN. The other authors have disclosed no conflicts of interest.
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