Endotracheal intubation (EI) is an essential technique in airway management. However, it can be associated to potentially serious complications, such as unrecognised oesophageal intubation (OI) or one-lung intubation. Consequently, it is important to verify the correct placement and depth of insertion of the endotracheal tube (ETT) after each intubation.1–3 Direct laryngoscopy allows the direct verification of the EI, but it requires proficiency by the operator and the interruption of resuscitation manoeuvres in patients with cardiac arrest.4,5 There are alternative methods such as auscultation, capnography, observation of chest movements, observation of condensation in the ETT, and raising the heart rate in neonates.6 Although none of the existing methods have been proven to be fully reliable, capnography is the most widely used and recommended.7 Chest radiography is routinely performed in most units to check the correct placement of the tip of the ETT after intubation. There is still little experience in the use of ultrasound in paediatric intubation. Studies in adults seem to suggest that ultrasonography is as reliable and fast as conventional methods and could be advantageous in specific situations, such as cardiopulmonary arrest.3,8–10

The purpose of our study was to assess the feasibility and efficacy of ultrasonography in EI compared with the most widely used methods, such as capnography or chest radiography.

The sample included 31 intubations in 26 patients. Thirteen were neonates in the NICU with a median gestational age of 32 weeks (range, 24–40 weeks) and a median weight of 1438g (range, 530–3450g). There were 13 children in the PICU with a median age of 4 years (range, 3 months–14 years) and a median weight of 21kg (range, 4–58kg). Tables 2 and 3 summarise the results of the capnography vs ultrasonography and the radiography vs ultrasonography comparisons. We found no significant differences in the ability to detect EI between capnography and ultrasound in NICU or PICU patients; however, ultrasound was significantly slower, a difference that was not observed in the PICU patient subset. We found no significant differences between radiography and ultrasound either. The ETT was not visualised by means of ultrasound in 2 neonates with positive capnography. On the other hand, ultrasound did not detect 2 malpositions (ETT placed too high) that were detected in the radiograph. Using capnography as the standard criterion, ultrasonography showed a sensitivity of 92% and a specificity of 100% in detecting the presence of the ETT in the trachea. Ultrasonography also showed a sensitivity of 100% and a specificity of 75% compared to radiography in detecting the correct depth of insertion of the ETT. Ultrasonography was significantly faster than radiography in every comparison.

Ultrasonography has been used in airway management to investigate anatomy, estimate the size of the ETT, verify ETT placement, and detect one-lung intubation.5,15–20 We believe that one of the most interesting aspects of ultrasound is that, besides visualisation of the ETT, it allows evaluation of its insertion depth and ruling out incorrect placement.

The aim of our study was to compare the usefulness of ultrasonography to identify EI with other, more widely used methods, such as capnography and chest radiography. We found that ultrasonography is efficacious in the identification of EI, with high sensitivity and specificity compared to capnography. However, it is a considerably slower method. We must highlight that the difference in time was observed in the NICU group. This is probably due to the small size of neck structures in neonates, which makes it more difficult to implement the technique. In older children, ultrasonography was as quick as capnography. Since it is safe and fast, capnography is currently the most widely used method to confirm EI.7,11 However, it may not be reliable in patients with cardiopulmonary arrest due to an insufficient tidal volume. In this context, ultrasound can be advantageous in emergent intubations. Studies with large samples conducted by Sim et al.12 and Chou et al.9 have demonstrated that ultrasound performed better than capnography in patients with cardiopulmonary arrest. Furthermore, we found that ultrasound is as fast as capnography in older children, which suggests it may be useful under these circumstances, in which reliability and speed are crucial.

Other situations in which ultrasound can offer advantages over capnography are low tidal volume, for instance in premature neonates, or the presence of severe bronchospasm. In the absence of these special circumstances, if capnography is available, ultrasound should not be used or should be used only as an adjunct technique. We also observed that performing this technique in neonates presented more difficulty, which may be the reason why the ETT was not visualised in 2 neonates that had been intubated correctly (false negatives). Finally, superior malposition of the ETT was not detected in 2 neonates. These aspects need to be taken into account when considering the use of ultrasound in neonates, especially if the operator is inexperienced.

Ultrasound was as efficacious as chest radiography both in the PICU and the NICU, with high sensibility and moderate specificity. The false negatives in our study corresponded to nondetection of the superior malposition of the ETT in neonates using ultrasound. This may have been due to the small size of the neck, which makes it difficult to determine whether the tip of the ETT is or is not in the extrathoracic trachea. Ultrasound clearly required less time than radiography. This finding was also reported by Sim et al.12 in the adult population and by Kerrey et al.21 and Galicinao et al.5 in children. Another study on adults conducted by Pfeiffer et al.3,10 showed that ultrasound is as quick as auscultation and outperforms capnography combined with auscultation in determining the placement of the ETT. Another advantage of ultrasound compared to radiography is that in situations where the ETT may be displaced by patient handling, ultrasound can be used to verify its placement as many times as needed without associated exposure to radiation.

There is little experience in the use of ultrasound to confirm ETT placement in the paediatric age group. Kerrey et al.21 reported that ultrasound is equivalent to chest radiography in determining the position of the ETT within the airway. It is worth noting that the ultrasound technicians in this study were inexperienced. Previous research shows that ultrasound can be used reliably by prehospital care providers with little training.22 Later, a paediatric study by Galicinao et al.5 showed a 100% sensitivity and specificity of ultrasound when compared to clinical detection methods and chest radiography. This study also compared ultrasound with capnography and concluded that ultrasound should be considered an adjunct method that offers some advantages in specific situations. We believe that ultrasonography can be useful to verify ETT placement and rule out malposition in a timely manner after intubation, avoiding routine performance of chest radiography, especially in older children. Our results suggest that in neonates, if there are any signs of superior malposition (such as excessive leaks from the ventilator), ultrasound may not be sufficient, and a radiograph needs to be performed.

The main strengths of our study are its prospective nature, that a single operator performed all ultrasounds, and that it is the first study simultaneously comparing ultrasonography with other standard methods, like radiography and capnography, in children and neonates. The main limitation is the small number of patients included in the study, as well as their heterogeneity. Another limitation is that the study was performed in the controlled environment of the ICU, where the number of oesophageal intubations or incorrectly placed ETTs tends to be low. This may limit the generalisability of its results to other settings, such as prehospital or emergency care.

Future research should assess the role of ultrasonography in airway management, specifically in the context of cardiopulmonary arrest of haemodynamic instability. Ideally, it would entail multicentre studies in large-volume paediatric hospitals.

Ultrasound is as efficacious as capnography in verifying ETT placement, although it may take more time, especially in neonates. Other disadvantages in neonates are that it may produce false negatives, and that it is difficult to identify superior malposition. Ultrasound is an efficacious and fast method for determining the depth of insertion of the ETT and ruling out one-lung intubation, so it could contribute to reduce the routine use of radiography.

The authors have no conflicts of interest to declare.