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A neonate has just been intubated on the Neonatal Intensive Care Unit (NICU). The tube has been confirmed to be within the trachea through a combination of clinical and physiological signs. These include observing for symmetrical chest movement, listening for air leak at the mouth and auscultation of the chest and abdomen. Capnography is positive for end-tidal CO2, and the patient has shown a clinical improvement in colour, saturations and heart rate. A chest X-ray (CXR) is requested to confirm that the endotracheal tube (ET) tip sits below the upper border of the T1 vertebral body and above the lower border of the T2 vertebral body. While waiting for the radiographer to arrive you wonder whether the NICU’s ultrasound (US) machine could be used to confirm the ET tip position.
Structured clinical question
In neonates who have been successfully intubated, can ultrasound accurately confirm ET tip position when compared with CXR?
Embase, Medline and the Cochrane library were searched. Original human studies were included. The following search terms were used: (newborn* OR neonat*) AND (intubation OR tracheal tube* OR endotracheal tube*) AND (ultrasound OR ultrasonograph* OR sonograph*) AND (confirm* OR placement OR position*). Additionally, Medical Subject Headings (MeSH) terms of ‘newborn/’; ‘intubation/’; ‘ultrasound/’ were used in Embase. MeSH terms of ‘infant, newborn/’ and ‘intubation/’ were used in Medline.
Conference abstracts, posters and letters were excluded. Studies that had a mixed population of patients from Neonatal and Paediatric intensive care were excluded. The Embase search identified one new study in addition to the nine studies found in the Medline search. In total, 10 observational studies were identified (see table 1).
It is important to confirm the position of the ET tip to avoid the risks of ventilating a neonate with a mispositioned tube. These risks include hypoxaemia, pneumothorax, lung collapse, accidental extubation, incorrect surfactant administration and death.1–4 CXR remains the ‘gold standard’ for confirming ET tip position1 and has the added benefit of potentially identifying coexistent lung, cardiac or skeletal pathology. However, performing an X-ray carries the risk of radiation exposure. US may offer an alternative way to confirm ET tip position and avoid this risk.
In 1986, Slovis and Poland5 pioneered the use of US in neonates to identify the placement of ETs. Technological advances meant that US probes were small enough to be used for this purpose and it became accepted that the air-filled ET could be visualised on US. Slovis et al used the aortic arch (AA) as the anatomical marker for the carina as the carina is not easily visualised on US.5
There are 10 observational studies that have looked at whether US can be used to confirm ET tip position in a neonate.2 4–12 The number of US scans performed within these studies are relatively small, ranging from 612 to 53.6 7 None of these studies reported adverse events when using US to identify the ET tip position.2 4–12
Data from seven of these studies support a good relationship between ET tip position on US when compared with X-ray.2 4–6 8 9 11 Four of the seven studies2 4 5 8 reported moderate to excellent correlation of ET tip position measured on US compared with CXR. The interclass correlation coefficients of these studies ranged from r2=0.61–0.95.2 4 5 8 Chowdhry et al 9 and Saul et al 11 reported high concordances of 95% and 100%, respectively, for US to report the same ET tip position when compared with CXR. Sethi et al reported a 91% sensitivity for US to identify a correctly sited ET tip.6
While these results are encouraging, many of the patients included within these studies had correctly sited ET tips on X-ray. Therefore, US was primarily being ‘tested’ on its ability to confirm a correctly sited ET tip instead of identifying a mispositioned ET tip. Only the study by Chowdhry et al 9 reported on US’s ability to identify a mispositioned tube; with a sensitivity of 86% (6/7) to identify a deeply positioned tube.
Two studies reported moderate and poor concordances between ET tip position on US compared with CXR, respectively.7 10 De Kock et al 10 suggested a reason for this poor concordance was the potential migration of the ET during imaging. They noted that X-rays were mainly performed with the head flexed and US was performed with the head extended.
The use of US in a NICU will clearly be dependent on equipment availability and the presence of a trained operator. Three studies looked at the time taken to confirm ET position using US compared with X-ray. All three studies reported that it was quicker to obtain an US than an X-ray.6–8 However, two studies only included patients based on operator availability; therefore, the reported times to obtain US in these studies are skewed due to an inclusion bias.6 7 Several studies only had one4–6 10 trained operator. This may have been intentional to reduce intraobserver variability, but it may also reflect the challenge of recruiting skilled operators. For most NICUs, it is likely that the limiting step in using an US in this context will be the availability of a trained operator.
A limitation of US is that it might not always visualise the ET tip with six studies reporting this problem in some of their patients.5–9 12 This problem is not exclusive to US as poor-quality X-rays may also require repeat studies. There is also a lack of consensus in the research for the position of the carina based on anatomical landmarks with some studies using the AA5–7 9–11 and others using the right pulmonary artery (RPA).2 4 8 Within these 10 studies there were a range of patient gestations and weights included but the optimal ET tip to carina measurements were not adjusted to account for this variable. Singh et al 13 demonstrated that the US measured ET tip to carina distances will vary based on weight and gestation and have created normative data tables. Future research in this field should use and evaluate these normative data.
US is a promising new adjunct to confirm the ET tip position. It offers a benefit over capnography by objectively identifying where the ET tip sits within the trachea and avoids the radiation exposure of X-ray. The procedure requires a trained operator. Importantly, there is variability in the literature as to the ‘correct’ landmark for the carina and the optimal measured distance from ET tip to carina. Further studies are also needed to evaluate US’s ability to identify a mispositioned ET tube.
Clinical bottom line
Ultrasound (US) can confirm a correctly sited endotracheal tube (ET),however, if the ET is mispositioned or not visualised, then a chest X-ray should be performed rather than adjusting based on US alone. (Grade C)
Patient consent for publication
Contributors The corresponding author, SC, was responsible for drafting this article. LM was responsible for revisions of this article. LM supervised the overall process.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.