Point of care ultrasound (USG) is an emerging bedside tool in management of sick neonates. It may be used to locate catheter position during and immediately after procedure, reducing the time lag and radiation exposure. Whereas few studies [2] in the past have evaluated the utility of USG in locating umbilical catheters, there is re-emergence of interest amongst neonatologists to evaluate the tip position of various central catheters in neonates [3-7]. We conducted this study to determine the agreement between radiological and USG-based assessment of central line tip position.

This was a prospective observational study conducted at the neonatal intensive care unit of a tertiary care centre in India from April, 2019 to August, 2019. All infants admitted to the NICU who underwent central line placement were eligible for enrolment. A written informed consent was obtained from parents of eligible infants. Central catheters [umbilical arterial and venous catheter (UAC, UVC), peripherally inserted central venous catheter (PICC) and femoral venous catheter] were placed by the attending neonatologist using standard techniques. The length of insertion for PICC in the upper and lower limb was measured from point of insertion along the venous pathway till suprasternal notch to right third intercostal space and till level of xiphisternum, respectively. For UAC and UVC insertion, Dunn shoulder　umbilical length normogram was used [8]. After placement of central catheter, USG assessment of position of catheter tip was done by a neonatologist, trained in ultrasound. A radiograph was also performed to assess catheter position as the standard of care. The ultrasonologist was blinded to the radiological findings.

For a disagreement of 10% between the two methods, as reported in a recent study [6], alpha error of 0.01 and power of 80%, the sample size was estimated to be 60.

Statistical analyses: Statistical analyses were performed using SPSS version 19. Catheter tip position was defined as optimal or suboptimal, both on USG and X-ray, as per predefined criteria. Agreement between USG and X-ray defined tip positions was determined using kappa statistics. A P value <0.05 was considered significant.

Of the 141 central catheters insertions performed during the study period, USG was performed for 65 central catheters (refusal of consent in 13, and investigator not available in 63). On USG, catheter tip position could be assessed and defined in 62 (95%) of cases. In three neonates, central lines (2 PICC and 1 UV) were misplaced at aberrant locations and not visualized on USG. Of the 62 catheters, 25 were PICC, 4 were femoral venous catheters, 16 were UVC and 17 were UAC.

The median (IQR) gestation and weight of the enrolled infants were 28 (26, 34.2) weeks and 1060 (860, 2120) g, respectively. Twenty four (38.7%) central lines were defined as optimally placed on radiograph and 20 (32.2%) were defined as optimally placed on USG. There was excellent agreement between radiographic and USG assessment of catheter tip position [K (95% CI) = 0.86 (0.73 – 0.99); P<0.001] (Table I). All 38 lines found to be mal-positioned on radiograph were assessed as sub-optimal on USG as well. Four lines, 3 PICC and 1 UVC, which were deemed to be optimal on radiograph were detected to be suboptimal on USG, all entering RA. The mean (SD) time from completion of central line insertion to completion of USG was less than time required for obtaining X-ray film [6.11 (2.7) min vs 122.46 (45.45) min; MD (95% CI) -116.35 (-128.11 to -104.58); P <0.001].

In this study, we could identify catheter tip position in 95% of cases and there was excellent agreement between USG and X-ray for optimal catheter tip position. In three cases, catheter tip was not visualized as it was mal-positioned in aberrant pathways, two in the neck veins both being upper limb PICC lines and one UV being coiled in the liver. Till date, few studies have reported utility of USG for placement of central catheter in neonates. Ohki, et al. [12] assessed the ability of USG to detect the tip of a percutaneous central venous catheter in neonates and reported a consistency of 87% between USG and radiography. Simanovsky, et al. [13] measured the distance of UVC tip from the diaphragm on USG and X-ray and reported no significant difference in the distance measured by using the two modalities. Greenberg, et al. [2] also demonstrated feasibility and safety of USG for assessment of umbilical venous catheter position. Other authors have also suggested high agreement coefficients　between point of care USG and X-ray with respect to overall central venous tip, UVCs and PICCs [14,15].

Although radiograph is considered a gold standard for defining optimal tip position, it has certain limitations. It is difficult to precisely identify junction of RA to IVC or SVC on plain X-ray, which could lead to misinterpretation of correct tip position. We found that 4/24 (16.6%) central lines that were deemed to be appropriate on radiograph were actually lying inside the cardiac chambers on USG assessment. Tauzin, et al. [5] have also described limitation of X-ray assessment for PICCs in low birth neonates. They reported that, of all PICCs deemed to be in good position on plain radiographs, 25% were within the heart [5]. Similarly, another small study found that 41% of PICC lines that were deemed to be correctly placed on X-ray were found to be malpositioned on USG [4].

Our study evaluated degree of agreement between USG and radiograph in locating the tip position of different central lines across wide range of weights and gestation. All USGs were performed by a single trained operator. We, therefore, emphasize that USG is a skill-based operator dependent technology and competency training is required before non-radiology users can evaluate central line tip positions at various locations. Sometimes examiners may find it difficult to visualize catheter tips within the liver, outside of IVC or SVC, especially if they are in aberrant pathways. The limitation that point of care ultrasound is performed for specific clinical purpose to answer a clinical question, and it may not mandate a detailed comprehensive examination is also acknowledged.

Ethical Clearance: Ethics Committee, Sir Ganga Ram Hospital; EC/12/18/1454, dated December 18, 2018.

Contributors: AT: conceptualized the project and developed the protocol; AT: had primary responsibility of patient screening, enrolment and data collection; AT: performed the data analysis; AT,VK: wrote the manuscript; NK, PG: participated in protocol development, supervising enrolment, outcome assessment and in writing the manuscript; AT, MM: participated in planning of project and writing of manuscript.

Funding: None; Competing interest: None stated.

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