Current guidelines are to avoid placement of neonatal long lines within the heart.¹ Placement within the heart is generally “excluded” radiologically. However, even with the benefit of contrast² and digital³ radiography, the tips of long lines may not be adequately visualised. Standard two dimensional ultrasonography may assist in localising line tips in neonates,⁴ but the technique requires significant experience, and images are not optimal (fig 1A, B). We therefore investigated the use of colour Doppler to aid ultrasonographic line tip visualisation.

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Figure 1

 (A) Line tip entering right atrium on subcostal view; (B) line passing along superior vena cava (SVC) on parasternal view; (C) normal colour Doppler flow pattern in superior vena cava; (D) line tip “illuminated” by saline flush.

A Vygon 24 gauge catheter has an internal diameter of 0.3 mm (area approximately 0.0007 cm²). When flushed at 0.1 ml/s, flow rate at the line tip is about 140 cm/s, well above usual venous flow rates. Using colour Doppler, the same line barely visible in fig 1A,B, and masked by superior vena caval blood flow in fig 1C, becomes clearly visible when flushed with saline at about 0.1 ml/s (fig 1D).

We are not aware of any centres routinely using colour Doppler to aid ultrasonic detection of long line tip position in neonates. This technique potentially offers a simple, reliable method of localising line tips and should be put through further rigorous assessment.