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Introduction: Correct tip positioning is a critical aspect in central vascular access devices insertion. The verification of positioning at the cavo-atrial junction is usually performed by intracavitary electrocardiography. Recently, echocardiographic techniques were proposed, including the direct visualization of the catheter or the visualization of a saline/air bolus (i.e. “bubble test”). As for the latter, a push-to-bubbles delay time below 2 s was proposed to indicate a correct positioning of the catheter tip. The aim of this study was to measure the variations of the push-to-bubbles time at increasing distance from the cavo-atrial junction, to verify if a cut-off of 1–2 s correspond to a well-positioned catheter.Methods: We performed a prospective study including patients with clinical indication of positioning a peripherally inserted central catheter. The catheter tip was positioned at the cavo-atrial junction (P0) via intracavitary electrocardiography, and the push-to-bubbles delay time was measured. The catheter was then retracted 5 cm (P1) and 10 cm (P2), and the test was repeated at this positioning. Push-to-bubbles time measurements were performed off-line by analyzing an audio/video recording which included the echography screen and the voice signal of the operator.Results: Forty-nine patients were included. The average push-to-bubble time when the catheter tip was in the reference position was 0.41 ± 0.21 s. Retraction of the PICC catheter of 5 and 10 cm determined a significant increase of the push-to-bubbles time: mean time difference was +0.34 (95% IC 0.25–0.43, p< 0.001) s between P0 and P1 (5 cm distance), and +0.77 (95% IC 0.62–0.92, p< 0.001) s between P0 and P2 (10 cm distance). When the catheter was at the reference position (i.e. cavo-atrial junction) only 2.1% of bubbles delay times were above 1 s.Conclusion: The push-to-bubbles time is very low when the catheter tip is at the cavo-atrial junction. This delay increases progressively with increasing distance from the target. Push-to-bubbles delay time above 1 s might indicate a catheter not close to the cavo-atrial junction.