Effects of positive airway pressure on basilic vein diameter and venous flow velocity in healthy volunteers

Introduction: The placement of vascular catheters of adequate size in accordance to catheter-to-vein ratio (CVR) recommendations represents one of the cornerstones of catheter-related upper vein thrombosis prevention. However there is scarcity of data on its effect on the venous dynamics of the basilic vein, a common site for long-term catheter placement. This study investigates the effects of the application of positive airway pressure on the diameter and blood flow velocity of basilic vein. We also measured the effects of under-armpit straps, a device commonly used to keep continuous positive airway pressure (CPAP) helmets in place. Methods: We enrolled 28 healthy volunteers. Basilic vein diameter and minimum/maximum blood flow velocity, according to respiratory venous flow oscillation, were measured by ultrasound on the midpoint of their dominant arm during spontaneous breathing and during breathing in a CPAP helmet with 10 cm H2O of airway pressure applied, with the helmet kept in place either through armpit straps or by tying the helmet to the bed. Results: The application of 10 cm H2O of positive airway pressure significantly increased basilic vein diameter by 0.9 +/- 0.2 mm, while reducing minimum blood flow velocity by 1.8 +/- 0.4 cm/s. These effects were amplified by the application of under armpit straps. Conclusions: Breathing with positive airway pressure increases basilic vein diameter while reducing blood flow-velocity. This phenomenon might lead to an incorrect assessment of CVR, misleading the operator into choosing improperly large catheters.