Ultrasound evaluation of the respiratory changes of the inferior vena cava and axillary vein diameter at rest and during positive pressure ventilation in spontaneously breathing healthy volunteers.

While the axillary vein could potentially be used as an alternative vessel to the IVC to assess for volume responsiveness in controlled, mechanically ventilated patients as well as in non-mechanically ventilated, spontaneously breathing patients, neither vein should be used to guide fluid management decisions in spontaneously breathing patients during positive pressure non-invasive ventilation.