Needle position for venous access

Global overview of ultrasound-guided vessel puncture and use of the isosceles right triangle.

(A) Taking a distance between the probe and the needle insertion point equal to the depth of the vessel, a probe perpendicular to the skin, and an angle between the skin and the needle of 45°, the third angle will be automatically positioned into the vein. Three points build an isosceles right triangle: the needle insertion point, the middle of the probe on the skin interface, and the center of the vein under the probe.

(B) The long-axis plane, which passes through the length of the vessel, corresponds to the view obtained in the in-plane technique with the vessel in the long-axis. Three points determine the long-axis plane: the needle insertion point, identified by inserting the needle in the skin just above the vessel, the vessel being viewed in the long axis; the middle of the probe on the skin, the vessel being visualized at the center of the ultrasound screen in the short axis; the middle of the probe's top, the probe being perpendicular to the skin. The operator should attempt to maintain the syringe in the axis of the probe top (dotted line).