The title says it all. Why is it that patients are placed in the trendelenburg position when a catheter is inserted in the sub clavian vein? What would happen if the patient wasn't placed in the trendelenburg position when placing the catheter? Thanks in advance for the help.


There are 2 main reasons for using the Trendelenburg position when placing and removing a central venous line catheter into the subclavian or even internal jugular vein.

  1. Exactly what C Rags mentioned-- to increase the size of the vein. This position utilizes the force of gravity to pool blood towards the head from the lower extremities. This makes the vein of interest easier to visualize compared to surrounding structures, to palpate since this increases pressure within the vein, and to ultimately puncture.
  2. To avoid air embolisms, which are particularly more damaging if they get into the brain causing a stroke than if they travel inferiorly to the leg, for example. Air embolisms can be introduced when inserting or removing a line.


  • $\begingroup$ I'm sorry if this seems to be too picky, but how does being in the Trendelenburg position make an air embolus travel against the flow of the blood (as you state, inferiorly?) Will an air embolus introduced into the subclavian vein go to the leg if a patient is placed in Trendelenberg? If so, how does it navigate back into the superior vena cava -> inferior VC -> etc.? $\endgroup$ Jan 11 '15 at 1:38
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    $\begingroup$ Great question, it is theoretically possible for an embolism to travel retrograde to blood flow depending on the position of a patient. This paper does not specifically test the subclavian vein, but the authors created a simulation of blood flow through a vein-mimic to determine at which angles an air embolism could flow retrogradely. $\endgroup$
    – Anne
    Jan 11 '15 at 1:55
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    $\begingroup$ Thanks for answering! Your paper states @ angles between 0 - 45°, air bubbles followed fluid flow (these are smaller bubbles, though). Trendelenburg is <45°. While it's is recommended for insertion and removal (it's always good when an answer sparks my curiosity), I read that it's to create a pressure gradient (blood is more likely to back up into the line than air to enter the vein). Once an air embolus is introduced, however, the left lateral decubitus (sometimes +Trendelenburg) position is recommended to trap the embolus in the R atrium until reabsorbed. Fascinating. $\endgroup$ Jan 11 '15 at 2:20

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