Venous embolisms by gas aspiration

Normally, for patients in supine position, a central venous pressure of 4 to 6 cm of water is enough to prevent air or gas at atmospheric pressure to enter the returning venous bloodstream. However certain circumstances can reduce the venous pressure under the atmospheric pressure: Examples include, surgery performed in partially seated position for veins located above the superior vena cava; Trendelenburg position for veins located under the inferior vena cava49; hypovolemia; and variations in central venous pressure during controlled ventilation. The risk of gas entering is proportional to venous diameter: trivial for small peripheral veins vs. life threatening for the dural venous sinuses, diploic bone veins that cannot collapse, and the large venous stems located within or in the vicinity of the thorax.

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