Wednesday, October 24, 2012

How to Survive an Air Embolism

The best way to survive a venous air embolism is to avoid getting one in the first place.

Symptomatic air embolism during the placement of a central venous catheter (as discovered by a radiolucency over the heart during fluoro) is a dangerous but fortunately uncommon event.  There is risk for entry of air into the blood stream with placement of an IJ or subclavian central venous catheter, due to the negative intrathoracic pressure. The traditional patient positioning for placement of a line to avoid entry of air is Trendelenberg and with the patient performing a Valsalva maneuver (to increase intrathoracic pressure).

Placement of a central line is not the only possible etiology for a venous air embolism -- they've also been reported with detachment of the IV tubing from the catheter hub, failure to close the hub, a fractured catheter, or air entering a persistent subcutaneous tunnel after catheter removal.  And, of course, it's also possible to introduce air into the venous system with power injection of contrast in CT.

Many small venous air emboli are asymptomatic and the incidence of small venous air emboli may be higher than currently thought since most are not detected.... but what if enough air is introduced into the right heart to cause an "air lock" of the pulmonary outflow tract? What if the patient starts crashing?

Trendelenberg, left lateral decubitus (left side down), and oxygen.

The idea is to trap the air in the right atrium -- rather than in the PVOT -- by putting the right atrium most superiorly -- swing the vena cava up. It seems to make mechanical sense... I doubt this maneuver is ever going to make it to a randomized controlled trial.

The use of oxygen is two-fold in that it helps keep blood oxygen levels up, but it's also theorized to decrease the size of the embolism itself by causing nitrogen to diffuse out of the air bubbles.  There have been case reports of attempting to introduce a catheter into the right heart to suck out the air, but it's debatable if this is really effective. If a catheter is in place, it may be worth a shot, but if not, it's doubtful if introduction of a new catheter would be worthwhile.

and of course, if this doesn't work...................... then start CPR.

1. Vesely TM. "Air Embolism during Insertion of Central Venous Catheters" J Vasc Interv Radiol 2001; 12:1291–1295
2. ACR Manual on Contrast Media, 8th ed (2012)