We’ve all seen it. Patients looking wide eyed and worried at a small bubble of air as it travels down the IV line and off into the mystery of their arm. “Don’t worry”, we assure them… “its far too small to cause any problems”.
So exactly how dangerous are those little air bubbles? And how much air would be needed to cause an adverse event?
Or to put it simply: would 10mls of air injected into the IV line by the evil ninja assassin disguised as Dr Singer (who has been tied up and thrown in a linen skip), be enough to kill our sleeping hero and stop him getting the girl?
Once a volume of air is introduced into a peripheral vein, it can potentially make its way through to the Right Atrium and Ventricle, and then on into the pulmonary vasculature. Here air may occlude the microvasculature increasing dead space and damaging the vessels endothelial lining. This in turn, may trigger an inflammatory response resulting in noncardiogenic pulmonary oedema and bronchoconstriction. In animal studies, the ability of the lung to filter air micro-bubbles fails when air enters the circulatory system at a rate greater than 0.30 mL/kg per minute
A large, rapidly-entrained bolus of air can fill the right atrium with air and cause an air lock, which leads to obstruction of the right ventricular outflow tract, decreased venous return, and decreased cardiac output. Myocardial and cerebral ischaemia soon follow.
Small amounts of air are probably absorbed by the plasma and haemoglobin, but larger amounts have been associated with interfering with pulmonary gas exchange, and causing cardiac arrhythmias.
Air bubbles may also occlude the micro circulation of other organs such as the brain, spinal cord and the skin.
OK. So now you’ve really scared me. But how much is safe?
Emedicine quotes that more than 5mls per kg is needed to cause significant complications. Although it states that as little as 20 mls (around the amount of air in an unprimed IV line) has been reported to cause some problems.
Large amounts (of between 100 to 300 mls) have allegedly been fatal.
So those pesky little bubbles travelling down the tubing are probably not going to do any damage. But never-the-less, it would be wise to take steps to minimize the risk of larger amounts of air entering the system.
- Dont forget to prime the IV line! Sounds stupid, but it happens more often than you think.
- When hanging a new bag on an existing line, check to make sure the previous fluid hasn’t run down the line leaving a large airspace.
- Do not place IV fluids down on the bed when transferring patients etc. Laying the drip chamber down on its side only encourages air to enter the tubing.
- Expel any air from syringes of IV antibiotics, analgesia etc that you are about to administer.
- And of course always check to make sure any drugs or fluids being injected into the line are compatible with the fluid. Incompatible fluids may crystallize or form a sediment that will cause similar problems.
Heres a quick tip.
When priming a new IV line, first invert the bag of fluids so you are spiking it from above.
Once you have inserted the giving set into bag of fluids open the roller clamp and gently squeeze the bag expelling all the air from the top of the IV bag into the giving set. Keep squeezing until the fluid from the bag is pushed up into the drip chamber.
Invert the bag back into its normal position and continue to prime the IV line.
Now, when your patients IV fluids are finished they will stop at the level of the bottom of the flask. There will be no air in the bag to run down into the giving set necessitating a re-priming of your line.
and another thing:
Never pull the cap off the spike with your teeth like they do on TV. It looks cool, but you run the risk of contaminating the IV fluids with your oral flora (and, no doubt, fauna).
Do not let the patient end of the IV tubing drag around on the ground while you are spiking the bag. It may be a hospital, but its still pretty dirty down there.
Do not let fluid squirt out onto the floor as you prime your line . Someone carrying a brimming bedpan is sure to slip arse over nipples on your mess.