Causes for air microbubbles
The occurrence of air microbubbles in the daily clinical routine can be influenced, but microair cannot be avoided. Larger amounts of air microbubbles arise from events such as starting the extracorporeal circulation, blood suchtion in the operating area, blood sampling and drug administration (examples for such events can be found in the Q&A section).
Even if these events are carried out very gently, microair will always be detected. Other factors such as variations in temperature and pressure gradients will result in the formation of microairbubbles.
Postoperative neuro-psychological damages
Patients often suffer from neuropsychological disorders after cardiopulmonary bypass. Reasons for neuropsychological dysfunctions are microemboli either of solid or gaseous nature. It is indisputable that solid emboli create a lot of damage because they cannot dissolve in contrast to air emboli. Depending on size and gas composition also microairbubbles need a very long time to dissolve in arterial blood. A 50 µm microbubble needs 2.3 minutes to dissolve, a 200 µm bubble 32 minutes (mathematical model assuming blood with 50% O2 and 50% N2).
The harmfulness of bubbles in enforced by the fact, that microbubbles always occur in large flushes, and that 15-20% of these bubbles go directly into the patients brain.
Any microbubble is harmful. At first sight microbubbles over 18µm seem to be most harmful, because they are very probable to obstruct microvessels in the brain. But also small microbubbles have been proven to cause stripping of the endothelium, which also results in adverse events.