I am trying to better grasp why they are important for the ECMO cannulae tube. Also, if anyone is familiar with ECMO for premature babies or ECMO in general and would not mind giving me information on the topic please contact me.
The drainage holes in the sides of the cannula provide alternative/additional pathways for the blood to leave the area and go into the cannula lumen to be removed. If the vessel wall(s) were to collapse into a entrance of single hole, the negative pressure inside the cannula will pull hard on that tissue, and blood would not be removed during this time. At some point, this retained blood builds up pressure in the area, pulling against the tissue that is "Stuck" in the hole, and the inevitable breakage of the vacuum pressure causes a sudden influx of this retained blood into the cannula lumen. This can be seen outside the body as "chugging" of the drainage line. It can be very damaging to the vessel tissue that keeps being sucked into that hole. Having multiple holes helps to mitigate this "chugging", but, it's not 100% effective, depending upon the site, the vacuum, and the blood flow in that area.
Multiple drainage holes reduces the risk of the cannula adhering to the inside of the vessels (due to the negative pressure generated by the pump) which can compromise extracorporeal circulation or even damage the blood vessel. A clinical sign of this happening is "kicking" drainage lines. This kicking can often be reduced by reducing flow in the extra corporeal circulation (reduce RPM) or by administering extra fluid to increase the circulating volume (makes the lumen of the blood vessel larger and thus decreases the risk of the cannula adhering to the inside of the vessel. Some dual lumen cannulas (bicaval) are contructed in a way where blood is drained from both the inferior and the superior caval vein and then infused into the right atrium when it returns from the external circulation - this explains the high number of holes in these types of cannulas.