Lumbo-peritoneal (LP) shunts seem to have become increasingly popular in the last few years, as they make it possible to avoid skull and brain injuries. With LP shunts, the spinal cavity is directly linked to the ventricles. The Liquor is drained from between the third and fifth lumbar vertebrae into the peritoneum. Even today, the view that hydrostatic suction does not play a significant role in LP shunts and that the risk of overdrainage is therefore lower, can still be found in the literature (Bloch8, 2012). This assertion is utterly false and misleading. It probably comes from the fact that in LP shunts, the source of the Liquor (the spinal cavity) and drainage site (the peritoneum) are not located on top of one-another: the shunt catheter between the puncture site and abdomen is actually roughly horizontal, meaning that the hydrostatic level appears to be h = 0.
It has been explained previously, in detail, that when the person stands up, the entire Liquor filled spinal cavity, all the way up to the ventricles, is raised up above the abdomen. Indeed, if the cavity is now open because of the shunt, the column of liquid in the spine can drain into the abdomen, creating the same hydrostatic suction in the ventricles (the height, "h") as would occur in a ventriculo-peritoneal shunt. Given that the spinal cavity is significantly wider than the narrow peritoneal catheter and produces a greater flow of liquid, the overdrainage actually occurs significantly more quickly. In a recent literature review (Miyake9, 2016) a similar misleading remark is made, stating the siphon effect is negligible in LP shunts. However this should be viewed in a distinct way. It is true that in the case of the LP valve, which, of course, is at the same height as the abdomen, not very much suction comes from the abdomen (i.e. from below). Nevertheless, because of this, the entire force of the hydrostatic pressure in the spinal cavity weighs down upon it from above. In the case of a VP shunt, the valve is at the same height as the ventricle and all of the hydrostatic suction comes from below, whereas there is only a relatively low amount of IVP to exert an effect from above. Still, when it comes to a standard differential pressure valve, the only thing that is relevant is the sum of both the amount of pressure and the amount of suction. Therefore, in both cases, the outcome in relation to overdrainage remains the same.