- Department of Neurosurgery, FUNFARME, São José do Rio Preto, SP; Founder and Owner for Ventura Biomedica Ltda, Brazil
- São Paulo Federal University, São Paulo, SP, Brazil
- Head of Department Neurosurgery, Hospital Municipal Miguel Couto, Rio de Janeiro, RJ, Brazil
- Department of Engineering, Ventura Biomédica Ltda, São José do Rio Preto, Brazil
- Department of Neurosurgery, São José do Rio Preto, Brazil
- Chairman, Department of Neurosurgery, FUNFARME, São José do Rio Preto, Brazil
- Professor and Chairman, São Paulo Federal University, São Paulo, SP, Brazil
Angelo Luiz Maset
Professor and Chairman, São Paulo Federal University, São Paulo, SP, Brazil
DOI:10.4103/2152-7806.139410Copyright: © 2014 Maset AL. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Maset AL, ĺtalo Capraro Suriano, Monteiro R, José Ricardo Camilo Pinto, José Ricardo de Andrade, Mancini BM, Sérgio Luiz Ramin, Moraes DF, Sérgio Cavalheiro. Shunt implantations and peritoneal catheters: Do not cut beyond 20 cm. Surg Neurol Int 22-Aug-2014;5:130
How to cite this URL: Maset AL, ĺtalo Capraro Suriano, Monteiro R, José Ricardo Camilo Pinto, José Ricardo de Andrade, Mancini BM, Sérgio Luiz Ramin, Moraes DF, Sérgio Cavalheiro. Shunt implantations and peritoneal catheters: Do not cut beyond 20 cm. Surg Neurol Int 22-Aug-2014;5:130. Available from: http://sni.wpengine.com/surgicalint_articles/shunt-implantations-and-peritoneal-catheters-do-not-cut-beyond-20-cm/
Background:Ventriculoperitoneal shunts are supplied with long peritoneal catheters, most commonly between 80 and 120 cm long. ISO/DIS 7197/2006 shunt manufacturing procedures include peritoneal catheter as an integrate of the total resistance. Cutting pieces of peritoneal catheters upon shunt implantation or revision is a common procedure.
Methods:We evaluated five shunts assembled with different total pressure resistances and variable peritoneal catheter lengths in order to clarify the changes that occurred in the hydrodynamic profile when peritoneal catheters were cut upon shunt implantation or shunt revision.
Results:Originally, all shunts performed within the operational range. Shunt 1 performed in a lower pressure range at 200 mm cut off peritoneal catheter and as a low-pressure shunt with –300 mm cut off. Shunt 2 was manufactured to run at the higher border pressure range, and it went out of specification with a 300 mm cut off. Shunt 3 was manufactured to run close to the lower border pressure range, and at 100 mm cutoff, it was already borderline in a lower resistive category. Other shunts also responded similarly.
Conclusion:The limit to maintain a shunt in its original pressure settings was 20 cm peritoneal catheter cutting length. By cutting longer pieces of peritoneal catheter, one would submit patients to a less-resistive regimen than intended and his reasoning will be compromised. The pediatric population is more prone to suffer from the consequences of cutting catheters. Shunt manufacturers should consider adopting peritoneal catheters according to the age (height) of the patient.
Keywords: Hydrocephalus, shunt hydrodynamics, shunt overdrainage
Neurosurgeons routinely cut off pieces of the peritoneal catheter upon shunt implantation/revision, and this occurs more frequently in the pediatric and newborn population due obviously to the height of the patients. In a previous work,[
Five pediatric shunt systems with different pressure settings were submitted to hydraulic forces in a rig according to ISO/DIS 7197 standard for 50, 40, 30, 20, 10, and 5 ml/h flow. The rig has been described in detail in previous publications[
Shunt 1, neonatal medium-pressure valve at average range [Figure
Shunt 1: (a) Neonatal medium-pressure shunt assembly at average range with 1000 mm peritoneal catheter; (b) same shunt as
Shunt 2, neonatal low-pressure calibrated at upper border range [Figure
Shunt 2: (a) Neonatal low-pressure shunt assembly at high-pressure range with 1000 mm peritoneal catheter; (b) same shunt as
Shunt 3, neonatal low-pressure calibrated at average range [Figure
Shunt 3: (a) Neonatal low-pressure shunt assembly at average pressure range with 1000 mm peritoneal catheter; (b) same shunt as
Shunt 4, neonatal low-pressure calibrated at average range for 800 mm peritoneal catheter [Figure
Shunt 4: (a) Neonatal low-pressure shunt assembly at average pressure range with 800 mm peritoneal catheter; (b) same shunt as
Shunt 5, neonatal low-pressure calibrated at average range for 700 mm peritoneal catheter [Figure
Shunt 5: (a) Neonatal low-pressure shunt assembly at average pressure range with 700 mm peritoneal catheter; (b) same shunt as
Graphs in Figures
All shunts performed within the operational range in their original assemblies. Shunt 1 performed in a lower pressure range, i.e. −200 mm cut off peritoneal catheter, and as a low-pressure shunt, i.e. with a −300 mm cut off. Shunt 2 was manufactured to run at the higher border pressure range to the maximum possible, and it went out of specification with a −300 mm cut off. Shunt 3 was manufactured to run close to the lower border pressure range, and at −100 mm cut off, it was already borderline and with −200 mm cut off, it was definitively in a lower resistive category. Again, shunts 4 and 5 were in a lower resistive category at −200 mm cut off despite their different original peritoneal catheter lengths at the shunt assembly.
Hydraulic disturbances are common after shunt implantation,[
PP = VFP + HP – (DCP + CP) (1)
where PP is the perfusion pressure through a shunt, VFP the intraventricular pressure, HP the hydrostatic pressure of the distal catheter, DCP the distal cavity pressure (in the right atrium or abdomen), and CP is the closing pressure of the valve, which ultimately is an expression of the resistance of the whole shunt assembly. CP is also known as “working pressure” or “performance level” of the valve. CP is submitted to Poiseuille's law, expressed mathematically as Equation (2):
R = 8ηL/πr4 (2)
where η is the viscosity (in centipoise), L the tubing length (in mm), and r the radius of the tubing. Thus, the peritoneal catheter tubing length (L) and the viscosity (η) of fluid within the tubing directly influence the shunt resistance to CSF flow, while the radius of the tubing influences the shunt resistance exponentially and inversely at the 4th potency. The flow (Q) is related to resistance as shown in Equation (3):
Q = PP/Ro (3)
where Q is flow and Ro is the shunt resistance to changes in flow rate.
According to ISO7197/2006[
As can be seen in Figures
Therefore, cutting 200 mm from the peritoneal catheter brought most of the shunts to the limit of the specified pressure range and cutting 300 mm definitively altered the hydrodynamic profile of any shunt tested, at any pressure and with any catheter length. Thus, 200 mm length seems to be the “safe” length limit to be cut in a peritoneal catheter in order to maintain a shunt in its original operational range.
Therefore, component changes which do not respect shunt original dimensions compromise the shunt hydraulic regimen intended by the neurosurgeon for a specific hydrocephalus shunt implant; for revisions, it may affect the hydraulic stability that the patient may have already reached/adapted himself. The fact is that the patient is submitted to a chronic overdrainage and lower pressure status than one would expect, which contributes to the well-known symptoms and signs mentioned by Aschoff et al.,[
The utilization of the same dimensions of ventricular and peritoneal catheters for low-pressure shunts and medium- and high-pressure shunts in adults and children is a common attitude among manufacturers. This attitude exacerbates the imbalance in shunt characteristics in the pediatric population in which low-pressure valves are more likely to be used. The relative resistance responsibility of the peritoneal catheter is exacerbated in low-pressure shunts, more commonly used in infants and children, exemplifying:
Sum R = R1 + R2 + R3 (4)
where Sum R is the total shunt resistance, R1 the ventricular catheter resistance, R2 the valve unit resistance, and R3 is the peritoneal catheter resistance. In our tests, individualized average result for R1=12 mmH2O and the individualized average for R3=28 mmH2O at 20 ml/h (results not shown). This means that for a medium-pressure shunt (such as 80 mmH2O), we would have
Thus, the estimated valve unit resistance should be pre-set at 40 mmH2O, which represents 50% of the total shunt assembly. The peritoneal catheter would represent 35% of the total shunt assembly. However, for a low-pressure shunt (such as 45 mmH2O) we would have
Thus, valve unit resistance should be pre-set at 5 mmH2O, which represents only 11% of the total shunt assembly. In this hypothetic situation, the peritoneal catheter would represent now 62% of the total shunt resistance. The lower the total shunt assembly pressure, the higher the relative responsibility of the peritoneal catheter. Therefore, the act of cutting off the peritoneal catheter is potentially more harmful to the pediatric population than to the adult population. We also must consider that the population of patients will grow, thus potentializing the hydraulic effect.
The operational range for each pressure shunt of this shunt manufacturer is relatively small; there are other manufacturers with a wider operational range, and the lengths would not necessarily apply to them. Still, this does not eliminate the fact that all first-generation shunts are exposed to the physical effects mentioned above, and they should impact approximately the same absolute values.
Also, rig tests are made in a horizontal position, and it is known that shunts not equipped with an anti-gravitational device or siphon control mechanism are strongly affected by the negative outlet pressure. Siphoning (−23 mmHg according to ISO standards) increases dramatically the drainage rate (>1 ml/min). The surgical maneuver of cutting down the peritoneal catheter potentializes the negative outlet pressure by decreasing CP in Equation (1). Overdrainage and associated subdural hygromas are generally considered to be caused by hydrostatically increased flow through the shunt in the upright position, which is in turn caused by increased negative hydrostatic pressure in the distal catheter.[
We advise not to cut more than 20 cm of the peritoneal catheter as this changes the shunt resistance in a major way to maintain a shunt in its original pressure settings. By cutting longer pieces of peritoneal catheter, one would submit patients to a less-resistive shunt than intended and their reasoning will be compromised; medium and long-term patient submission to a low operational pressure range may be an adjunctive to favor overdrainage. The pediatric population is more prone to suffer the effects of inadvertent peritoneal catheter shortening upon shunt implantation. Shunt manufacturers should consider adopting peritoneal catheters according to the age (height) of the patient.
We wish to express our gratitude to Ms Geovania Marquini Laurentino Pereira for her invaluable help in the preparation and revision of this article.
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