This document discusses shunt systems used to treat hydrocephalus. It provides a brief history of shunt development, from early unvalved shunts in the 1890s to modern shunts with valves. It describes the physics of pressure, flow and resistance that influence shunt function. Key components of modern shunt systems include ventricular and distal catheters and various valve designs, including fixed differential pressure valves, flow-regulated valves and programmable valves. Problems like overdrainage and siphoning are also discussed.

1. Shunt Systems
Dr SANJOG CHANDANA
(MIND)

2. Introduction
• Insertion of cerebrospinal fluid (CSF) devices for the management of
hydrocephalus is one of the most common procedures performed in
neurosurgery.
• Many CSF shunt components are commercially available
• There is no consensus which devices are the best for a given indication.
• No single shunt or catheter design is suitable for all patients.

3. History
• 1890s, J. Miculicz developed a gold, flanged hollow tube that
diverted CSF from the ventricle to the subgaleal space, but this
valveless device was only rarely effective.
• 1914, Heile described the first diversion of CSF from the lumbar
subarachnoid space to the peritoneum with the use of a valveless
rubber tube,- unsuccessful.
• 1939, Torkilsden described a shunt from the lateral ventricles to the
cisterna magna for obstructive hydrocephalus that was modestly
successful

5. History
• 1949, Matson described a shunt from the lumbar subarachnoid
space to the ureter.
• Modern CSF shunt devices  by the publication of Nulsen and
Spitz’s paper
• Describing a ventriculojugular shunt with a ball-and-spring
differential-pressure valve.

6. History
• The first shunt made with silicone was the Spitz-Holter valve, a
slit valve designed by engineer John Holter for his son, who had
hydrocephalus.
• Pudenz and colleagues  a distal-slit valve and a sleeve
valve, both differential-pressure silicone valves for use in
ventriculo-atrial shunts.
• Initial preferred site for shunt placement was the vascular
system.
• Due to complications and identification of peritoneum site.

7. Shunt hydrodynamics
• Pressure
• Flow
• Resistance

8. PHYSICS

9. Pressure
• Pressure is force (F) per unit area (A).
• For a cylindrical column of fluid, as in a shunt tube
• The pressure at the base of the tube is equal to the weight
divided by the tube’s surface area, which is equated with the
height of the column (h) multiplied by the density of the fluid (ρ)
and the force of gravity (g)
• P = ρ • g • h

10. Pressure
• In shunt systems : Pressure is generally measured in relation to
atmospheric pressure  0.
• Pressure expressed in : mmHG / mmH2O.
• 1 mm HG = 13.65 mm H2O.
• Cerebrospinal space  One column.
• Right atrium – Zero , in supine position.

11. Pressure
• When a person is sitting or standing  Jugular venous pulse.
• The pressure in head is slightly negative, and in the Lumber CSF is
positive.
• The pressure in the abdominal cavity – varies according to body
habitus, abdominal wall tone – can be generally considered to
atmospheric pressure.
• Pleural cavity – negative intrapleural pressure.

12. Pressure
• Shunt systems depends in the difference between the two ends of
thee shunt.
• Which is also responsible for flow in the shunt.

13. FLOW and RESISTANCE
• Flow ( Q ) in a tube is defined as the volume of fluid ( V ) passing a
point in space during a given time (t).
• Millimeters / minute.
• Flow from one end of the shunt system to the other is defined
by the equation Q = ΙP/(RT + RV), where ΙP is the difference in
pressure between the ventricle and distal catheter location,
RT is the resistance of the tube, and RV is the resistance of the
valve.

14. FLOW and RESISTANCE
• Resistance to the flow of fluid through a shunt system (RT + RV)
depends on a number of factors.
• Because flow of fluid through catheters is laminar (smooth),
resistance of catheters (RT) is defined by Poiseuille’s law:
• RT = 8 L u /Pgr4
• R – radius of the tube, L = length of the tube , u = viscosity of
the fluid (CSF ), p = density of fluid, g = force of gravity.

15. FLOW and RESISTANCE
• Lab studies  90 cm long distal catheter – provides an additional
resistance to flow that is approximately equivalent that provided by a
differential – pressure valve.
• The increase in CSF viscosity – (eg. Proteinaceous CSF ) – doesn’t have
a great effect.
• When most proteinaceous – 7 % CSF flow reduced.

16. FLOW and RESISTANCE
• CSF viscosity decreases with increasing temperature; flow rates
at body temperature are approximately 30% higher than at
room temperature.
• important implications in new shunt designs, particularly those
in which CSF flow occurs through a very small orifice
• Shunt catheter resistance rises as a fourth power of the radius.
• Standard catheter diameter of 1.0 to 1.6 mm

17. FLOW and RESISTANCE
• Debris and air bubbles in the shunt valve or catheter
significantly increase turbulence and restrict the diameter of the
lumen, both of which significantly increase resistance to flow.
• The pressure gradient driving CSF flow in a ventriculoperitoneal
shunt system is determined by the formula.

18. • IVP = intraventricular pressure
• Pgh = ( h – difference in vertical height between the head and distal
height)
• OPV= opening pressure of the valve
• IAP = intra abdominal pressure.

19. • In the upright
position, the
predominant
influence on the
pressure gradient
(and therefore CSF
flow) is hydrostatic
pressure, not opening
pressure of the valve

20. SIPHONING
• Once the patient
moves to the upright
position and the
valve opens, the
hydrostatic forces
acting on the shunt
system will
predominate and
result in excessively
high flow rates,
despite negative
intracranial pressure
(ICP).

21. • In a valveless
system, ICP would
continue to fall until
IVP = −ρhg to
balance the siphon
effect.
• Such a drop in ICP
does not occur in a
normal brain because
there is no posture-
related change in the
CSF–sagittal sinus
pressure gradient

22. • “sinking skin-flap syndrome”.
• Low pressure symptoms – 10 %.
• Ventricular collapse.
• Tearing of bridging veins
• Subdural hematoma formation
• Premature suture closure
• Aquired aqueductal stenosis
• Slit ventricle syndrome

23. Components of Shunt systems
• 1 – ventricular catheter - proximal
• 2 – a valve
• 3 – distal catheter.

24. Ventricular ( proximal ) and distal catheter
• Silicone elastomer or Polyurethane
• Mixed with barium / tantalum.
• Entire Barium coated – may leach barium over time ,,
local tissue reaction
Calcification
loss of elasticity
strength of distal catheter tubing
FOCAL TETHERING
FRACTURE
USE OF SINGLE STRIP OF BARIUM

25. • Ventricular end – rounded tip,
multiple holes .
• MC – catheter obstruction.
• Secondary to growth of choroid
plexus and glial tissues.
• Flanged tips – no changes.
• 500 micro m diameters.

27. • Distal catheter
• Blunt / Open end.
• Distal slit valves.
• Medicated with : Rifampicin +
Clindamycin.
• Also carry risk of allowing resistant
strains to emerge.

28. • Parker and colleagues – 2011 : antibiotic impregnated shunt
significant reduction in incidence of in both adult and paediatrics
population.
• Klimo and coworkers : significant benefit 2011.

29. Valves
• Fixed differential pressure valves
• Flow regulated valves
• Programmable valves

30. Fixed differential pressure valves
• First to be developed
• Valves close to prevent flow of CSF when the difference in pressure across
the valve ( driving pressure ) drops below a fixed threshold ( closing
pressure of the valve ).
• When pressure exceeds OPV – valve opens.
• Q = (delta)P / R,
• Q = flow, (delta)P = driving pressure , R = total resistance

31. Differential pressure valves
• Ball in spring
• Diaphragm
• Slit
• Miter
• Despite difference goal to achieve normal ICP.
• Available in Low , Medium, High pressure gradient .

35. • Problems with fixed-pressure valves increased was that of
overdrainage, which occurs by and large secondary to “siphoning.”
• In the recumbent position, the proximal and distal ends of the shunt are
at nearly equal height, and the hydrostatic pressure (ρgh) in the shunt is
more or less zero.
• The shunt will equilibrate (ΙP = 0) when IVP becomes OPV + DCP
• When the proximal end lies at a greater height than the distal end (i.e.,
when the patient sits or stands), siphoning occurs.

36. • Under these circumstances,
the hydrostatic pressure is no
longer zero and contributes to
the driving pressure through
the shunt by ρgh.
• Ultimately, there is rapid flow
of CSF through the shunt to
equilibrate this additional
pressure flow persists until
IVP becomes (OPV + DCP)
− ρgh.
• If the hydrostatic pressure
exceeds OPV + DCP, IVP will
become negative
• Low pressure symptoms – 10 %.

37. Anti siphon devices
• The problem of shunt overdrainage spurred the development of
ASDs over 40 years ago.
• ASDs are coupled ( positioned distal) to a standard differential
pressure valve.
• In general, these devices lie in direct contact with the overlying
scalp, and their flow-pressure characteristics are dependent on the
pressure gradient between the internal lumen of the shunt and the
surrounding atmosphere.
• This pressure differential is transmitted through the skin and ASD
membrane.

38. • When the internal
shunt pressure
falls below the
atmospheric
pressure (e.g.,
negative pressure
created by postural
change to an
upright position),
• The ASD
membrane is
drawn inward,
which increases
resistance and
thus decreases
flow through the
shunt system.

39. Gravitational devices
• Gravitational devices  to prevent overdrainage,
• Their mechanism differs from that of ASDs.
• These devices, which, like ASDs, are add-ons to a differential
pressure valve, use a gravity-dependent mechanism to change
the shunt’s opening pressure based on body position, from
recumbent to upright.
• Switcher
• Counterbalance.

41. Flow regulating valves
• These valves work by increasing the resistance through the valve as
the driving pressure increases.
• Maintains stable flow rate.
• 3 stages of operation.

42. • At low pressures
(stage 1), they
function like low-
resistance
differential
pressure valves,
and flow increases
proportional to the
pressure
differential until a
CSF flow rate of
approximately
20 mL/hr is
reached.

43. • During stage 2, as
the pressure
differential
continues to
increase beyond
this point, the valve
uses a variable
resistance
mechanism to
maintain flow at a
relatively constant
rate regardless of
pressure. This rate
is meant to closely
match physiologic
CSF production and
thereby prevent
overdrainage.

44. • If the pressure
differential
exceeds a set
threshold (usually
300 mm H2O or
so), the variable
resistance
mechanism is
overcome and
the valve again
allows rapid flow
of CSF against
low resistance
(stage 3).

45. • Prone to obstruction – due to small outlets.

46. • Flow restriction may also be achieved by
a device added in series to a differential
pressure valve,
• The Codman SiphonGuard, which is
described as an “anti-siphon and flow-
control device.”
• The SiphonGuard houses two pathways
for CSF flow: a primary, low-resistance
and a secondary, high-resistance
pathway.
• With normal flow, both pathways function
in concert to drain CSF. However, during
excessive flow, only the secondary
pathway is operational, which is said to
decrease the flow rate by 90%.

48. Programmable differential pressure valves
• Identical in function to standard
differential pressure valves.
• Opening pressure is not fixed. –
adjustable.
• Ball in cone and spring mechanism.
• Transcutaneous electromagnetic
programmer is used to set magnetic
rotor to adjust tension on the spring 
there by altering opening pressure of
the valve.

49. • Useful in patient prone to overdrainage.
• Cost factor.
• Magnetic Fields affects.
• Should be verified and readjusted after MRI.

50. Choosing a Valve.
• Neither ASDs nor flow-regulating valves, for instance, have
been shown to prevent overdrainage or lengthen overall shunt
survival in well-designed, prospective studies.
• The Shunt Design Trial randomized 344 hydrocephalic children
to undergo treatment with a standard fixed differential pressure
valve, with a valve containing an ASD (the Delta valve), or with
a flow-regulating valve (the Orbis-Sigma; Cordis, Fremont, CA).
• No significant difference in  the rate of ventricular reduction,
final ventricular size, or overall shunt failure.

51. Choosing a Valve.
• A multicenter, randomized controlled trial comparing the
Codman HAKIM programmable valve to a conventional valve
system found no difference between the two systems with
regard to shunt survival or rate of complication.
• In the absence of a clear universally superior valve design, the
choice of valve should be adapted to the individual clinical
scenario and guided by the surgeon’s sound clinical judgment.

52. Indian shunt systems
• Chhabra shunt system
• Upadhyay shunt system
• Shri Chitra Shunt system

54. Chhabra shunt system
• Slit and spring

55. Z flow

56. SHUNT SURGERY
• Ventriculoperitoneal shuts ( MC )
• Ventriculoatrial Shunts
• Ventriculoperitoneal shunts
• Ventriculosubgaleal shunts.
• Ventricular resorviours.

59. 0utcomes
• In the Shunt Design Trial, only 61% of patients were free of shunt
failure at 1 year and 47% at 2 years.
• After the high failure rate in the first and second years following
shunt implantation, there appears to be a steady decline in shunt
survivability extending for several years.
• Tuli and colleagues287 found that patient age at initial shunt
placement and time interval since previous revision were important
predictors of repeated shunt failure.
• Most cases of shunt failure are related to mechanical failure (e.g.,
obstruction), infection, or overdrainage