General
- Siphon is a term used to describe the flow of liquids through tubes
- It occurs due to the gravitational potential difference between the upper and lower reservoirs leaving reduced pressure in the top of the siphon proportional to the height difference
- In physics this is governed by Bernoulli's principle
- "For an inviscid flow of a nonconducting liquid, an increase in the speed of the flow occurs simultaneously with a decrease in pressure or in the fluid's potential energy"
- Derived from the conservation of energy
- Effectively means that in a steadily flowing fluid, where there is a decrease in pressure, there is an increase in flow velocity
Siphoning in shunts
- Refers to the difference in CSF drainage as the patient moves from recumbency to upright
- Occurs due to the difference in height between the ventricular and peritoneal catheters, and the gravitational effect on the resulting column of fluid
- Does not occur in the normal brain
- Raising opening pressure does not prevent it
- Can result in
- LPH
- Subdural haematoma
- Slit ventricles
- Premature suture closure
- Present as
- Postural headaches:
- No point increasing shunt setting as long as the valve opens there will always be siphoning.
Structure
Right angle design with Codman SiphonGuard
A. Side view
B. Top view
C. Inlet connector
D. Reservoir
E. Direction of flow
F. Inlet valve
G. Valve seat
H. Valve ball
I. Spring calibrating fulcrum
J. Flat spring
K. Spring pillar
L. Titanium base plate
M. O-ring
N. Antisiphon device
O. Valve seat
P. Valve ball
Q. Central passage
R. Spiral passage
Antisiphon devices
- Delta valve
- Integra antisiphon device
- Flow restricted when pressure within device becomes negative
- May be affected by scarring
- Codman valve
- Codman antisiphon device
- Less susceptible to external factors e.g. scarring
Made with Bullet