7. Cerebral auto regulation is a mechanism whereby
over wide range, large changes in systemic BP
produce only small changes in CBF.
CPP would have to drop below 40 in a normal brain
before CBF would be impaired,
13. Compliance
reflects the ability
of the intracranial
system to
compensate for
increases in volume
without subsequent
increases in ICP.
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15. The shape of the CSF waveform is similar to
the arterial waveform .
Brain tissue pressure and ICP changes with
each cardiac cycle and thus the ICP waveform
is a modified arterial pressure wave
16-Feb-15ICP MONITORING/CNK 15
22. comprise a steep rise in ICP from near
normal values to 50 mm Hg or more,
persisting for 5–20 minutes and then falling
sharply.
These waves are always pathological and
indicate greatly reduced compliance.
They are frequently accompanied by
neurological deterioration.
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25. These rhythmic oscillations occur every 1–2
minutes.
ICP rises in a crescendo manner to levels 20–
30 mm Hg higher than baseline and then falls
abruptly.
These waves were associated with Cheyne-
Stokes respiration.
Due to a vasomotor center instability
16-Feb-15ICP MONITORING/CNK 25
27. oscillations occur with a frequency of 4–8 per
minute and are of smaller amplitude than B
waves.
More rapid sinusoidal fluctuation (0.1 Hz)
synchronous with fluctuations in arterial
pressure brought about by oscillations in
baroreceptor and chemoreceptor reflex control
systems
Seen in normal ICP waveform so limited
pathological significance.
16-Feb-15ICP MONITORING/CNK 27
35. Cannulated into of lateral ventricles
The catheter is connected to a fluid-filled
system
The transducer converts the measured
pressure to an electrical signal.
the catheter to be zeroed with the transducer
positioned at the level of the center of the
brain (level of foramina of Monroe / tragus)
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37. Advantages
Most accurate
Allows drainage of CSF as treatment or for
culture
Inexpensive
Can give intrathecal antibiotics
Can re-zero in situ
16-Feb-15ICP MONITORING/CNK 37
39. Disadvantages
Higher infection rate (less so with antibiotic
impregnated)
Can block with air, blood and debris
Haemorrhage
Difficulty in accessing with ventricular
collapse
CSF drainage can cause herniation
16-Feb-15ICP MONITORING/CNK 39
40. Inserted through a support bolt or tunnelled
subcutaneous from burr
Common site: non dominant frontal lobes
16-Feb-15ICP MONITORING/CNK 40
41. Advantages:
Can use with collapsed ventricles
Not dependent on fluid coupling
Low infection rate
Disadvantages:
Cannot recalibrate in vivo(issue after 5d)
Cannot drain CSF
Local not global pressure measure
expensive
16-Feb-15ICP MONITORING/CNK 41
44. Based on an assumption that changes in ICP
affect the physical dimensions and/or
acoustic properties of the cranial vault or
intracranial structures .
The common drawback of all these methods
is that they measure only relative changes of
ICP
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45. Ultrasound Time of the Flight Techniques
Transcranial Doppler Ultrasonography
Mechanical / Acoustic Methods
Magnetic Resonance Imaging
Electroencephalography
16-Feb-15ICP MONITORING/CNK 45
46. Ultrasound Time of the Flight Techniques
Transcranial Doppler Ultrasonography
Mechanical / Acoustic Methods
Magnetic Resonance Imaging
Electroencephalography
16-Feb-15ICP MONITORING/CNK 46
47. Ultrasound Time of the Flight Techniques
Transcranial Doppler Ultrasonography
Mechanical / Acoustic Methods
Magnetic Resonance Imaging
Electroencephalography
16-Feb-15ICP MONITORING/CNK 47
48. Ultrasound Time of the Flight Techniques
Transcranial Doppler Ultrasonography
Mechanical / Acoustic Methods
Magnetic Resonance Imaging
Electroencephalography
16-Feb-15ICP MONITORING/CNK 48
49. Ultrasound Time of the Flight Techniques
Transcranial Doppler Ultrasonography
Mechanical / Acoustic Methods
Magnetic Resonance Imaging
Electroencephalography
16-Feb-15ICP MONITORING/CNK 49
CPP-Effective pressure that allows the perfusion of blood through the brain
Brain 80 – 85 %
CSF 8 – 12 %
Cerebral blood volume 5 – 8 %
Total Intra cranial volume 1500 ± 100ml
Upward head elevation <=20 increased ICP
Pathologic States that increase the volume of one component necessitate decrease in the volume of another to maintain normal Intra-Cranial Pressure
Cerebral auto regulation is a mechanism whereby over wide range, large changes in systemic BP produce only small changes in CBF.
CPP would have to drop below 40 in a normal brain before CBF would be impaired,
Causes of ICP divided into vascular and non-vascular
The normal ICP waveform contains three phases:
P1 (percussion wave) from arterial pulsations
P2 (rebound wave) reflects intracranial compliance
P3 (dichrotic wave) represents venous pulsations
The systolic BP is too high
If the systolic BP is too low, P1 decreases and eventually disappears, leaving only P2.
P2 and P3 are not changed by this.
The intracranial compliance has decreased
Hyperventilation
ICP critically high
EVD clogged / kinked
Patient expired
Cannulated into of lateral ventricles
The catheter is connected to a fluid-filled system
The transducer converts the measured pressure to an electrical signal.
the catheter to be zeroed with the transducer positioned at the level of the center of the brain (level of foramina of Monroe / tragus)
Fiber optic-independent of head position drift 0.6mm hg
Cathetor tip-low drift 0.1
Dimensions of the cranium or its structures are determined
measures the transit time of an ultrasound wave and its (potentially multiple) echoes on their path through the cranium
and calculates the corresponding distance(s) using known ultrasound propagation velocities in different tissues (e.g. bone, brain, or fluid)
velocity of blood flow through the major intracranial vessels by emitting a high frequency (>2MHz) wave
ICP can be estimated from the TCD measurements because it impedes the
blood flow and consequently decreases the velocity of blood flow.
indirectly by assessing the elasticity of the biological material in a defined part of the brain
changes in ICP result in a small but measurable skull expansion which creates additional stress within the skull bones and modifies their mechanical properties.
ICP is estimated from the latency of the second negative-going wave (N2) of the visual evoked potential,
Transmission of intracranial pressure (ICP) to the perilymph of the cochlea may occur via the cochlear aqueduct and possibly other routes. Indirect measurement of perilymphatic pressure may be investigated by observing tympanic membrane (TM) displacement during stapedial reflex contraction.
Inward displacement (negative peak pressure on audiogram) is suggestive of high, and outward of normal or low ICP .
linear relationship between ICP and the sheath diameter measured with a trans-orbital ultrasound probe
use of B-scan (or planar) ultrasound which provided longitudinal cross-section images of the optic nerve and its sheath
ONSD be used for identification of patients with intracranial hypertension that requires treatment (ICP>20mmHg, i.e. ONSD>5mmHg) rather than for a measurement of ICP.
measurement of the retinal venous outflow pressure
applying external pressure on the sclera,
while observing the retinal vessels through an ophthalmoscope.
The pressure is gradually increased until the central retinal vein begins to pulsate,point when the applied external pressure nears the VOP and is approximately equal to ICP.
occluding the jugular vein for a short period of time (~ 5 seconds) and measuring non-invasively, with a Hall sensor or an ultrasound transducer, the rate of change of blood flow in the jugular vein upstream of the occlusion.
