Seminar on ICP Monitoring - From basics to cutting edge

1. Principles and Techniques of ICP
Measurement
and
Waveform Interpretation
Presented by – Dr. Dhritiman Chakrabarti
Moderated by – Dr. Sudhir Venkataramaiah

2. Introduction
Alexander Monro – 1783 -

3. Francois Magendie - 1842 – Idea of Fluid in brain accepted
George Burrows – 1846 – Reciprocity of intracranial CSF and
Blood volumes
Harvey Cushing – 1926 – Reciprocity of CSF, Blood and
Brain in Intact skull

4. Indications

5. ICP Monitoring Techniques
Invasive:
Based on Technological differences:
1) External Ventricular Drainage (EVD) – Gold Standard
2) Microtransducer ICP Monitoring Devices
Fiberoptic
Strain Gauge
Pneumatic
Based on location:
1. Intraventricular
2. Intraparenchymal
3. Epidural
4. Subdural
5. Subarachnoid

6. Non Invasive:
1. Transcranial Doppler Ultrasonography (TCD) – Based on PI
2. Tympanic Membrane Displacement (TMD)
3. OpticNerve Sheath Diameter (ONSD) – via Transocular USG
4. Magnetic Resonance Imaging (MRI) & Computer Tomography (CT)
5. Pupillometry
6. Near-Infrared Spectroscopy (NIRS)
7. EEG

7. Invasive Techniques
• Type of Monitor?
• Optimal location of sensor?
• Validity of the measured value?

8. External Ventricular Drain
Gold Standard for ICP monitoring.

9. Complications:
1) Hemorrhage 5.7% (of clinical importance 0.61%)
2) Bacterial Colonization (0 – 27%) – Prevention by sterility
while insertion, tunneling (10 cm.), avoid routine sampling,
avoid changing catheter.
3) Malposition.
4) Blockage.
EVD inserted for pressure relief, specially in ICSOL, may cause
displacement of intracranial structures due to magnification
of pressure gradients set up due to pathology.

10. Microtranducers
Strain Gauge
Fiberoptic Device
Pneumatic Sensor

12. Optimal Location of Sensor
Intercompartmental pressure gradients

13. TCD
Based on Gosling/Pulsatility Index
PI= (FVpeak sys - FVend dia)/(FVmean)
Bellner et al – ICP = (10.972 x PI) - 1.284

14. 2 Depth TCD
A. Ragauskas, DSc, et al
Neurology 78 May 22, 2012

15. Optic Nerve Sheath Diameter
Cutoff values, varying between 4.8 and 5.9mm for ICP
estimation.
Corr coeff between 0.46 and 0.74

16. Tympanic Membrane Displacement
Based in intact stapedial reflex and patency of cochlear aqueduct.
High cochlear fluid pressure causes an inward-directed movement of the
tympanic membrane, low cochlear fluid pressure causes an outward
movement.
This movement is measured as the mean volume displacement (Vmean [nL])

17. Oto-acoustic Emissions
• Change in evoked OAE due to displacement of stapes because
of increased cochlear fluid pressure.
• Distortion product otoacoustic emissions (DPOAEs), evoked
by a pair of primary tones – significant phase shift in 750 –
1500 Hz range with ICP changes.
• Corr Coeff. between invasive ICP and DPOAE phase shift in
degrees – Buki et al – 0.77.

18. Near Infrared Spectroscopy
• THx (total Hb reactivity index) – Corr. Coeff between
THI (from NIRS) and ABP.
• PRx and THx show linear correlation with r = 0.56.
• CPPopt found based on lowest value of CPP in PRx -
CPP plot also shows significant correlation with
CPPopt from THx-CPP plot. (r=0.74)
• Thus THI may be used as surrogate for ICP when
calculating CPPopt.

19. Pupillometer
• Hand-held infrared system which automatically tracks and
analyzes pupil dynamics over a 3-second time period.
• Neurologic Pupil Index (Npi) – A scalar value derived
from size, percent constriction, latency, constriction velocity,
and dilation velocity.
• Npi 0 – 5.
• Npi < 3 predictor of increased ICP.
• Npi abnormalities started 16 hrs prior to peak
ICP
Chen et al (2011)
Surg Neurol Int. 2011; 2: 82.

20. EEG for ICP Estimation
Median Frequency
Delta Ratio - ratio of delta
power to the sum of
alpha power and beta
power.
Pressure Index = 1 / (median frequency×delta ratio)

21. ICP Waveform
• Normal ICP waveform:
P1 = (Percussion wave)
represents arterial pulsation
P2 = (Tidal wave) represents
intracranial compliance
P3 = (Dicrotic wave) represents
aortic valve closure

22. ICP Waveform Analysis
Time Domain Analysis:
1) Mean ICP and visual inspection of trends.
2) ICP Wave Trends – Lundberg Waves A, B
3) AMP – Pulse pressure amplitude.
4) RAP – Corr. Coeff. b/w AMP and ICP
5) PRx – Pressure Reactivity Index (MAP-ICP corr. coeff.)
6) PRx-CPP Curve – Optimal CPP
7) ICP Variability Analysis: Successive Variation
8) Detrended Fluctuation Analysis
9) Multiscale Entropy Analysis

23. Frequency Domain Analysis:
1) High Frequency Centroid
2) Slow Wave Power
Fourier Transform: Time domain to frequency domain

24. Mean ICP
(A) Low and stable intracranial pressure (ICP).
(B) Stable and elevated ICP
(C) ‘‘B’’ waves of ICP.
(D) Plateau waves of ICP

25. (E) High, spiky waves of ICP caused by sudden increases in ABP.
(F) Increase in ICP caused by temporary decrease in ABP.
(G) Increase in ICP of ‘‘hyperaemic nature’’
(H) Refractory intracranial hypertension

26. Lundberg Waves A

27. Lundberg Waves B
Two proposed Mechanisms:
1) Rosner’s Theory – Based on ABP variations (akin to A waves, but
on a smaller scale).
2) Neuropacemaker Theory.

28. ICP Pulse Pressure Amplitude
AMP – Amplitude of frequency component of ICP
waveform which corresponds to heart rate.
Used for computing RAP.

29. RAP
• Correlation coefficient between AMP and ICP.
• Represents Compensatory reserve.

30. PRx
• Pressure Reactivity Index: Correlation coefficient between
time averaged slow waves of ABP and ICP.

31. PRx – CPP Curve
The U shaped plot suggests that at too low CPP, vascular
reactivity is impaired, which could produce ischemia, and at too
high CPP vascular reactivity is also impaired, aggravating the
risk of hyperemia.

32. ICP Variability Analysis
Time averaged variability (termed Successive Variation) of
mean ICP values correlates positively with increased mortality.
ICP-SV2 showed a positive relationship with ICP, and hematoma
volume , while the relationship with CPP was inversed.
Cut off value for mortality – 2.8 mm Hg.

33. Breakdown of ICP Waveform
• High frequency components - ?Harmonics
• AMP
• Respiratory Variations
• Slow Waves: IB, B, UB, A

34. High Frequency Centroid
Used as a measure of intracranial compliance.

35. Slow Waves
Infra B (IB) below 8 mHz,
B from 8 mHz to 50 mHz,
Ultra B (UB) beyond 50 mHz up to 200 mHz

36. Is ICP Monitoring Useful?
• There were no RCTs comparing ICP monitoring vs Clinical
examination based management before 2012.

37. The hidden questions that need to be addressed:-
1) Whether fixed mean ICP thresholds are a good guide?
2) Whether change in treatment protocol due to the monitoring has
deleterious effect on outcome?
3) Whether focus on instantaneous ICP readout rather than trends
influences outcome?
4) Focus on ICP based management rather than CPP?
The authors acknowledge that ICP monitoring (as is any monitoring
modality) is just a useful guide for management.
The outcomes are decided by the differences in management
protocols that the knowledge of the said parameter bring about.
This brings the focus of future research on evaluation of the
parameter being used for management and the management
protocol used for treatment.

38. ICP Monitoring in Trauma
Brain Trauma Foundation Guidelines – When to use?
Level II:
Intracranial pressure (ICP) should be monitored in all salvageable
patients with a severe TBI and an abnormal computed
tomography (CT) scan. An abnormal CT scan of the head is
one that reveals hematomas, contusions, swelling, herniation,
or compressed basal cisterns.
Level III:
ICP monitoring is indicated in patients with severe TBI with a
normal CT scan if two or more of the following features are
noted at admission: age over 40 years, unilateral or bilateral
motor posturing, or SBP < 90 mm Hg.

39. BTF Guidelines – What to use?
In the current state of technology (as of 2007), the ventricular
catheter connected to an external strain gauge is the most
accurate, low-cost, and reliable method of monitoring
intracranial pressure (ICP).
Association for the Advancement of Medical Instrumentation
(AAMI) has developed the American National Standard for
Intracranial Pressure Monitoring Devices –
• Pressure range 0–100 mm Hg.
• Accuracy ± 2 mm Hg in range of 0–20 mm Hg.
• Maximum error 10% in range of 20–100 mm Hg.