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X
- •Foreword
- •Foreword
- •Acknowledgements
- •Contents
- •List of Videos
- •2.1 Introduction
- •2.2 Vascular Anatomy
- •1.1 Introduction
- •1.3 Transcranial Colour-Coded Duplex Ultrasonography
- •1.4 Final Remarks
- •References
- •2.3.1 Anatomic Landmarks
- •2.3.2 Clinical Implications
- •2.3.2.1 Intracranial Hemorrhage
- •2.3.2.2 Epidural/Subdural Hematomas
- •2.3.2.3 Brain Midline Shift
- •2.3.2.4 Hydrocephalus
- •2.3.2.5 Stroke
- •2.4 Conclusion
- •References
- •3.1 Introduction
- •3.2 Anatomy Abnormalities
- •3.4 Setup
- •3.5 The MOTOr Approach
- •3.5.1 Mandibular
- •3.5.2 Occipital
- •3.5.3 Transtemporal
- •3.5.4 Orbital
- •3.5.4.1 Optic Nerve Sheath
- •3.6 Troubleshooting
- •3.7 Summary
- •References
- •4: Optic Nerve Sheath Diameter
- •4.1 Introduction
- •4.2 Anatomical Background
- •4.3.1 Technology
- •4.3.2 Methods
- •4.3.3 Normal Views
- •4.4.1 Limits
- •4.4.2 Safety
- •4.6 Conclusion
- •References
- •5.1 Introduction
- •5.2 Technical Considerations
- •5.2.3 Ultrasound-Related Artifacts
- •5.3 Anatomical Considerations
- •5.4 Clinical Considerations
- •5.4.4 Cerebral Circulatory Arrest
- •5.5 Summary
- •References
- •6.1 Introduction
- •6.3 Training Strategies
- •6.6 Competence
- •References
- •7.1 Introduction
- •7.2 Flow Velocity
- •7.3 Pulsatility Index
- •7.4 Critical Closing Pressure
- •7.5 Autoregulation
- •7.5.1 Static Autoregulation
- •7.5.2 Dynamic Autoregulation
- •References
- •8.1 Introduction
- •8.4.3.2 Data Mining
- •8.7 Final Remarks
- •References
- •9.1 Introduction
- •9.2 TCD: Velocity or Flow?
- •9.3.2 Cerebral Vasospasm
- •9.3.3 Hyperperfusion
- •9.3.4 Hypoperfusion
- •9.3.5 Brain Death
- •9.4.1 Acute Stroke
- •9.4.2 Severe Traumatic Brain Injury
- •9.4.4 Acute Liver Failure
- •9.5 Conclusion
- •References
- •10.1 Introduction
- •References
- •11: Sepsis, Liver Failure
- •11.1 Introduction
- •11.2 Sepsis
- •11.3 Liver Failure
- •11.4 Conclusion
- •References
- •12: Stroke
- •12.1 Introduction
- •12.2 Acute Ischemic Stroke
- •12.2.4 Cerebral Autoregulation
- •12.2.5 Hemorrhagic Transformation
- •12.2.6 Midline Shift
- •12.2.7 Multimodal Neuromonitoring Approach
- •12.2.8 Sonothrombolysis
- •12.3 Conclusions
- •References
- •13: Cardiac Arrest
- •13.1 Introduction
- •13.4 Conclusions
- •References
- •14.1 Introduction
- •14.2 Brain Ultrasonography
- •14.2.2 Prone Positioning
- •14.2.3 ECMO
- •14.3 General Ultrasonography
- •14.3.1 Lung Ultrasound
- •14.3.2 Cardiac Ultrasound
- •14.4 Conclusion
- •References
- •15: Intracerebral Hematomas, Midline Shift, Hydrocephalus
- •15.1 Introduction
- •15.2 Cerebral Hemodynamics
- •15.3 Intracerebral Hematoma
- •15.4 Midline Shift
- •15.5.1 Hydrocephalus
- •15.5.2 Subdural Hematomas
- •15.5.3 Cerebral Venous Drainage Assessment
- •15.6 Conclusions
- •15.7 Future Directions
- •References
- •16: Vasospasm After Subarachnoid Hemorrhage
- •16.1 Introduction
- •16.8 Conclusions
- •References
- •17.1 Introduction
- •17.2 Pseudotumor Cerebri Syndrome
- •17.4 Posterior Reversible Encephalopathy Syndrome (PRES)
- •17.5 Acute Mountain Sickness (AMS)
- •17.7 Hydrocephalus
- •17.11 Conclusion
- •References
- •18: Brain Death
- •18.2 Diagnosis
- •18.3 TCD Procedure
- •18.3.2 Other Tests
- •18.3.2.1 Cervical Colour Doppler
- •References
- •19.1 Introduction
- •19.2.2 Possible Scenarios
- •19.2.3 Explanatory Cases
- •19.2.3.1 Case n. 1
- •19.2.3.2 Case n. 2
- •19.3 Future Perspectives
- •References
- •20.1 Introduction
- •20.4 Tuberculous Meningitis
- •20.5 Cryptococcal Meningitis
- •20.6 Neurocysticercosis
- •20.7 Cerebral Malaria
- •20.8.1 Sickle Cell Anaemia
- •20.8.2 Hydrocephalus
- •20.8.3 Traumatic Brain Injury
- •References
- •21.1 Introduction
- •21.2 Diagnostic Techniques
- •21.2.1 Transcranial Doppler Sonography (TCD)
- •21.2.2 Transorbital Imaging
- •21.2.3 Transcranial Imaging
- •21.4 Intraoperative Navigation
- •References
- •22.1 Introduction
- •22.2 Brain Ultrasound
- •22.4.2 Postpartum Angiopathy
- •22.4.3 Cerebral Venous Sinus Thrombosis
- •22.5 Conclusions
- •References
- •23.1 Introduction
- •23.2.3 Embolism Detection
- •23.3 Clinical Applications
- •References
- •24: Cardiac Surgery
- •24.1 Introduction
- •24.4.1 Preoperative Transcranial Doppler
- •Technique
- •24.7 Conclusions
- •References
- •28: Case 4: aSAH during Pregnancy
- •32: Case 8: Cerebral Circulatory Arrest
- •36: Case 12: Intracranial Hypertension after Ischemic Stroke

78
Specicity
(%) AUC
nICP method accuracy and
correlation measures with ICP Sensitivity (%)
a
prior to shunting was
signicantly increased.
Pre-shunting ICP and PI were
not correlated (R=0.37)
with midline shift as indication
)
of elevated ICP (R=0.66
69
(threshold
of
10mmHg)
99
(threshold
88 (threshold of
10mmHg)
83 (threshold of
20mmHg)
a
(ICP=10.93×PI−1.28)
In the ICP range of
5–40mmHg, the correlation
was R=0.94
formula is:
of
20mmHg)
a
)
a
=0.73
2
In this interval, SD for nICP_PI
was ±2.5mmHg in the ICP
ICP=11.5×PI–2.23
(R
ICP and PI was R=0.64
range of 5–40mmHg
95% CI of ±4.2mmHg
D. Cardim and C. Robba
a
=0.22
2
For ICP ≥20mmHg,
correlation was R=0.82aPI allows early identication of
patients with low CPP and risk
(ICP=23×PI+14)
of cerebral ischaemia
was R
95% CI for a mean ICP of
20mmHg was −3.8 to
43.8mmHg
PI is not a reliable predictor of
ICP
Invasive ICP
monitoring
Epidural PI in patients with elevated ICP
Sample size and
disease
29,
Rainov etal. [59] Investigate a
Method Author Study purpose
Table 8.1 (continued)
Hydrocephalus
possible
relationship
between PI, RI, FV
and ICP changes in
adult patients with
NM Increases in PI were correlated
18, Stroke and
MCA infarction
hydrocephalus.
with clinical
Asil etal. [60] TCD was compared
Intraventricular Correlation between PI and ICP
81 (SAH, TBI
and other
intracranial
relationship
ndings.
between ICP and PI
examination and
neuroradiologic
Bellner etal. [61] Investigate the
disorders)
in neurosurgical
patients.
37, TBI Intraparenchymal Overall correlation between
a tool for detection
of cerebral
haemodynamic
Voulgaris etal. [62] Investigate TCD as
10, INPH Intraparenchymal Correlation between PI and ICP
changes
Behrens etal. [63] Validate TCD as a
method for ICP
determination of
INPH

8 Transcranial Doppler andOptic Nerve Ultrasonography forNon-invasive ICP Assessment
79
88
(threshold
of
20mmHg)
25 (threshold of
20mmHg)
a
No signicant relationships
between PI and ICP when
differences within individuals
or binary examination of PI (PI
<1 and ≥1) were considered
PI and ICP of R=0.36
PI is not a reliable non-invasive
95 (for
detecting
initial ICH)
94 (for
detecting initial
ICH)
nICP similar to measured ICP,
with nICP of 10.6±4.8 and
indicator of ICP in children
with severe TBI
ICP of 10.3±2.8mmHg
PI ≥1.31 was observed in 94%
of cases with initially elevated
ICP, and 59% of those with
0.62 (ICP
≥15mmHg)
a
normal initial ICP values
TCD is an excellent rst-line
examination to screen children
who need urgent treatment and
continuous invasive ICP
monitoring
was R=0.31
0.74 (ICP
≥35mmHg)
a
95% Prediction interval
>±15mmHg
The value of PI to assess nICP
is very limited
in such situations was R=0.70
(continued)
95% CI of ±21mmHg
NM Marginal correlation between
34 Children,
TBI
relationship
between PI, ICP
and CPP in children
with severe TBI
Figaji etal. [64] Examine the
Intraparenchymal
45, TBI Intraventricular Bellner’s equation resulted in
Brandi etal. [65] Assess an optimal
117 Children,
TBI
nICP and nCPP
following TBI using
TCD.
Evaluate the
accuracy of TCD in
Tude Melo etal.
[66]
emergency settings
to predict
intracranial
hypertension and
abnormal CPP in
290, TBI Intraparenchymal Correlation between PI and ICP
diagnostic tool for
nICP and nCPP
children with TBI.
estimation.
Zweifel etal. [67] Assess PI as a
345, TBI Intraparenchymal Correlation between PI and ICP
relationship
between PI and
CVR in situations
where CVR
increases (mild
hypocapnia) and
decreases (plateau
waves of ICP) in
TBI patients.
De Riva etal. [8] Assess the

80
Specicity
(%) AUC
81.1 96.3 0.84
a
nICP method accuracy and
correlation measures with ICP Sensitivity (%)
0)
2
(threshold
≥20cmH
Binomial logistic regression
indicated a strong signicant
relationship between raised ICP
and PI (OR: 2.44; 95% CI:
1.57–3.78)
(CSF pressure) was R=0.65
with rapid elevations of PI.On
Initial 24h
post-injury
82
Initial 24h
post-injury
100 (threshold
a
recording day 4, PI was
reported to be 1.93 (considering
a normal range of 0.6–1.2). ICP
was deemed elevated according
to clinical status (level of
consciousness, headache) and
papilledema
Initial 24h post-injury
Correlation between PI and ICP
was R=0.6
(threshold
≥20
mmHg for
PI of 1.3)
diastolic ow velocity, ICH intracra-
d
≥20mmHg for
PI of 1.3)
Beyond 24h
post-injury
47 (threshold
≥20mmHg for
PI of 1.3)
a
Beyond 24h post-injury
Correlation between PI and ICP
was R=0.38
D. Cardim and C. Robba
Invasive ICP
monitoring
LP Correlation between PI and ICP
Sample size and
disease
78,
Miscellaneous
intracranial
disorders
correlation between
PI with CSF
pressure.
Wakerley etal. [68] Assess the
NM Increasing ICP was associated
Case report,
sagittal sinus
thrombosis
where TCD serves
as an effective tool
for nICP
monitoring.
Wakerley etal. [69] Present a case
Intraventricular/
intraparenchymal
36 Children,
TBI
d
and ICP in children
with severe TBI.
relationship
between PI, FV
O’Brien etal. [70] Determine the
coefcient of determination, RI resistance index, SAH subarachnoid haemorrhage, SD
2
jugular bulb venous blood oxygen saturation, TBI traumatic brain injury
2
Method Author Study purpose
Table 8.1 (continued)
ABP arterial blood pressure, AUC area under the curve, CI condence interval; CT computerised tomography, CSF cerebrospinal uid, FV
Correlation coefcient is signicant at the 0.05 level
nial hypertension, INPH idiopathic normal pressure hydrocephalus, LP lumbar puncture, MCA middle cerebral artery, NA not available, NM not measured, NPV negative predic-
tive value, OR odds ratio, PPV positive predictive value, R correlation coefcient, R
a
standard deviation, SJO

()
Pm
=-
8 Transcranial Doppler andOptic Nerve Ultrasonography forNon-invasive ICP Assessment
81
8.3 Methods Based
ontheCalculation ofNoninvasive CPP (nCPP)
Many authors have also investigated methods
based on the primarily intended calculation of noninvasive cerebral perfusion pressure (nCPP), and
secondarily calculating non-invasive ICP based on
the assumption that “nICP=ABP−nCPP”. nICP
methods based on TCD-derived cerebral perfusion
pressure are listed in Table8.2.
8.3.1 Aaslid etal. [12] (nICP
Aaslid etal. (1986) [12] were the pioneers in
the development of a mathematical model for
non- invasive estimation of CPP based on TCD
waveform analysis. Supported by the knowledge that increased ICP was related to decreases
of the ow waveform in the internal carotid
artery [13], the authors deemed feasible that
less evident changes in the ow pattern could
be detected by more rened methods of waveform analysis. TCD, in such a perspective,
could be used to obtain an estimate of
ICP. Considering CPP as the driving force to
ow through the cerebral vascular bed and the
main factor determining pulsatile dynamics, the
ow would be approximately proportional to
CPP [12].
During increases in ICP, the proportion of the
systolic to the diastolic CPP increases as ICP
approaches the diastolic ABP.Consequently, the
pulsatile component of CPP increases proportionally to its mean value and this would also be
reected in the FV waveform. Thus, the ratio
between mean FV (FVm) and pulsatile amplitude
of FV (f1) would be expected to be related to
CPP.The simplest approach, in this case, would
be using this ratio as an index for CPP.However,
it does not consider changes in the ratio caused
by variations in the amplitude of ABP waveform.
Such limitation was solved by multiplying the
ratio described above by the amplitude of the rst
harmonic of ABP (a1) [12]:
nCPP FV mmHg
=
Aaslid m
´/ fa11
Aaslid
)
This method was tested in patients with supratentorial hydrocephalus undergoing ventricular
infusion tests. The linear regression determined
for nCPP estimation considering all cases was
CPPnCP
11 5.
Aaslid
mHg
In the individual case, there was a strong correlation between nCPP and CPP, R=0.93–0.99. The
standard deviation between nCPP and CPP was
8.2mmHg at 40mmHg, while the mean deviation
was only 1mmHg. Overestimation occurred in two
cases, 10 mmHg and 18 mmHg, respectively.
Underestimation was present in other two cases, 9
and 8mmHg, respectively. For the six remaining
cases, the estimates were within ±5mmHg of measured CPP. The method could differentiate correctly between low (<40 mmHg) and normal
(>80mmHg) CPP in all patients. At higher levels
of CPP, the estimates presented with low accuracy,
showing correct differentiation between CPPs of
70 and 100mmHg in 80% of the cases.
8.3.2 Czosnyka etal. [14] (nICP
FVd
)
Some studies have demonstrated that certain patterns of the TCD waveform, like a decrease in FVd,
reect impaired cerebral perfusion caused by a CPP
decrease [14, 15]. Czosnyka et al. [14] described
this relationship as the following formula:
FV
nCPP ABP
=´+ 14mmHg
FV
d
FV
d
m
The correlation between nCPP and invasively
measured CPP in traumatic brain injury (TBI)
patients was R= 0.73, p<0.001. In 71% of the
examinations, the estimation error was below
10mmHg, and in 84% of the examinations, the
error was less than 15mmHg. The method had a
high positive predictive value (94%) for detecting
low CPP (<60 mmHg). Estimated CPP was
highly specic for detecting changes in measured
CPP over time, caused by either increases in ICP
(plateau waves) or systemic hypotension. In six
patients presenting plateau waves, nCPP compared with measured CPP had an average
goodness- of-t coefcient R2 of 0.82.

82
94 (CPP
≤60mmHg)
D. Cardim and C. Robba
(≥20mmHg)
nICP/nCPP method accuracy and
correlation measures with ICP/CPP AUC PPV (%) NPV (%)
40mmHg
Able to differentiate between low
(≤40mmHg) and normal (≥80mmHg) CPP
in all cases
Low accuracy (80%) at higher levels of CPP
Invasive ICP
monitoring
Intraventricular SD for nCPP estimation of 8.2mmHg at
Sample size and
disease
10, Supratentorial
hydrocephalus
Sensitive to detect changes of CPP over time
(70–100mmHg)
. 96, TBI Intraparenchymal 95% PE for nCPP estimation was >27mmHg
Aaslid
Describe and assess a
method for nCPP
calculation based on
FV and ABP.
Aaslid etal.
[12]
Assess nICP
Czosnyka
etal. [14]
a
Estimation error was less than 10 and
R=0.73
=0.82
2
15mmHg in 71% and 84% of the cases,
respectively
Highly specic for detecting changes over
time: R
Averaged correlation considering day-by-day
variability between CPP and nCPP was
R=0.71
96, TBI Intraparenchymal Correlation between nCPP and CPP was
Describe and assess a
method for nCPP
calculation based on
FV (using the
concept of FVd) and
ABP.
Czosnyka
etal. [14]
a
Mean values of nCPP and CPP were
66.10±10.55mmHg and
and 13mmHg in 89% and 92% of the cases,
respectively
95% CI of ±12mmHg
R=0.92
65.40±10.03mmHg, respectively
Bias of 5.6mmHg and 95% CI of
±17.4mmHg
nCPP:
45, TBI Intraparenchymal nICP:
. 25, TBI Intraparenchymal Error for nCPP estimation was less than 10
FVd
Assess nICP
Schmidt
. 47, TBI Intraparenchymal Correlation between nCPP and CPP was
FVd
Assess an optimal
nICP and nCPP
following TBI using
Assess nICP
etal. [71]
Gura etal.
[72]
TCD.
Brandi etal.
[65]
Bias of 6.2mmHg and 95% CI of 11.8mmHg 0.96
Bias of −5.5mmHg and 95% CI of
±20.6mmHg
28
Intraparenchymal,
10 intraventricular
injury
. 38, Acute brain
FVd
Assess nICP
Rasulo etal.
[73]
Aaslid
Method Author Study purpose
Table 8.2 nICP methods based on non-invasive cerebral perfusion pressure estimation
nICP
FVd
nICP

8 Transcranial Doppler andOptic Nerve Ultrasonography forNon-invasive ICP Assessment
83
0.91
(≥20mmHg)
0.34
(≥20mmHg)
a
(R=−0.17)
R=0.30
nCPP and CPP were correlated (slope, 0.76;
intercept, 10.9; 95% CI, −3.5 to 25.4mmHg)
During hypercapnia:
nCPP and CPP were correlated, but with
increased discrepancy, as reected in
Intraparenchymal Correlation between ICP and nICP was
ischaemic brain
injury after
cardiac arrest
20, TBI Intraparenchymal During normocapnia:
. 100, TBI Intraparenchymal No correlation between ICP and nICP
. 11, Hypoxic-
FVd
FVd
reactivity
2
>0.8
a
Bias of 6.8mmHg and 95% CI ±19.7mmHg
nCPP:
condence interval (slope, 0.55; intercept,
32.6; 95% CI, 16.3–48.9mmHg)
Bias of −6.8mmHg and 95% CI ±45.2mmHg
Bias ± SD of 4.02±6.01mmHg
R=0.85
280, TBI Intraparenchymal Correlation between nCPP and CPP was
. 45, TBI Intraparenchymal nICP:
Edouard
nCPP estimation error was below 10mmHg in
83.3% of the cases
Temporal analysis:
Mean correlation in time domain was R=0.73
(0.23–0.99)
a
Correlation between nCPP and CPP was
Bias of 3.45mmHg (range: 4.69–9.03mmHg)
Mean SD of 5.52mmHg (range: 1.52–
R=0.67
10.76mmHg) and 95% CI of the SD of
1.89–5.01mmHg
Bias of 19.61mmHg
95% CI: ± 40.1mmHg
Temporal analysis:
Mean correlation in time domain was R=0.55
(±0.42)
2
coefcient of determination, SD standard deviation, SAH subarachnoid haemorrhage, TBI traumatic brain injury
Assess nICP
Assess nICP
Cardim etal.
[74]
Cardim etal.
[42]
Describe and assess a
method for nCPP
calculation based on
Edouard
etal. [16]
Edouard
test.
FV and ABP under
stable conditions and
during CO
nICP
Assess nICP
Brandi etal.
[65]
Describe and assess a
method for nCPP
calculation based on
FV (using the
concept of CrCP) and
ABP.
Varsos etal.
[18]
CrCP
nICP
Describe and assess a
method for nCPP
calculation based on
FV and ABP.
Abecasis &
Cardim etal.
[24]
Spectral
nCPP
AUC area under the curve, ABP arterial blood pressure, CI condence interval, FV cerebral blood ow velocity, NPV negative predictive value, PPV positive predictive value,
PE prediction error, R correlation coefcient, R
Correlation coefcient is signicant at the 0.05 level
a

84
()
ë
û
D. Cardim and C. Robba
Furthermore, nCPP was very sensitive to detecting decreases in ABP below 70 mmHg (in ten
patients) with an average R2 of 0.92. A good correlation was found between the average measured
CPP and nCPP when day-by-day variability was
assessed in a group of 41 patients (R=0.71).
8.3.3 Edouard etal. [16] (nICP
Edouard
)
This method is based on a non-invasive
assessment of CPP using a combination of
phasic values of both FV in the MCA and
æ
FV
nCPP
Edouard
=
ç
FV FV
-
md
è
m
ABPm and ABPd represent the mean and dia-
stolic ABP, respectively.
Twenty adults with bilateral and diffuse brain
injuries were included in the study and subdivided into two groups. In group A (N=10), the
comparison was repeatedly performed under stable conditions. In group B (N=10), the comparison was conducted during a CO2 reactivity test.
nICP was not estimated in this study. In group A,
nCPP and measured CPP were correlated (slope,
0.76; intercept, +10.90; 95% CI, −3.50 to
+25.40). The relationship persisted during ICP
increase caused by the reactivity test in group B
(slope, 0.55; intercept, +32.60; 95% CI, +16.30
to +48.90). However, the discrepancy between
nCPP and measured CPP increased as reected
by the increase in bias and variability.
8.3.4 Varsos etal. [18] (nICP
CrCP
)
The concept of critical closing pressure (CrCP)
was first introduced by Burton’s model,
ABP.It was primarily validated in preeclamptic and healthy pregnant women by comparing
nCPP with CPP measured at the epidural
space [17].
In Edouard etal.’s prospective study [16], the
objective was to assess the adequacy of such
method for TBI patients with invasive ICP monitoring, in both a stable state and during a rapid
change in cerebrovascular tone following an
induced alteration in arterial blood carbon dioxide pressure (PaCO2).
The non-invasive CPP (nICP
Edouard
) was calcu-
lated using the following formula:
ö
ABPABP mmHg
´-
÷
ø
md
described as the sum of ICP and vascular wall
tension (WT) [19]. WT represents the active
cerebral vasomotor tone that combined with
ICP determines the CrCP. Clinically, CrCP
represents the lower threshold of ABP below
which blood pressure in the brain microvasculature is inadequate to prevent the collapse and
cessation of blood flow [19]. CrCP can be
assessed non-invasively using TCD, by comparing the pulsatile waveforms of FV and
ABP.Given the relationship with the vasomotor tone of small blood vessels, CrCP can provide information regarding the state of
cerebral haemodynamics and reflect changes
in CPP [19–23].
The conception and assessment of the
model for the non-invasive estimator of CPP
(nCPP
) were performed using a cohort of
CrCP
280 TBI patients, divided into two subgroups:
the formation group with 232 patients
(including 455 recordings) and the validation
group with 48 patients (including 325
recordings):
nCPP ABP
=´ -
CrCP
é
ê
.
ê
ê
()
0 266
.
CVRC HR
×× ×
a
21
ù
ú
-0 734
2
ú
p
+
ú
.
7 026
m
mmHg

ABP
FV
C
CBV
a
1
1
8 Transcranial Doppler andOptic Nerve Ultrasonography forNon-invasive ICP Assessment
85
CVR
=
a
=
a
CVR (mmHg/(cm/s)) represents cerebral vas-
cular resistance, C
(cm/mmHg) denotes compli-
a
ance of the cerebral arterial bed (arteries and
arterioles) and HR represents heart rate given in
beat/s. a1 represents the pulse amplitude of the
rst harmonic of the ABP waveform; f1 the pulse
amplitude of the rst harmonic of the FV waveform; and CaBV1 the pulse amplitude of the rst
harmonic of the cerebral arterial blood volume
waveform (CaBV). The pulse amplitude of rst
harmonics is determined with fast Fourier transformation (FFT).
nCPP
using data from the validation group. nCPP
was tested against invasive CPP
CrCP
CrCP
was correlated with measured CPP (R = 0.85,
p<0.001), with a bias of 4.02±6.01mmHg, and
in 83.3% of the cases with an estimation error
below 10mmHg. nCPP
prediction analysis at
CrCP
low CPP limits (50, 60 and 70mmHg) resulted in
AUCs greater than 0.8 for all limits. nCPP
CrCP
was found to be strongly correlated with CPP
changes in the time domain (mean R = 0.73,
range 0.23–0.99). For each patient, nCPP
CrCP
presented a mean difference from CPP of 3.45mmHg
(range 4.69–19.03mmHg), and a mean standard
deviation of this difference of 5.52mmHg (range
1.52–10.76mmHg). nCPP
could predict CPP
CrCP
between multiple recording sessions with a 95%
CI of 1.89–5.01mmHg.
8.3.5 Abecasis andCardim etal.
(Spectral nCPP) [24]
This recently proposed method is based on
accounting for changes in pulsatile cerebral arterial blood volume (CaBV) applied to the analysis
of a simplied hydrodynamic model of CBF and
CSF dynamics [25–27]. The spectral feature of
the method has some advantages: it creates partial independence from the inaccuracy associated
with zeroing ABP transducers at heart level (a
common clinical practice) and partially elimi-
nates the issue of the time delay between peripheral ABP and FV in the MCA.The dynamical
model of CSF and cerebral blood circulation proposed by Ursino and Lodi [25, 26] is the theoretical basis for the spectral nCPP method; the
former has also been modied by other authors to
incorporate changes in cerebral blood volume
and adapted to nICP or nCPP estimations.
nICP
[28] described in Sect. 8.4 is one exam-
Heldt
ple. Similarly to this method, spectral nCPP produces patient-specic CPP estimates and does
not require calibration datasets of reference
patients.
Abecasis and Cardim etal. [24] assessed spectral nCPP on a retrospective analysis from 19
children (69 TCD recordings). Spectral nCPP
presented good correlation with CPP measure
invasively (R= 0.67 (p< 0.0001)), and a good
mean correlation in time domain (R=0.55±0.42).
Spectral nCPP also demonstrated strong ability
to predict values of CPP below 70mmHg (AUC
of 0.908 (95% CI=0.83–0.98)). The agreement
between spectral nCPP and invasive CPP assessed
by Bland-Altman analysis revealed that nCPP
overestimated invasive CPP by 19.61 mmHg
with a wide 95% CI of ±40.4mmHg.
8.4 Methods Based
onMathematical Models
Associating Cerebral Blood
Flow Velocity andArterial
Blood Pressure
Several authors have proposed mathematical
models that simulate the cerebrovascular dynamics using simultaneous FV and ABP measurements. nICP methods based on mathematical
models are listed in Table8.3.
8.4.1 Black-Box Model forICP
Estimation (nICP
In this model, the intracranial compartment is
considered a black-box (BB) system, with ICP
being a system response to the incoming signal
ABP [29]. This mathematical model originates
)
BB

86
Specicity
(%) AUC
Sensitivity
(%)
CSF
D. Cardim and C. Robba
For Mx: 92
For PRx: 67
For Mx: 97
CSF
CSF
CSF
a
For PRx: 61
and R
CSF
a
nICP method accuracy and
correlation measures with ICP
1.8mmHg
In this cohort a maximum 95% CI of
±12.8mmHg was found
Correlation between nR
was R=0.73
Invasive ICP
monitoring
Sample size and
disease
11, TBI Epidural Bias of 4.0mmHg and SDE of
Epidural Analysis across all records:
21, Different
types of
hydrocephalus
and R
CSF
a
prediction of 2.2mmHg minute/ml
Analysis specic to different
subtypes of hydrocephalus:
Bias of 4.1mmHg and SDE for R
Correlation between nR
was R=0.89
during ICP increase was R=0.98
prediction of 1.7mmHg min/ml
Bias of 2.7mmHg and SDE for R
Intraparenchymal Correlation between nICP and ICP
17, TBI (plateau
(A) waves
.
BB
during plateau
BB
Analysis considering the baseline of
plateau waves:
Bias of 8.3mmHg and SDE of
5.4mmHg
Analysis considering the top of
plateau waves:
Bias of 7.9mmHg and SDE of
4.3mmHg
Increases of nICP and direct ICP
Correlation between nMx and Mx
during plateau waves:
R=0.98 (p<0.001)
Intraparenchymal/
observed in 7
patients)
145 (135 TBI, 10
a
was R=0.90
Correlation between nPRx and PRx
was R=0.62aMedian bias of 6.0mmHg
Only TBI:
Bias of 7.1mmHg
Only stroke:
Bias of 4.3mmHg
intraventricular
stroke)
using nICP
Describe and assess a method
for nICP calculation based on
FV and ABP using a black-box
model.
This study aimed at predicting
Schmidt
etal. [29]
Schmidt
BB
Method Author Study purpose
Table 8.3 nICP methods based on mathematical models
nICP
CSF
the time course of raised ICP
during CSF infusion tests and
its suitability for estimating the
R
etal. [75]
waves of ICP.
Assess nICP
Schmidt
etal. [76]
to adapt to the SCA,
BB
using Mx and PRx as
This study aimed at
Schmidt
parameters
investigating the ability of
nICP
etal. [77]

8 Transcranial Doppler andOptic Nerve Ultrasonography forNon-invasive ICP Assessment
0.83
(≥20mmHg)
0.88
(≥20mmHg)
70
80
83
90
(linear)
BB
0.92
87
resistance to cerebrospinal
CSF
Correlation between nICP and ICP
was R=0.90
Bias of 1.6 and SDE of ±7.6mmHg
Inferred 95% CI of ±14.9mmHg
Across bilateral TCD records:
Correlation between nICP and ICP
was R=0.76
Bias 1.5 and SDE 5.9mmHg
Inferred 95% CI of ±11.6mmHg
On a patient record basis:
Intraparenchymal Across all TCD records:
37 (45 TCD
recordings in
total, 30 bilateral),
TBI
Describe and assess a method
for nICP calculation based on
FV and ABP.
Kashif and
Heldt etal.
[28]
Biases for non-linear models were
<6.0mmHg compared to 6.7mmHg
Correlation between nICP and ICP
was R=0.90 (N=45 recordings)
of the nICP
Inferred 95% CIs for non-linear
models were ≤±10.8mmHg,
Intraparenchymal/
intraventricular
23 (14 TBI, 9
hydrocephalus)
.
BB
Describe and assess a method
for nICP calculation based on
FV and ABP, using an
appropriated model for nICP
Xu etal.
[33]
mining nICP and ICP was R=0.80
compared to 10.6mmHg of the
linear model
9, TBI Intraventricular Median correlation between data
Describe and assess a method
for nICP calculation based on
[38]
Decision curve analysis showed that
method presented a median bias of
57, TBI NM Kernel spectral regression-based
FV and ABP based on the
concepts of data mining.
Describe and assess a method
for nICP calculation based on
Kim etal.
[39]
the semi-supervised method is more
4.37mmHg
Intraparenchymal/
intraventricular
90 (44 TBI, 36
SAH, 10 NPH)
Describe and assess a method
for nICP calculation based on
FV and ABP based on the
concepts of data mining.
Kim etal.
[40]
accurate and clinically useful than
the supervised or PI-based method
coefcient of determination, SDE standard deviation of the error, R
2
; NPH normal pressure hydrocephalus, TBI traumatic brain injury, SAH subarachnoid haemorrhage, SCA state of cerebral
CSF
FV and ABP based on the
concepts of semi-supervised
machine learning.
nICP-derived R
CSF
Heldt
nICP
BB
Modied
nICP
Data mining Hu etal.
Semi-
supervised
learning
Correlation coefcient is signicant at the 0.05 level
Inferred 95% CI was calculated as 1.96*SDE
a
AUC area under the curve, CI condence interval, R correlation coefcient, R
uid (CSF) outow, R
autoregulation
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