Transcranial Doppler Ultrasonography Holds Promise
in Monitoring Patients with Traumatic Brain Injury
By Katherine Salisbury and Aarti Sarwal, MD
Traumatic brain injuries
(TBI) are a major cause of
hospitalization and death
in the United States, with an
estimated 1.7 million people
sustaining TBIs annually
and 52,000 of those dying
from TBI-related factors1.
While the hemodynamic
and neurological responses
depend upon severity,
patient risk for significant injury does not conclude after primary
impact. Modern TBI management centers around the need to reduce
risk associated with secondary brain injuries resulting from a variety
of factors, including hypoxia, hypotension and ischemia2. Up to 80
percent of TBIs are initially diagnosed as mild to moderate (typically
characterized by a Glasgow Coma Score of 9-15), but neurological
deterioration may continue to occur for days following initial trauma2.
Currently, a number of physiological measurements are used in TBI
patients as surrogates for titrating management to prevent secondary
brain injury. Cerebral perfusion pressure (CPP) is one such marker
that reflects oxygen and metabolite delivery to the brain. After TBI,
the homeostatic mechanisms autoregulating cerebral perfusion can
be lost, making the brain susceptible to adverse blood flow changes.
Management paradigms targeting optimal CPPs have been shown
to reduce mortality3. However, CPP monitoring requires an invasive
monitor to track intracranial pressure (ICP). Other physiological
parameters like clinical determination of the pressure reactivity
index (PRx), a continuous autoregulatory capacity measure shown
to correlate to TBI outcome have also not translated into widespread
clinical practice due to invasive nature. Transcranial Doppler
(TCD) offers a potential noninvasive way to measure CPPs in such
management paradigms as well offer corresponding metrics like the
mean Flow Index (Mx) which is the moving correlation coefficient
between mean flow velocity on TCDs and patient’s CPP5.
In addition to loss of autoregulation, one other pathological perfusion
abnormality hypothesized in severe TBI is the triphasic hemodynamic
response. The response initializes on Day 0 of injury with a period
of hypoperfusion subsequently followed by hyperemia (Days 1-3)
and then vasospasm (Days 4-15)4. Despite published reports, limited
attempts have been made to tailor treatment paradigms in severe TBI
that take in account this perfusion pattern. Better characterization of
this response could allow for more targeted and timely therapies for
these patients. TCD also offers a great noninvasive diagnostic platform
to characterize this triphasic response as a potential target for therapies
and continues to be underutilized.
Transcranial Doppler ultrasound (TCD) is an accurate, non-invasive,
bedside modality capable of continuously monitoring changes
in cerebral blood flow velocities (CBFV) through insonation of
intracranial vasculature6. Hemodynamic indices, including the
Pulsatility Index (PI) and Lindegaard index (LI), can be calculated
from measured TCD velocities. These indices can serve as indicators
of distal resistance or vasospasm. Despite its presence in most
healthcare systems, TCD is not common within current guidelines
for severe TBI diagnosis and care2. However, prior studies have
demonstrated the potential for TCD in guiding TBI treatment in
adult populations1, 2, 5. Early TCD goal-directed therapy can help
restore normal CPP and reduce risk of secondary brain injury2. A
strong relationship has also found between PRx and TCD-derived
indices like the mean Flow Index (Mx), predicting a future ability
to be able to calculate PRx using non-invasive means5. Additionally,
initial detection of hypoperfusion or vasospasm using TCDmeasured
changes in middle cerebral artery (MCA) blood flow
velocity has been shown to be a strong predictor of severe TBI
patient outcome1. High PI values have also been associated with
elevated ICP although this has not been established with certainty2.
Given the potential of use of a noninvasive monitor like TCD and
its utility in managing cerebral hemodynamics, more research is
needed into the clinical application in TBI.
At Wake Forest Baptist Health Center, as a summer research intern, I
began a research study with the intent to provide better insight into
the cerebral hemodynamic patterns after TBI and emphasize the
incorporation of TCD into routine clinical evaluation of such patients.
All adult patients presenting to the neuro-ICU or trauma-ICU at our
academic medical center were screened for diagnosis of TBI, which was
confirmed using CT scans providing radiographic evidence of head
injury. Patients who met a set of eligibility criteria were consented and
enrolled in the study. A TCD was performed on these patients using
a continuous TCD machine utilizing a headset with simultaneous
insonation of the left and right middle cerebral arteries (MCA)
creating continuous waveform recordings of cerebral blood flow
velocities (CBFV) (See Figure). As the study is actively enrolling, we
hope to analyze any abnormalities in CBFV recordings to gain better
insight into the brain’s triphasic response after TBI and illustrate the
effectiveness of TCD in monitoring these changes. I hope to present
results of this project at a future Neurocritical Care Society meeting.
Figure 1: Representative snapshot of normal transcranial
Doppler spectrogram obtained on a continuous transcranial
Doppler assessment.
Katie Salisbury is a rising junior at the University of North Carolina at
Chapel Hill who is interested in pursuing medicine as a career following
graduation. She spent the summer of 2018 as a research intern at the
Neurocritical Care Unit at Wake Forest Baptist Medical Center to learn
about clinical research in neurocritical care.
Bibliography
1. Ziegler, D., et al., Use of Transcranial Doppler in Patients with Severe
Traumatic Brain Injuries. J Neurotrauma, 2017. 34(1): p. 121-127.
2. Bouzat, P., M. Oddo, and J.F. Payen, Transcranial Doppler after
traumatic brain injury: is there a role? Curr Opin Crit Care, 2014.
20(2): p. 153-60.
3. Rosner, M.J. and S. Daughton, Cerebral perfusion pressure
management in head injury. J Trauma, 1990. 30(8): p. 933-40;
discussion 940-1.
4. Martin, N.A., et al., Characterization of cerebral hemodynamic
phases following severe head trauma: hypoperfusion, hyperemia,
and vasospasm. J Neurosurg, 1997. 87(1): p. 9-19.
5. Zeiler, F.A., et al., Estimating Pressure Reactivity Using
Noninvasive Doppler-Based Systolic Flow Index. J Neurotrauma,
2018.
6. Reuter-Rice, K., Transcranial Doppler Ultrasound Use in Pediatric
Traumatic Brain Injury. J Radiol Nurs, 2017. 36(1): p. 3-9.
Katherine Salisbury Aarti Sarwal, MD
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