Diagnostic ultrasound ( PDFDrive )

1618 PART V Pediatric Sonography
at less than 10 seconds following contrast injection on TCD
examination with Valsalva maneuver is diagnostic of right-to-let
shunt with high sensitivity and speciicity. 29 In pediatric patients,
TCD can detect shunt resolution in patients with a moderate to
large patent ductus arteriosus by a decrease in RI as the duct
closes. 159
Brain Death
Establishing brain death can be problematic, with rapid identiication
useful when considering organ transplant donation. Neurologic
examination, electroencephalography, brainstem-evoked
potentials, and nuclear blood low studies can be used at times
to establish brain death. TCD is another noninvasive tool, which
can be repeated as oten as required, is portable, inexpensive,
and easy to perform. For patients in phenobarbital coma in which
electroencephalography is not diagnostic, TCD is particularly
helpful in demonstrating the severity of cerebrovascular
compromise. 160-162
Ater a severe asphyxiating event, an initial drop in RI may
be caused by vasodilation from loss of autoregulation. As cerebral
edema develops, there is loss of forward diastolic low, followed
by reversal of diastolic low. Cessation of cerebral blood low
then occurs at the microcirculation level. he larger vessels will
distend, then constrict, and eventually thrombose or collapse.
As ICP increases above mean arterial pressure, arrest of cerebral
circulation results in a decrease in antegrade systolic velocity.
Small, early systolic spikes and complete cessation of antegrade
low then develops. Eventually, no systolic or diastolic low can
be detected 142,161 (Fig. 47.23, Videos 47.4 and 47.5).
Sonographic Criteria for Brain Death After
Fontanelle Closure
Sustained reversal of diastolic low
Small, early systolic spikes
No low in middle cerebral artery (MCA), with reversal of
diastolic low in extracranial internal carotid artery (in
patient with previously documented low)
Mean velocity in MCA < 10 cm/sec for more than 30
minutes
here is some concern as to the reliability of TCD sonography
in assessing infant brain death. Many factors are associated with
reversal of diastolic low (thus RI > 1.0) in the neonate, most
oten increased ICP with or without hydrocephalus and a patent
ductus arteriosus 4,163 (see Table 47.4). In neonates, low RI has
been described in patients clinically dead, whereas infants with
high RIs have survived. 163,164 A greatly elevated RI (1-2) in a term
infant with no evidence of hydrocephalus or a patent ductus
arteriosus strongly suggests brain death. 165
Sustained reversal of diastolic low is characteristic of essentially
absent efective cerebral blood low in the adult and older
child 164,166 (Fig. 47.24). In two independent studies of a total of
91 comatose patients, Petty et al. 167 and Feri et al. 168 found a TCD
waveform of absent or complete reversed diastolic low or small,
early systolic spikes in at least two intracranial arteries in all 43
brain-dead patients, but in none of other patients with coma
(age range, 2-88 years). Bulas et al. 169 reported a study in 19
children (aged 4-14 years) who sustained severe closed-head
injury. All seven children with complete retrograde diastolic low
on the initial examination met brain death criteria within 24
hours of that study. Feri et al. 168 and Shiogai et al. 166 described
three unstable patients who briely showed diastolic reversal low
followed by a forward diastolic low in the same waveform who
improved, but of the patients Feri et al. observed, none with
complete reversal of diastolic low survived.
here have been a few reported pediatric cases of mild diastolic
reversed low who later demonstrate recovery of forward diastolic
low and brainstem function. Kirkham et al. 160 therefore suggested
using a direction of low index (DFI = 1 − maximum diastolic
velocity area/maximum systolic velocity area). All children with
substantial diastolic reversed low and a time-averaged velocity
of less than 10 cm/sec over a 30-minute period died. Some
investigators have advocated continuous TCD monitoring. Powers
et al. 161 showed that a mean velocity in the MCA of less than
10 cm/sec for longer than 30 minutes was not compatible with
survival. Qian et al. 170 found that in children, reversed diastolic
low, small systolic forward low, or a direction of low index
less than 0.8 in the MCA for more than 2 hours was a reliable
indicator of brain death. Undetectable low in the brain has also
been described in brain death. 166,168-171 he occurrence of undetectable
MCA low, however, could sometimes be caused by technical
factors, including absence of an appropriate acoustic window.
he use of contrast agents may improve the level of conidence
when no low is encountered.
Some investigators have studied both the extracranial and
the intracranial carotid circulation simultaneously in their evaluation
of brain death. Feri et al. 168 described three waveform
patterns in the MCA as well as in the extracranial internal carotid
and vertebral arteries as speciic for brain death: (1) diastolic
reversed low without systolic forward low, (2) brief systolic
forward low, and (3) undetectable low. Absence of MCA low
on TCD sonography, with a simultaneous recording of complete
reversal of diastolic low in the extracranial ICA, was a reliable
sign of cerebral circulatory arrest. Some investigators have studied
only the extracranial carotid circulation in the neck. Jalili et al. 172
reported 100% speciicity for brain death with bilateral reversal
of diastolic low in the ICA of children with brain death.
he ease of performing TCD sonography and the ability to
repeat the study as oten as necessary also assist in proving the
absence of brain death, particularly when a patient has taken
sedative drugs (Fig. 47.25). It is important to remember that
TCD examination is a proven useful conirmatory examination
and is not used in isolation 173 ; when used in combination with
electroencephalography, speciicity is up to 100%. 174 A recent
study by Sharma et al. 175 evaluated the utility of TCD as a
diagnostic test when clinical diagnosis was not possible due to
confounding factors. hey demonstrated that TCD can help make
an early diagnosis of brain death and can also be used to assess
prognosis. hus, in patients where brain dead criteria are not
met, the presence of a waveform consistent with cerebral circulatory
arrest in at least one major cerebral artery is associated with