TCD Flashcards
Transcranial Doppler free hand method uses a
2MHz pulse wave Doppler with spectral analysis.
Angle of incination at 0 degrees.
TCD
Detects intracranial stenosis and occlusion.
Asses collateral circulation and arteriovenous malformation.
Evaluate onset, severity, and time course of vasoconstriction.
Provide info related to blood flow patterns in patients with sickle cell disease.
Evaluar patients with suspected patent foramen ovale, suspected brain death, suspected intracranial pressure.
Limitations
Hyperostosis (thickening or temporal bone) 10% of population
Recent eye surgery may r/o transorbital window.
Operator dependent. Vessel identification.
TCD used for
Micro emboli detection for carotid surgery, coronary bypass graft, and stenting.
Cerebral auto regulation- vasoreactivity to Co2
Monitoring of real time blood flow to brain during surgical procedures
Head gear for TCD bilateral monitoring
Records bilateral hemispheres, long periods of spectral Doppler info.
Receives signal from middle cerebral arteries
TCD access windows
Transorbital
Submandibular
Suboccipital / transforaminal
Transtemporal
Transtemporal
Probe placed ant to ear and sup to zygomatic arch in thinnest portion or skull.
Can see: MCA ACA PCA TICA (terminal ica) PcoA and AcoA only if functioning as collaterals
3 areas:
Anterior
Middle (preauricular)
Posterior
Transtemporal window
MCA. 3-6cm depth, toward, 55+|-12 cm/sec
MCA/ACA 5.5-6.5cm, bidirectional
ACA (A1) 6-8cm away 50 +|-11 cm/sec
PCA (P1) 6-7cm, towards, 39+|-10 cm/sec
TICA 5.5-6.5cm, towards, 39+|-9 cm/sec
Transforaminal/suboccipital window
Transducer placed at concave area at neck/back of head at the foramen magnum.
Rt and left vertebral, 6-9cm depth, away, 38+|-10cm/sec
Basilar 8-12cm depth, away, 41+|-10cm/sec
Transorbital window
Transducer placed over closed eyelid.
Carotid siphon can be imaged at specific depths and ranges.
Carotid siphon 6-8cm depth:
•supraclinoid: away, 41+|-11cm/sec
•genu: bidirectional
•parastellar: towards 47+|-14cm/sec
Ophthalmic artery: 4-6cm depth, toward, 21+|-5 cm/sec
Carotid siphon
Parastellar
Genu (bend)
Supraclinoid portion (distal)
Submandibular window
Under jawline. Evaluates distal extra cranial ICA to provide velocities to get the extra cranial to intracranial ratio.
Transcranial Imaging TCI
Aka
Color coded duplex sonography
Bigger transducer. 1.8-2.5MHz. Dec Doppler sensitivity. Higher failure rate than TCD
Visualize location and course of intracranial vessels.
TCI
Color, pulses, b mode
MCA not always identified with TCI compared to TCD.
Images vasculature and brain parenchyma
Access windows: transtemporal and suboccipital windows.
Collateral pathways occur through circle of Willis when
Proximal pressure drops from stenosis or occlusion of carotid or vertebral arteries.
Little to no flow seen in communicating arteries unless used as collateral pathways.
Cerebral aneurysm
Ruptures 28,000 people annually
Mortality rate >50%
Survivors face aneurysm clipping/coiling
At risk for subarachnoid hemorrhage SAH
Vasospasm
Transient narrowing of intracranial arteries. Occurring and Resolving within 2 weeks of initial bleed.
Complication if subarachnoid hemorrhage related to rupture of an intracranial aneurysm, AV malformation, hypertensive bleed, or head trauma.
1/3 of permanent neurological deficits
Ipsilateral or contralateral to side of aneurysm or bilaterally
May involve any of the major intracranial arteries
If velocities increase in a TCD, patient will most likely be treated urgently to negate the development of neurologic events.
Cerebral vasospasm symptoms
Confusion Dec level of consciousness Goofy Stroke Death
Hemispheric ratio aka delindenguard ratio
Vasospasm criteria
Degree of vasospasm, Time Avg Mean Vel cm/sec, ratio
- Normal, <120cm/sec, <3
- Mild, 120-149, >|= 3
- Moderate, 150-199, >3
- Severe, >|=200, >|=6
- Hyperdynamic flow >|=80, < 3 (secondary to low hematocrit, volume expansion, and HTN)
Rato = TAMV of MCA / ipsilateral distal extra cranial ICA TAMV. Both obtained with submandibular approach TCD.
Patent foramen ovale
Hole between Rt atrium and Lt atrium. (Incomplete closure of foramen ovale)
TCDs pick up high intensity transient signals (HITS) from agitated saline (contrast agent) in patients with a PFO.
Pt wears headgear to evaluate bilateral MCA. Injected agitated saline into vein, either resting or valsalva maneuver performed. Evaluate for micro bubbles or microemboli, grading criteria based on number of hits.
Emboli shower.
Cryptogenic Stroke
Stroke of unknown origin. 40%.
Suspicion of paradoxical brain emboli arising from venous circulation.
Emboli from venous system can pass to the arterial circulation through a PFO.
Brain death
TCD can confirm cerebral circulatory arrest
Correlates well with electro encephalography
4 characteristic stages of brain death:
•inc pulsatility with end diastolic reaching zero
•oscillating flow (reverberatory flow). Forward and reverse flow that are equal.
•narrow, reduced velocity systolic spikes
•no flow signal (can be due to absence of temporal bone window, and requires confirmation by investigating extra cranial carotid and vertebrals. Study performed twice, 30 mins apart.
Intraoperative monitoring with TCDs
Identifies flow abnormalities during cerebrovascular/ cardiovascular procedures.
(Examples: endarterectomy, carotid stenting, PFO closure, and cardiac surgery)
Continuous monitoring of MCA
Cerebral emboli can be
- Air bubbles
- Particulate matter
- Microemboli signals MES
- High intensity transient signals HITS
Emboli shower
Flow reversal in ophthalmic artery (away from transducer in TCD) would indicate
Stenosis or occlusion in ipsilateral ICA with ECA to ICA collateral flow
