1/🧵
In the early days of fellowship, I remember checking our SAH patients’ transcranial dopplers (TCD), scanning the Vmeans & if they were ~<70 cm/sec throughout thinking:
“Great. Perfect. TCDs globally low. Nothing to worry about here!”
🚨Note. This is not a #tweetorial about if large vessel vasospasm is the cause of DCI or just an epiphenomenon OR if treating vasospasm is the way to improve functional outcomes …That is important!... but that is not this tweetorial. pubmed.ncbi.nlm.nih.gov/21285966/
3/ Given #TCDs is a pretty large topic, this @medtweetorial will be told in 3 parts:
Part 1⃣:
⭐️Basic principles of TCDs
⭐️Use of TCDs to detect Vasospasm
Part 2⃣: The Pulsatility Index - why it matters
Part 3⃣: The Utility of TCDs as an ancillary test in BDT
4/ 1⃣st up: Basics
A TCD examination is performed using a 2MHz ultrasound probe.
It transmits u/s to the flowing intracranial vessels.
The change in freq. between the waves emitted and those reflected back is directly proportional to the blood’s velocity (Doppler Shift)
5/ Important to note that the Reflector Speed “Velocity” (cm/s) involves some math… most importantly, it is dependent on the cosine of the angle of insonation 🔽
6/ We assume this angle is 0, as in the pic below⬇️. The prob is directly aligned with the blood flow:
7/ But if the probe is not directly in line with the blood vessel, the cos(x) does not = 1.
And the speed reported is ⬇️⬇️ than actual flow.
Thus, the flow is *AT LEAST* as fast as what’s reported & may be FASTER!
8/ Since blood flow is laminar the reflected arrays have a spectral display representing the mixture of velocities.
Each waveform can be analyzed to calc:
✅Peak Systolic Velocity
✅End Diastolic Velocity
✅Pulsatility Index
✅Time-average mean velocity (Vmean)(MFV)
9/ For a standard vasospasm study, the MCA, ACA and PCA are insonated through the transtemporal widow (A).
The suboccipital window (D) is used for the basilar and vertebral arteries.
10/ If two views are being used to give the details of 5 arteries, how do you know which is which?
Because each vessel has a characteristic waveform; and can be ID’ed by the speed and director of flow + characteristic depth.
11/ Ok. Got it.
🔊TCDs = form of ultrasonography
📈Track the speed of blood by the doppler equation
🌊Generate a waveform b/c of laminar flow
🏄♂️Vessels have characteristic waveforms
12/ 🚨Section 2: TCDs in Vasospasm (VSP) Monitoring
Although TCDs have many uses, they really take center stage in aSAH, where (at least in all the institutions I’ve practiced in), everyone follows the TCD tech around like:
13/ Why because TCDs help detect VSP.
VSP causes narrowing of the arteries (diffusely or focally)➡️an increase in the flow velocity [Poiseuille’s law (🙀)🔽].
All things being otherwise constant (a BIG if, as we’ll see)*, if the Vmean ⬆️, our concern for VSP ⬆️.
14/ At what point is the velocity fast enough to be concerning?
Honestly for how much we all worry about these #⃣, how well the speed correlates w/ DCI is investigated & debated.
Each artery is different.
ExMCA
🔥Mild = 120-149 cm/s
🔥🔥Moderate =150-199
🔥🔥🔥Severe>200
15/ An example:
Post-Bleed Day 1: Nice plump vessels in the DSA, Low Vmean (in the 50s cm/sec)
16/ Compared to Post-Bleed Day 9
Sig narrowing of communicating segment of ICA, M1 and PComm, and PCA. Elevated TCD VMeans (in the 120s/130s cm/sec).
17/ A nice analysis by @samBsnider showed that patients that developed DCI were enriched with earlier increased in mean velocities, and that the risk of infarction increases with vasospasm severity
medrxiv viewer disq.us/t/3wesh7
19/ That all said, it’s INCREDIBLY important to recognize many variables affect blood's velocity:
Such as
✨Age
✨Gender
(not likely to change during hospitalization)
✨Hematocrit
✨Blood viscosity
✨pCO2
✨BP
(highly likely to change during hospitalization)
20/ 🚨 Lots of patients develop anemia during hospitalization.
🚨we manipulate the pCO2 to reduce ICP via vasoconstriction… (hopefully not when a patient is in vasospasm tho!)
🚨Induced hypertension (something we may try in vasospasm) may also ⬆️velocity
21/ How can we account for these changes?
The Lindegaard ratio (LR)
LR = MCA Vmean / ICA Vmean
The above changes should affect the ICA and MCA. But vasospasm ⬆️ flow in the MCA and not the proximal ICA.
22/ LR between 3-6 is a sign of mild VSP
LR > 6 should concern you for severe VSP.
Remember though that a lower but abrupt change from baseline is also concerning!
23/ If you are interested in a more in-depth look at the principles of TCD monitoring, I highly recommend this review by Dr. Farzaneh Sorond (@SorondLab), which is a beautiful overview of all the applications and science behind TCDs. pubmed.ncbi.nlm.nih.gov/23361485/
24/ Finally, started all of this saying “Vmeans <70, we all good!” … so far everything in this tread would confirm that narrative, yes??
1/ A 20 yo woman comes in because she has recurrent headaches. She describes visual aura, photo-/phonophobia & pain that improves with rest. She also describes a sharp, stabbing, lancinating pain from the back of her head during the episodes.
A #ContinuumCase
2/ What is this?
(PS ChatGPT FTW with "what does an aura look like?" !!)
3/ The patient likely has TWO things:
1⃣Occipital neuralgia causing the pain that radiates from the back of her head
2⃣chronic migraine with aura.
Patients with occipital neuralgia OFTEN have both, and occipital neuralgia is very rarely an isolated headache syndrome
1/ 🥳Big News! This is the 1⃣0⃣0⃣th #CONTINUUMCASE!!
To celebrate? A must know dz, bc w/ this disease:
Time is Spine!
A 39 yo woman with Sjogren’s syndrome comes to the ED with sudden neck pain. Then arm weakness. Then leg weakness. All within 24 hours.
Now she can’t urinate
2/ On your exam, mental status=intact. But she has terrible vision in the right eye, which she reports is from a sjogrens attack.
She has 3/5 arm strength, 2/5 leg strength.
As shown above 🔼 she has a longitudinally extensive lesion w/ contrast at C2 and C3.
Is this Sjogrens?
3/ You complete a spinal tap.
‼️There are 120 WBC with a lymphocytic predominance‼️
A 58 yo woman with breast cancer on active chemo presented with shortness of breath.
She was just found to have (A).
Unfortunately, a head CT reveals (B).
They want to know – can she be a/c’ed? A #ContinuumCase
2/ Thoughts?
3/ Why does this feel like such a common conundrum? A few reasons.
1⃣incidence of brain mets may be 🔼 due to improved detection & better control of extracerebral dz
2⃣VTE is common in cancer patients & may also be 🔼 (more detection, longer life expectancy & novel treatments)
1/ A 35 yo M has lower limb weakness & painful hand & foot paresthesias.
EMG suggested axonal neuropathy and a presumed diagnosis of GBS was made.
After PLEX he was not better, instead he was becoming confused & ataxic.
How might a Thanksgiving Turkey solve this #ContinuumCase?
2/ Note: PLEX does not work immediately. In fact, many pts fail to have a response to immunotherapy during their hospitalization. Many continue to progress DESPITE treatment.
This does not mean that the treatment isn’t working. More is not better!
3/ Ok, off my soap box!
As you should for all confusing cases, you go back to the bedside and the patient tells you that over the last 2 months, he’s had increasing stress that resulted in an escalation of alcohol intake and reduced food intake.