Shunt Thrombosis by Dr. Anjuli Sinha and Dr. Sarah Teele.
Hello, I am Dr. Anjuli Sinha and in this video, I'll be discussing shunt thrombosis.
Case study.
First I would like to lay out a case.
Patient is Jessica Simmons and she is a 14-day-old girl who weighs 3.2 kilos.
Her medications include aspirin and digoxin and she has no known drug allergies.
She has pulmonary atresia with intact ventricular septum and a very small right ventricle who
is post-operative day 9 from a single ventricle repair with a 3 and 1/2 millimeter right modified
Blalock-Taussig shunt.
She had a relatively uneventful intra-operative and post-operative course and was extubated
on post-op day 2.
She was transferred out of the CICU on post-op day five and has been mostly working on feeding
and growing on the floor.
Her baseline oxygen saturations have been in the mid 80s on room air.
She hasn't been gaining consistent weight on PO plus NG feeds and the team just fortified
her feeds this morning.
Since then she has been having intermittent episodes of spit up and emesis.
The daytime resident got an abdominal X-ray this afternoon, which showed a nonspecific
bowel gas pattern.
You've just gotten sign out from the day team and are running through vitals and labs.
Her last heart rate was 140, oxygen saturation 82% on room air, respiratory rate was 36,
and blood pressure is 60 over 32 with a MAP of 40.
You're about to go get some dinner and you receive a page from the nurse.
Jessica in 8 East, room 32 with intermittent desats, can you come assess?
As you walk to the room you should generate a differential diagnosis.
First, you should identify normal saturations in a single ventricle patient in order to
identify deviation from normal.
In a normal biventricular circulation, the pulmonary blood flow and systemic blood flow
travel and the series and situations are typically normal.
However, this patient has a single ventricle with complete mixing of blood in the heart
and a single pump sending blood to both the lungs and body, so normal saturations should
range 75 to 85%.
Higher saturations indicate that there may be too much pulmonary blood flow and lower
saturation suggests that there is not enough pulmonary blood flow or there is ineffective
pulmonary blood flow.
The factors that determine how much pulmonary blood flow you have include adequate cardiac
output, a patent shunt, and a difference in downstream pulmonary and systemic vascular
resistances.
Whether your patient has one or two ventricles, when a patient is desaturated you should always
think about the five causes of hypoxemia.
These include V/Q mismatch, shunt, low partial pressure of oxygen, restricted diffusion,
and end stage hypoventilation.
You'll often hear cardiologists state that there are two causes of hypoxemia, which are
shunt and pulmonary venous desaturation.
We tend to lump the other four causes of hypoxemia all together under pulmonary venous desaturation.
Under V/Q mismatch, think of possibilities such as aspiration, especially since this
patient has been vomiting, pulmonary edema, which in this patient may result from excessive
pulmonary blood flow, atelectasis, or a new respiratory tract infection.
This patient has shunt dependent pulmonary blood flow.
If flow across the shunt is restricted acutely or over time, the patient will be hypoxemic.
Etiologies of this may include shunt obstruction, low cardiac output, hypotension, hypovolemia,
and anemia.
Shunt obstruction is an emergency and is the number one thing you want to rule out before
looking for other causes.
Anemia is an odd one on the list but I categorize it as decreased effective pulmonary blood
flow.
Remember that in a single ventricle circulation, each time the heart pumps the blood is choosing
to go to the body or the lungs.
With a higher hematocrit more of that blood going to the lungs can get oxygenated, which
should improve your saturations and your oxygen delivery.
Hypovolemia and low cardiac output similarly can cause desaturation from decreased effective
pulmonary blood flow and potentially increases risk of clot developing in the shunt.
We typically do not worry about the other three causes of hypoxemia but that doesn't
mean they don't happen.
Always keep them in the back of your mind.
Always also troubleshoot mechanical things such as the pulse oximetry.
Is it actually plugged in and picking up?
Changing the pulse ox out and changing its position can be helpful but remember that
if you have poor perfusion your pulse ox will not read either.
While you are on the phone with the nurse, you should ask the following questions.
Is the patient on the monitor?
If not, can you please place them on the monitor and check a blood pressure?
Is there oxygen set up in the room?
What IV access does the patient have?
Once you arrive in the room, the first thing you should do is assess the vital signs.
Red flags would include oxygen sats less than 70% and a normal or narrow pulse pressure.
Normal oxygen sats for this patient are 75 to 85%, so if they are lower you should begin
thinking about the five causes of hypoxemia.
With regards to blood pressure, remember that our patient's initial blood pressure at the
start of the shift was 60 over 32.
Notice that this is a pretty wide pulse pressure with a relatively low diastolic pressure.
This is in fact normal when you have a BT shunt with diastolic runoff from the systemic
to the pulmonary circulation.
As flow across the shunt becomes restricted, there is decreased runoff and the pulse pressure
narrows.
This can be a helpful vital sign trend but it is more reliable with invasive real time
arterial monitoring.
Tachycardia can be a sign that the patient is trying to augment their cardiac output
and this may be a late sign in shunt thrombosis.
It can also represent an arrhythmia or distress.
Perform a targeted physical exam.
Start with observing the mental status, degree of respiratory distress, and looking for cyanosis
while also feeling for distill and central pulses in capillary refill.
You quickly want to listen for a shunt murmur.
I encourage all residents to go listen to their patients with a BT shunt at the start
of their shift and to note with the shunt murmur sounds like, how loud it is, and where
they hear it best.
It is harder to say a murmur sounds different or quieter if you haven't heard it before.
Notice then shunt thrombosis, your systemic output is initially preserved, so your pulses
and capillary refills should remain normal.
Finally, if you have reassured yourself about the shunt murmur, listen to the lungs for
aeration, crackles, and focality.
Based upon your evaluation you may start an initial workup if the patient appears stable.
Never hesitate to call for help early from your fellow or the ICU team.
If you suspect that you cannot hear the shunt murmur but the patient seems stable, call
your fellow.
If you feel comfortable that there is shunt flow, take some time to gather more data,
including what the oxygen saturations have been during the day, the last hematocrit,
the patient's volume status, any signs of respiratory illness, and review the last chest
radiograph as another assessment of pulmonary blood flow.
If you did not hear a shunt murmur or it is significantly quieter and the patient is unstable,
call a code and your fellow immediately.
This is a surgical emergency.
Place oxygen on the patient, obtain emergent IV access, order a bolus of normal saline,
and a bolus of 50 units per kilo of heparin, and get ready to perform CPR if needed while
help arrives.
If you hear a shunt murmur, continue to evaluate for causes of hypoxemia.
Remember, the patient may be progressing towards clotting their shunt so continue to keep that
in your differential.
Augment the patient's delivered FiO2 with blow-by or cannula.
It is rarely wrong to put oxygen on a cardiac patient who is hypoxemic.
Even if the reason for desaturation is fluid overload and the patient really needs diuresis,
you will not worsen them acutely by giving them oxygen.
Response to oxygen also lets you know that there actually is some pulmonary blood flow
and some amount of hypoxemia may be due to V/Q mismatch.
Consider a portable chest X-ray to assess the amount of pulmonary blood flow as well
as for signs of infection.
Consider getting an EKG to evaluate for arrhythmias.
Depending on when the patient's most recent labs were and their presentation consider
sending a CBC and CRP to evaluate for anemia and signs of infection.
A type and screen if the patient does not have an active one and a chemistry to evaluate
for electrolyte imbalances.
If your patient does not have IV access, you should start mobilizing resources to obtain
IV access.
Now, let's return to your patient for a moment.
Upon your arrival, the vital signs are heart rate of 164, oxygen saturation of 62%, respiratory
rate of 32, and blood pressure of 78 over 42.
With these vital signs you will want to apply oxygen immediately and quickly perform a targeted
physical exam.
Upon examination you find the patient to be irritable and slightly blue.
She has clear lungs, no clear shunt murmur, a soft abdomen, normal capillary refill, and
normal pulses.
Difficulty hearing a shunt murmur should be a red flag and you should call your fellow
and activate a staff assist or a code blue immediately to get additional nursing and
physician resources into the room.
Make sure your patient has IV access.
This presentation is concerning for shunt thrombosis, which is an emergency.
Evidence that supports this diagnosis includes desaturation without tachypnea, narrowed pulse
pressure, and preserved cardiac output on exam.
As you are waiting for your fellow to arrive in the room, the vital signs change to a heart
rate of 178, oxygen saturation of 48%, respiratory rate of 50, and blood pressure of 52 to over
35.
If you have not already, activate a code to get additional nursing and physician resources
into the room for help.
In the setting of likely shunt thrombosis with worsening desaturation despite oxygen
therapy and decreasing pulse pressure, you should anticipate the following interventions
will be likely and ask the nursing staff to prepare a normal saline bolus to augment preload,
cardiac output, and any shunt flow possible.
As well as a heparin bolus of 50 units per kilo to decrease further formation of clot.
The situation can rapidly deteriorate and should the patient lose pulses, PALS should
be initiated and the cardiac surgical team should be called immediately to proceed with
re-exploration of the surgical site and ECMO cannulation.
Summary.
Now let's recap.
In a single ventricle patient who has the same pump supplying blood flow to their body
and lungs, their normal situations are expected to be 75 to 85%.
Always think of the five causes of hypoxemia whenever you are evaluating desaturation in
any patient.
But in this patient, this will most likely be due to worsening shunt or V/Q mismatch.
A worsening shunt meaning decreased total or effective pulmonary blood flow can be due
to shunt thrombosis, hypotension, hypovolemia, low cardiac output, or anemia.
Shunt thrombosis is the emergency that you want to rule out.
You should apply oxygen early and listen for a shunt murmur.
An absence of a shunt murmur is a red flag indicating possible shunt obstruction, which
can progress rapidly to a surgical emergency.
If you appreciate a shunt murmur then you can proceed down the pathway of evaluating
for other causes of desaturation.
Thank you for watching this video on shunt thrombosis.