Critical Care Mini-Fellowship: Aortic Dissection

Author: Robby Allen

Edited by: Taylor Douglas and Eden Kim

Case

A 56-year-old male with PMH of hypertension, CHF, HIV, and obesity presents to the ED with a chief complaint of chest pain. He states the chest pain awoke him from sleep, radiates to the back and jaw, and began approximately 40 minutes prior to arrival.

BP: 168/70, HR 105, O2 97%, T 97.6F, RR 20

The patient appears uncomfortable, shifting in the stretcher in pain. Lungs are clear with normal work of breathing. Cardiac exam is within normal limits except for regular tachycardia. Pulses are equal bilaterally, and there is no peripheral edema. The abdomen is soft without any tenderness or palpable masses. Skin is intact without any rashes. The patient is oriented without any neurologic deficits.

Problem list?

Chest pain, tachycardia.

Differential

Occlusion MI?

You order an ECG which shows sinus tachycardia without any signs of acute coronary occlusion. Nevertheless, you suspect MI and order serial ECG and troponins.

PE?

You consider pulmonary embolism given your patient has chest pain and tachycardia with clear lungs. You perform bedside ultrasonography which is notable for an absence of McConnel’s sign or D-sign. You skim the post on TAPSE and note it to be >2.0. This evidence is limited, but given these findings and a lack of signs of DVT, you move PE (submassive) lower on your differential.

Pneumothorax?

The x-ray tech is upstairs in the ICU. Fortunately, your handy ultrasound machine is still at the bedside. You whip out the linear probe, lay your patient supine, and note lung sliding at the most anterior chest site, bilaterally.

Tox?

Sympathomimetic, anticholinergic, withdrawal syndromes can all cause tachycardia. Your patient strongly denies any substance use and is thinking clearly without agitation or diaphoresis.

Aortic Dissection?

Could it be? Maybe order a d-dimer to rule it out? Or maybe you’ve read Trevor’s recent post, and you know better. What about overhead paging the x-ray tech to look for the widened mediastinum? You’ve read this save-of-the-month and think “is it my time to be featured on the blog?” Your attending slaps you on the head (gently, we don’t support violence at our residency), and you focus back on the patient in front of you.

Picasso, Michelangelo… We’re talking about Art (lines)

Remember, whenever suspecting aortic dissection, the priority should be to reduce pulsatile pressure and shear stress while awaiting definitive diagnosis and management. Don’t forget to treat the patient’s pain (e.g. fentanyl) as it’s easy, humane, and will decrease the sympathetic response and tachycardia. Prioritize lowering the heart rate as much as hemodynamically tolerable (typically with a rapidly titratable agent like esmolol) to prevent rebound tachycardia. You can then start an afterload reducing agent (ideally titratable like nicardipine or clevidipine).

Now your patient has returned from CTA which confirmed your diagnosis of aortic dissection and you’ve called your CT surgeon colleagues, your patient is on esmolol and nicardipine drips, perhaps we’ll want an accurate method to measure hemodynamics?

How accurate is the typical noninvasive blood pressure cuff versus an arterial line? Most of the data, unsurprisingly, comes from sick patients in the ICU. Examining data from Ribezzo et al, in which only 26% had septic shock (not the population we are examining here), oscillometric metric (OBP) did differ significantly from invasive monitoring (IBP), especially at higher systolic blood pressures. Therefore, it may be reasonable to place an invasive arterial line for more accurate hemodynamic monitoring.

But where to place?

What if a patient has a blood pressure differential (pseudohypotension) between arms? Do you titrate to the higher or lower number?

Going back to pathophysiology, we recall pseudohypotension can occur when the dissection flap extends and can partially occlude the left subclavian artery. The goal of medical management is to limit shear forces, aka the pressure on the aortic wall. This pressure can’t be falsely lowered. Therefore, you’ll want to titrate your pressures to your high pressure between your two extremities. Typically, this will be your right arm. Consider placing an arterial line in your right upper extremity. If unsure, you can still place a blood pressure cuff on the left arm for comparison.*

*This is an opinion only. This subject is not addressed by major guidelines and has no supporting evidence.

Pro (faculty reviewer)- tip: Be sure to infuse your esmolol (or titratable agents of choice) drip in the extremity with the arterial line, contralateral to the extremity with the BP cuff.

The “I’m going to need a change of scrubs” patient

Your nurse runs to you, “doc, your patient’s blood pressure is 60/30.” Having just read about pseudohypotension, you reply calmly “it’s probably inaccurate, check the other arm” as you take another sip of your coffee. The nurse rolls their eyes but walks to recheck the pressure. A moment later they return, now more panicked, “doc, I checked the other arm and it’s 55/20, and they’re not looking so hot.”

You sheepishly apologize to the nurse for “being that resident”, change your soiled pants, and realize that this is true hypotension in aortic dissection. You go back to your differential:

Tamponade:

In a type A dissection, this will be your cause of hypotension until proven otherwise. The most common mechanism will be transudative pericardial effusion resulting from a false lumen extending to the pericardium. Less commonly, the dissection will rupture into the pericardium.

So this is finally your time to take the skills you learned in sim day and perform a pericardiocentesis, right?

Not so fast. Pericardiocentesis in cases of aortic dissection is associated with rebleeding and increased mortality. This should be a temporizing measure, only performed if you think your patient will not make it for definitive repair (OR).

Ok, so you call up to the OR, the CT surgeon is en-route from the country club, but the room won’t be ready for 15 minutes. You present the case and they advise you to go ahead with the bedside, temporizing procedure. 

“Give me a 60 cc syringe! I have to pull off all the blood!” Not so fast…. Only remove small volumes (10-15 cc at a time) to restore hemodynamics. Outcomes are worse with larger aspiration volumes.

MI:

Remember, a proximal ascending dissection should be on the differential for your “STEMI” while the cath lab is getting ready. Hopefully, your cath center has access to a CT surgeon if this diagnosis is made on the cath table…

Aortic valve insufficiency:

If the false lumen of type A ascends proximally, it can protrude into the aortic root, preventing leaflets from closing completely. Aortic regurgitation can result in cardiogenic shock. If unstable, provide supportive care (pressors as last resort) while arranging emergent operative repair.

Aortic Rupture:

As it sounds, this is bad. Unfortunately, even if you can get the patient to the OR, the outcomes are dismal.

Reverse?

It’s not uncommon now to encounter a patient on a blood thinner. In the case of an aortic dissection, it would make sense to want to reverse them… right?

In a type A dissection who will be undergoing operative repair what happens to those patients? Well, patients undergoing cardiopulmonary bypass will be anticoagulated for the procedure. If so, what’s the point of giving an expensive and potentially dangerous reversal agent if they’re just going to be anticoagulated in the operating room?*

*This is an opinion only. This subject is not addressed by major guidelines and has no supporting evidence.

Take home:

1. 1. If you don’t consider aortic dissection, you’ll miss it
2. 2. Treat the higher BP in cases of pseudohypotension
3. 3. Less is more when performing a pericardiocentesis
4. 4. Consider consulting your surgeons before reversing blood thinners
5. 5. Always bring a change of scrubs

References

[1] Winters ME, DeBlieux PMC. Chapter 11: Aortic Catastrophes. In: Emergency Department Resuscitation of the Critically Ill. 2nd ed. Dallas, Tx: American College of Emergency Physicians; 2017.

[2] Hanuscin C. Tricuspid Annular Pulmonary Systolic Excursion (TAPSE). Published July 23, 2020. http://blog.clinicalmonster.com/2020/07/23/tricuspid-annular-pulmonary-systolic-excursion-tapse/

[3] Daley JI, Dwyer KH, Grunwald Z, et al. Increased Sensitivity of Focused Cardiac Ultrasound for Pulmonary Embolism in Emergency Department Patients With Abnormal Vital Signs. Acad Emerg Med. 2019;26(11):1211-20.

[4] Greene A. Ditching the Dichotomous D-dimer. Published June 11, 2020. http://blog.clinicalmonster.com/2020/06/11/ditching-the-dichotomous-d-dimer/

[5] Cerbini T. D-dimer for aortic dissection screening: is it ADvISEDable? A (relatively) brief lit review. Published May 14, 2020. http://blog.clinicalmonster.com/2020/05/14/d-dimer-for-aortic-dissection-screening-is-it-advisedable-a-relatively-brief-lit-review/

[6] Murchison C. Save of the Month: The Case of the Widened Mediastinum. Published June 20, 2019. http://blog.clinicalmonster.com/2019/06/20/save-of-the-month-2/

[7] Farkas J. PulmCrit: A-lines in septic shock: the wrist versus the groin. Published August 13, 2018. https://emcrit.org/pulmcrit/a-line/

[8] Ribezzo S, Spina E, Di Bartolomeo S, Sanson G. Noninvasive techniques for blood pressure measurement are not a reliable alternative to direct measurement: a randomized crossover trial in ICU. Scientific World Journal. 2014;2014:353628.

[9] Swaminathan A, Weingart S. Reversal of Anticoagulation in Dissection. EM:RAP. Published August 1, 2019. https://www.emrap.org/episode/emrap2019august/criticalcare

[10] Isselbacher EM, Cigarroa JE, Eagle KA. Cardiac tamponade complicating proximal aortic dissection. Is pericardiocentesis harmful? Circulation. 1994;90(5):2375-2378.

[11] Hiratzka LF, Bakris GL, Beckman JA, et al. ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM guidelines for the diagnosis and management of patients with Thoracic Aortic Disease: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines, American Association for Thoracic Surgery, American College of Radiology, American Stroke Association, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Society of Thoracic Surgeons, and Society for Vascular Medicine. Circulation. 2010;121(13):e266-e369.

[12] Lo BM. An evidence-based approach to acute aortic syndromes. Emerg Med Pract. 2013;15(12):1-23; quiz 23-24.