In this conversation, Alex & I discuss thoracic dissections - specifically, the management of blood pressure and heart rate in an attempt to decrease the shearing force against the walls of the aorta.
Dissection Goals (Anti-Impulse Therapy)
Most sources will state a goal systolic of 100-120 mmHg and heart rate < 60 BPM.
Typical Workflow
Pain First
A large amount of the sympathetic surge patients experience during a thoracic dissection is from the pain. The first step should always be to get their pain down. Pain management is typically my go-to because it is what I have available. I believe Dilaudid is also a great option.
Rate Second
The next step is bringing down the heart rate. Administering a chronotropic targeted beta blocker like Esmolol will help avoid reflexive tachycardia when you reach the vasodilators in step three.
Esmolol Dosing
0.5 mg/kg loading dose (bolus)
25-200 mcg/kg/min Infusion
Blood Pressure Third
With a goal systolic of <120, it is important to see where you land after steps one & two. From my experience, you will still have a very hypertensive patient and need to add on an anti-hypertensive medication. For Alex & I, that drug is nicardipine.
Nicardipine is a dihydropyridine calcium channel blocker. This means that its primary effect is on vasculature and not on heart rate.
Nicardipine Dosing
Start at 5mg/Hr & titrate up by 2.5 mg every 5 minutes until the BP goal is met.
The maximum dose is 15mg/hr.
Once you hit your target BP (which I rarely do with a thoracic dissection), you turn the nicardipine down to 3mg/hr.
Still not hitting your blood pressure goals?
Nitroglycerin
Nitroglycerin infusions seems like a very reasonable option when trying to tackle stubborn hypertension. I came across one article in JEMS that specifically recommended not to use nitro in aortic dissections because of the reflexive tachycardia.
This may be true in EMS if they do not have access to esmolol, but if esmolol is already on (which it should be), the literature does not show nitroglycerin to be any more likely to cause reflexive tachycardia compared to other anti-hypertensive medications.
Dosing
Initial dose starts at 20 mcg/min to a max of 400 mcg/min
Titrations are typically every 3-5 min if using a non-invasive cuff. Some guidelines will allow these titrations to occur more frequently when an arterial line is placed.
Nitroprusside
Nitroprusside is a potent vasodilator used to rapidly lower blood pressure, which is essential for reducing stress on the aortic wall. It's given as an IV infusion. Continuous blood pressure and cardiac monitoring are crucial, and I would be hesitant to have this on during transport without an arterial line.
The main difference between nitroglycerin and nitroprusside lies in their mechanisms of action. Nitroprusside's release of nitric oxide (NO) is not reliant on enzymatic conversion like nitroglycerin. Nitroprusside directly releases nitric oxide, which similarly activates guanylate cyclase, increasing cGMP and causing vasodilation.
Does this mean there is actual nitric oxide in the bottle?
No, nitroprusside does not actually contain nitric oxide in the bottle. Instead, it releases nitric oxide when it is metabolized in the body. When nitroprusside is administered intravenously, it is rapidly metabolized in the bloodstream. The iron-nitroso bond in nitroprusside breaks down, releasing nitric oxide (NO) into the blood.
Dosing
typically starting at 0.3-0.5 mcg/kg/min and can be titrated up to 10 mcg/kg/min based on the patient's blood pressure.
Labatelol
bolus or Infusion?
I personally have used a labetalol infusion only a handful of times for refractory hypertension, and I was not impressed. However, my sample size of experience using this for thoracic dissections is limited. There are also some case reviews of Labatelol causing significant hemodynamic compromise - but these cases are almost always prolonged infusions (>5 hours).
Bolus
Initially, labetalol hydrochloride injection should be given in a dose of 20 mg labetalol HCl (which corresponds to 0.25 mg/kg for an 80 kg patient) by slow intravenous injection over a 2-minute period.
Additional doses of 40 mg or 80 mg can be given at 10 minute intervals until a desired supine blood pressure is achieved or a total of 300 mg labetalol has been injected. The maximum effect usually occurs within 5 minutes of each injection.
Infusion
Draw up 200 mg of labetalol hydrochloride and add it to 250 mL of 0.9% saline or D5W.
This will give you a concentration of approximately 2 mg/3 mL. The diluted solution should be administered at a rate of 3 mL/min to deliver approximately 2 mg/min.
Since the half-life of labetalol is 5 to 8 hours, steady-state blood levels (in the face of a constant rate of infusion) would not be reached during the usual infusion time period (which is probably why I rarely see the effect during flight) The effective intravenous dose is usually in the range of 50 to 200 mg. A total dose of up to 300 mg may be required in some patients.
Managing a thoracic aortic dissection requires a strategic approach to control blood pressure and heart rate, minimizing the shearing forces on the aorta. The typical workflow involves addressing pain first with medications like fentanyl to reduce sympathetic surge, followed by heart rate control with beta-blockers such as esmolol to prevent reflexive tachycardia when administering vasodilators. Blood pressure management is critical, often requiring the use of nicardipine, a calcium channel blocker that focuses on vasodilation without affecting heart rate. While nitroglycerin and nitroprusside are options for persistent hypertension, nitroprusside’s direct release of nitric oxide makes it effective for rapid blood pressure reduction, though careful monitoring is necessary. Labetalol, though not my preferred choice, can be used in bolus or infusion form but may cause hemodynamic compromise with prolonged use. Each medication's dosing must be carefully titrated to achieve the desired hemodynamic targets, ensuring patient safety and optimal outcomes during transport and treatment. As always, this blog does not serve as a protocol or guideline for patient care and EMS should always manage patients based on their guidelines.
References
Aronow W. S. (2018). Treatment of thoracic aortic aneurysm. Annals of translational medicine, 6(3), 66. https://doi.org/10.21037/atm.2018.01.07
Fahed, S., Grum, D. F., & Papadimos, T. J. (2008). Labetalol infusion for refractory hypertension causing severe hypotension and bradycardia: an issue of patient safety. Patient safety in surgery, 2, 13. https://doi.org/10.1186/1754-9493-2-13
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