Many paramedics argue strongly for including nitroglycerin paste as an arrow in their pharmacologic quiver when treating acute congestive heart failure.
True, you don’t need to break the seal of the CPAP to give it, and you don’t need to use an IV. But this medication hardly belongs in the emergency department, let alone a 21st century EMS rig.
Before I get to the most recent evidence, I first want to highlight this perspective about why prehospital use of paste doesn’t make sense.
First off, let me ask: In what other medical emergency, where a patient is diaphoretic, ghost-white, and tachy-crazy, do we apply an ointment stat!
And why not? Because we already know that pharmacokinetics proves that this is not a “stat!” kind of drug:
- Nitro paste takes a looong while to reach a peak level (about 60 minutes), and
- You end up with pretty weak blood levels with paste. Like, 18 times lower blood levels, compared with IV.
So maybe a poultice of nitroglycerin and tail-of-toad was all the rage back in 1780, but we’ve made a few other medical advances since then…
But even more importantly, dosage is measured in inches?!? No other medication is measured this way! Even in the 19th century, the commonly prescribed (and completely toxic) mercury pills were prescribed in precise weights (e.g. 1 grain). Even if we don’t dose nitro paste in milligrams, you would at least expect that a liquid drug would be dispensed in 3-dimensional units (i.e. volume), or maybe even 2-dimensional units (i.e. area).
Instead, we administer it in 1-dimensional quantities, squeezed out of a fancy ketchup packet. Depending on how you rip the packet, and how thick (and how wide) your “1-inch” glob is, the patient could receive widely different doses.
Utterly nonsensical. It’s like we don’t even care about getting the dose right.
Well there’s a reason we don’t care: It doesn’t work.
This wasn’t randomized or controlled (but then again, the early studies that are usually cited in support of NTG paste weren’t exactly high-quality either). However, the data was collected prospectively.
Physicians in an emergency department enrolled patients who appeared to be in acute CHF, and who had NTG paste ordered for treatment.
Before the paste was slathered on, impedance cardiography (a noninvasive hemodynamic test) was performed. This test is supposed to provide data similar to that which could only be obtained with the use of complicated heart catheters (“Swans”) in the past. They measured not only the mean arterial pressure (MAP), but also systemic vascular resistance (SVR), cardiac output (CO), and thoracic fluid content (TFC), a rough measure of edema in the chest. This testing was repeated at intervals after the paste was applied.
MAP and SVR were the primary outcomes.
Most patients got “1 inch” of paste. Interestingly, while 20% of the patients received morphine, none got CPAP. Old school, brah!
A modest decrease in the MAP was seen after 120 minutes (106 mm Hg –> 99 mm Hg), but it’s unclear if this was because of the NTG paste. Since this study was uncontrolled, this mild improvement could have been the natural course of the episode; i.e. regression to the mean, or “tincture of time.”
The SVR did not show any improvement; also known as afterload, SVR is the main target when treating acute hypertensive CHF, so this is pretty disappointing.
So, basically a negative study. The nitro paste didn’t change the hemodynamics.
So what do you expect us to do now?
Either maximize your use of sublingual tabs or oral spray, or work to get IV NTG included in your protocols. If you are going to break the seal on the CPAP to give NTG tabs or spray, give a good amount, and maximize absorption.
- Hypertensive acute CHF patients require a stout dose of NTG to address the afterload – 2, 3, or even 4 tabs of SL NTG may be needed, and are quite safe.
- These same patients may have (paradoxically) dry mouths, and squirting a bit of saline can enhance absorption of the tabs.
- If you are using the spray, be aware that you don’t have to get under the tongue, you can also paint the top of the tongue as well.
And if you really want to avoid messing with your nice mask seal, and your service can’t afford fancy IV pumps, advocate for “push-dose vasodepressors.” Bolus doses of IV NTG as high as 2 mg, or even 3 mg, have been shown to be both effective and safe.