Snow Shoveling is Bad Part II: Nitroglycerin

Continuing the discussion of the patient from last week, we turn our attention to the question of whether or not to give the patient nitroglycerin.  As a reminder, we are dealing with a 60-year old male patient complaining of 10 out of 10 chest pain that radiates to his left shoulder, with some air hunger.  The patient is warm, pink, and dry, with a blood pressure is 110/70, a heart rate of 40, a respiratory rate of 20, and a pulse ox reading of 98% on room air.  His 12-lead shows a 2° AV Block with 2:1 Conduction and an inferior STEMI:

Courtesy DogMan41 via Wikimedia Commons, with permission.

So you gave oxygen, aspirin, and fentanyl, plus called ahead to the receiving facility with a STEMI alert.  Would you give this patient nitroglycerin?

After reminding you that I have nothing to do with your reputation, your protocols, or whether you keep your job, I think I would - based on a couple of preconditions.  But he is a close case.  If his systolic blood pressure was over 150mmHg I certainly would.

Paramedics seem to have an irrational fear of NTG administration.  We seem to treat nitroglycerin like it will explode a patient.

Well, apparently someone gave nitro without looking at V4R…
Photo credit: NIST [Public domain], via Wikimedia Commons

I guess it comes from a paramedic school instructor who said that patients would crash their pressure.  That instructor heard that from another instructor.  What does the literature say?

Wuerz’s group performed a 5-month prospective observational study with 300 patients who were given prehospital nitro.  Only four (1.3%) had adverse effects and all of those recovered.  Mean fall in systolic BP was 14 mmHg after the first dose and 8 mmHg following the second dose.  The authors report that nitroglycerin “…seems to be a relatively safe advanced life support drug…”(1)

Engelberg, et al, performed a retrospective review of 1,662 patients receiving NTG over 18 months.  The mean decrease in SBP was 11.8 mmHg and in diastolic BP was 4.0 mmHg.  Twelve patients (0.7%) had serious adverse reactions, including a transient drop of SBP of 100mmHg that responded to fluids.  No deaths occurred.(2)

Herman, et al, published a weird study with hard to follow methodology.  They seem to be trying to check whether providers were following the standing order protocol.  In any case, I think they looked at 310 patients who received NTG.  Of those, SBP decreased in 121 – but the mean initial SBP was 176±44 mmHg and the repeat pressures were 164±41mmHg.  A mean decrease of 12±22mmHg was noted.  Not much difference, huh?  Only one patient became hypotensive, but their pressure returned to normal after 300mL of normal saline.(3)

Clemency, et al, published a report of a system that changed prehospital protocols to allow “high dose” NTG consisting of three sprays at once for some patients based on blood pressure (that doesn't sound all that high to me) and performed a retrospective cohort study to compare pre- and post-nitro vitals.  Seventy-five patients were included.  The average change in SBP following multi-spray NTG was a decrease of 14.7 mmHg with a range of -132 to +59 mmHg. That’s right, an increase of up to 60 points!  Only three patients had hypotension (SBP <100 mmHg) in the post-administration vital signs.  All three patients were over 65 years old, were administered multiple NTG tabs, improved their respiratory status, and had repeat SBP over 100 mmHg.  The incidence of hypotension following multi-dose NTG administration was 3.2%.   Keep in mind, though, that this protocol was for CHF patients with hypertension – not cardiac ischemia patients.(4)

“That’s all well and good, Bill,” you might say, “But what about inferior STEMIs?  Those are specifically dangerous with nitro!”  Not necessarily.  Robichaud, et al, published a retrospective review of 1,466 prehospital STEMI cases, 798 of which received NTG and had complete documentation (what’s the matter with medics and documentation, anyway?).   Hypotension (SBP <90mmHg) occurred in 36 of 461 inferior STEMIs and 29 of 227 noninferior STEMIs.  A 30mmHg or greater drop in SBP occurred in 23.5% of inferior STEMIs and 23.8% of noninferior STEMIs.  There was no statistical difference between inferior MIs and other MIs in regard to complication rate.  The authors state: “Patients with chest pain and inferior wall STEMI…who receive nitroglycerin do not seem to develop hypotension more frequently than patients with STEMI in other locations.”(5)

What this means to me is that nitroglycerin is not necessarily harmful.  But I will agree that it should be used with caution.  It is a beneficial medication that I should want to give to a STEMI patient.  NTG relaxes smooth muscles, which causes vasodilation, reducing both preload (venous effect) and afterload (arterial effect).  The result is to lower the myocardial oxygen demand, thus decreasing cardiac ischemia.  There is also the benefit of dilating the coronary arteries.  It is a good thing. 

Think of it like this.  It can’t be all that crazy-dangerous: People are prescribed NTG and take it on their own.  Without IVs in place!  Before a 12-lead is done!  Oh emm gee!

Hypotension would complicate the care of a STEMI patient.  So I feel more comfortable giving NTG to a STEMI patient if two conditions are met.  First, I like to have a solid, patent IV line that is 18g or bigger.  The patient may need fluids.  Related to giving fluids, I need the patient to have clear breath sounds.  This is especially true with a pressure between 100 and, say, 130 mmHg.  If their breath sounds are clear, I can lay them flat and open the IV line without immediately drowning them.

NTG doesn’t make blood volume permanently disappear – it dilates blood vessels.  So positioning works well to counteract hypotension.  Add a little fluid and we’re good to go.  The studies above looked at the average decrease in SBP: 14 mmHg, 11.8 mmHg, 12 mmHg, and 14.7 mmHg.  Robichaud found that about a quarter of STEMIs saw a drop of 30mmHg or greater.  So I have to be prepared for a 10 to 15 point drop and for a 1 in 4 chance of a 30+ mmHg drop.  The question to ask yourself is whether or not you have 30 points to spare.

I have given NTG to patients exactly like the one in the scenario, with inferior STEMIs.  The worst reaction I saw was that the patient booted so hard the puke hit the back doors of the bus on a horizontal path.  I quit giving him nitro, but his chest pain decreased.  (Man, my partner that day was bent!  In my system, the driver cleans after the call.  He was MAD!)  I’ve had many patients drop their pressure into the 80s systolic.  They lay flat and the IV gets turned on, then their pressure comes up.  I’ve given NTG to inferior, inferolateral, and inferoposterior MIs (which anatomically should involve the RV) and not changed their pressure at all.  I know all of that is anecdotal evidence, but it conforms to the literature examined above. 

Please allow me to include another rant.  I do not place right-sided ECGs.  Sorry.  I know that most medics immediately want to look at Lead V4R after they identify an inferior MI, but I don’t care.  An MI is already present.  Adding another location of the heart doesn’t make me transport even faster.  There is no “super-freaky emergency” transport mode that you can go to above your lights-and-siren.  Why don’t I just assume that the RVMI is there and move on with my job?  As I have explained before, our job is insanely difficult.  Whatever you are doing in a moving, under-heated closet will be done by five or six trained people as soon as you get to the hospital.  Simplify your care on sick people.  When I consider my priorities with an inferior MI patient, right-sided leads rank below a lot of other procedures.  Screw V4R.

1. Wuerz R, Swope G, Meador S, Holliman CJ, Roth GS. Safety of prehospital nitroglycerin. Ann Emerg Med. 1994; 23(1): 31-36.

2. Engelberg S, Singer AJ, Moldashel J, Sciammarella J, Thode HC, Henry M. Effects of prehospital nitroglycerin on hemodynamics and chest pain intensity. Prehosp Emerg Care. 2000; 4(4): 290-293.

3. Herman LL, Koenigsberg M, Ward S, Sloan EP. The prehospital use of nitroglycerin according to standing medical orders in an urban EMS system. Prehosp Disaster Med. 1993; 8(1): 29-33.

4. Clemency BM, Thompson JJ, Tundo GN, Lindstrom HA.
 Prehospital high-dose sublingual nitroglycerin rarely causes hypotension.
 Prehosp Disaster Med. 2013; 28(5): 477-481.

5. Robichaud L, Ross D, Prouix M, et al. Does prehospital nitroglycerin for chest pain cause hypotension in acute inferior wall STEMI? A retrospective cohort study. CJEM. 2013; 15(S1)