Clarification on the use of Nitroglycerin by NYS EMTs

The other night one of our hospitals sponsored a CME on cardiac emergencies.  A local cardiologist spoke to a group of EMTs from New York and New Jersey about the in-hospital management of the STEMI (ST elevation myocardial infarction) patients at this hospital.  In the course of the discussion the use of nitroglycerin was discussed.  In less than a minute it became clear that confusion exists on the pre-hospital BLS use of nitroglycerin in NYS by EMTs. Hopefully this post will clear up some of the confusion.

Let’s review:

The NYS BLS Protocol (Adult Cardiac Related Problem) allows NYS EMTs to assist a patient with the use of THEIR previously prescribed nitroglycerin in certain situations.

This means that we are assisting a patient with taking their own prescribed nitroglycerin. NYS EMTs and NYS BLS EMS units do not carry nitroglycerin.  If the patient does not possess their own prescribed nitroglycerin at the time of their cardiac event we would therefore be unable to assist them in taking nitroglycerin. In other words, you cannot use anyone else's nitroglycerin on your patients.

The situations where it may appropriate for NYS EMT's to consider the use of nitroglycerin include Angina Pectoris and Acute Myocardial Infarction.

So to assist a patient with nitroglycerin the following criteria should exist:

1.  The patient should be experiencing signs and symptoms of symptomatic Angina Pectoris or Acute Myocardial Infarction.  This may include but is not limited too.  Chest, back and/or abdominal pain and/or discomfort from myocardial ischemia. (Lack of O2 to the myocardium), difficulty in breathing, nausea / GI complaints, diaphoresis (cool, pale, clammy skin), Always beware of atypical presentations in some patients, especially the elderly, diabetics, and women. Some patients may only present with fatigue, weakness, mild shortness of breath, and pain to the jaw / arm.

2.  The patient must consent to treatment.

3.  The patient's systolic blood pressure must be higher than 120 mmHg.

4.  The patient must not have taken Sildenafil citrate (Viagra, Levitra, or Cialis) or similar medications within 72 hours. These medications are primarily used to treat erectile dysfunction in males; but may used to treat pulmonary hypertension in both males and female patients.

5.  Use nitroglycerin with caution in suspected nitroglycerin.   An inferior wall myocardial infarction occurs when the inferior myocardial tissue supplied by the right coronary artery (RCA), is injured due to thrombosis of that vessel. When an inferior myocardial infarction extends to posterior regions as well, an associated posterior wall myocardial infarction may occur. Inferior wall myocardial infarction involves the lower (inferior) wall of the heart which sits above the diaphragm / stomach. Because of proximity to the abdomen many patients experiencing an inferior wall MI have more abdominal versus cardiac complaints. The reason why nitroglycerin should be used with caution is that approximately 40 % of inferior wall MIs have what is called right ventricular extension.  Right ventricular extension means that the myocardial damage has extended from the inferior wall to include the right ventricle also. The right ventricle is pre-load dependent.  Pre-load is the amount of de-oxygenated blood that is returning to the heart via the inferior and superior vena cava. Nitroglycerin causes vaso-dilation, which pools blood in the venous system.  This pooling reduces the amount of blood available to return to the heart (pre-load).  If we reduce pre-load we reduce cardiac output which leads to decreased blood pressure.  Reduction to pre-load and blood pressure may reduce blood flow to the coronary arteries which may lead to larger damage in the myocardium. To summarize, if we give nitroglycerin to a patient who is experiencing an inferior wall MI we may drop perfusion to the heart muscle which may cause a larger amount of heart damage.  

The next question should be:  How do we suspect an inferior wall MI on a BLS level?  If you have a suspected AMI patient who has more GI / Abdominal complaints then chest complaints think inferior wall.  There may also be an associated bradycardia with inferior wall MI.  Most AMI patients have an increase in their heart rate to the chest pain and anxiety about their medical condition. Some inferior wall MI patients will have bradycardia (HR 50 to 60) from ischemia to the AV node or increased vagal tone. Suspected AMI patients with abdominal symptoms / Complaints and bradycardia should receive nitroglycerin with extreme caution even if their blood pressure is above 120mmHg.  If in doubt about what to do, start transport, and contact medical control while enroute to your PCI (angioplasty) center.  What’s amazing is that the NYS protocol does not even address this, nor do most BLS instructors even mention this.

Some facts about inferior wall MIs:

• Inferior MIs account for 40-50% of all myocardial infarctions.
• Up to 40% of patients with an inferior STEMI will have a concomitant right ventricular infarction. These patients may develop severe hypotension in response to nitrates and generally have a worse prognosis.
• Up to 20% of patients with inferior STEMI will develop significant bradycardia due to second- or third-degree AV block. These patients have an increased in-hospital mortality (>20%).
• Inferior STEMI may also be associated with posterior infarction, which confers a worse prognosis due to increased area of myocardium at risk.

6.  If symptoms persist you may administer up to 3 doses of nitroglycerin, 5 minutes apart, as long as the B/P remains above 120 mm/Hg systolic.  Just remember the more nitroglycerin a patient receives the more likely it is for them to drop their blood pressure.

7.  Never give nitroglycerin to a standing patient, wait to get them on the stretcher. 

8.  Sublingual nitroglycerin is carried in spray or tablet (pill) form.  Tablet form does not have a great shelf life. One spray or one tablet is the same dose (0.4mg or 1/150th of a grain).  If a patient took their nitroglycerin prior to your arrival and does not have relief from their symptoms check that they took it right way and that it is not expired.  Potency may also be an issue.

9.  Potent (good) nitroglycerin usually will cause a mild tingling / burning sensation under the tongue if it is in the tablet form. Nitroglycerin spray or tablet usually causes a mild headache.

10.  Beside nitroglycerin the treatment for the AMI patient should include:

     a. Early notification and transport to a PCI (angioplasty) center.

     b. Position of comfort.  (To help relieve anxiety)

     c. O2 therapy.  Even though it may not be clinically correct, NYS protocol calls for high concentration O2. See my early post: EMS Myth -There's no such thing as too much oxygen. What we should be saying: - Can Oxygen Hurt??? For more info.

    d. Aspirin.  See my early post on Pharmacology for more info.

Hope this help.  If you have any questions or comments please reply to this post.

Frank