Funny, I didn t realize how much baseball had permeated our lives until I started writing EMS protocols. I m familiar with the "base system" used to judge progress on a date and the "three strikes" laws promulgated by states to discourage repeat criminal offenders, but did you know we also apply baseball logic to nitroglycerin administration in EMS?
The only explosive used in EMS, sublingual (SL) nitroglycerin, has long been a mainstay of prehospital therapy for patients with chest pain. Nitroglycerin (NTG) acts as a systemic vasodilator, with especially prominent activity within the coronary vessels that provide blood flow to the heart. When someone suffers from ischemic chest pain due to lack of cardiac blood flow, the goal of immediate care is to restore the oxygen supply to the heart. We do this by enhancing blood flow to the heart with NTG and by administering oxygen, maximizing the oxygen content of the blood.
So if you have chest pain, NTG is a pretty good drug. Like all drugs, it has side effects that limit its administration. These include hypotension and severe headache. One great thing about nitroglycerin: it is very short acting. If a serious side effect, such as hypotension, occurs, you simply stop giving the drug and the effect goes away.
What does baseball have to do with all this? Somewhere along the line, medicine assigned a "three strikes rule" to nitroglycerin use. Many prehospital systems are limited to the administration of three NTG tablets in the field. To my mind, this is a practice without basis, and you can find the clearest argument against it right in the hospital emergency department.
Let s say a 65-year-old man comes into the ED complaining of severe substernal chest pain. Just to make it easy, we ll say he has a known history of angina and this episode is like his past episodes. We ll even give him a bypass surgery or two and a zillion risk factors. The patient doesn t respond to the NTG in the field or to doses of morphine sulfate or to high-flow oxygen therapy. He s already had his aspirin. What do you do?
If you re in the ED, you'll probably hook up the patient to an IV infusion of NTG. That s right, nitroglycerin the same thing you stopped after giving three tablets or sprays is now running full-blast into his veins. It will continue to do so until the patient gets better, develops an intolerable headache or becomes hypotensive. During an adverse event, the patient will receive some fluids, and staff will stop the drip, its effect "burning off" in a few short minutes.
You can see where I m going with this. Limiting prehospital care providers to three doses of NTG is contradictory to what we do in the hospital. If prehospital care is an extension of the ED, the care provided must be consistent. Giving additional doses of NTG matches what the ED does, requires no additional paramedic training or certification and has no contraindications other than those that might prevent any NTG administration. So I think you can take four, five, six strikes at the patient s chest pain or as many swings as you need. So what s the right dose? The right dose is enough.
The use of intravenous (IV) NTG in the prehospital setting is a bit trickier, but not for clinical reasons. Pharmacologically, NTG works no differently in the hospital than in the prehospital setting, and there s no reason to think paramedics can t administer the drug in a safe and effective manner. However, setting up an NTG drip can be time consuming. Most importantly, it requires a new dosage calculation. Given my perception of how much paramedics like math, this is not a trivial obstacle. (Now, before you go thinking this is a doctor vs. paramedic issue, let me note that I ve always said that in emergency medicine, there are really only two IV rates: wide open and keep open. And while I try to justify this principle clinically, I realize I don t want to do the math, either.)
It s really a matter of transport times. In EMS systems with transport times of 30 minutes or more, IV NTG (administered under the supervision of online medical control) is probably a valuable adjunct, if only because it permits a continuous infusion of the drug not logistically possible with multiple, repeat SL dosing. With short transport times, the burden of repeated NTG administration is less, and the clinical effect is likely to be identical.
An often-neglected form of NTG worth mentioning is nitroglycerin paste. Although absorbed more slowly than SL or IV nitro, it has a longer duration of action and may provide a means to avoid the peaks and valleys of serum drug levels that occur with intermittent SL administration. An EMS protocol might call for an initial spray or tablet of NTG, followed by one or two inches of NTG paste applied to the chest; repeating SL NTG doses as required. As with SL or IV nitroglycerin, if the patient suffers from a severe headache or becomes hypotensive, simply wipe the paste off the chest. Other forms of NTG, including transdermal patches or oral nitrate preparations (Isordil, etc.) are slowly absorbed, long acting and likely inappropriate for prehospital use.
Two final thoughts about nitro. We keep talking about NTG use for chest pain, but remember that NTG is an incredibly valuable adjunct in the management of congestive heart failure, especially where there is no IV access for morphine or diuretic administration or when diuretics are likely to be of minimal benefit (such as patients with renal failure who require dialysis). Vasodilating the systemic vasculature decreases the work of the heart (afterload), so the heart is able to pump fluid out of the lungs more effectively. Its effect on vasodilating the pulmonary arteries reduces preload as well. Finally, if your state allows EMTs to administer NTG, I d encourage you to do so. Some states (such as Florida) allow only EMTs to assist patients with their own NTG tablets. I think this is unnecessarily limiting. After all, if patients can give NTG to themselves, a trained EMT should be able to do so as well.