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Clotbusters in EMS: Clinical & Practical Considerations

The evidence is clear: Thrombolytic therapy helps reduce the mortality of heart attack victims. So how do you determine if your EMS service should offer "clotbuster" care? Although academic discussions and articles about thrombolytics abound, we often fail to discuss the more practical considerations dictated by the EMS environment.

The time frame for thrombolytic administration is a primary practical issue. The longer one waits to reperfuse the heart, the higher the risk of myocardial cell death (infarction) from the lack of blood flow. But how much time is too much? There is a time limit beyond which thrombolytic care does little good and puts the patient at increased risk.

In the United States, most literature indicates thrombolytic therapy should be administered within six to eight hours of the onset of symptoms (not from time of contact with the EMS system). A few studies extend this window of opportunity to 12 hours. (For the record, European studies may give thromboltyic agents up to 24 hours after the onset of pain and may give the agents to people without ECG changes.)

Given the well-known risks of thrombolytic therapy, how does one determine which patients truly have an acute myocardial infarction (MI), and which are experiencing chest pain related to angina, arrhythmia or heart failure? The only prehospital ECG findings that prompt prehospital thrombolytic therapy are distinct ST segment elevations in two or more adjoining leads or a documented new bundle branch block. Given that the latter can only be diagnosed if you have an old ECG on hand, the paramedic is really only looking for ST elevation.

It s important to note that the amount or description of pain, degree of dyspnea, presence of associated symptoms or the responsiveness of pain to therapy do not necessarily correlate with the presence of an MI. Neither do rhythm disturbances serve as a marker for MI; the one exception to this rule might be bradycardias, which seem to be linked to inferior and posterior MIs, but even that's going out on a limb. Finally, I would always be wary of administering thrombolytic drugs on the basis of an ECG prior to administration of oxygen, nitroglycerin, aspirin, and morphine sulfate (as indicated by local protocols). Any of these measures may relieve the ischemia, so a follow-up ECG demonstrating continued ST segment elevation is mandatory to prevent the unnecessary and risky use of the "clotbuster" agent.

Knowing how many patients qualify for thrombolytic care within your EMS system is key to determining if this mode of therapy is something your service wishes to offer. Like you, I deplore the fact we even need to consider cost-effectiveness in prehospital care. The closet liberal in me would like to see all patients receive all the care they wish, no matter what the cost. Unfortunately, the Gates of Utopia remain closed, and both paramedics and EMS administrators who do not understand basic system modeling and cost-benefit analysis inevitably divert resources from critical needs to unwarranted luxuries. (The "get some business skills" lecture is over for the moment, but will be revisited at a later date.)

So how do you determine if your service should offer clotbuster care? Let me suggest the following framework for evaluation. This sample sequence of questions can, and should, be modified to reflect the peculiarities of each individual EMS system. Nonetheless, I think it s a good place to start.

1) Are you an ALS service, and can you legally provide thrombolytic care?

This seems redundant, but only ALS services may be able to perform all the skills required for IV thrombolytic administration. This level of care is often found in state law. Statute often provides baselines; a service may provide care above the baselines, but not below. The capability to provide thrombolytic therapy is the province of the individual service.

2) Does your medical director endorse the concept of prehospital thrombolytic use?

If your medical director initially opposes the idea, you might try to convince the physician of a patient need with data collected by this model, but don t bet on it. If your medical director is dead-set against it, don t try. Their licenses are on the line, and they have a perfect right to say what treatments may be administered in their names. Doctors can be pretty hardheaded about their opinions. (I know that s a surprise to you.)

3) How many patients with chest pain have you transported during the past month, quarter or year?

This number establishes the initial group of patients who might be eligible for thrombolytic care. Though patients may manifest with other symptoms (dyspnea, etc.) as the initial presentation of their MI, reviewing patients with chest pain will provide your most obvious source of cases.

4) How many of the chest pain patients transported to receiving facilities were diagnosed with an MI?

This will require some legwork and confidential disclosure of diagnostic information between the EMS service and community hospitals. Again, we re trying to find out how many people would have received thrombolytic care; only patients with diagnosed MI would qualify.

5) How many of the patients identified with a diagnosed MI had elevated ST segments or new bundle branch block on a prehospital 12-lead ECG?

6) How many of the patients with ST segment elevation or new bundle branch block presented within 12 hours from symptom onset?

7) How many of the patients who presented within 12 hours of symptom onset spent more than 30 minutes with EMS personnel?

I m trying to be generous and grant the system a large margin for error. In reality, 30 minutes with EMS is probably not enough contact time to justify prehospital thrombolytic administration, especially if the patient can be transported to a facility with advanced cardiac capabilities.

You ve now identified the population of potential thrombolytic candidates. I'd be stunned if it were more than 5% of the total patients with chest pain.

Now it s time for the cost analysis. Find out how much the drug costs per dose, and then determine how much it will cost to stock your system with the drug on every appropriate EMS unit (responding engine, ambulance or supervisor vehicle).

It should be mentioned that although these agents are costly, most manufacturers are willing to work with EMS agencies. Several companies will replace any expired drug for free, which means you only pay for the drug you use.

The final step in the process is to determine if you can balance the cost of the agents against the number of patients who might qualify for thrombolytic care. This is the trickiest part of the analysis and the part most influenced by external factors, such as budgets, local hospital resources and geography.

For those who want to keep the decision strictly in the realm of science, there are tables that can determine how many years of life might be saved by clinical interventions and the costs to society of losing that life. However, these statistics (years of productive life lost or YPLLs) are weighted against the elderly, the very population in which most interventions occur. Morals and values inexorably influence these decisions, and the argument that each life, indeed each day, is precious and priceless still carries considerable weight. The final decision belongs to each agency, but this framework can set the stage for that discussion.

If you decide that your service should provide this level of care, a significant amount of training must focus on both the indications and contraindications for thrombolytic use. There are extensive lists of contraindications to clotbuster therapy in the literature, but some conditions may be difficult to detect. For example, gastrointestinal bleeding and esophageal varicies (swollen, distended veins of the lower esophagus prone to massive bleeding) are often considered contraindications to thrombolytic therapy.

Although most GI bleeding is obvious, paramedics in systems that opt to use thrombolytic therapy should also be trained in the use of a stool test for occult blood. Only endoscopy can diagnose esophageal varicies; however, because most varicies result from the "rerouting" of blood from a firm (cirrhotic) liver, a history of hepatic disease may prove a useful marker in prehospital care. Signs and symptoms of liver failure, such as yellow sclera (icterus), jaundice and a swollen, distended abdomen, are clues to a patient at risk. Needless to say, the sheer number of possible contraindications and the potential hazards of clotbuster care mandate consultation with online medical control before administration of any thrombolytic drug.


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