In its early days, EMS was fairly straightforward and not too complex. Treatment modalities were simple and patient assessment focused mostly on the physical exam and patient history.
Over just a few short years, ambulances went from carrying single-lead cardiac monitors to monitors that can obtain 12-lead tracings. Pulse oximetry devices that originally gave providers just a number are now accompanied with a waveform and a capnography value and waveform as well. Manual blood pressure cuffs have been supplemented with automatic cuffs that can display blood pressure as well as the mean arterial pressure and pulse pressure. Blood glucose machines have been joined with lactic acid monitors, and in some systems both have been replaced with devices that give EMS providers a near complete picture of a patient’s blood chemistry. Portable ultrasound machines add to the physical exam allowing providers to actually see into the patient.
These advancements are exciting but at the same time, EMS providers must know when to use the proper tool and how to correctly interpret the results. Just as it would be impractical to administer every test to every patient in the ED, so is the practice of performing every test on every patient in the back of an ambulance. Over-testing of patients has been associated with increased cost and incorrect diagnosis. On the other hand, under-testing can also result in inappropriate care.
Patients present with a chief complaint. Something hurts, something feels weird or something isn’t working. After receiving the chief complaint from the patient, and then managing acute threats to the patient’s airway, breathing and circulation, the EMS provider should establish a list of possible causes-a differential or “working” diagnosis. This list will determine the tests and exams to be performed.
This is often very straightforward. For example, a 22-year-old who twists her ankle and is now complaining of ankle pain should receive an assessment that focuses on the ankle. There’s no need to apply a 12-lead ECG or evaluate blood chemistry with an i-STAT. It could be considered negligent, however, to not obtain a blood glucose reading on a patient found unconscious and unresponsive. Other patient presentations may be less intuitive and are owed further discussion.
A 58-year-old woman experiences a mechanical fall after tripping on the vacuum cord. She denies dizziness or a loss of consciousness. She has no chest pain or shortness of breath. Her only complaint, besides being irritated she fell, was a sore knee.
EMS arrives and performs a complete exam, including the acquisition of a 12-lead ECG. It could be argued that the patient didn’t need an ECG based on the events and the patient’s current presentation. Nonetheless, the ECG reveals a left bundle branch block. It’s unknown when this patient developed the bundle branch block but it didn’t appear to be associated with this event. The medics interpret the tracing as a myocardial infarction, and the patient receives aspirin, two IV lines, a dose of nitroglycerin, and then the EMS crew activates the hospital’s quick-response cardiac team. An incorrect diagnosis based on an arguably unnecessary exam.
EMS providers should also remember the limitations of the tests they perform. EMS providers learn that pulse oximetry measures oxygenation but must remember the pulse oximetry number doesn’t tell what the hemoglobin is bound with and it also doesn’t tell how many red blood cells the patient has (hematocrit). A person with extra red blood cells (polycythemia) may have an abnormally low pulse ox reading and a person with a low number of red blood cells (anemia) may read abnormally high.
Tests should be repeated as needed, but not more than needed to establish a treatment plan. Test and exam results must be considered as a whole and not just as individual values.
Consider a post-cardiac arrest patient who has a pulse of 80, blood pressure of 68/44, is currently being ventilated and has a capnography value of 28 mmHg and a pulse oximetry value of 70%. An initial response may be to slow ventilations, but capnography values shouldn’t be corrected at the expense of oxygenation. The concern in this presentation is the blood pressure. Select the appropriate tests for the patient being evaluated and interpret the results as a whole.
Each new “thing,” brings along with it discussion within EMS agencies. This is good. Not all agencies need i-STATs or ultrasound machines. Agencies must evaluate their community and system to see which tools will most benefit their patients.
A statement used many times over the years rings true here: “With great power comes great responsibility.” EMS providers with the power to access multiple diagnostic tools have the responsibility to know when and how to use them.