EMS Use of the PERC Rule for Pulmonary Embolism

Your patient, a 54 year-old Female, looks at you with a subtle yet perceptible look of panic in her eyes and winces slightly with every breath. You arrived with your Engine company a few minutes ago and are riding the EMT spot today. The Medic unit is inbound, but is coming from across town and has several minutes of drive time before it can get there.

“The pain started suddenly, it just hit me.” She tells you. “One minute I was fine and the next minute it was like two hands were on my shoulders pushing me to the floor.”

She points with her hand to roughly the center of her chest, just to the left of her sternum, telling you that she’s having pain right where her fingers would be if she had placed her hand over her heart to say the Pledge of Allegiance. She says “It feels like I’m getting stabbed with a knife right here on the side of my breast bone. It hurts every time I breathe.”

She coughs and contorts her face with pain. “Oh yeah… That hurt… Ow!”

As you’re waiting for the ambulance to arrive, you assess the patient’s vital signs. Her pulse is elevated at 122 beats per minute, her blood pressure is slightly lower than it should be for her age and body type at 102/64, and her respiratory rate is 22 and shallow. You take a reading and find that her room air oxygen saturation is 93%. Her temperature is normal at 97.6 degrees F, but who knows how accurate that is because of the inferior thermometers you carry on your trucks. As you take her vital signs you perform a detailed physical assessment to give to the medics and find that the patient’s skin is pale, cooler than normal, and slightly moist to the touch. Her pupils are PERRL, her chest has equal rise and fall with mostly clear lung sounds other than some crackles at the bases, and her abdomen is soft and non-tender. Looking at her as she sits upright in the kitchen chair, you can almost swear that you see her jugular veins puffing out on the sides of her neck. She’s definitely anxious too, and seems to be getting more so by the minute.

Before the medic unit arrives, you help the patient take off her two shirts and place her into a patient gown while protecting her modesty. Then, using your service’s progressive BLS protocols you obtain a 12-lead EKG for the responding medic unit before you place the patient on oxygen. Your BLS protocols have changed to reflect current science in regards to oxygen administration and you place her on 4 liters per minute of oxygen via nasal cannula which seems to help a bit and brings her pulse-ox up to 97%. You have her chew four baby aspirin tablets per your chest pain protocol as well. As the Medic unit arrives your crew has clears a path for them and readies the patient to hop on the cot. The paramedics wheel the cot in the house and you help them stand and pivot the patient on to it from the chair. They listen to your detailed hand-off report and scan over your EKG. One of them says “There’s no ST-segment elevation, but if I’m not mistaken… Isn’t that an S1Q3T3?”

One of the paramedics asks the patient a few questions as you help secure her onto the cot. “Ma’am, have you recently been on any long trips or travel? Have you been sick and immobile or inactive for a long period of time lately?”

The patient tells them that she had gone on a business trip by car about two weeks ago and that while she was in her company’s other office she spent most of her time sitting at a desk poring over financial records. She denies taking hormone replacement therapy or birth control, but admits to being a former smoker. She tells you that she’s noticed her ankles swelling more than usual lately as the medic bends down to check them.

As the paramedics load the patient up in the ambulance they thank you for making the diagnosis so easy for them. They place the patient on their cardiac monitor, start an IV, continue the oxygen therapy, and proceed to the patient’s hospital of choice in an emergent fashion as the facility is over 30 minutes away in traffic.

If you read the above case, you probably made the diagnosis based off of just a few of the patient’s signs and symptoms. She’s practically a walking billboard for the most common presentation of a pulmonary embolism (PE), exhibiting not only the common complaints but also many of the most common risk factors for the condition.

A pulmonary embolism is caused by a blockage in a pulmonary artery that causes diminished blood flow in the lungs. The blockage can be caused by a blood clot, fat, air, tumor cells, or other material but is commonly caused by a venous thromboembolism that has broken off from a deep vein thrombosis (DVT) in the legs. It can have various associated symptoms and presentations, but the most common ones are:

  • Sharp chest pain that may worsen with deep inspiration or cough
  • Shortness of breath – Onset may be sudden or gradually increase
  • Increased heart rate
  • Increased respiratory rate
  • Diaphoresis
  • Anxiety
  • Hemoptysis – Coughing up blood or pink, foamy mucus.
  • Loss of consciousness
  • Palpitations
  • Hypotension

Additionally, the blockage in blood flow can create back pressure that affects the right ventricle of the heart, creating a right ventricular strain pattern on a 12-lead EKG, also known as the “S1Q3T3” pattern shown below thanks to our friends at www.EMS12lead.com

Courtesy EMS12lead.com

Courtesy EMS12lead.com

Note the large S-wave in lead 1, a Q-wave in lead 3, and the inverted T-Wave in lead 3 as well. For a better look, EMS 12-lead has a great article on the above EKG.

With any patient who presents with a complaint of “chest pain” it is important to perform an exceptionally thorough patient assessment which includes a 12-lead EKG performed before any intervention, to check for and consider your differential diagnoses, and remember to “Call PAPPA for Chest Pain” to help remember the most severe and life threatening causes. However, since many of the causes of the “Chest Pain” complaint can have similar symptoms caused by different pathophysiology, it’s helpful to remember a few tricks.

The “PERC Score,” also known as the “Pulmonary Embolism Rule-Out Criteria” is a diagnostic mnemonic used by emergency physicians to help guide their decisions in pursuing a full work-up of a patient for a possible PE. It works on the principle that if a patient has a cluster of symptoms that might possibly be a PE but could also quite possibly be another condition with similar symptoms, it is safe to rule-out a PE based upon a negative score on the scale. They use this scale to spare patients unnecessary costs and risks associated with unnecessary testing, namely a blood test (D-Dimer) and exposure to unnecessary radiation via a chest x-ray or CT scan. These tests are not without risk and should not be performed if not required.

While the PERC score isn’t exactly designed to guide EMS decision making and was intended to guide imaging decisions, I believe that it can help EMS providers make appropriate treatment and transport decisions in the field and help cut through the myriad differential diagnoses possible for patients with chest pain. I use it in my practice as a tool both for assessment and documentation of the patient’s condition.

Here it is:

  1. Is the patient’s age greater than 50 years?
  2. Is the patient’s pulse over 100 beats min?
  3. Is the Patient’s SpO2 greater than or equal to 95%?
  4. Does the patient have hemoptysis?
  5. Does the patient use estrogen (Birth control, hormone replacement therapy)
  6. Has the patient had any surgery/trauma requiring hospitalization within 4 weeks
  7. Has the patient had any form of venous thromboembolism (VTE, DVT)?
  8. Is there any unilateral leg swelling? (Is one leg swollen and the other not?)

The PERC rule states that if any of those questions are a “YES” in the case of a patient experiencing symptoms that may indicate a PE, then PE cannot be ruled out without further testing. Does that guide your EMS treatment decisions? Not exactly, however it does help you possibly zero in on the patient’s ultimate diagnosis and treatment plan as more YES answers may help clue you into one diagnosis over another possibility. Always remember that a thorough assessment and a 12-lead EKG are mandatory for patients presenting with chest pain or possibly cardiac-related conditions and good clinical judgment should be used.

I believe the PERC score is a good tool for EMS providers and have had good luck using it personally in the field. You may as well.

The Emergency Medicine blog “Life in the Fast Lane” has a good article on the PERC score where the also introduce the “HAD CLOTS” mnemonic to help you zero in on possible pulmonary embolisms in your patients. Also, if you’re looking for a fast way to calculate this score in the field and/or jog your memory, MDCalc.com has a PERC score calculator online that works exceptionally well on a mobile device.


Want to learn more? Don’t miss:

Call PAPPA for Chest Pain – A Helpful Mnemonic for Paramedics and EMTs

Pulmonary Embolism – An EMS Case Review

– 12-lead EKG tips for EMS – Making the Most of the Squiggly Lines

  • Brooks Walsh

    Great review of the PERC score – EMS needs to know about simple, important tools such as this.

    One important point though – the PERC score only applies when you have a LOW suspicion of PE. It isn’t valid if you have a significant concern for PE.

    As the author of the test has said, if a 37-week pregnant female smoker gets off the plane from Indonesia, with unilateral leg pain and subjective dyspnea (but nml exam and vitals), they would get a PERC score of zero.

    Thanks for highlighting this issue!

  • Braden Peters

    Great Article. I learned somthing new. One thought:

    “The PERC rule states that if any of those questions are a “YES PE cannot be ruled out”

    A better way to phrase that as used on the LIFTL post you reference would be “the answer to ALL of the questions must be NO…” and then slightly modify the rule to state “Is SpO2 = 95% is not an issue.

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