• Tue. Sep 27th, 2022

Prehospital tools to identify pulmonary embolism – JEMS: EMS, Emergency Medical Services

This cross-sectional imaging (CT Scan) reveals the saddle pulmonary embolism described in the case.

Use this case study to guide discussion in identifying a pulmonary embolism.

Staff at a rehabilitation center called 911 for a patient whose mental state was rapidly declining. The EMS team found the patient lying in a recovery position in a bed with medical personnel present. The patient was lethargic and could not communicate verbally due to a recent stroke. The airway was intact with good chest rise and fall and the patient was diaphoretic, mildly tachypneic, and had rapid/weak radial pulses. A 12-lead ECG was performed and confirmed tachycardia with right bundle branch block (RBBB) and no ST segment elevation or depression.

A 12-lead ECG was performed and confirmed tachycardia with right bundle branch block (RBBB) and no ST segment elevation or depression.

The patient was transferred to the ambulance for further assessment and management. Cardiac monitor confirmed sinus tachycardia with RBBB at 102 BPM, Sp02 ~85% on room air, BGL 125 (~7.0 mmol/L), and end-tidal carbon dioxide on lateral flow [PetCO2] the level was 15 mm Hg. The patient was afebrile and placed on high flow oxygen without a rebreather, and a bolus of 0.9% normal saline was initiated. During transport, there were minimal changes in the patient’s heart rate (102), SpO2 (96%), blood pressure (92/60 (MAP 71)), and PandCO2 (18mmHg).

In the emergency department, the patient was afebrile, vital signs notable for mild tachycardia, hypoxia, and the patient was started on 2LNC with improvement in SpO2. Repeat ECG showed sinus tachycardia with RBBB. A fluid bolus was administered.

Chest x-ray was negative, lactate was moderately elevated (3.7), which improved to 1.8 after fluids. BNP and troponin were not elevated. A CT thoracic angiogram showed a large saddle pulmonary embolism with signs of right heart strain. A heparin infusion was started and the patient was admitted to cardiac intensive care.


In the above case, the patient was in shock secondary to a massive pulmonary embolism (PE). A PE is a venous thromboembolism, a blood clot that likely originates in the deep veins of the leg or pelvis.3

There are many tools at our disposal that can be used to help identify a possible pulmonary embolism, but which tool is the best? Is it our technical monitoring devices that can provide us with blood pressures, oxygen saturation, heart rate, end-tidal CO2, BGL and temperatures? Or is it something much simpler, like our clinical and bedside skills as EMS providers? Or is it a combination of both?


PandCO2PandCO2 is the gold standard for confirming endotracheal intubation and monitoring high quality CPR. PandCO2 reflect the partial pressure of exhaled carbon dioxide and can be measured by both lateral flow and inline applications.4 In the pathophysiology of PE, acute blockage of the pulmonary vessels reduces perfusion to the alveoli. The alveolar dead space, the zone of the lung without perfusion, then begins to increase. With this, the elimination of carbon dioxide is reduced and the gas without carbon dioxide mixes with the gas of the perfused alveoli, which results in a drop in PandCO23.4 Unfortunately, these manifestations of PE often overlap with those of other pulmonary disease processes. Therefore, PandCO2 can only be used with confidence to support, but not prove, the presence of a massive PE.3

12-lead ECG

For patients presenting to EMS with chest pain, cardiac dysrhythmia, or difficulty breathing, the 12-lead ECG is the primary diagnostic tool for identifying acute myocardial infarction (AMI). Pre-hospital ECGs can significantly reduce door-to-balloon times and AMI mortality rate.5 Some ECG changes may also occur in the presence of hemodynamically significant PE. In the above case, the patient presented with an RBBB with tachycardia. It has been observed in patients with RBBB, tachycardia, S1Q3T3 pattern, inverted T waves in V1-V4 and ST elevation in aVR who are likely to have a greater possibility of circulatory collapse and of choc.6 Regardless of its sensitivity rate, this confirms the importance of prehospital ECG transmission to reduce intervention times.


There are many reasons why a patient may have vital signs that fall outside normal limits. When these are measured, it is essential to correlate the results on the monitor to a good clinical assessment. Evaluation pneumonias such as SAMPLE and OPQRST can be used. An excellent clinical assessment can confirm or alter the course of clinical care. For example, asking about the patient’s medical history might reveal that the patient had surgery recently and was sedentary, the likelihood of PE.


When trying to recognize or rule out a potential PE, use capnography to identify a decrease in PandCO2 or capturing a 12-lead ECG to identify electrocardiographic changes can undoubtedly add value. With PetCO2 and 12-lead ECG having roles considered the gold standard, prehospital providers can now move forward with the concepts outlined above. However, it should be emphasized that this value certainly does not replace a good clinical evaluation.

The references

  1. Pich H, Heller AR. Obstruction Shock [Obstructive shock]. Anesthetist. 2015 May;64(5):403-19. German. doi: 10.1007/s00101-015-0031-9. PMID: 25994928. Ofhttps://pubmed.ncbi.nlm.nih.gov/25994928/>
  2. Essien EO, Rali P, Mathai SC. Pulmonary embolism. Med Clin North Am. 2019 May;103(3):549-564. doi: 10.1016/j.mcna.2018.12.013. PMID: 30955521. Fromhttps://pubmed.ncbi.nlm.nih.gov/30955521/>
  3. Prentice D, Deroche CB, Wipke-Tevis DD. Excluding pulmonary embolism with end-tidal carbon dioxide: accuracy, cost, and harm prevention. West J Nurs Res. 2020 Dec;42(12):1022-1030. doi: 10.1177/0193945920914492. Published online May 14, 2020. PMID: 32406785. Ofhttps://pubmed.ncbi.nlm.nih.gov/32406785/>
  4. Long B, Koyfman A, Vivirito MA. Capnography in the emergency department: review of uses, waveforms and limitations. J Emerg Med. 2017 Dec;53(6):829-842. doi: 10.1016/j.jemermed.2017.08.026. Published online October 7, 2017. PMID: 28993038. Fromhttps://pubmed.ncbi.nlm.nih.gov/28993038/>
  5. Diercks DB, Kontos MC, Chen AY, Pollack CV Jr, Wiviott SD, Rumsfeld JS, Magid DJ, Gibler WB, Cannon CP, Peterson ED, Roe MT. Use and impact of prehospital electrocardiograms for patients with acute ST-segment elevation myocardial infarction: data from the National Cardiovascular Data Registry (NCDR) ACTION (Acute Coronary Treatment and Intervention Outcomes Network). J Am Coll Cardiol. 2009 Jan 13;53(2):161-6. doi: 10.1016/j.jacc.2008.09.030. PMID: 19130984. Fromhttps://pubmed.ncbi.nlm.nih.gov/19130984/>
  6. Islamoglu MS, Dokur M, Ozdemir E, Unal OF. Massive pulmonary embolism showing hemoptysis and S1Q3T3 ECG findings. BMC cardiovascular disorder. 2021 May 1;21(1):224. doi: 10.1186/s12872-021-02035-0. PMID: 33932981; PMCID: PMC8088573.Ofhttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC8088573/>