Prehospital Tools to Identify Pulmonary Embolism

Use this case study to guide discussion in the identification of a pulmonary embolism.

Staff at a rehabilitation facility called 911 for a patient with a rapid decrease in mental status. The EMS crew found the patient lying in the recovery position in a bed with medical staff 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, slightly tachypneic and had rapid/weak radial pulses. A 12-Lead ECG was performed and confirmed tachycardia with a right bundle branch block (RBBB) and no ST-segment elevation or depression.

The patient was transferred to the ambulance for further evaluation and management. The cardiac monitor confirmed sinus tachycardia with RBBB at 102 BPM, Sp02 ~85% on room air, BGL 125 (~7.0mmol/L), and the side stream end-tidal carbon dioxide [P_etCO₂] level was 15 mm Hg. The patient was afebrile placed on high flow oxygen via non-rebreather, and a 0.9% normal saline bolus was initiated. During transport, there were minimal changes to the patient’s heart rate (102), SpO2 (96%), blood pressure (92/60 (MAP 71)), and P_etCO₂ (18mmHg).

In the Emergency Department the patient was afebrile, vitals 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 given. 

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 chest angiogram showed a large saddle pulmonary embolus with signs of right heart strain. A heparin drip was started, and the patient was admitted to the cardiac ICU. 

Discussion

In the case above, the patient suffered from shock secondary to massive pulmonary embolism (PE). A PE is a venous thromboembolism, a blood clot that likely originated in the deep leg or pelvic veins.³

There are many tools at our disposal that can be used to help identify a potential 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 far more straightforward, such as our bedside and clinical skills as EMS providers? Or is it a combination of both?

Related

• Danger, Diagnosis & Treatment of Pulmonary Embolisms
• A Look at a Common Cause of Sudden Death: Pulmonary Embolism

P_etCO₂P_etCO₂ is the gold standard to confirm endotracheal intubation and monitor high-quality CPR. P_etCO₂ reflect the partial pressure of exhaled carbon dioxide and can be measured through both side stream and inline applications.⁴ In the pathophysiology of a PE, an acute blockage of pulmonary vessels reduces perfusion to alveoli. Alveolar dead space, area of the lung without perfusion, then begins to increase. With this, the elimination of carbon dioxide is reduced, and carbon dioxide-free gas mixes with gas from perfused alveoli resulting in a lower P_etCO₂^3,4 Unfortunately, these manifestations of PE often overlap those of other pulmonary disease processes. Therefore, P_etCO₂ can only be confidently used to support, but not prove, the presence of a massive PE.³ 

12-Lead ECG

For patients who present to EMS with chest pain, cardiac dysrhythmia, or difficulty breathing, 12-lead ECG is the primary diagnostic tool for identifying acute myocardial infarction (AMI). Prehospital ECGs can significantly decrease door to balloon times and the AMI mortality rate.⁵ Certain ECG changes may also occur in the presence of a hemodynamically significant PE. In the case above, the patient presented with a 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 are prone to a greater opportunity for circulatory collapse and shock.⁶ Regardless of its sensitivity rate, this supports the importance of prehospital ECG transmission to reduce time to interventions.

Assessment

There are many reasons that a patient can have vital signs that fall outside of normal limits. When those are measured, it is essential to correlate findings on the monitor to a good clinical assessment. One can use assessment pneumonics such as SAMPLE and OPQRST. An excellent clinical assessment can confirm or change the course of clinical care. For example, asking questions about the patient’s past medical history could reveal that the patient had surgery recently and had been sedentary, the likelihood of PE. 

Conclusion

When attempting to recognize or rule out a potential PE, using capnography to identify decreased P_etCO₂ values or capturing a 12-Lead ECG to identify electrocardiographic changes can undoubtedly add value. With PetCO2 and 12-Lead ECG having roles that are considered gold standard, prehospital providers can now move forward with the concepts described above. However, it needs to be stressed that this value certainly does not replace a good clinical assessment.

References

1. Pich H, Heller AR. Obstruktiver Schock [Obstructive shock]. Anaesthesist. 2015 May;64(5):403-19. German. doi: 10.1007/s00101-015-0031-9. PMID: 25994928. From <https://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. From <https://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 Avoidance. West J Nurs Res. 2020 Dec;42(12):1022-1030. doi: 10.1177/0193945920914492. Epub 2020 May 14. PMID: 32406785. From <https://pubmed.ncbi.nlm.nih.gov/32406785/> 
4. Long B, Koyfman A, Vivirito MA. Capnography in the Emergency Department: A Review of Uses, Waveforms, and Limitations. J Emerg Med. 2017 Dec;53(6):829-842. doi: 10.1016/j.jemermed.2017.08.026. Epub 2017 Oct 7. PMID: 28993038. From <https://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. Utilization and impact of prehospital electrocardiograms for patients with acute ST-segment elevation myocardial infarction: data from the NCDR (National Cardiovascular Data Registry) ACTION (Acute Coronary Treatment and Intervention Outcomes Network) Registry. J Am Coll Cardiol. 2009 Jan 13;53(2):161-6. doi: 10.1016/j.jacc.2008.09.030. PMID: 19130984. From <https://pubmed.ncbi.nlm.nih.gov/19130984/>
6. Islamoglu MS, Dokur M, Ozdemir E, Unal OF. Massive pulmonary embolism presenting with hemoptysis and S1Q3T3 ECG findings. BMC Cardiovasc Disord. 2021 May 1;21(1):224. doi: 10.1186/s12872-021-02035-0. PMID: 33932981; PMCID: PMC8088573.From <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8088573/>