Acute Pulmonary Edema

What is SCAPE?

For this podcast, we're discussing the acute pulmonary edema presentation.

This patient is hypertensive (SBP >140mmHg), severely dyspneic, with diffuse rales and clearly anxious. The "no-shitter, drowning-before-your-very-eyes" type of pulmonary edema. 

This is the SCAPE patient. SCAPE = Sympathetic Crashing Acute Pulmonary Edema.

The core causative factor in the SCAPE patient is an acute increase in left ventricular filling pressure.

There are a myriad of causes for a sudden increase in LV pressure, but the end result is a redistribution of fluid into the lungs.

1) Acute increase in LV filling pressure.
2) Fluid redistribution into the lungs and alveolar space.
3) Hypoxia ensues.
4) Catecholamine production and increase in SVR.
5) Activation of the RAAS.

It's important to remember that the majority of these patients are not volume overloaded. This is a fluid distribution problem due to increased LV pressure. As the RV continues to pump fluid into the pulmonary circulation, the LV cannot move that fluid forward because of the increased afterload. This creates a pressure gradient that transmits that pressure back into the pulmonary capillaries.

5 Major Causes of SCAPE
- Exacerbation of chronic LV failure
- Acute myocardial ischemia or infarction involving 25% or more of the myocardial mass
- Severe systemic hypertension
- Left sided valvular disorders
- Acute tachydysrhythmias and bradysrhythmias

In the out of hospital realm, the core treatments are Non Invasive Positive Pressure Ventilation (NIPPV) via CPAP or BiPAP, coupled with nitroglycerine as a first-line medication.

For the "regular guy" toolbox, the treatment pathway looks a little like this:

1) Treating the underlying cause if evident.
2) NIPPV
3) NTG
4) More NTG
5) More NTG
6) More NTG

 Do not delay NIPPV to see if other therapies (like a NRB) will work first. In the awake patient maintaining their own airway presenting with SCAPE, have a low threshold to apply your NIPPV mode of choice.

These patients need PEEP: they generally have an oxygenation problem, and not a ventilation problem.

To that point, most prehospital disposable CPAP systems do not deliver 100% FiO2.

The O_two and Pulmodyne O2-MAX systems we generally use are either fixed FiO2 or provide a titration of FiO2 based on oxygen flow.

The O_two system will provide between 59% and 77% FiO2 at oxygen flow rates between 8L/min and 25 L/min respectively.

The Pulmodyne O2-MAX system provides 30% FiO2 regardless of PEEP, or with an additional adapter may provide 30%, 60%, or 90% FiO2 independent of the set PEEP.

Nitrogylcerin

If sublingual NTG is all you have, give it. Often, too. Lifting up the CPAP mask for 20 seconds is highly unlikely to cause clinically relevant harm.

If you have the option of IV NTG, that should be your go-to.

Standard dosing strategies for IV NTG of 5-40mcg/min are likely ineffective, and there is literature to support higher dosing strategies.

Consider that we bolus 400mcg of SL NTG, and that the bioequivalence of SL NTG is comparable to around an IV NTG dose of 60-80mcg/min, so rapid titration of IV NTG even up to 100mcg/min is not entirely unreasonable and largely supported by current literature.

Dec, G. W. (2007). Management of Acute Decompensated Heart Failure. Current Problems in Cardiology, 32(6), 321–366. https://doi.org/10.1016/j.cpcardiol.2007.02.002

Mosesso, V. N. J., Dunford, J., Blackwell, T., & Griswell, J. K. (2003). Prehospital therapy for acute congestive heart failure: state of the art. Prehospital Emergency Care : Official Journal of the National Association of EMS Physicians and the National Association of State EMS Directors, 7(1), 13–23. Retrieved from http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=reference&D=med4&NEWS=N&AN=12540139

Aguilar, S., Lee, J., Castillo, E., Lam, B., Choy, J., Patel, E., … Serra, J. (2013). Assessment of the addition of prehospital continuous positive airway pressure (CPAP) to an urban emergency medical services (EMS) system in persons with severe respiratory distress. The Journal of Emergency Medicine, 45(2), 210–9. https://doi.org/10.1016/j.jemermed.2013.01.044

Levy, P., Compton, S., Welch, R., Delgado, G., Jennett, A., Penugonda, N., … Zalenski, R. (2007). Treatment of Severe Decompensated Heart Failure With High-Dose Intravenous Nitroglycerin: A Feasibility and Outcome Analysis. Annals of Emergency Medicine, 50(2), 144–152. https://doi.org/10.1016/j.annemergmed.2007.02.022

Mebazaa, A., Gheorghiade, M., Piña, I. L., Harjola, V.-P., Hollenberg, S. M., Follath, F., … Filippatos, G. (2008). Practical recommendations for prehospital and early in-hospital management of patients presenting with acute heart failure syndromes. Critical Care Medicine, 36(Suppl), S129–S139. https://doi.org/10.1097/01.CCM.0000296274.51933.4C

Agrawal, N., Kumar, A., Aggarwal, P., & Jamshed, N. (2016). Sympathetic crashing acute pulmonary edema. Indian Journal of Critical Care Medicine, 20(12), 719. https://doi.org/10.4103/0972-5229.195710

Mattu, A., Martinez, J. P., & Kelly, B. S. (2005). Modern management of cardiogenic pulmonary edema. Emergency Medicine Clinics of North America. https://doi.org/10.1016/j.emc.2005.07.005

Scott Weingart. EMCrit Podcast 1 – Sympathetic Crashing Acute Pulmonary Edema (SCAPE). EMCrit Blog. Published on April 25, 2009. Accessed on September 11th 2018. Available at [https://emcrit.org/emcrit/scape/ ].