PRESSORS, Part 4: Phenylephrine

Mon, 02/14/2022 - 7:35am
Author: 
Laura Di Taranti, MD
Editor: 
Alison Jaworski, MD

About phenylephrine 

  • Mechanism of action: pure α1 agonism, which results in peripheral vasoconstriction. This increases preload, afterload, and SVR. This does not directly affect the heart, but it can cause a reflex bradycardia (more so than with norepinephrine) because of the increase in afterload.  

  • Uses: directly counteracts the mechanism of action of most anesthetics, so it is great for post-anesthesia hypotension. The reflex bradycardia can also be exploited for primary tachyarrhythmias. Phenylephrine is the go-to pressor for critical aortic stenosis because the increase in afterload is fixed at the level of the valve, and the increase in SVR can induce that reflex bradycardia that can improve supply/demand mismatch. Since the increase in afterload is fixed at the level of the heart, peripheral increases in SVR do not make the obstruction at the valve worse. By lowering chronotropy, the heart spends more time in diastole, which increases coronary perfusion.  

  • Avoid: if high doses are needed, as phenylephrine usually comes in dilute formulations. Using high doses can dump a lot of volume into the patient. 

 

Again, the obligatory table for comparison:

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References  

  • Farkas, Josh. The Internet Book of Critical Care. Vasopressors. Accessed on December 7th, 2021. Available at https://emcrit.org/ibcc/pressors/.  

  • Farkas, Josh. The Internet Book of Critical Care Podcast 78 – Vasoactive Agents. Published on February 20th, 2020. Accessed on December 7th, 2021. Available athttps://emcrit.org/pulmcrit/pressors/.  

  • Kim SM, Aikat S, Bailey A. Well recognised but still overlooked: norepinephrine extravasation. BMJ Case Reports 2012;2012:bcr2012006836:. doi: 10.1136/bcr-2012-006836. 

 

  • Khanna, A et al. Angiotensin II for the treatment of vasodilatory shock. NEJM 2017;377:419-430. doi: 10.1056/NEJMoa1704154. 

  • Manaker, Scott. Use of vasopressors and inotropes. Post TW, ed. UpToDate. Waltham, MA: UpToDate Inc. http://www.uptodate.com. (Accessed December 7th, 2021)  

  • Parekh M, Andreae M. EM Resident. The Crashing Patient with Critical Aortic Stenosis. Published October 3rd, 2017. Accessed on December 9th, 2021. Available at https://www.emra.org/emresident/article/the-crashing-patient-with-critical-aortic-stenosis/. 

  • Rezaie, Salim. Rebel EM. Peripheral Pressors: 6 Pearls Not to F*#k Up the Arm. Published on June 4th, 2020. Accessed on December 7th, 2021. Available at https://rebelem.com/peripheral-pressors-6-pearls-to-not-fk-up-the-arm/.  

  • Shields SH, Holland RM. Pharmacology of vasopressors and inotropes. In: Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 9th edition. New York, NY: McGraw-Hill Education; 2020: 133-137.