How Low Can You Go? Hypotension is an Emergency w/Scott Weingart, MD

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“This used to be merely intuition…even a minute or two at low MAPs may be too much and certainly waiting 20 minutes for pharmacy to send up a drip is probably way too long…and your kidneys may actually be getting damaged in that short period of time.” – Scott Weingart, MD

Who is Scott Weingart, MD?

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Courtesy of Scott Weingart, MD

Scott D. Weingart, MD FCCM FUCEM DipHTFU

Scott is an ED Intensivist from New York. He did fellowships in Trauma, Surgical Critical Care, and ECMO.

He is currently an attending in and chief of the Division of Emergency Critical Care at Stony Brook Hospital. He is a clinical associate professor of emergency medicine at Stony Brook Medicine and an adjunct associate professor at the Icahn School of Medicine at Mount Sinai.

He is best known for talking to himself about Resuscitation and Critical Care on a podcast called EMCrit, which has been downloaded > 19 million times. EMCrit Twitter Team @emcrit

What is a MAP? (Mean Arterial Pressure)

  • Average pressure in a patient’s arteries during one cardiac cycle
  • Really good number to measure organ perfusion
  • Systolic BP is a useless measurement in super hypotensive patients
  • Calculations:
    • MAP = CO x SVR
    • MAP = SBP + 2(DBP)/3

Low MAPs should be treated as an Emergency = Requires Good Nursing!!

What is a minimal MAP for adequate perfusion?

No one knows!! 

Minimal MAPs (what we think and have made up) to adequately perfuse 3 main organs. Use this as a loose guideline. May have to individualize for each patient.

  • Brain
    • MAP 60-65
    • but can go lower for a bit of time before damage
    • MAP 40 starts to have altered mental status
  • Heart
    • MAP 60-65
  • Kidney
    • MAP 65
    • super sensitive to low MAPs
    • May not be able to measure output in ED if kidneys were hit hard and due to shunting

In the ED, we like MAP 65…

  • because the organs will have minimal perfusion and we often don’t know what the medical history is or have had 24 hours of patient observation.
 Normal MAP + Low SBP + Normal DBP = Okay
  • Organs are being perfused
Low MAP + Normal SBP + Low DBP (Ex: 100/20) = Badness
  • Can be in cardiac arrest if you don’t pay attention and do something ASAP

Low MAP, How long is too long?

  • New Anesthesia literature that shows a minute or two may be too much.
  • Concern for kidney injury
  • Hearts may dislike low MAP esp. Pts with cardiac history.
  • React quickly to low MAPs (MAP 40s and 50s)
    • No barrier to treating low MAPs
    • No Harm in treating low MAPs
    • Can start peripheral NE drip and if in 45 minutes, NE drip is titrated off – no harm done to Pt
  • Wait and See approach with fluids doesn’t work
    • Fluids don’t last to maintain MAPs, it will drop 30-60 minutes later
    • Harm to keep Pt at low MAPs

“Permissive Hypotension” A confusing term

  • No one is really in a permissive hypotension state lower than the minimal MAP 65

Trauma

  • A confusing term because the trauma studies still show that a Pt is being perfused and hovering around MAP 60-65
  • Rick Dutton Approach for penetrating trauma management as described by Scott
    • Keep your patient from being vasoconstricted
    • Organs are not being perfused with higher MAP but in fact exsanguinating due to vasoconstriction
    • Manage by hovering around a MAP 60-65 and perfuse organs
      • MAP <65 give product (like 1 unit of PRBC, FFP, etc.)
      • MAP >80 (or whatever upper limit you decide), give them some anesthetic and dilate them.
        • Fentanyl is an indirect vasodilator
  • Read more about Richard Dutton and trauma at emcrit.org

Neuro – term doesn’t really apply

  • I always hear nurses say “oh, neuro patients can LIVE at a MAP of 40” But personally, I still don’t see good evidence to support this and it is somewhat contradictory to what these patients need physiologically.
  • Neuro patients need HIGHER MAPs because of a barrier to brain perfusion and to guarantee cerebral perfusion pressure
  • Cerebral Perfusion Pressure (CPP) = MAP – ICP (intracranial pressure)
    • Ex: CPP 60 = MAP 80 – ICP 20
  • Hemorrhagic stroke patients usually need MAPs 80 or higher and SBP <140
    • upper thresholds of blood pressures
    • Use SBP to monitor highest BP during a cardiac cycle
  • Ischemic stroke patients
    • save the penumbra
    • Certain class of patients, basilar stroke patient – waiting for reperfusion therapy (need transfer)
      • May want to push MAP to 90-100
      • at MAP 90 – no neuro deficit
      • at MAP 68 – all of a sudden recurrence of stroke symptoms
        • Mgmt: push MAP high to 90 and stroke symptoms will resolve
        • MAP may drop to 68 due to furosemide kicking in

Medications and Drips in Hypotensive Patients

Scott’s method:

Norepinephrine drip first choice vasopressor for all hypotensive patients
  • except maybe anaphylaxis patients who may benefit with an epinephrine drip
Norepinephrine drip hits 20mcg/min – getting higher on the drip?

STOP and think, Did we miss something?

  • Hypothyroid?
  • Adrenally insufficient?
  • GI Bleed?
    • guaic
  • Profoundly hypocalcemic
  • Toxicologic emergency
    • beta blocker or calcium channel blocker overdose
  • Fluid depletion?
    • benefit from fluids?
  • Bedside US of heart
    • Poor cardiac output?
    • Add inotropic epinephrine drip
  • Vasodilatory?
    • Add vasopressin drip

Scott’s EMCrit episode with Mink Chawla and Athos 3 trial that started this whole episode.

This is the last 2017 episode, next one will be in February 2018. Happy Holidays!

Now listen to the episode….

References:
  1. Magder, S. A. (2014, May). The highs and lows of blood pressure: toward meaningful clinical targets in patients with shock. 
  2. Bickell WH, Wall Jr MJ, Pepe PE, Martin RR, Ginger VF, Allen MK, et al. Immediate versus delayed fluid resuscitation for hypotensive patients with penetrating torso injuries. N Engl J Med. 1994;331(17):1105–9.
  3. Dutton RP, Mackenzie CF, Scalea TM. Hypotensive resuscitation during active hemorrhage: impact on in-hospital mortality. J Trauma. 2002;52(6):1141–6.
  4. Scott Weingart. Hemostatic Resuscitation by Richard Dutton, MD. EMCrit Blog. Published on June 11, 2011. 
  5. Scott Weingart. EMCrit Podcast 30 – Hemorrhagic Shock Resuscitation. EMCrit Blog. Published on August 15, 2010. 
  6. Kudo, D., Yoshida, Y., & Kushimoto, S. (2017). Permissive hypotension/hypotensive resuscitation and restricted/controlled resuscitation in patients with severe trauma. Journal of Intensive Care, 5(1). doi:10.1186/s40560-016-0202-z
  7. Scott Weingart. EMCrit 201 – Deeper on Vasopressors and Athos 3 with Mink Chawla. EMCrit Blog. Published on June 12, 2017.

Cite this post as:

Yun Cee Dirsa. How Low Can You Go? Hypotension is an Emergency w/Scott Weingart, MD. Resus Nurse Podcast and Blog. Published on December 14, 2017. Date accessed June 21, 2018. Available at https://resusnurse.com/2017/12/14/low-can-go-hypotension-emergency-w-scott-weingart-md/.