Anatomy & Physiology, Lesson 2.13: Taking blood pressure, without gear

“So doc, I was practicing my anatomy, you know, me an’ my girl, and lo’ and behold another feller popped up all upset as to how she was his girl, see, and now I’m out in the wild with nothing on but my boxers, and now how do I check blood pressure?”

Ah, dude.  TMI.  But a valid question nontheless.

Taking blood pressure without gear is more subjective, more error-prone.  The ATLS guidelines used to argue that you can guesstimate blood pressure, depending on where you can feel a pulse.

Carotid only: Systolic BP (hereafter SBP) 60-70 mmHG

Carotid & Femoral: SBP 70-80mmHG

Radial pulse: SBP > 80.

There are a couple of studies that disagree on the details.  We will focus on the most recent one, found here.

They took various hypotensive patients, placed arterial lines (the gold standard for blood pressure measurement) and then had folks try to feel pulses.

They found that the pulses all disappeared in the same order: first radial, then femoral, then carotid.

They split the patients into 4 groups:

Group 1: all 3 pulses present

Group 2: radial pulse drops, others present

Group 3: femoral pulse drops as well, only carotid pulse

Group 4: no pulses anywhere

(I’ll point out that the shorthand for Group 4 is: dead. And I do hope CPR was invoked soon after).

Here are the results:

The green bars are the expected SBPs from ATLS; the red dots are the SBPs as measured.  You can see that there is quite a bit of scatter, and no hard and fast rules.  However, in Group 1 they more-or-less cluster around the low 70s; Group 2 averages 66 (I can’t really call that a cluster.  Well, not in the scientific sense). Group 3 and 4 show the actual data quite a bit lower than predicted from ATLS.

The above is important.  This article indicates that there is a floor, below which your patient will simply undergo circulatory collapse (this is the irreversible shock Ivy Mike refers to late in this post, and it means your patient is dying right now).  There is some wiggle room, as certain diagnoses confer a slightly higher SBP at which your patient just flat-out dies, but once you crack a SBP of 50, your patient has very big problems.  If they are not in a full-fledged ICU, they are not likely to live.

That threshold, on the graph above, shows 1 person that still has a femoral pulse, and about 50% of those with only a carotid pulse, fall into the Dying Right Now category.  If you are truly out in the wild, with no resources, you would triage these folks as black–not recoverable–and move on, despite how hard that decision might be.

 Assignment #1: practice taking carotid, femoral, and radial pulses.  And time yourself–see how quickly you can find and feel the pulse.  Ask yourself–is this a strong, bounding pulse that about knocks my fingers off the neck?  Or am I having to imagine a little bit to feel it?  Find one of the pulses from A&P lesson 2.11, Assignment #1, that is a weak pulse–the popliteal is frequently weak–and get in your head, and in your fingers, what weak vs strong feels like.

Assignment #2: Make sure there are no competing interests, prior to reviewing “anatomy lessons.” Geez.


6 responses to “Anatomy & Physiology, Lesson 2.13: Taking blood pressure, without gear

  1. “(this is the irreversible shock Ivy Mike refers to late in this post, and it means your patient is dying right now).”

    When I click on “this post” I get a message that states “you are not allowed to edit this item”


  2. When rapidly evaluating patients initialy or in triage, I reach out to shake hands and put a index finger on the pulse, look em in the eye and ask where it hurst or how are they doing etc… noting skin color, breathing patterns, ability to respond apropriately, anxiety, etc…
    Airway, breathing circulation and disability in one swift move.
    I triage based not on the injury but on the reponse or compensation or tolerence to it if you will.
    Airway/Breathing (rate depth effort) – stable or unstable
    Circulation (radial pulse and blood sweep) – stable or unstable
    Disability (AVPU and ability to comunicate well track visually and pin point pupils) – stable or unstable.

    The radial pulse being present along with LOC gives a measure of reassurance of at a mimimim they are currently perfusing brain, kidneys and other vital organs.

    I triage black red or green as triage is so inherently inacurate that yellow seems quite useless.


  3. Before you flat out panic, if the person isn’t well known to you, find out if they’re aggressive runners or swimmers. This shifts the above graphs WAY down.
    Got a couple friends with systolic BP’s sub 50 at rest. ‘Course their resting PULSE is sub 40. Long ago when digital electronic BP cuffs were bleeding edge tech, someone brought one to our squad meeting and a chief says “Check her”

    Guy walked out thinking his gear was broke.

    Lady involved was mid 50’s swam 2-3 miles a day and ran in the warm months.
    NORM BP for her was 50/30 with a pulse of 40 if she was excited.

    Helps to know your patient.

    Like the 70 yr old guy in a car accident with a BP of 100/70. At my age this is great., at HIS age he was in shock, heading to decompensated shock.


  4. Pingback: The rapid trauma assessment – part I | Hogwarts School of Grid-Down Medicine and Wizardry·

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