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Why does tapping on a vein make it bulge?

Discussion in 'Clinical Rotations' started by SmokD, 09.09.11.

  1. SmokD

    SmokD

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    SDN Members don't see this ad. (About Ads)
    Tittle speaks for itself. Anesthesiologist asked the question in the room and I told him I'd look it up. Please do my homework for me :D (I did do a brief google search to no avail)
  2. KSDeacon

    KSDeacon Rock Chalk Jayhawk!!!!

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    only thing i could think of would be related to some form of auto-regulation, whereby tapping on it causes compression and then some rapid expansion. I dunno...
  3. Tired

    Tired Still winning.

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    Wave your hands all over, spout off the names of various cytokines, and use the words "autoregulation" and "vasodilator".

    That will summarize whatever answer it is he's looking for.
  4. septoplasty

    septoplasty Exceptional

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    "Idiopathic" would be a good word to use in conjunction when describing the above.
  5. peytonm

    peytonm

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    I always thought it was because you were holding the hand down (allowing gravity to work), and then tapping on more proximal veins which opens the venous valves, thus allowing blood to pool at the distal veins. Just a thought.
  6. scudrunner

    scudrunner ASAPAC Supporter

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    It doesn't. I worked as a phlebotomist for a few years and never noticed a bulging reaction just by tapping on a vein. Some old-timers will slap the skin but that doesn't help either. Maybe they were looking for something like reactive hyperemia. The only thing that makes the vein bulge is a downstream occlusion with a tourniquet.
  7. tkim

    tkim D-d-d-dilaudid

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    Worked as a medic for 12 years. It works.
  8. thepoopologist

    thepoopologist Ph.D in Clinical Meconium

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    "Idiopathic-Autoregulating-Vasodilation"

    oH yEs, iNdeed
  9. McGillGrad

    McGillGrad Building Mind and Body

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    I'll go ahead and give a quasi-physiological reason:

    Tapping the vein causes reflex mechanism producing venous dilation in response to venous congestion. In other words, you trick your vein into thinking there is a lack of blood flow to the area for a split second, so a compensatory (and fleeting) increase in blood flow follows. Then it all returns to normal seconds later.
  10. Arch Guillotti

    Arch Guillotti Senior Member Administrator SDN Senior Moderator Lifetime Donor

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    Don't know but it definitely works.
  11. Tired

    Tired Still winning.

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    The tourniquet is already on, so venous flow is already congested before you tap.
  12. McGillGrad

    McGillGrad Building Mind and Body

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    Local stasis = area where you're tapping.
  13. Tired

    Tired Still winning.

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    Stasis in an area that is already static? I dunno, I'm not buying.

    How about this: tapping tricks the body into thinking the area is injured, triggering the local release of inflammatory factors that transiently increase blood flow in the "injured" area, which then flows into the local vein, dilating it.
  14. McGillGrad

    McGillGrad Building Mind and Body

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    You might want to look up what the word 'stasis' means. If there was real stasis below the tourniquet, you wouldn't be able to fill up vials of blood with the needle.

    Real stasis is tapping/rubbing the vein and causing a stop of blood flow for a split second.
  15. SmokD

    SmokD

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    That sounds sciency enough, I think I'll go with that :cool: Thanks!

    EDIT: On second thought, I dont get this. Can veins be autoregulated? They lack smooth muscle, so how do you alter the capacitance of a vein?
  16. Tired

    Tired Still winning.

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    A touniquet exerts quite a bit more than the 10-30 mmHg pressure in a vein, which means blood is no longer flowing through the vein once you apply the tourniquet. When you puncture the vein, pressure from below pushes it up through the needle (plus the vacuum from the tube) causing flow. Basically, no flow when tourniquet applied, then flow when secondary channel is created...
  17. McGillGrad

    McGillGrad Building Mind and Body

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    I don't buy it.
  18. Tired

    Tired Still winning.

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    That's why I originally suggested hand-waving and random medical-sounding terms to explain it...
  19. McGillGrad

    McGillGrad Building Mind and Body

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    Sounds fair enough.
  20. Isoprop

    Isoprop Fascinating, tell me more

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    From http://www.ncbi.nlm.nih.gov/pubmed/15219306

  21. McGillGrad

    McGillGrad Building Mind and Body

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  22. leviathan

    leviathan Drinking from the hydrant Moderator Emeritus

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    Veins do have smooth muscle (but less than arteries) and have the ability to alter their capacitance via alpha and nitric oxide receptors among other things.
  23. septoplasty

    septoplasty Exceptional

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    That should sufficiently deter the pimping session away from you, possibly onto a fellow classmate who is asked to explain the above, which would be quite the situation. LOL
  24. 45408

    45408 aw buddy

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    The stasis no longer applies when you apply a vacuum tube upstream of the occlusion. You're now providing a way out.
  25. Tired

    Tired Still winning.

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    I think I just threw up a little in my mouth.

    Go back to studying for Step 1. Your big words and fancy talk have no place here. :cool:
  26. McGillGrad

    McGillGrad Building Mind and Body

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    There would not be a build-up of pressure if it was static. Pressure would only build if there was flow.
  27. 45408

    45408 aw buddy

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    If you have a capped syringe full of fluid, you can push on the plunger and increase the pressure without any flow. It will be static. As soon as you provide a way out, then you'll have flow.
  28. McGillGrad

    McGillGrad Building Mind and Body

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    Unless a tourniquet can block off deep veins, there is no stasis. I don't know what type of tourniquets that you use, but I haven't cut off all circulation in over a 1000 blood draws. Heck, with teenage boys, I sometimes don't even use a tourniquet.
  29. DrHogFan

    DrHogFan

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    could seriously be taken out of context
  30. McGillGrad

    McGillGrad Building Mind and Body

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    Not by a normal person.
  31. Morsetlis

    Morsetlis SGU MS-4

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    None of you are normal people.
  32. 45408

    45408 aw buddy

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    Yes, there is. We aren't talking about cutting off all circulation. We're talking about occluding the primary outflow for a superficial vein, not whether or not an insignificant perforator is still allowing a microliter of blood through it.
  33. Tired

    Tired Still winning.

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    ... says the guy in Grenada.
  34. ToldYouSo

    ToldYouSo Student

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    :corny:
  35. Instatewaiter

    Instatewaiter But...There's a troponin

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    Now I don't know what you Canadians call residency but from this comment I imagine it involves no shirts and a significant amount of leather
  36. mrwesticles

    mrwesticles

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    It's it answering the door to your knocking, duh.
  37. leviathan

    leviathan Drinking from the hydrant Moderator Emeritus

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    If you don't know what those words are you might want to hit the step 1 books a few more times. :rolleyes:
  38. tkim

    tkim D-d-d-dilaudid

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    Why would he read step 1 books when he's already a resident?
  39. WildMed16

    WildMed16

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    I was told recently by an anesthesia resident that tapping the vein actually causes a histamine release and subsequent vasodilation. Thought it made sense...
  40. McGillGrad

    McGillGrad Building Mind and Body

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    meh, sounds like mumbo jumbo.
  41. Tubed

    Tubed

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    I'm an anesthesia resident and that's what I was told by a senior resident during my PGY1 year. I later regurgitated it to an attending when he asked why I was tapping my pt's veins and he looked at me very disapprovingly. I now use the hand-waving mumbo-jumbo response and people seem to accept that just fine...

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