Why does tapping on a vein make it bulge?

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

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  1. SmokD

    SmokD 5+ Year Member

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    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)
     
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  3. KSDeacon

    KSDeacon Rock Chalk Jayhawk!!!! 5+ Year Member

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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...
     
  4. septoplasty

    septoplasty Exceptional 5+ Year Member

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

    peytonm 2+ Year Member

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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 7+ Year Member

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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 10 cc's cordrazine 10+ Year Member

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

    thepoopologist Ph.D in Clinical Meconium 5+ Year Member

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    "Idiopathic-Autoregulating-Vasodilation"

    oH yEs, iNdeed
     
  9. McGillGrad

    McGillGrad Building Mind and Body 10+ Year Member

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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 Lifetime Donor SDN Administrator 10+ Year Member

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

    McGillGrad Building Mind and Body 10+ Year Member

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    Local stasis = area where you're tapping.
     
  12. McGillGrad

    McGillGrad Building Mind and Body 10+ Year Member

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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.
     
  13. SmokD

    SmokD 5+ Year Member

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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?
     
  14. McGillGrad

    McGillGrad Building Mind and Body 10+ Year Member

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    I don't buy it.
     
  15. McGillGrad

    McGillGrad Building Mind and Body 10+ Year Member

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    Sounds fair enough.
     
  16. Isoprop

    Isoprop Fascinating, tell me more 5+ Year Member

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

     
  17. McGillGrad

    McGillGrad Building Mind and Body 10+ Year Member

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  18. leviathan

    leviathan Drinking from the hydrant Moderator Emeritus 10+ Year Member

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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.
     
  19. septoplasty

    septoplasty Exceptional 5+ Year Member

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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
     
  20. 45408

    45408 aw buddy 7+ Year Member

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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.
     
  21. McGillGrad

    McGillGrad Building Mind and Body 10+ Year Member

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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.
     
  22. 45408

    45408 aw buddy 7+ Year Member

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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.
     
  23. McGillGrad

    McGillGrad Building Mind and Body 10+ Year Member

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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.
     
  24. DrHogFan

    DrHogFan 2+ Year Member

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    could seriously be taken out of context
     
  25. McGillGrad

    McGillGrad Building Mind and Body 10+ Year Member

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    Not by a normal person.
     
  26. Morsetlis

    Morsetlis Preliminary Medicine 5+ Year Member

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    None of you are normal people.
     
  27. 45408

    45408 aw buddy 7+ Year Member

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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.
     
  28. ToldYouSo

    ToldYouSo Student 7+ Year Member

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    :corny:
     
  29. Instatewaiter

    Instatewaiter But... there's a troponin 10+ Year Member

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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
     
  30. mrwesticles

    mrwesticles

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

    leviathan Drinking from the hydrant Moderator Emeritus 10+ Year Member

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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:
     
  32. tkim

    tkim 10 cc's cordrazine 10+ Year Member

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

    WildMed16 5+ Year Member

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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...
     
  34. McGillGrad

    McGillGrad Building Mind and Body 10+ Year Member

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    meh, sounds like mumbo jumbo.
     
  35. Tubed

    Tubed 5+ Year Member

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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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