Why does tapping on a vein make it bulge?

[SmokD]

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 😀 (I did do a brief google search to no avail)

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[KSDeacon]

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...

 

[septoplasty]

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.

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

 

[peytonm]

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.

 

[scudrunner]

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.

 

[tkim]

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.

Worked as a medic for 12 years. It works.

 

[thepoopologist]

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.

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

"Idiopathic-Autoregulating-Vasodilation"

oH yEs, iNdeed

 

[McGillGrad]

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.

 

[Arch Guillotti]

Don't know but it definitely works.

 

[McGillGrad]

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

Local stasis = area where you're tapping.

 

[McGillGrad]

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.

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.

 

[SmokD]

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.

That sounds sciency enough, I think I'll go with that 😎 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?

 

[McGillGrad]

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...

I don't buy it.

 

[McGillGrad]

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

Sounds fair enough.

 

[Isoprop]

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

Tapping a superficial vein once or twice augments vein distention (8). The mechanism by which this occurs is unclear (2). Given the rapidity of venodilatation after this stimulus, venodilatation theoretically may be related to antidromic effects of nociceptive C-fibers or release of chemical mediators such as nitrous oxide found in the venous endothelium [11] and [12] . Applying a mild, sliding pressure (“milking”) along a short length of vein, from proximal to distal, displaces blood distally resulting in vein distention (2).

 

[McGillGrad]

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

Sounds a lot like:

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

 

[leviathan]

That sounds sciency enough, I think I'll go with that 😎 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?

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.

 

[septoplasty]

"Idiopathic-Autoregulating-Vasodilation"

oH yEs, iNdeed

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

 

[45408]

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.

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

 

[McGillGrad]

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

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

 

[45408]

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

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.

 

[McGillGrad]

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.

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.

 

[DrHogFan]

Heck, with teenage boys, I sometimes don't even use a tourniquet.

could seriously be taken out of context

 

[McGillGrad]

could seriously be taken out of context

Not by a normal person.

 

[Morsetlis]

None of you are normal people.

 

[45408]

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.

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.

 

[ToldYouSo]

... says the guy in Grenada.

 

[Instatewaiter]

Heck, with teenage boys, I sometimes don't even use a tourniquet.

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

 

[mrwesticles]

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

 

[leviathan]

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. 😎

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

 

[tkim]

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

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

 

[WildMed16]

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

 

[McGillGrad]

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

meh, sounds like mumbo jumbo.

 

[Tubed]

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

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...