How does compression affect BP?

[Danielle_Nicole887]

Two scenarios:

1) If you put a tourniquet on an arm, waited a bit then took BP on that same arm (below the tourniquet), would bp be artifically increase or decreased?

2) If you applied manual compression or a compression dressing to a femoral arterial site and took BP on the calf of that same leg while compression was being applied, would BP be artificially increased or decreased?

Thanks!

[mrsboots87]

This is not google. First, what do you think?

[Danielle_Nicole887]

I think that it will cause an artificially high BP.. Compression will decrease circulation and cause blood to pool in the limb (because the veins are compressed and can't return the blood effectively to the heart). More blood in the vascular system in the limb would mean it would take more pressure to occlude the vein/artery which means the bp machine would give a higher reading.

[Danielle_Nicole887]

is this correct?

[Danielle_Nicole887]

.....

[Rose_Queen, BSN, MSN, RN]

What flow does BP measure? Arterial or venous? If you are compressing an artery, what does that do to the flow distal to the compression site?

[Danielle_Nicole887]

BP measures the force that the blood exerts on the arterial wall, if you are decreasing an artery, you are decreasing diameter of the artery which increases the flow and resistance the blood has to go through (like vasoconstriction), increasing the force exerted on the arterial wall, increasing bp

[macawake, MSN]

Two scenarios:

1) If you put a tourniquet on an arm, waited a bit then took BP on that same arm (below the tourniquet), would bp be artifically increase or decreased?

2) If you applied manual compression or a compression dressing to a femoral arterial site and took BP on the calf of that same leg while compression was being applied, would BP be artificially increased or decreased?

Thanks!

I think that it will cause an artificially high BP.. Compression will decrease circulation and cause blood to pool in the limb (because the veins are compressed and can't return the blood effectively to the heart). More blood in the vascular system in the limb would mean it would take more pressure to occlude the vein/artery which means the bp machine would give a higher reading.

Despite not having been a nurse for all that long, I am old school in some ways. I think that a (student) nurse should know how to take a manual blood pressure despite the fact that we use machines most of the time in daily practice. I think that it would have be easier for you to figure out the answer to your question if you'd done it the "old-fashioned" way.

The part of your post which I've bolded made me ask you the following questions:

* What is it exactly that you are measuring when you take a non-invasive blood pressure? What are you listening to when you use your stethoscope? Arteries? Veins? Both?

* What are Korotkoff sounds?

When you say tourniquet or compression dressing, what pressure are they applied with?

* Would you expect the same result if you take a blood pressure distally to the tourniquet/ compression dressing if the tourniquet/dressing was applied at 100 mm Hg vs 250 mm Hg on a normotensive patient?

(100 mm Hg would be a rather poor tourniquet. I'm just using it as an example to make you reflect).

(OP, I didn't see your most recent post before I wrote my post).

[Danielle_Nicole887]

You are listening to the artery, specifically turbulent blood flow within it. You inflate the cuff to the point it totally occludes the artery (and hear nothing), the point you first hear a sound - turbulent blood going through is the systolic. When the sounds stop is diastolic because the pressure is no longer obstructing the flow in anyway so there are no turbulent sounds. These are korotkoff sounds and they change in quality from the systolic to diastolic.

I am assuming you are applying compression with your first or hands. I suppose a loose tourniquet would not have much of an effect or decrease the reading (like a tight sleeve).

However, assuming you have a tight tourniquet or manual compression ongoing for 10-15 minutes, you would also be compressing veins since they are much easier to compress than arteries, leading to blood accumulating in that limb since it can't return to the heart. Venous congestion can lead to an artifically high systolic and low diastolic bp. Similar to why if you take bp twice right in a row the second reading might be artifically high. This is why I think if you are taking bp on the calf of a leg you are actively manually compressing (more than just like one or two minutes), that it will be a higher than normal (systolic) bp.

[Rose_Queen, BSN, MSN, RN]

But if you are compressing an artery with enough pressure to halt the blood flow distally (the entire purpose of the tourniquet) how will you see higher pressures if there is no additional arterial flow?

[Danielle_Nicole887]

I suppose the distinction here is the purpose of the tourniquet - I'm assuming it's used for phlebotomy for example (not to stop uncontrolled bleeding), in which case the purpose is not to entire stop arterial blood flow but rather to reduce it, and compress veins to stop blood from returning to the heart (and allowing veins to become distended and easier to poke). Similarly, the goal of applying manual compression to a femoral artery is not to entirely occlude blood flow to that limb (hence why you want to check peripheral pulses distal to the site), but rather decrease it to allow clotting to take place.

Therefore, if you are not entirely compressing the artery, blood will enter the limb, but if you are applying sufficient pressure to compress the veins, it will not leave, or return to the heart at a slower rate. The accumulated blood would cause venous congestion over time and increase systolic bp and decrease diastolic bp.

Do you agree?