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CRAAB 3 > Nordgren: Central Venous Pressure > Flashcards

Nordgren: Central Venous Pressure Flashcards

1
Q

What components of the CVS system are crucial factors that determine how well the CV system will be operating?

A
  1. Ventricular EDV is VERY sensitive to small changes in filling pressure
  2. Cardiac filling pressure
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2
Q

How much volume does it take to fill the circulatory system if there is no pressure or stretching?

A

3.56 L

About 20 mmHg

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3
Q

What is our total systemic volume?

A

4.5 L

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4
Q

What does the extra volume in our system do?

A

The extra volume causes steretching and in turn pressure to build inside the system and …about 7 mmHG

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5
Q

What are the two major variables that affect mean circulator filling pressure?

A
  1. circulating blood volume

2. state of peripheral venous tone*

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6
Q

What does constriction of the venous vessels do?

A

Increase pressure throughout the system

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7
Q

What happens when there is increased tone in the other compartments?

A
  1. Arterioles don’t have much volume—very small effect

2. arteries and capillaries essentially do not change their volume (no effect)

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8
Q

How does cardiac pumping affect flow?

A

It shifts the location of some blood from venous to arterial.

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9
Q

What happens to veins and arteries when flow changes?

A

Veins- are VERY compliant, so pressure doesn’t change much in them when this happens

Arteries- NOT compliant (added blood causes pressure to rise above the mean circulatory pressure)

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10
Q

What is central venous pressure?

A

An indicator of circulatory status

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11
Q

How would you describe the CV system?

A

It’s a CLOSED hydraulic system. Changes in one area WILL cause changes in pressure, flow and volume throughout the circuit.

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12
Q

What is cardiac output?

A

The rate at which blood is LEAVING the central venous compartment (RA)

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13
Q

What is venous return?

A

The rate at which blood is COMING BACK to the central venous compartment (RA)

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14
Q

How are venous return and cardiac output related in a stable situation?

A

They’re equal!!

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15
Q

What happens when venous return and CO aren’t equal?

A

This produces a CHANGE in central venous pressure

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16
Q

What effects central venous pressure?

A
  1. Increased stroke volume
  2. decreased venous return

THEREFORE CVP is always driven to a value that makes CO = VR

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17
Q

What governs the flow between PV and CV compartments?

A

Q= change in pressure (drop between peripheral and central venous compartments) / resistance (small resistance associated with peripheral veins)

18
Q

What does a crop in central venous pressure do?

A

It increases the pressure drop across the venous resistance and consequently causes an elevation in venous return

19
Q

What does the venous function curve demonstrate?

A

As central venous pressure DECREASES, venous return INCREASES (to RA)

20
Q

True or false…An increase in peripheral venous pressure can be just as effect at increasing venous return as a drop in central venous pressure.

A

True

21
Q

What are two components that influence peripheral venous pressure?

A
  1. changes in blood VOLUME

2. changes in venous TONE

22
Q

What does an increase in blood volume do to veins?

A

Increase in volume > increase in pressure (veins are elastic)

23
Q

What does an increase in sympathetic activity do to venous tone?

A

Increase in sympathetic activity > increased vasoconstriction > increase pressure (external compression of veins does the same thing)

24
Q

What happens to the CVS when there is significant blood loss?

A
  1. Increased sympathetic nerve activity (subnormal CO evokes compensatory mechanisms)
  2. Venous constriction after hemorrhage
25
Q

Do cardiac sympathetic nerves affect the venous function curve?

A

NO

26
Q

How does peripheral venous constriction affect CO after a significant blood loss?

A

It increases CO by raising the central venous pressure and moving the heart’s operation upward along a fixed cardiac function curve.

27
Q

What is indicated by a pt with abnormally HIGH central venous pressure?

A

Depressed cardiac function, a RIGHT shifted venous function curve or both.

28
Q

What is a hallmark of patients with CHF?

A

VERY high central venous pressure

29
Q

What are the clinical implications of a pt with abnormally LOW CVP?

A

Must have an elevated cardiac function curve, a LEFT shifted venous function curve, or both.

30
Q

How do you estimate CVP?

A

By observing the external jugular veins.

  1. Gravity keeps veins in head/neck collapsed when in upright position.
  2. When recumbent, w/ jugular at about 7 cm above RA can visualize distension.
31
Q

How is CVP monitored in critical care settings?

A

It’s monitored continuously via a catheter inserted in a peripheral vein and advanced until it is in the central venous compartment.

32
Q

What IS vascular control?

A

Change in the TONE of smooth muscle lining the walls of the vasculature.

33
Q

What part of the CVS DON’T have smooth muscle?

A

capillaries

34
Q

Why is the vascular smooth muscle unique?

A
  1. can maintain tension for a long time w/ little energy cost
  2. contract and relax slowly
  3. activated by stretch
35
Q

When an organ responds to an increase in metabolic activity with a decrease in arteriolar resistance, this is known as?

A

Active hyperemia

36
Q

What are the key components of the venous system?

A

Central

Peripheral

37
Q

What is the volume that can be held in the peripheral venous compartment?

A

2.5 L

That’s a lota blood!

38
Q

If you gave a blood transfusion to a pt who had recently experienced a severe hemorrhage you would expect?

A

To EXPAND venous volume–there will be the MOST compliancy in the venous vasculature

39
Q

What happens when you get below a venous pressure of 0?

A

Veins in the thorax compress and you get NO flow

40
Q

How does an increase vs a decrease in blood volume affect the venous function curve?

A
  1. Increased blood volume/venous tone increases venous return
  2. Decrease in blood volume or venous tone decreases venous return
41
Q

When are CO and VR equal?

A

ONLY when central venous pressure is 2 mmHg

42
Q

According to Starlings Law, cardiac output always decreases when central venous pressure decreases. True or False?

A

False

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