module 1

---

Explain the difference between volume status and volume responsiveness.

Critique the use of the central venous pressure [CVP] as a marker of volume status and volume responsiveness.

Draw the Guyton Diagram [from memory] incorporating each of the following clinical parameters into its genesis: volume status, venous tone, cardiac contractility, cardiac rhythm, valve function and afterload.

Hypothesize how common ICU interventions alter the CVP using the Guyton Diagram as an explanatory model.

A 58 year old man presents to the emergency department with acute onset shortness of breath and chest pain. Walking into the room you note that he is in moderate respiratory distress, he is coughing and his jugular vein is quite distended.  Suddenly he becomes hypotensive and tachycardic; no one is able to obtain a peripheral IV on him and you quickly place a subclavian central line.  The RN connects one port to the monitor and his CVP is about 25 mmHg.

T or F: you should first give fluids
T or F: you should first give vasopressors
T or F: his volume status is high
T or F: this is likely a cardiac event
T or F: his BNP will be elevated
T or F: a TTE will reveal at least one dilated ventricle

Reflect on a patient you've cared for in whom you've measured a CVP.  How was the value used?  If you have not used a CVP to manage a patient, what are your impressions of how it's used?  As a physician spending time in the ICU, is it important to understand the physiology of the CVP?  Should ICU RNs understand this physiology?  Why or why not?

1. Please meet with your partner(s) and create a "concept" or "mind" map for the determinants of the CVP.  Superimpose your mind map with the Guyton diagram and keep this diagram for use in the following exercises and in future modules.

2. With your partner, create a non-biological analogy for the CVP.  Describe it; an example of such an analogy is saying that increasing afterload is like putting one's finger over the nozzle of a hose with flowing water.  How does your analogy relate to the mind map you created in activity 1?

3. With your partner, use the Guyton Diagram and CVP to explain a clinical symptom, a sign, a blood test, a radiographic or ultrasonographic finding.

4. Critique the use of the CVP as a marker of volume responsiveness and volume status

5. Predict what would happen to the CVP of a patient upon whom you do each of the following: increase the PEEP, increase the propofol dose, fluid challenge the patient and increase the levophed dose?  What would happen to the BNP with each of the aforementioned?  The size of the RV on a bedside echo?

6. Reflect on the case in part 1.  Can you imagine a disease process in which the patient's RV is dilated?  Compressed?  How?  Reconsider the true or false questions that you answered in part A and use your mind map/Guyton diagram as an explanatory tool.

7. With your partner, reflect on how you will use the CVP going forward in your practice; did both of you meet the learning outcomes for this module? 

8. Find another group and share your ‘mind map’ & ‘non-biological analogy’ with them; explain your reasoning and give feedback.