module - 5

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Understand that the Campbell diagram represents the intersection of the pulmonary and chest wall compliance curves at rest

Depict changes in chest wall and pulmonary compliance using the Campbell diagram

Determine how the Campbell diagram can be transformed into the respiratory system compliance curve

Differentiate between plateau pressure, intrathoracic pressure and transpulmonary pressure using the modified Campbell diagram

Predict how changes in intrathoracic pressure and transpulmonary pressure alter right ventricular [RV] hemodynamics

Explain the use of the esophageal pressure balloon

You are a newly-minted physician assistant working your first overnight shift in the SICU.  You are dealing with two new admissions in beds 1 & 2.

Bed 1 is a morbidly obese woman (BMI 47) intubated for airway protection.  She suffered an intra-cerebral hemorrhage as a complication of Reux-en-Y gastric bypass.  The respiratory therapist is calling you for plateau pressures in the low-40s even after administration of vecuronium.  Her blood pressure is sagging as is her oxygen saturation.

T or F: her pleural pressure is relatively high
T or F: her transpulmonary pressure is relatively high
T or F: her RV afterload is likely diminished
T or F: a bedside TTE will reveal a dilated RV

Bed 2 is an elderly man with severe emphysema.  He is cachectic (BMI 17) and was intubated for both transfusion-associated circulatory overload and aspiration pneumonia.  he is 4-days post an ax-fem bypass for severe peripheral arterial disease.  He too has plateau pressures in the low-40s even following the administration of vecuronium; his blood pressure and oxygen saturation are sagging.

T or F: his pleural pressure is relatively high
T or F: his transpulmonary pressure is relatively high
T or F: his RV afterload is likely diminished
T or F: a bedside TTE will reveal a dilated RV

Reflect on a patient you've cared for in whom you've encountered a high plateau pressure.  What have you thought about this number?  What is your understanding of how it relates to the intra-thoracic [or pleural] pressure?  How do you think the plateau pressure relates to RV preload?  RV afterload?  How would you explain the difference between the plateau pressure and the intra-thoracic pressure to a PA student?

1. With your learning partner choose a patient (i.e. one person choose bed 1, the other bed 2) and draw the patient's Campbell diagram.  From the Campbell diagram draw the respiratory system compliance curve.  Explain to each other your results; contrast each patients' diagrams.  Keep these drawings for future questions and modules.

2. Continue with the diagrams you have drawn and explain to each other where the esophageal pressure would fall on the diagram.  How is this different between the two patients?  Recall that the esophageal pressure is a surrogate for pleural pressure.

3. Imagine that each patient has an esophageal pressure balloon. Create a mathematical formula for calculating the trans-pulmonary pressure.  Which patient's trans-pulmonary pressure would be higher and why? 

4. Draw a cartoon of a hypothetical alveolus for the patient in bed 1 and in bed 2.  Which alveolus has a greater stress applied across it?  Use the Campbell diagram's you've drawn to help illustrate your reasoning.

5. Which patient is at higher risk for pneumothorax?  Critique the use of only the plateau pressure as surrogate for pulmonary stress fracture.  Use the Campbell diagram's you've drawn to help illustrate your reasoning.

6. Reason with your partner how each patient's differences in intra-thoracic (i.e. pleural pressure) and trans-pulmonary pressure will affect the right ventricle as assessed by bedside echocardiography; think in terms of preload and afterload.

7. Hypothesize what would happen to each patient's RV if you gave a liter of crystalloid?  Increased the PEEP?  Decreased the PEEP? Administered furosemide?  Began inhaled nitric oxide?

8. Discuss with your partner what would happen to the esophageal pressure when the vecuronium wears off.  How might this manifest on the Campbell Diagram?  How would the patient’s inspiratory effort contribute?

9. Return to the true or false questions you answered by yourself.  Discuss these with your partner and use the Campbell diagram as an explanatory model.

10. Review the intended learning outcomes with your partner.  Have you both met them?  Create 3 unanswered questions you have and meet with another learning pair to find answers to these questions.