How are pressure-volume loops useful in determining optimal PEEP levels?

Learning Objectives Covered:

1. Identify changes in ventilator graphics based on the patient’s lung condition

2. Identify changes in ventilator graphics caused by inappropriate ventilator settings or equipment or device malfunctions

Background

Ventilator graphics provides the clinician with a valuable monitoring and diagnostic tool to help them achieve the best possible patient outcomes.  Though mechanical ventilators measure various lung pressures, volumes and mechanics these values within themselves are not enough to give us a complete understanding of the various changes that can occur within a patient’s lungs. The values measured and provided by ventilators are invaluable; however, these values are enhanced when we also consider ventilator graphics. Let’s look at an example of how graphics work. We take a patient’s blood pressure which gives us a digital numerical display of the pressures within the blood vessels and the rate of their heartbeat. Assessing a patient’s blood pressure and heart rate helps us to evaluate the rate and strength of their heartbeat. However, what if we were to perform an EKG or place a patient on a heart monitor? Not only will we assess their heart rate and the strength of their heartbeat but it will also provide us with valuable insight into the heart’s rhythm. The heart is electrically conducted so being able to view the heart’s function during each heartbeat provides us with more information. It also gives us an opportunity to identify many more abnormalities that we would otherwise overlook.

Instead of only looking at numerical values to help us understand patient-ventilator interaction, ventilators incorporate graphical displays (waveforms) which give us greater insight into the changes that occur in a patient’s lung mechanics over a period of time. Ventilator waveforms are a useful tool in detecting abnormalities such as

Abnormal ventilatory parameters/lung mechanics

· Alveolar overdistention

· Auto-PEEP (air trapping)

Patient-ventilator Interaction

· Patient-ventilator dyssynchrony

· Flow starvation

· Auto-triggering

Ventilatory circuit related problems

· Auto-cycling

· Secretion buildup in the ventilator circuit

Interpreting ventilator waveforms takes practice so don’t become discouraged if you don’t become an expert by the end of this course (I don’t expect you to).

As we previously discussed there are two types of ventilator waveforms: scalars and loops. Scalars are waveform representations of pressure, flow or volume on the y- axis vs. time on the x- axis. Loops are representations of pressure vs. volume or flow vs. volume.

Let’s take a closer look at recognizing lung overdistention. There are many waveforms we can look at to recognize lung overdistention but let’s take a look specifically at a pressure-volume loop. Since lung overdistention can be caused by the delivery of too much pressure or volume during inspiration then the pressure-volume loop is ideal. A normal pressure-volume loop is shown below.

 

Now notice below what can happen when we deliver high tidal volumes during volume ventilation or too much pressure during pressure- controlled ventilation.

Correcting lung overdistention is done by first recognizing that it is occurring and secondly by decreasing either tidal volume (if in volume control ventilation) or peak inspiratory pressure (if in pressure control ventilation).

Prompt

For this assignment, you will provide detailed responses to the following questions:

Pressure-volume loops assess compliance, which is measured by the change in volume for a given change in pressure. Another benefit of pressure-volume loops is the assessment of PEEP during mechanical ventilation. Application of PEEP may increase compliance.

1. How does the addition of PEEP increase compliance and affect the pressure-volume loop?

2. How are pressure-volume loops useful in determining optimal PEEP levels?

Use a pressure-volume image in your responses that illustrate your response. Be sure to cite your source.

Flow volume loops are used to obtain information about airway resistance.

3. List and describe at least two conditions that are easily recognized with flow volume loops.

Use a flow-volume image for each condition in your response. Be sure to cite your source.

Submit your answers in at least 500 of your own words on a Word document. You must cite at least three references in APA format to defend and support your position.