The partial pressure of end-tidal carbon dioxide (PetCO2) reading ...

[Mr. Wonderful]

The partial pressure of end-tidal carbon dioxide (PetCO2) reading is taken at what point in the figure?
 
  a. Point A
  b. Point B
  c. Point C
  d. Point D

Question 2

A patient receiving mechanical ventilation is being continuously monitored for oxygen saturation measured by pulse oximeter (SpO2) for the past 48 hours.
 
  When initially applied, the SpO2 and the arterial oxygen saturation (SaO2), as well as the pulse on the pulse oximeter, ECG, and manual pulse, were consistent. During clinical rounds, the respira-tory therapist notices that although the probe is appropriately placed and capillary refill is normal, the SpO2 reading is down to 90 from 95. The most appropriate immediate action is to do which of the following?
  a. Replace the probe.
  b. Reposition the patient.
  c. Draw an arterial blood gas.
  d. Move the probe to a different site.

[Anton]

Answer to Question 1

ANS: C
Point C shows the concentration of carbon dioxide (CO2) at the end of the alveolar phase, just before inspiration begins. This occurs in phase 3 of the four phases of a capnogram. Point A de-picts phase 1, which is the initial gas exhaled from the conducting airways. As a person exhales, the amount of CO2 in the exhaled gas increases. The amount of CO2 exhaled levels off at point B. This coincides with phase 4 or the alveolar plateau. Point D is showing the fall in CO2 that occurs during inspiration.

Answer to Question 2

ANS: C
The oxygen saturation measured by pulse oximeter (SpO2) has dropped from 95 to 90. Since the SpO2 and arterial oxygen saturation (SaO2) previously correlated, this situation could mean that the patient is becoming hypoxemic. The probe is appropriately placed, so changing sites is not appropriate. The patient has already been checked for and has adequate circulation to the site of the probe, so moving the probe to a site with more perfusion is not appropriate. Therefore, the patient needs to have an arterial blood gas to ascertain the SaO2 and partial pressure of oxygen (PaO2).