#1)  Match the oxygen titration curves below with the following five patients:

• (a) Carboxyhemoglobin poisoning.
• (b) Methemoglobinemia.
• (c) Aspirated foreign body completely occludes the right lower lobe bronchus.
• (d) Asthma exacerbation.
• (e) Bronchopneumonia, with CT scan showing some areas of mildly affected lung and some areas of completely consolidated lung.

#2)  List situations in which pulse oximetry is inadequate for assessment of oxygenation (such than an ABG is needed to measure the PaO2).  I can think of six situations, but there are probably more.

#3)  A patient is being sedated for a shoulder reduction.  The patient is on room air.  Due to excessive sedation, the patient starts to hypoventilate and becomes increasingly hypercapnic.  At roughly what PaCO2 will the pulse oximetry signal fall below 90%?

• (a) PaCO2 45 mm
• (b) PaCO2 70 mm
• (c) PaCO2 120 mm
• (d) PaCO2 240 mm

#4)  A patient is being sedated for a shoulder reduction.  Although the patient has normal lungs, the patient is placed on four liters of oxygen as a precautionary measure (to be extra safe!).  Due to excessive sedation, the patient starts to hypoventilate and becomes increasingly hypercapnic.  At roughly what PaCO2 will the pulse oximetry signal fall below 90%?

• (a) PaCO2 45 mm
• (b) PaCO2 70 mm
• (c) PaCO2 120 mm
• (d) PaCO2 240 mm

More information about oximetry…

• Racial bias in oximetry
  • Racial bias in pulse oximetry (2020).
  • Systemic racism of pulse oximetry: Even worse than we thought? (2022)
• Oximetry beats PaO2 for assessing oxygenation,
• Converting a VBG into an ABG.