Oxygenation Flashcards
What are the causes of hypoxemia?
- hypoventilation
- v/q mismatch
- diffusion defect
- shunt
What are the types of hypoxia?
- hypoxemia (low PaO2)
- anemic (low hb)
- circulatory (poor perfusion, dec cmo)
- histotoxic (cyanide poisoning)
What does oxygen delivery depend on?
- FIO2
- CaO2
- CMO
To avoid oxygen toxicity, what should you keep the FIO2 at?
Under 60%
What are the strategies to improve oxygenation?
- increase FIO2
- improve ventilation and reduce Vd
- assess hb
- peep/cpap
- improve circulation
What is a good rule of thumb for expected PaO2?
FIO2 x 5
What should the A-a gradient be?
< or = to 20
For COPD patients, what should you keep the PaO2 at and why?
50-60 torr or you take away the drive to breathe
What should you keep the PaO2 at for normal patients?
60-90 torr
What kind of relationship is there between PaO2 and FIO2?
Linear
What is the equation for finding the appropriate FIO2?
PaO2 known = PaO2 desired
————— —————-
FIO2 known FIO2 desired
What is a normal P/F ratio?
500
What should you adjust your FIO2 to before adding peep?
60
How much peep should you come down to before coming down on the FIO2?
5
How much of an increase in CO2 will result in how much of a decrease in O2?
Increase in CO2 by 1mmhg will decrease O2 by 1.25mmhg
Excessively high FIO2 will result in the formation of what free oxygen radicals?
- superoxide
- hydrogen peroxide
- hydroxyl groups
Excessively high FIO2 causes inflammatory response of the lung causing what?
- alveolar capillary membrane injury
- pulmonary edema
What kind of oxygenation issue does not respond to oxygen?
Shunt
What are increased shunt fraction conditions?
- atelectasis
- pulmonary edema
- pneumonia
- pneumothorax
- complete airway obstruction
What is atelectasis?
- shrunken airless state
- blockage of air passages, shallow breathing or surfactant deficiency
What is helpful with treating atelectasis?
Peep (can rein flare alveoli)
What worsens are the % shunt increases?
Hypoxemia
An increase in mean airway pressure (paw) can increase what?
PaO2
What does mean airway pressure affect?
Mean alveolar pressure and alveolar recruitment, therefore affecting oxygenation
What else can increase mean airway pressure?
- peep
- hfov
- aprv
What is the 50/50 rule?
If you can’t keep a PaO2 of 50 on 50% FIO2 then consider peep
How does peep treat ARDS?
- improves oxygen transfer
- protective effect by preventing repetitive collapse and reinflation of alveoli
What else responds to peep?
Refractory hypoxemia
What are the goals of peep?
- enhance oxygenation
- maintain PaO2>60, SpO2>90 at acceptable ph
- recruit and maintain alveoli
- reduce FRC, shunting and FIO2 to safe level
- cardiac tamponade
- compliance varies
How does peep affect compliance?
- decreases in normal lung
- increases in ARDS lung
What happens to VD/VT as you add peep?
Ou
Who are poor candidates for peep?
- unilateral or localized lung disorders
- highly compliant lungs
- head injuries
How is cpap applied?
- mask cpap
- nasal cpap
- high flow oxygen
What are flow resistors?
Create resistance to airflow during all of expiration. The diameter determines the peep/cpap. BAD.
